JPH0269767A - Toner - Google Patents

Abstract

PURPOSE:To provide the toner which exhibits an electrical conductivity in a low electric field and has excellent fixability and reliability and to obtain high image quality by consisting a carbon black of >=2 kinds of plural kinds of the carbon blacks which are different in average grain size. CONSTITUTION:The carbon black of the toner having the structure in which the carbon black is fixed to the surface of the particles formed by incorporating a coloring material and magnetic material into a binder material consists of >=2 kinds of plural kinds of the carbon blacks which are different in the average grain size. Namely, the carbon blacks are dispersed on the surface in such a state that the conductive carbon black having the large grain size is embedded in the entire part of the toner surface. The conductive carbon black of the small grain size is, therefore, incorporated at a fairly high rate into and on the binder substrate embedding the spacings thereof. As a result, the carbon blacks of the small grain sizes surely form conductive paths. The sure electrical conductivity in the low electric field is exhibited in this way and the fixability, reliability and image quality are maintained at a high level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in toners that are dry inks suitable for use in electrophotographic image formation.

The present invention particularly relates to improvements in toner exhibiting electrical conductivity having conductive particles fixed to its surface.

[Prior art] Examples of conductive toners with conductive particles fixed on the surface include Japanese Patent Publication No. 55-6897, Japanese Patent Publication No. 5B-40182, and Japanese Patent Publication No. 59-826. , U.S. Pat. No. 3,639,245, U.S. Pat. No. 3,92521
It is shown in No. 9 etc.

[Problems to be Solved by the Invention] However, in Japanese Patent Publication No. 55-6897, a layer of an electronic resistance adjuster having a maximum particle size of 0.02 μm or less is formed on the outer layer of the toner particles to prevent the occurrence of offset. are doing. However, electronic resistance adjusters with such small particle sizes cannot effectively lower the resistivity unless the toner particles are made spherical, and in addition, a large amount is required to make the toner in the crushed shape of normal toner conductive. of carbon black is required, and as a result, more carbon black is liberated from the toner, and a phenomenon of increased background smearing is observed.

Japanese Patent Publication No. 58-40182, U.S. Patent No. 363924
No. 5, U.S. Pat. No. 3,925,219, the specific electrical resistance changes as the electric field strength changes, and a toner structure is shown that has good conductivity under high electric fields and low conductivity under low electric fields. has been done. For this purpose, it has been shown that a structure in which conductive particles are completely buried in a highly insulating material in a thin layer on the outside of toner particles is sufficient. However, when charge injection is performed using toner with this configuration, a high voltage is required.
The development processes that can be used are limited.

Japanese Patent Publication No. 59-826 specifies the characteristics of carbon black that can be efficiently coated on the surface of toner particles, thereby achieving low resistance. However, if the carbon black is simply attached to the surface, if it continues to be agitated in the developing device, the carbon black will separate from the toner and become highly resistive.Therefore, in order to increase the adhesion of carbon black to the toner particle surface, heat treatment etc. The process of embedding carbon black in the toner resin is necessary to improve the stability of the toner, but the carbon black used has a high electrical resistance when dispersed in the resin, so the specific electrical resistance of the toner increases. This will prevent stable development. This increases the amount of carbon black attached, and as a result, the amount of carbon black that is not embedded in the resin increases, and the reliability of the toner does not improve.

Therefore, the present invention aims to solve these conventional problems, and aims to provide a toner that reliably exhibits conductivity in a low electric field and maintains high levels of fixing performance, reliability, and image quality. It is something to do.

[Means for Solving the Problems] In order to solve the above problems, the toner of the present invention contains a coloring material,
A toner having a structure in which carbon black is fixed to the surface of particles containing a magnetic material in a binding material, characterized in that the carbon black is composed of two or more types of carbon black having different average particle sizes.

Further, the toner of the present invention has a minimum average particle size of d1 and a maximum average particle size of d among the plurality of types of carbon black.
2, it is characterized in that 0.1d2<dl<0.4d2.

As the colorant, pigment particles such as carbon black, black titanium oxide, or dyes such as nigrosine can be freely used.

As the magnetic material, magnetic powders such as iron oxide, ferrite, iron, cobalt, and nickel can be used.

There are no restrictions on the binding material, and any material suitable for the purpose of image formation may be used. Examples of materials include waxes such as Candilla wax, carnauba wax, rice wax, beeswax, lanolin, montan wax, osikelite, paraffin wax, microcrystalline wax, polyethylene wax, ester wax, hydrogenated wax, acrylic resin, and styrene. resin, butyral resin, polyester resin, polycarbonate resin,
Thermoplastic resins such as simple substances, polymers, and mixtures of resins selected from cellulose resins, polyarylate resins, polyethylene resins, etc., thermosetting resins such as epoxy resins, urethane resins, and silicone resins, polyvinyl alcohol, polyallyl alcohol, etc. water-soluble resins, etc., and these can be used alone or in combination.

