JPH02291566A - Developer for electrostatic latent image - Google Patents

Abstract

PURPOSE:To satisfy both characteristics of developability and transferability by forming the developer of a mixture composed of a high electric resistance magnetic toner and conductive magnetic particles having a coating layer dispersed with conductive fine particles in a high-polymer material on the surface. CONSTITUTION:This developer consists of the mixture composed of the high electric resistance magnetic toner 5a and the conductive magnetic particles 5b. The high electric resistance magnetic toner 5a is essentially constituted of the high-polymer material and magnetic fine powder and is added with a coloring agent, flow reforming agent, etc., at need. The conductive magnetic particles 5b consist of the particles formed by using magnetic particles as nuclei and coating the surface thereof with the coating layer of the high-polymer material contg. the conductive magnetic particles. The charge of the polarity reverse from the polarity of a latent image charge is induced from a sleeve to the conductive particles 5b and is accumulated in the high electric resistance magnetic toner 5a which is nearly a partial latent image. The magnetic toner 5a and the conductive magnetic particles 5b are thus attracted to the electrostatic latent image, by which the latent images are developed. Both the characteristics of the developability and transferability are satisfied in this way and the failure of the photosensitive body by the conductive particles 5b is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developer for electrostatic latent images, which is a mixture of magnetic toner and conductive fine particles and is used in copying machines, facsimile machines, printers, and the like.

[Prior Art] Conventionally, a so-called one-component magnetic toner development method using only magnetic toner has been known as a method for developing an electrostatic latent image. In this method, the conductive magnetic toner is held on the sleeve by the magnetic force of a magnet provided in the conductive and non-magnetic carrier sleeve, and the magnetic toner is transported onto the electrostatic latent image by the relative movement between the sleeve and the magnet. In this state, a conductive path is formed between the conductive backing member of the electrostatic latent image carrier, the sleeve, and the magnetic toner, and a charge having a polarity opposite to that of the latent image is induced in the magnetic toner, thereby developing the image. It is. The conductive magnetic toner used in this developing method is, for example, as proposed in US Pat. No. 3,839,245, in which the surface portion of the toner particle is made more electrically conductive than the center portion. However, toner images developed using such conductive magnetic toners have a drawback in that it is difficult to electrostatically transfer them onto other recording media.

Further, as a technology related to this developing method, an invention by Ikugga has been made. (JP-A No. 58-142540, JP-A No. 5 [i-159653, JP-A No. 513-1815)
No. 52, JP-A No. 57-119313fi, JP-A No. 5
No. 8-40558, etc.) In these, highly hard conductive particles such as magnetite powder were used. When an electrostatic latent image on a photoconductor is developed using a developer containing loose conductive particles mixed with magnetic toner, the presence of the conductive particles causes wear on the photoconductor, reducing the life of the photoconductor. Ta.

[Problems to be Solved by the Invention] The present invention satisfies both the characteristics of developability and transferability, which are disadvantages of magnetic toner development, and prevents damage to the photoreceptor due to conductive particles.

[Means for Solving the Problems] The present invention provides a high electrical resistance magnetic toner containing magnetic fine powder, a volume average particle size smaller than the volume average particle size of the toner, and a polymer substance on the surface. This is a developer for electrostatic latent images, characterized in that it consists of a mixture with conductive magnetic particles having a coat layer in which conductive fine particles are dispersed.

The high electrical resistance magnetic toner used in the present invention may be of any conventionally known type, and is essentially composed of a polymeric substance and magnetic fine powder, with colorants, fluidity modifiers, etc. added as necessary. Examples of polymeric substances include styrene resins, acrylic resins, vinyl resins, epoxy resins, polyester resins, phenol resins, polyurethane resins, natural resins, and celluloses.

As the magnetic fine powder, a powder of a magnetizable material of metal such as Fe, Ni, Co, Mn, or an oxide or alloy of these metals with a diameter of 1 μm or less is used.

As the coloring agent, for example, pigments or dyes such as carbon black, aniline blank, crystal violet, rhodamine B1 malachite green, nigrosine, steel cap cyanine, and azo dyes are used.

In addition, wax, fatty acids or fatty acid metal salts, silica powder,
It is also possible to add zinc oxide powder or the like.

The conductive magnetic particles used in the present invention are composed of a magnetic particle as a core, the surface of which is covered with a coating layer of a polymer material containing conductive fine particles. Examples of polymeric substances include styrene resins, acrylic resins, silicone resins, epoxy resins, polyester resins, phenolic resins, polyurethane resins, natural resins, and celluloses, and examples of magnetic particles include FeSNi, Co., Ltd. Particles of magnetizable material of metals such as Mn or oxides or alloys of these metals are used.

