JPH0424654A - Two-component developer - Google Patents

Abstract

PURPOSE:To suppress the void of images by carrier flying by specifying (resistance value of carrier core material )/(carrier resistance value) to >= 0.020 and specifying the electric conductivity of a toner to >= 3.0X10<-16>S/cm. CONSTITUTION:The (resistance value of carrier core material)/(carrier resistance value) is >= 0.020 and the electric conductivity of the toner is specified to >=3.0X10<-16>S/cm. Namely the resistance value of the coating layer of the carrier is decreased and the holding power of the counter charge in the coating layer is optimized by specifying the (resistance value of carrier core material)/(carrier resistance value) to >= 0.020. The charge quantity of the toner is decreased and the counter charge remaining in the coating layer of the carrier is decreased by specifying the electric conductivity of the toner to >= 3.0X10<-16>S/cm. The void of the images by the carrier flying is prevented in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a two-component developer, and more particularly to a two-component developer used in an image forming apparatus such as an electrostatic copying machine.

<Prior Art> Conventionally, in image forming apparatuses such as copying machines that utilize the Carlson process, a charging process is performed in which a photoconductor is uniformly charged by corona discharge, and a document image is formed by exposing the charged photoconductor to light. an exposure process to form an electrostatic latent image corresponding to The so-called Carlson process, which consists of a fixing step of fixing a toner image transferred onto a material to obtain an image, is widely used.

As the developer used in the developing process, a two-component developer consisting of a carrier and a toner has been widely used.

The carrier consists of a carrier core material and a polymeric coating layer covering the surface of the carrier core material.

The carrier charges the toner positively or negatively by frictional charging, causes the toner to adhere to its surface, and supplies the toner to the surface of the electrostatic latent image.

<Problems to be Solved by the Invention> However, in electrostatic copying using conventional two-component developers, a phenomenon called carrier fly-off occurs, in which carrier adheres to the surface of the electrostatic latent image along with toner. As a result, fine spots of white spots may appear in the image area. Such white spots are also called carrier fireflies.

The following is presumed to be the cause of such carrier flying.

In other words, due to the edge effect (edge phenomenon) in which the density at the center of the image becomes thinner than at the periphery, the potential around the outside of the image area is lower than the residual potential level. The potential on the top is solid black (solid black)
A potential difference v1 is generated between the potential around the solid black part of the image and the residual potential.

On the other hand, in the proximity line image, the potential difference V2 between the potential between the proximity lines and the residual potential is V2 due to the influence of the potential around the outside of the side proximity lines.
It becomes something bigger than (V2 Shizu 2v,). moreover,
In the fine mesh image, the potential difference V between the potential of the white portion surrounded by each line and the residual potential is larger than the potential difference V2 of the adjacent line image (V,>V2>V). On the other hand, since a bias voltage of the same polarity as the electrostatic latent image is applied to the sleeve of the image forming device, the carrier that has left the sleeve tends to adhere to the periphery of the image area due to the principle of reversal development, resulting in carrier flying. or occur. As is clear from the above description, such carrier skipping is more likely to occur in the order of mesh images, proximity line images, and solid black images.

SUMMARY OF THE INVENTION An object of the present invention is to provide a two-component developer that prevents the carrier flying phenomenon from occurring and suppresses image area blanking due to carrier flying to such an extent that it does not pose a problem in actual use.

Means and Effects for Solving Problems> Carrier flying, where the carrier adheres to the surface of the electrostatic latent image, is caused by electric lines of force near the photoreceptor and by the toner remaining in the carrier when it is separated from the carrier during development. It is thought that this occurs due to interaction with a counter charge (accumulated charge), and the larger the counter charge, the higher the frequency of carrier jump occurrence.

Conventionally, it has been thought that the magnitude of the 20 counter charge is determined by the resistance value of the entire carrier. but,
As a result of extensive research by the inventors, we found that there is no correlation between the resistance value of the entire carrier and the carrier flyoff, and that the carrier flyoff is determined by the resistance value of the polymer coating layer covering the surface of the carrier and the toner flyoff. We discovered a completely new fact that it is deeply related to electrical conductivity.