In addition to the above-mentioned substances, the toner of the present invention may contain a dispersion aid such as a metal soap, a fluidity improver such as silicon dioxide particles, fluororesin particles, and the like.

[Function] In the toner configured as described above, the dispersion state of the carbon black on the surface is such that conductive carbon black with a large particle size is embedded in the entire toner surface, and the binding that fills the gaps Conductive carbon black with a small particle size is contained inside and on the surface of the material at a fairly high concentration, and as a result, the small particle size carbon black reliably forms a conductive path with each other. Therefore, the charge can easily move between the large particle size carbon black particles through the conductive path of the small particle size conductive particles. Further, in the present invention, since carbon black with a large particle size can be used, the thickness of the conductive layer can be increased and electrical resistance can be lowered. Furthermore, since the conductive path is thick, low electrical resistance can be achieved without covering the entire surface of the toner with carbon black.

Further, by embedding relatively large carbon black in the binding material, the adhesion to the toner is strong and conductive particles are less likely to be separated from the toner, resulting in high reliability.

Hereinafter, the details of the present invention will be shown by examples.

[Example] Example 1゜20 parts by weight of oxidized polyethylene wax as a binding material,
20 parts by weight of paraffin wax, 20 parts by weight of polystyrene, 40 parts by weight of magnetite as a magnetic material, 0.5 parts by weight of carbon black as a coloring agent, and 0.5 parts by weight of black titanium dioxide were thoroughly mixed in a well-known screw extruder. After pulverizing with a jet airflow pulverizer and classifying with an airflow classifier, toner particles having an average particle size of 12 microns were obtained.

The particles thus obtained were dispersed in an acetone solution containing 10 wt.% PMMA and spray-dried to form a very thin PMMA film on the particle surface. The film thickness cannot be observed even when looking at the cross section, and is thought to be less than a few hundred angstroms. As a result of this treatment, the toner particles did not aggregate and exhibited good fluidity. The subsequent manufacturing steps can be easily carried out.

Next, surface area 25m”7g% DBP oil absorption 171cc71
00g, average particle size 0. 075 μm, 1) Carbon black of H8°5 was fixed to the surface of the toner particles.

The higher the pH, the lower the resistance and better results can be obtained.

The fixing method involved adhering fine carbon black particles to the toner surface by thoroughly agitating the toner using a high-speed flow smoother or a ball mill, and then applying an impact force to the toner particles to embed the carbon black particles into the toner surface. Since this method minimizes the temperature increase of the toner particles, it was possible to prevent the toner particles from aggregating even if the main component of the binder resin is wax, which tends to agglomerate toner particles. The impact force was controlled so that the fixed carbon black particles were almost completely buried within the toner particles. The amount of fixed carbon black is 4 to the toner particles.
wt,%. This is the amount that is formed on the surface of the toner.

Next, surface area 1475m2/g, DBP oil absorption fi330
c c / 100 g, average particle size 0.015 μm,
Carbon black having a pH of 8.6 was adhered to the surface of the toner particles by stirring well with a high-speed agitation slider or a ball mill. The amount of adhesion is 5w based on the weight of toner particles.
t,%. In this case as well, the higher the pH, the lower the resistance and better results can be obtained.

Further, the higher the surface area and DBP oil absorption, the easier it is to lower the resistance. The carbon black particles are then embedded into the toner surface by applying an impact force to the toner particles, by heat treating the toner particles in a hot air stream, or by both processes. At this stage, the small-sized carbon black particles fixed on the toner surface are dispersed in the binder that fills the gaps between the large-sized carbon black particles, and a conductive layer with low electrical resistance forms on the toner. formed on the particle surface.

The electrical resistance of the obtained toner was measured. The measurement was carried out by filling toner particles between parallel disk-shaped electrodes of 3 mm diameter with a distance between the electrodes of about 5 mm, and applying a pressure of 10 kg/cm2 between the electrodes. The specific electrical resistance when an electric field of 60 V/Cm was applied was 3xlO'Ωcm.Although conductivity was attempted using only one type of carbon black shown in this example, grain IQ.

075 μm carbon black did not become conductive even when 10 wt% carbon black was added.

10wt for 0.015μm carbon black.

Although it was possible to lower the resistance by adhering to the surface, uneven development occurred in the image forming test described later. Also, there was a lot of dirt on the ground. It is believed that the electrical properties of the toner are non-uniform.