Examples of the conductive material include carbon black, fine metal powder, and tin oxide compounds.

Such conductive fine particles dissolve a polymer substance in a solvent,
It can be obtained by spray coating magnetic particles with a solution containing a conductive material and mechanical dispersion, or by immersing the magnetic particles in this solution and drying the solvent in an air stream to coat the magnetic particles.

In addition, the volume average particle diameter of the magnetic toner in the present invention is 5 to 5.
20μ■ is appropriate.

Furthermore, in the developer of the present invention, it has been confirmed that the transfer efficiency is better when the magnetic toner tends to be triboelectrically charged to a polarity opposite to the polarity applied to the transfer recording paper in the electrostatic transfer process. Nigrosine, monoazo dyes, zinc hexadene succinate, alkyl esters or alkylamides of naphthoic acid, nitrofumic acid, N. N'-tetramethyldiaminebenzophenone, N. It is preferable to add a strongly polar substance called a charge control agent in this field, such as N'tetramethylbenzidine, triazine, and a salicylic acid metal complex.

The developer of the present invention is prepared by mixing the above-mentioned conductive magnetic particles and a high electrical resistance magnetic toner, and the appropriate mixing ratio of the two is (2 to 40): (98 to 60) by weight. , more preferably (10-30): (90-7
0).

What is important in the developer of the present invention is that the average particle size of the conductive magnetic particles is smaller than that of the high electrical resistance magnetic toner.

If the magnetic particles are larger than the magnetic toner, the magnetic particles will be surrounded by smaller magnetic toner, and the larger the magnetic particles, the stronger the magnetic attraction to the magnet, so the magnetic toner will be supported around the magnetic particles. It appears that the magnetic particles are just removed from the electrostatic latent image, and spots called self-drops appear in the image. Furthermore, this phenomenon also occurs during the transfer process because conductive magnetic particles are difficult to be electrostatically transferred. On the other hand, it is also not preferable if the conductive magnetic particles are too small. In other words, if the particle size is too small, the fine magnetic particles around the magnetic toner will be strongly attracted by the Van der Waals force, resulting in a structure similar to that of conventional conductive magnetic toner in which the surrounding area of the toner is conductive, and the electrostatic This will worsen transferability.

From the above, it is preferable that the volume average particle diameter of the conductive magnetic particles is about 1/5 to 475 of that of the magnetic toner, and more preferably about 3/10 to 2/3 of that of the magnetic toner.

In the present invention, the electrical conductivity of the conductive magnetic particles means that the volume electrical resistance is 10 9 Ωcrn or less, and the high electrical resistance of the magnetic toner means that the volume electrical resistance is 10 12 Ωcm or more. In addition, the volume electrical resistance is determined when the bottom surface has an inner diameter of 20 mm+
After placing 11 magnetic toner or conductive magnetic particles in a cylindrical container consisting of an electrode and a side wall made of an insulating material, an electrode plate with a diameter of just under 20 mm and a weight of 100 g was placed on top of the test material, and the container was heated for 1 hour. After being allowed to stand still, a DC voltage of 100V is applied between both electrodes, and the current value 1 minute after application is determined to be 7IIJ and can be calculated.

It is also possible to add and mix known property improving agents such as fluidity to the developer of the present invention, such as silica, hard resin fine powder, lead oxide, higher fatty acids, higher fatty acid metal salts, silicone oil, and fluorine oil. It is.

The developer of the present invention described in detail above exhibits excellent effects in both developability and electrostatic transferability. To develop an electrostatic latent image using this developer, a developing device known as a device conventionally used in a one-component magnetic development method can be applied as is.

Furthermore, since the developer of the present invention can develop an electrostatic latent image mainly by utilizing the charge induced in the magnetic toner, it is not possible to triboelectrically charge the toner like the conventional two-component developer for magnetic brushes. There is also the advantage that operations such as thorough stirring within the developing device are not required, and therefore a simple developing device and management are required.