That is, the larger the resistance value of the coat layer, the more likely the counter charge remains in the coat layer. Carriers with a high counter charge tend to adhere to the surface of the electrostatic latent image, and carrier flying tends to occur.

Furthermore, when the conductivity of the toner is low, the resistance becomes high, and the electric charge of the toner becomes high accordingly. When highly charged toner is developed, the counter charge in the carrier coating layer becomes high and carrier flying frequently occurs.

Therefore, the two-component developer of the present invention is a two-component developer consisting of a carrier whose surface is covered with a polymer coating layer and a toner, in which (resistance value of carrier core material)/( The carrier resistance value) is 0.020 or more, and the toner has an electrical conductivity of 3, Qx 10-'' S/cm or more.

In such a configuration, "(resistance value of carrier core material)/(
Since it is difficult to measure only the resistance value of the coat layer, "carrier resistance value" is an indirect expression of this value. By setting this (resistance value of carrier core material)/(carrier resistance value) to 0.020 or more, the resistance value of the coat layer of the carrier is reduced, and the ability to retain counter charges in the coat layer is optimized. Carrier flying is prevented.

Furthermore, by setting the conductivity of the toner to 3.0XIO-''S/cm or more, the amount of charge on the toner decreases, the counter charge remaining in the carrier coating layer also decreases, and carrier scattering is further prevented. Ru.

The present invention will be explained in detail below.

The carrier of the present invention consists of a carrier core material and a polymeric coating layer covering the surface of the carrier core material. Any commonly used polymeric materials can be used for the carrier core material and the coating layer.

For example, carrier core materials include iron powder, oxidized iron, reduced iron, magnetite, copper, silicon steel, ferrite, nickel, cobalt, alloys of these with manganese, zinc, aluminum, etc., and iron-di-methyl alloys. , magnetic materials such as iron-cobalt alloys, iron-aluminum alloys, particles in which magnetic materials are dispersed in binder resin, titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide,
Zirconium oxide, silicon carbide, magnesium titanate, barium titanate, lithium titanate, lead titanate,
Ceramics such as lead zirconate and lithium niobate, AD
P (NH4H2PO4), KDP (KH2PO4)
, high dielectric constant substances such as Rochelle salt, etc. Among these, iron powders such as iron oxide and reduced iron, and ferrite are preferred because they are inexpensive and have excellent image characteristics.

The carrier core material is not limited to one type, and a mixture of two or more types may be used.

Further, the particle size of the carrier core material may be about 30 to 200 μm, preferably about 50 to 130 μm.

Examples of the polymer material for forming the coat layer include acrylic polymers, styrene polymers, and styrene polymers.
Acrylic polymers, polyethylene, chlorinated polyethylene, olefin polymers such as polypropylene, polyvinyl chloride, polyester, unsaturated polyester, polyamide, polyurethane, epoxy resin, polycarbonate, silicone resin, polytetrafluoroethylene, polychlorotrifluoro Examples include various polymers such as ethylene, fluororesins such as polyvinylidene fluoride, phenol resins, xylene resins, and diallyl phthalate resins. Among them, from the viewpoint of triboelectricity with toner and mechanical strength,
It is preferable to use an acrylic polymer, a styrene polymer, a styrene-acrylic polymer, a silicone resin, or a fluororesin.

The coating layer is not limited to using only one type of polymer, but a mixture of two or more types may be used.

Further, a resistance adjusting agent or a charge controlling agent may be contained in the coating layer.

As a method for coating the carrier core material with a polymeric material, any conventionally known method such as a fluidized bed method or a transfer layer method can be employed. For example, when ferrite is used as the carrier core material and silicone resin is used as the coating layer, it can be manufactured as follows.

That is, ferrite as a carrier core material is placed in a fluidized bed type coating device, and air is supplied from the bottom of the coating device to suspend the ferrite and bring it into a fluidized state. On the other hand, a silicone resin solution in which a predetermined amount of silicone resin is dissolved in a solvent is prepared, and is sprayed from above the coating device onto the floating and fluid ferrite to coat it with the silicone resin.

