JPH0424655A - 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 compressibility of a toner to <= 40%. CONSTITUTION:The (resistance value of carrier core material)/(carrier resistance value) is >= 0.020 and the compressibility of the toner is specified to <= 40%. 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 flowability of the toner is improved and the number of toner sticking to one piece of the carrier is uniformized by specifying the compressibility of the toner to <= 40%. 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.

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

The following may be considered to be the cause of such carrier jump.

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 Vl due to the influence of the potential around the outside of the side proximity line.
(V2:2V+). Furthermore, in a fine mesh image, the potential difference ■ between the potential of the white part surrounded by each line and the residual potential is the potential difference V of the nearby line image.
2 (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. occurs. 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 the problem> Carrier flying, where the carrier adheres to the surface of the electrostatic latent image, is caused by lines of electric force near the photoreceptor and by the toner remaining in the carrier when it is separated from the carrier by 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 have discovered a completely new fact that it is deeply related to the degree of compression.

The degree of compression here is a concept representing the fluidity of particles, and is expressed by the following formula (I).

X100 (%) (I) In formula (I), the apparent density of the toner is 10
It is determined from the weight of 100 cc passed through a 0 mesh sieve and allowed to fall naturally into a 100 cc cell.

In addition, in the above formula (I), the hard appearance is the density, and the loose appearance is the density. It is determined from the capacity when packed and the weight. Therefore, the apparent density exhibits a substantially constant value regardless of the mixing time, etc., as long as the amounts of components such as the binder resin and colorant are constant.

The relationship between carrier flying, the resistance value of the coat layer, and the degree of compression of the toner will be explained below.

The larger the resistance value of the carrier coating layer, the more likely the counter charge remains in the coating 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, the higher the degree of compression of the toner, the lower the fluidity of the toner, resulting in variations in the amount of toner attached to one carrier. When the amount of attached toner is small, the electrostatic attraction between the carrier and toner increases, making it difficult for the toner to separate from the carrier.

On the other hand, if the amount of attached toner is large, the image density after development will be high, or on the other hand, the counter charge remaining in the carrier coating layer will be large, resulting in frequent carrier flying.

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 degree of compression of the toner is 40% or less.

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.

In addition, by setting the toner compression degree to 40% or less,
The fluidity of the toner is improved, and the number of toners attached to one carrier is made uniform. Therefore, there is no carrier that is significantly larger than the counter charge, and carrier flying is further prevented.

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., iron-nisokel alloy, iron - Magnetic materials such as cobalt alloys, iron-aluminum alloys, and particles in which magnetic materials are dispersed in binder resin, as well as titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, and magnesium titanate. , barium titanate, lithium titanate, lead titanate, lead zirconate, lithium niobate and other ceramics, ADP
Examples include high dielectric constant substances such as (NH4H2PO4), KDP (KH2PO4), and Rochelle salt. 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 limited to only one type, or a mixture of two or more types may be used.

Further, the particle size of the carrier core material is preferably 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, styrene-acrylic polymers, polyethylene, chlorinated polyethylene,
Olefin polymers such as polypropylene, polyvinyl chloride, polyester, unsaturated polyester, polyamide,
Examples include various polymers such as polyurethane, epoxy resin, polycarbonate, silicone resin, fluororesin such as polytetrafluoroethylene, polychlorotrifluoroethylene, and polyvinylidene fluoride, phenol resin, xylene resin, and diallyl phthalate resin. Among these, acrylic polymers, styrene polymers, styrene-acrylic polymers, silicone resins, or fluororesins are preferably used from the viewpoint of frictional charging properties with toner and mechanical strength.

The coating layer is not limited to using only one type of polymer, or 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 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) or 0.
If it is less than 020, counter charges remain in the carrier 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 resins such as styrene-α-methyl chloroacrylate copolymer, styrene acrylonitrile-acrylic acid ester copolymer (styrene or styrene-substituted monopolymers or copolymers), vinyl chloride resin, styrene-acetic acid Vinyl copolymer, rosin modified maleic acid resin,
Examples include phenyl resin, epoxy resin, polyester resin, low molecular weight polyethylene, low molecular weight polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-dityl 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 various colored pigments, extender pigments, conductive pigments, magnetic pigments, photoconductive pigments, and the like. 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 yellow, cadmium yellow, yellow iron oxide, nickel titanium yellow, naphthol yellow 81 and Hansa yellow 61.
Quinoline Yellow Lake, Permanent Yellow NCG
, yellow pigments such as tartrazine lake; orange pigments such as red yellow lead, molybdenum orange, permanent orange, red iron, cadmium red, red lead, permanent red 4R, pyrazolone red, lake red D1 brilliant carmine 65B10-damin lake B1 alizarin lake , Brilliant Carmino 3B, and other red pigments; manganese purple, First Violet B1, methyl violet lake, and other purple pigments; ultramarine blue, cobalt blue, phthalocyanine blue partially chlorinated product, first sky blue, and blue pigments such as Indan Stremburu-BC, nichrome green, 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% based on 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 adjusted not only by a pulverization process but also by classification.

