US-12625441-B2 - Electrostatic charge image developing toner and image forming method

US12625441B2US 12625441 B2US12625441 B2US 12625441B2US-12625441-B2

Abstract

Disclosed is an electrostatic charge image developing toner including: toner base particles containing at least a binder resin and a magnetic material; and an external additive, wherein the binder resin contains a crystalline resin; and the external additive contains strontium titanate particles doped with metal elements other than titanium and strontium.

Inventors

Yuya KUBO
Takanari KAYAMORI
Naoya TONEGAWA
Noboru Ueda

Assignees

Konica Minolta, Inc.

Dates

Publication Date: 20260512
Application Date: 20220421
Priority Date: 20210430

Claims (10)

1 . An electrostatic charge image developing toner comprising: toner base particles containing at least a binder resin and a magnetic material; and an external additive, wherein the binder resin contains a crystalline resin and a hybrid amorphous polyester resin, the external additive contains strontium titanate particles doped with metal elements other than titanium and strontium, and a content of the magnetic material is in a range of 35 to 50 mass % based on a total mass of the toner base particles.
2 . The electrostatic charge image developing toner according to claim 1 , wherein the strontium titanate particles are doped with lanthanum.
3 . The electrostatic charge image developing toner according to claim 1 , wherein a number average primary particle dimeter of the strontium titanate particles is in the range of 20 to 300 nm.
4 . The electrostatic charge image developing toner according to claim 1 , wherein a number average primary particle dimeter of the strontium titanate particles is in the range of 20 to 100 nm.
5 . The electrostatic charge image developing toner according to claim 1 , wherein an average circularity of primary particles of the strontium titanate particles is in the range of 0.82 to 0.94.
6 . The electrostatic charge image developing toner according to claim 1 , wherein the crystalline resin is made of crystalline polyester.
7 . An image forming method comprising the step of forming an image using the electrostatic charge image developing toner according to claim 1 .
8 . The electrostatic charge image developing toner according to claim 1 , wherein the metal elements other than titanium and strontium are at least one element selected from the group consisting of cerium, aluminum, calcium, magnesium, barium, phosphorus, sulfur, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, yttrium, zinc, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, tantalum, tungsten, rhenium, osmium, iridium, platinum, bismuth, zirconium, and tin.
9 . The electrostatic charge image developing toner according to claim 1 , wherein the toner base particles further contain a magenta colorant, a red colorant, an orange colorant, a yellow colorant, a green colorant, or a cyan colorant.
10 . The electrostatic charge image developing toner according to claim 1 , wherein the toner base particles have a core/shell structure, in which a core comprises the crystalline resin, and a shell comprises the hybrid amorphous polyester resin.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The entire disclosure of Japanese Patent Application No. 2021-077557 filed on Apr. 30, 2021 is incorporated herein by reference in its entirety. BACKGROUND Technological Field The present invention relates to an electrostatic charge image developing toner and an image forming method. More specifically, the present invention relates to an electrostatic charge image developing toner having improved low-temperature fixability, fog suppression and durability. Description of the Related Art In image forming devices such as electrophotographic devices, electrostatic recording devices, and electrostatic printing devices, a method of forming a desired image by developing an electrostatic charge image formed on a photoreceptor with a toner is widely implemented. It has been applied to copiers, printers, facsimiles, and multifunction devices thereof. Such toner is called an electrostatic charge image developing toner. In the following, it is also simply referred to as a “toner”. For example, in an electrophotographic apparatus using an electrophotographic method, in general, the surface of a photoreceptor made of a photoconductive substance is uniformly charged by various means, and then an electrostatic charge image is formed on the photoreceptor. Next, the static charge image is developed with a toner, the toner image is transferred to a recording material such as paper, and then the toner image is fixed by heating to obtain a copy. As a developer used in an image forming apparatus, a one-component developer containing only a toner, and a two-component developer in which a toner and a carrier are mixed are known. In recent years, image forming apparatus has been required to be miniaturized and energy saving in addition to high quality, and it is effective to use a one-component developer for miniaturization. Further, for higher quality, it is effective to perform image formation by a one-component contact development method, which is a development method in which a toner carrier and an electrostatic charge image carrier are contact-arranged (contact arrangement). However, in the one-component contact developing method, a large pressure is applied to the contact portion, so that high durability and high transportability of the toner are required in order to obtain a high quality image. Further, for energy saving, it is effective to improve the low-temperature fixability of the toner. As for the high transportability of the toner, a magnetic toner containing a magnetic material is known. However, in general, since most of the magnetic materials have low electric resistance, the charge amount of the magnetic toner tends to decrease (charge attenuation) in the developing process. Therefore, it is preferable to use a high resistance external additive for the purpose of preventing charge attenuation. Strontium titanate is known as such an external additive, but strontium titanate particles tend to take the shape of a cube or a rectangular parallelepiped due to their high crystallinity, and it is difficult adhere to the surface of the toner base particles described later. Therefore, as a technique for forming strontium titanate into a shape that easily adheres to the surface of toner base particles, in Patent Document 1 (JP-A 2019-28239), strontium titanate is doped with metal elements other than titanium and strontium. Thereby, a technique for reducing the crystallinity, forming a rounded shape, and making the diameter small and having a high circularity is disclosed. Although the charge attenuation of the toner is suppressed by this technique, the magnetic toner has a problem that the low-temperature fixability is insufficient because the magnetic material penetrates between the binder resins and functions as a filler, and it is required to improve the low-temperature fixability. Patent Document 2 (JP-A 2020-56920) discloses a technique for introducing a crystalline polyester into a binder resin which is a component of the toner as a method for improving the low-temperature fixability of the magnetic toner. However, crystalline polyester exudes to the surface of the toner base particles in a high temperature and high humidity environment and softens the vicinity of the surface, so that the magnetic material is newly exposed on the surface and charge attenuation occurs, causing fog. There was also a problem that the external additive was buried, and there was room for further improvement in the durability of the toner. SUMMARY The present invention has been made in view of the above problems and situations, and a solution thereof is to provide an electrostatic charge image developing toner and an image forming method having improved low-temperature fixability, fog suppression and durability. The present inventor has found the following as a result of examining the causes of the above problems in order to solve the above problems in the magnetic toner. It was possible to improve low