The carrier of the two-component developer of the present invention has a ratio of (resistance value of carrier core material)/(carrier resistance value) of 0.020 or more, preferably 0.020 to 0.20.

(Resistance value of carrier core material)/(Carrier resistance value) is 0.
If it is less than 020, counter charges tend to remain in the coating layer, and carrier flying tends to occur.

The toner is colored fine particles composed of a binder resin, a colorant, a charge control agent, a mold release agent, and the like.

Examples of the binder resin include polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, and styrene-vinyl chloride copolymer. Vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic ester copolymer (styrene-methyl acrylate copolymer, styrene-
Ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer,
styrene-phenyl acrylate copolymer, etc.), styrene-methacrylate ester copolymer (styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-phenyl methacrylate copolymer, etc.)
, styrene-based resins such as styrene-α-methyl chloroacrylate copolymer, styrene-acrylonitrile-acrylic acid ester copolymer (styrene or a homopolymer or copolymer containing styrene substituted product), vinyl chloride resin, styrene - Vinyl acetate copolymer, rosin modified maleic acid resin, phenyl resin, epoxy resin, polyester resin,
Examples include low molecular weight polyethylene, low molecular weight polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl butyral resin, and the like.

Among these, styrene resins and styrene-acrylic resins are preferred.

The binder resin is not limited to one type, and a mixture of two or more types may be used.

Examples of the coloring agent include coloring pigments, extender pigments, conductive pigments, magnetic pigments, photoconductive pigments, etc., which will be described later. These may be used singly or in combination of two or more depending on the purpose.

Examples of colorants include black pigments such as carbon black, acetylene black, and aniline black; yellow lead, zinc, cadmium yellow, yellow iron oxide, nickel titanium yellow, naphthol yellow S1 Hansa yellow 61
Quinoline Yellow Lake, Permanent Yellow NCG
, tartrazine lake and other yellow pigments: red yellow lead, molybdenum orange, permanent orange and other orange pigments; red iron, cadmium ret, red lead, permanent red 4R, pyrazolone red, lakelet D1 brilliant carmine 65B10-damin lake B1 alizarin lake, Red pigments such as Brilliant Carmino 3B; Violet pigments such as manganese purple, First Violet B1, Methyl Violet Lake; Blue pigments such as ultramarine blue, cobalt blue, partially chlorinated phthalocyanine blue, First Sky Blue, Indan Stremburu-BC; Chrome Clean, Green pigments such as chromium oxide, Pigment Green B1 Malachite Green Lake; White pigments such as zinc white, titanium oxide, antimony white, zinc sulfide; Extender pigments such as pallite powder, barium carbonate, clay silica, talc, alumina white; electrical conductivity Conductive pigments such as carbon black and aluminum powder; magnetic pigments such as various ferrites; photoconductive pigments such as zinc oxide, selenium, cadmium sulfide, and cadmium selenide.

The colorant is used in an amount of 1 to 20 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the binder resin.

There are two types of charge control agents: one for positive charge control and one for negative charge control.

As a charge control agent for positive charge control, an organic compound having a basic nitrogen atom, such as a basic dye, aminopyrine,
Examples include fillers surface-treated with pyrimidine compounds, polynuclear polyamino compounds, aminosilanes, and the like. On the other hand, examples of charge control agents for controlling negative charges include compounds containing a carboxy group (for example, alkyl salicylic acid metal chelates, etc.), metal complex dyes, fatty acid soaps, naphthenic acid metal salts, and the like.

The charge control agent is used in an amount of 0.1 to 100 parts by weight of the binder resin.
It is used in a proportion of 10 parts by weight, preferably 0.5 to 8 parts by weight.