Generally, the particle size of toner is 3 to 35 μm, especially 5 to 25 μm.
It is preferable that it is within the range of .

The degree of compression of the toner in the two-component developer of the present invention is 40% or less, and if the degree of compression of the toner exceeds this range, the amount of toner attached to one carrier will vary greatly, and the degree of compression of the toner after development will increase. The counter charge of the coating layer becomes high, and carrier flying becomes more likely to occur.

As a method for adjusting the degree of compression of the toner, for example, a fluidity imparting agent such as hydrophobic silica, titanium oxide, alumina, etc. is added to the toner 1.
The amount may be selected from the range of 0.05 to 3 parts by weight per 0.00 parts by weight, and may also be adjusted by adjusting the particle size, particle size distribution, shape, etc. of the toner.

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

Examples 1 to 6 and Comparative Examples 1 to 3 (1) Preparation of carrier Core material: ferrite particle center particle diameter: about 100 μm Saturation magnetization: 50 e mu / g Coating layer polymer: styrene-acrylic copolymer above A coating layer was formed by coating the surface of the core material with a polymer using a fluid coating method, and carriers having different resistance values were produced. The resistance values of each carrier obtained are shown in Table 1. 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.

[Measurement method of carrier resistance value] Modeling the magnetic brush development method, with a spacing of 5 mm between the electrodes, 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) Styrene-acrylic copolymer carbon black Charge control agent (monoazo dye) Low molecular weight polypropylene (parts by weight) 1 (Jo, 0 8.5 3.0 1.8 of the above formulation) After mixing each component, melting and kneading, and cooling, crush,
The toner was obtained by classification. Next, 100% of the obtained toner
Hydrophobic silica was mixed with a stirrer in the ratio (parts by weight) shown in Table 1 to the parts by weight to adjust the degree of compaction. Table 1 shows the degree of compression of each toner thus obtained.

The degree of compression of the toner was measured using a powder tester manufactured by Hosokawa Micron.

The carrier and toner obtained as described above were mixed in a weight ratio of 100:15 to obtain a developer.

[Carrier Flying Evaluation Test] Each of the developers obtained in Examples 1 to 6 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 of a large number of horizontally and vertically parallel straight lines drawn at intervals of approximately 0.57 mm was pasted at 30 locations within a square frame with a side length of 24 mm. Using this mesh chart as a manuscript, the copying machine
000 copies were made, and 5 copies each were sampled seven times at 0 copies, 500 copies, 1000 copies, 2000 copies, 3000 copies, 4000 copies, and 5000 copies.
Confirm the presence or absence of image mortar missing due to carrier flying,
Evaluation was made using the following criteria. The results are shown in Table 1.

O... Image missing in 9 places or less X... Image missing in 10 places or more
DEL TC-6D) and the results were also
Also listed in the table.

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 6 in which the carrier resistance value) is 0.020 or more
(resistance value of carrier core material) /
In Comparative Examples 1 and 2, which have a small (carrier resistance value), although the degree of compression of the toner is as low as 37.4 and the fluidity is good, a lot of carrier flying occurs and the initial image density is also lower than that of Example 1. It is lower than 6.

In Comparative Example 3, (resistance value of carrier core material)/(resistance value of carrier) is 0.020 or more, but since the compression degree of the toner is 40.9%, the fluidity of the toner is poor and the carrier Not fly-proof.

As described above, the two-component developers obtained in Examples 1 to 6 all showed less carrier scattering and good initial image densities than Comparative Examples 1 to 3.

<Effects of the Invention> According to the two-component developer of the present invention, (resistance value of carrier core material)/(resistance value of carrier) is 0.020 or more,
In addition, since the degree of compression of the toner is 40% or less, it is possible to prevent the image from disappearing 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 degree of compression of 40% or less.