Next, the obtained toner was placed in a conductive magnetic brush developing device and developed on a dielectric substrate on which an electrostatic latent image was formed, and an image forming test was conducted. The dielectric substrate may be selected from substrates with charge retention properties such as organic photoconductors, inorganic photoconductors, and insulating organic or inorganic films.In development with the toner of the present invention, the edge effect is very weak and line images are Both solid images were developed uniformly and clearly, and excellent image quality was obtained. Furthermore, when toner was placed in a developing device and left for over an hour with the mag roller rotating, no release of carbon from the toner was observed, indicating high reliability.

Comparative example 1゜Surface area 25 m2/g, DBP oil absorption fi 71 c c
/ 1oog, average particle size 0.075μm, pH 8.5
carbon black, surface area 800m2/g, DEP oil absorption 360cc 7100g, average particle size 0゜0
An experiment similar to that in Example 1 was conducted using carbon black of 3 μm and pH 9.0, but scumming occurred, which was thought to be due to the release of carbon.

Comparative example 2゜Surface area 25 m'/g, DBP oil absorption M71 c c /
10og, average particle size 0.0”75)tm, pH 8.5
carbon black, surface area 50 m2/g, DBP oil absorption 180 cc/100 g, average particle size Q,
An experiment similar to that in Example 1 was conducted using carbon black having a diameter of 0.04 μm and a pH of 7.0. However, the image quality was degraded due to a lot of unevenness and background smearing.

Example 2゜Surface area 20m27g, DBP oil absorption 11112cc/10
0g, average particle size 0.1μm, pH 7.0 carbon black and surface area 1475m2/g, DBP oil absorption J133
0cc/100g, average particle size 0゜015μm, p
An experiment similar to that in Example 1 was conducted using H8.6 carbon black, and good results similar to those in Example 1 were obtained.

Example 3゜Surface area 20m"7g, DBP oil absorption ff1112cc/1
00 g, average particle size 0.1 μm, pH 7.0 carbon black and surface area 254 m2/g, DBP oil absorption 185 cc/100 g, average particle size 0.03
Example 1 using carbon black of μm, pH 8.5
An experiment similar to that of Example 1 was conducted, and good results similar to those of Example 1 were obtained.

Comparative example 3゜Surface area 20m"7g, DBP oil absorption 1112cc7100
g, average particle size 0.1 μm, pH 7.0 carbon black and surface area 50 m'/g, DBP oil absorption M 180 c
c/100 g, average particle size 0.04 μm, pH
An experiment similar to Example 1 was conducted using 7.0 carbon black. However, the image quality was degraded due to a lot of unevenness and background smearing.

Example 5 An insulating dielectric film with a thickness of 3 to 6 microns is used as the image forming body, and an electrode or a group of electrodes are arranged on the back side of the dielectric film so as to be close to or in contact with the dielectric film.
A magnetic brush developer was placed on the surface side of the dielectric film at a position facing the electrode or group of electrodes, and a voltage was applied to the electrode or group of electrodes and development was carried out simultaneously to form a toner image on the image forming body. The electrode group can control voltage application independently to each electrode, and image formation is possible. When we attempted to develop a film with an insulating film thickness of 4 microns and an ITO electrode formed on the back surface using the toner shown in Example 1, the maximum amount of development was achieved with a potential difference of 30 volts or less between the ITO electrode and the sleeve of the developing device. Indicated. It has become clear that image formation can be performed at sufficiently low voltages. Similar results were obtained even when the electrode group was brought into contact with the back surface of the insulating film.

As a characteristic of the development experiment shown in Examples, one or more toner layers were difficult to develop, and the amount of developed toner was constant above a certain development voltage. Utilizing this characteristic, the toner of the present invention can be applied not only to electrophotographic printers, copiers, and display devices, but also to inking processes, such as recycling of ink sheets of thermal transfer printers, and printing. It is also extremely effective for uniformly supplying ink to printing plates in machines.

[Effects of the Invention] As described above, the toner of the present invention reliably exhibits conductivity in a low electric field, has excellent fixing properties and reliability, and can provide high image quality. In addition, there is great flexibility in selecting the binder resin, and it can be applied not only as a heat fixing toner or a pressure fixing toner for image forming devices such as electrophotographic printers and electrostatic printers, but also for thermal transfer type image forming devices. It is also possible to apply it to ink sheet recycling devices, image displays using conductive toner, etc., and its application fields are extremely wide.

that's all Applicant: Seiko Epson Corporation Agent: Patent Attorney Tosuzu Honban 3rd Department (1 other person)

Claims (1)

[Scope of Claims] 1. A toner having a structure in which carbon black is fixed to the surface of particles containing a coloring agent and a magnetic material in a binding material, wherein the carbon black is of two or more types having different average particle sizes. A toner comprising carbon black. 2. In the plurality of types of carbon black described in item 1,
2. The toner according to item 1, wherein 0.1d2<d1<0.4d2, where d1 is the minimum average particle size and d2 is the maximum average particle size.