Examples of the mold release agent (offset inhibitor) include aliphatic resins, aliphatic metal salts, higher fatty acids, fatty acid esters, and partially saponified products thereof. Among these, low molecular weight aliphatic resins having a weight average molecular weight of 1,000 to 10,000 are preferred. Specifically, one or a combination of two or more of low molecular weight polypropylene, high molecular weight polyethylene, paraffin wax, and low molecular weight olefin polymers consisting of olefin units having 4 or more carbon atoms are suitable. In addition to the above-mentioned substances, silicone oil, various waxes, etc. can also be used.

The mold release agent is used in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the binder resin.
It is used in proportions of 0.5 to 8 parts by weight, preferably 0.5 to 8 parts by weight.

The toner is prepared by premixing the above-mentioned components homogeneously using a dry blender, a Henschel mixer, a ball mill, etc., and melting this mixture using a kneading device such as a Banbury mixer roll, a screw-screw or twin-screw extrusion kneader, etc. Knead,
This mixed material is cooled, pulverized, and classified if necessary to produce it.

The particle size distribution of the toner can be controlled not only by the pulverization process but also by classification.

Generally, the particle size of toner is 3 to 35 μm, preferably 5 to 2 μm.
It is desirable that the thickness be within the range of 5 μm.

In particular, particles with a particle size of 16 μm or more are preferably 1.5% or less in terms of number ratio. If the content of toner with a particle size of 16 μm or more exceeds 1.5%, the counter charge in the carrier coating layer becomes high and carrier scattering is likely to occur, which is not preferable.

Further, the degree of compression of the toner is preferably 40% or less in order to improve the fluidity of the toner, to make the adhesion of the toner to the carrier uniform, and to equalize the counter charge of the carrier.

Note that the degree of compression of the toner is determined by the following equation.

X100 (%) Here, the loose apparent density is determined from the weight of 100 cc when the toner is passed through a 100 mesh sieve and allowed to fall naturally into a 100 cc cell.

In addition, after measuring the density for a hard appearance, and for a loose appearance, the capacity is calculated by attaching an extension cell to the cell and hardening the toner by tapping once/second for 180 seconds. It is determined from the above weight.

The toner of the two-component developer of the present invention has an electrical conductivity of '3.0.
X10 bow is 0S/cm or more, and the conductivity of the toner is 3.
If it is less than 0x'o 37 cm, the counter charge remaining in the carrier coating layer will be high, and carrier flying will likely occur.

The conductivity of the toner can be adjusted by adding a colorant such as carbon black to 5 parts by weight per 100 parts by weight of the toner.
In addition to selecting from the range of 15 parts by weight, the amount may be adjusted by adjusting the dispersion state of the colorant. The dispersion state of the colorant can be set by the mixing and operating conditions of the crosstalk device.

<Example> Hereinafter, the two-component developer of the present invention will be explained in detail by giving examples.

Examples 1 to 5 and Comparative Examples 1 to 3 (1) Preparation of carrier Core material: ferrite particle center particle diameter: approximately 100 μm Saturation magnetization + 50 e mu/g Coat employed polymer: Styrene-acrylic copolymer Molecules were coated on the surface of the core material using a fluid coating method to form a coating layer, and carriers with different resistance values were produced. Table 1 shows the resistance values of each carrier obtained. Further, (resistance value of carrier core material)/(carrier resistance value) was determined from the resistance value of this carrier and the resistance value of the core material determined in advance.

Note that the resistance value of the carrier was measured as shown below.

[Method for measuring the resistance value of the carrier] Imitating the magnetic blank development method, the N
The poles and south poles are opposed. In this case, the surface magnetic flux density of the magnetic pole is 1500 Gauss, and the area of the opposing magnetic pole is 10
The size shall be 10×30. Parallel plate electrodes are arranged between the magnetic poles with an inter-electrode spacing of 2 mm, and 200 mg of a sample is placed between the electrodes and held by magnetic force. Then, the resistance value was measured using an insulation resistance meter or an ammeter.

(2) Preparation of toner (ingredients) (Parts by weight) Styrene-acrylic copolymer 100.0 Charge control agent (monoazo dye) 3.0 Low molecular weight polypropylene 1.8 Each component of the above formulation were added in the proportions (parts by weight) shown in Table 1, mixed, melted and kneaded, cooled, pulverized and classified to obtain toners having different conductivities. Table 1 shows the electrical conductivity of each toner obtained.