The case of developing using the developer of the present invention will be explained with reference to the drawings. Figure 1 is. This is an example in which an electrostatic latent image 3 formed on a photoconductive layer or a reading layer 2 having a conductive backing 1 is developed. The developer 5 of the present invention, which is made of a mixture of high electrical resistance magnetic toner 5a and conductive magnetic particles 5b, is supported on the conductive non-magnetic sleeve 4, and the developer 5 is formed by the considerable movement of the sleeve 4 and the magnet 8. 5 is conveyed to the latent image development position. In this state, a charge having a polarity opposite to that of the latent image charge is guided from the sleeve to the conductive particles 5b+, and is partially accumulated in the high electrical resistance magnetic toner 5a near the latent image. 5a and conductive magnetic particles 5b are attracted and developed. FIG. 2 is a model diagram of the developed state, and the developed image is composed of both magnetic toner 5a and magnetic particles 5b.
It has been confirmed that (1) the magnetic toner 5a is preferentially attached to the latent image because the magnetic particles have a larger attraction force. Further, the developed image shown in FIG. 2 is carried to a transfer step, a transfer recording medium such as plain paper is superimposed on the developed image, and the image is transferred by electrostatic means such as corona discharge.

In this step, the high resistance magnetic toner 5a is preferentially transferred, but some of the conductive magnetic particles ab are transferred to the magnetic toner 5a.
The magnetic toner 5a is attracted to the magnetic toner 5a due to the weak attraction force between the magnetic toner 5a and the magnetic toner 5a.

[Example] Next, the present invention will be described with reference to specific examples and comparative examples.

Example 1 Styrene-ro-butyl methacrylate copolymer 100 parts by weight Diglosine 2 parts by weight Magnetite
A mixture consisting of 100 parts by weight was heated and kneaded using a hot roll mill, cooled, and then crushed and classified to obtain a magnetic toner having a volume average particle diameter of 11 ltm and a volume electric resistance of 7.5 X 1 (1'' ΩCl).

On the other hand, as conductive particles, 100 parts by weight of silicone resin and toluene were added to magnetite powder with a particle size of 3 μm.
1000 parts by weight carbon black
A conductive layer was coated by spraying 20 parts by weight of the mixed solution while fluidizing the particles in a fluidized bed and then drying. The volume electrical resistance of the obtained particles is 4.5×l
It was O$Ωelm.

A developer was prepared by mixing 85 parts by weight of magnetic toner and 15 parts by weight of conductive fine particles.

Next, an electrostatic latent image formed by ordinary electrophotography on the organic semiconductor photoreceptor is developed by the developing device shown in FIG. 3, and this is transferred onto plain paper while applying a θ corona discharge. After heat fixing, a clear copy image with no white spots was obtained.

When 10,000 copies were continuously made using this developer, there was no damage to the organic semiconductor photoreceptor, and the images after 10,000 copies were clear.

Comparative Example 1 For 85 parts of the magnetic toner of Example 1, the volume average diameter was 3 parts.
Electrical resistance made of μI magnetite3. OX107
A developer was prepared by mixing with 15 parts by weight of conductive magnetic particles of ΩCrA.

When copying was performed in the same manner as in Example 1, a clear copied image was obtained.

When 10,000 copies were continuously made using this developer, it was found that minute scratches were generated on the surface of the organic semiconductor photoreceptor. Due to abrasion and deterioration of the photoreceptor, the background potential increased and the image potential decreased, and after 10,000 copies were made, the background was stained and an unclear image with low image density was obtained.

Example 2 Methyl methacrylate resin 100 parts by weight Carbon black 20 parts by weight Toluene
100 parts by weight of magnetite powder with a particle size of 4 μm was immersed in 2000 parts by weight of the mixed solution, and dried by fluidizing the magnetite powder in a fluidized bed to obtain 5×108
Conductive particles with a volume electrical resistivity of Ωcm were obtained.

85 parts of the magnetic toner in Example 1 and 15 parts by weight of conductive fine particles were mixed to prepare a developer.

When copying was performed using the method of Example 1, a clear copied image was obtained.

When 10,000 copies were continuously made using this developer, there was no damage to the organic semiconductor photoreceptor, and the images after 10,000 copies were clear.

[Effects of the Invention] The developer of the present invention satisfies both the characteristics of developability and transferability, which are disadvantages of magnetic toner development, and has the effect of preventing damage to the photoreceptor due to conductive particles.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the development method using the developer of the present invention, Figure 2
The figure is an explanatory diagram of the developing state, and FIG. 3 is an explanatory diagram of a developing device suitable for applying the present invention. l... Conductive backing, 2... Photoconductive (dielectric) layer, 3
... Electrostatic latent image, 4... Sleeve, 5... Developer,
5a... High electrical resistance magnetic toner 5b... Conductive magnetic particles, 6... Magnet.

Claims (1)

[Claims] A conductive toner containing a high electrical resistance magnetic toner containing magnetic fine powder and having a volume average particle size smaller than the volume average particle size of the toner, and having a coating layer on the surface of which conductive fine particles are dispersed in a polymeric substance. A developer for electrostatic latent images characterized by comprising a mixture with magnetic particles.