Furthermore, among the toners obtained in Examples 1 to 5, the particle size was 16 μm.
The number ratio of the above items was 0.45% in Examples 1 to 4, and 1.35% in Example 5. Further, the degree of compression of the toners of Examples 1 to 5 was all 37.4%. In order to adjust the degree of compression, 0.3 parts by weight of hydrophobic silica was added to 100 parts by weight of each toner.

Note that the conductivity of the toner was measured as follows.

[Measurement of electrical conductivity of toner] Each toner obtained as described above was measured using parallel plate electrodes (
Powder electrode manufactured by Ando Electric Co., Ltd.) is filled with a porosity of 25%, and the vehicle peak is 100KH from +1V to -1V.
An alternating current voltage of z was applied and the conductivity of each toner was measured.

The electrodes used had an electrode area of 2.27 cm2, and were filled with toner so that the distance between the electrodes was 0.5 mm±0°1 mm.

The carrier and toner obtained as described above were mixed in a weight ratio of 100:3.5 to obtain a developer.

[Carrier Flying Evaluation Test] Each developer obtained in Examples 1 to 5 and Comparative Examples 1 to 3 was loaded into a copying machine (DC3255 manufactured by Sanda Kogyo Co., Ltd.). On the other hand, a mesh chart was prepared in which a mesh pattern was pasted at 30 locations in which a large number of parallel straight lines were drawn vertically and horizontally at intervals of about 0.57 mm from each side within a square frame with a side length of 24 mm.

Using this mesh chart as a manuscript, 500 copies were made using the copying machine.
When 0 copies are made, when 0 copies are made, when 500 copies are made, when 1000 copies are made,
2000 sheets, 3000 sheets, 4000 sheets and 50 sheets
At the time of 00 sheets, 5 sheets were each sampled 7 times, and the presence or absence of image blanking due to carrier flying was checked and evaluated according to the following criteria. The results are shown in Table 1.

O... The missing parts of the image are within 9 places ×... 1
In addition, the initial image density (I
D) using a reflection densitometer (MODEL TC) manufactured by Tokyo Juishokusha.
-6D), and the results are also shown in Table 1.

In addition, in the same table, the core material resistance value indicates the resistance value of the carrier core material.

(Left below) As can be seen from Table 1, (resistance value of carrier core material)/(
Examples 1 to 5 in which the carrier resistance value) is 0.020 or more
In the case of (resistance value of carrier core material) /
(Carrier resistance value) is less than 0.020 in Comparative Example 1 and Comparative Example 2, both toner conductivity is 8.5X10-'°
Although S/cm is the same value as Examples 1 to 5, a large number of carrier jumps occur and the initial image density is low.

In Comparative Example 3, (resistance value of carrier core material)/(carrier resistance value) is 0.020 or more, but because the conductivity of the toner is as low as 2°4X10-10S/cm, carrier flying cannot be prevented. There are many missing images of the mortar.

As described above, compared to Comparative Examples 1 to 3, the two-component developers obtained in Examples 1 to 5 were all prevented from carrier flying, had almost no missing images, and had good initial image density. It showed the value.

<Effects of the Invention> According to the two-component developer of the present invention, (resistance value of carrier core material)/(carrier resistance value) is 0.020 or more,
In addition, since the conductivity of the toner is 3.0 x 10 -'' S/cm or more, it is possible to prevent image blanking due to carrier flying. Moreover, the initial image density is high, and a high quality image can be provided.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing potential patterns on the photosensitive drum when copying solid black, proximity lines, and mesh patterns, respectively.

Claims (1)

[Claims] 1. In a two-component developer consisting of a carrier whose surface is covered with a polymer coating layer and a toner, (resistance value of carrier core material)/(carrier resistance value) is 0.
020 or more, and the toner has a conductivity of 3.0×
A two-component developer characterized in that it has a developer density of 10^-^1^0 S/cm or more.