JP2577799B2 - Dry two-component developer - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a dry two-component developer for electrophotography, and more particularly, to excellent reproducibility of a line image and high density of a solid image. And a two-component developer simultaneously achieving the above.

(Conventional technology and problems to be solved) A two-component developer containing a magnetic carrier and a toner is widely used in a commercial electrophotographic copying machine. A magnetic brush is formed on a developing sleeve having a magnetic pole therein, and the magnetic brush is rubbed against a photosensitive member having a charge image to form a toner image.

As magnetic carriers, spherical ferrite sintered particles and those coated with resin on the surface have recently been widely used, and in order to improve the quality of copied images,
It is common practice to increase the resistance of a magnetic carrier. When the resistance of the carrier is increased, the reproducibility of the line image is improved, but in the solid image portion, the edge effect causes
The density of a solid image tends to be reduced.

As described above, the electrical characteristics of the developer due to the increase in the resistance of the carrier have not yet been sufficiently grasped, and it is necessary to obtain an image that can sufficiently satisfy both a high-density solid image and a line image with less deviation. The situation is still difficult.

Accordingly, the present invention has been made in view of the above points, and an object of the present invention is to provide a dry two-component developer for electrophotography capable of simultaneously achieving excellent reproducibility of a line image and high density of a solid image. Is to do.

Further, the object of the present invention is a broadly applicable two-component electrophotographic copying machine using a magnetic brush development, and in addition to the above-mentioned combination characteristics, a dry two-component component having a high charge amount, a small amount of toner scattering, and excellent durability. To provide a system developer.

(Means for Solving the Problems) According to the present invention, in a dry two-component developer for electrophotography containing a magnetic carrier and an electrophotographic toner, the magnetic carrier is a resin-coated ferrite carrier. And has a dynamic resistivity (R _C ) of 5 × 10 ^{9 to} 5 × 10 ¹¹ Ω · cm, and the toner has a dynamic resistivity of 6 × 10 ^{−10 to} 4 × 10 ⁻⁹ s / cm. the ratio of the static conductivity and 2.7 to 3.9 dielectric constant has a (epsilon), the dynamic resistivity of the developer (R _D) and the dynamic resistivity of the carrier with (R _C) (R _D / R _C ) is in the range of 0.20 to 0.99.

(Function) The present invention relates to a two-component developer containing a resin-coated ferrite carrier and a toner, the ratio (R _D ) between the dynamic resistivity of the developer (R _D ) and the dynamic resistivity of the carrier (R _C ). _D / _RC )
Is set within the range of 0.20 to 0.99, based on the surprising finding that excellent reproducibility of a line image and high density of a solid image can be achieved at the same time.

In the present specification, the dynamic resistivity means the resistivity when a carrier or a developer forms a magnetic brush on a developing sleeve and is moving, and conventionally, a resistance that is statically measured. The rate is a completely different measure and means.
This dynamic resistivity is measured as follows using the measuring device shown in FIG.

That is, as shown in FIG. 1, a carrier (developer) 3 is introduced into a developing device 2 provided with a stirring roller 1, the carrier (developer) 3 is carried on a sleeve 4, and The carrier (developer) 3 is transported in a state where the thickness of the carrier (developer) 3 is adjusted to a predetermined thickness.
Further, along a virtual line 6 on the surface of the photoconductor facing the sleeve 4 at a predetermined interval, a detection unit 8 having a predetermined surface area by a micrometer 7 as an inter-electrode distance adjusting means.
And a carrier (developer) 3 together with the sleeve 4.
While applying an AC voltage of a predetermined frequency to the sleeve 4 to supply the detection signal y from the detection unit 8 to a parallel circuit of the dummy and the oscilloscope 9 and read the waveform data on the oscilloscope 9. And the calculation unit 11 calculates the electrical resistivity.

In the drawing, reference numeral 12 denotes a cleaning blade as cleaning means for removing the carrier (developer) 3 remaining on the sleeve 4.

As specific measurement conditions, the distance between the sleeve 4 and the detector 8, that is, the inter-electrode distance d = 1.2 mm, the surface area of the detector 8, that is, the electrode area s = 0.785 cm ² , and the frequency 50
Hz alternating current is used. The dynamic resistivity R _C is determined by using the carrier as a magnetic brush, and the dynamic resistivity R _D is determined by using a two-component developer as a magnetic brush.

In the present invention, the fact that the upper limit of the dynamic resistivity ratio (R _D / R _C ) is 0.99 means that the dynamic resistivity R _D of the developer is lower than the dynamic resistivity R _{C of the} carrier. In other words, it shows that the state in which the carrier is blended with the electroconductive toner has a lower electric resistance and the development current flows more easily than in the case of the carrier alone. In the present invention, when the formula: 0.20 ≦ R _D / R _C ≦ 0.99 (1) is satisfied, when reproducing dense dense lines, there is no chipping at the front end and rear end, and there is no deviation of the thin lines, The fact that the solid image is excellent and the density of the solid image can be significantly improved at the same time was obtained as a result of a number of experiments, and the theoretical basis is not sufficiently clear yet. Can be With this developer, the carrier has a high resistance and the developer has a lower resistance, so that the edge effect of the electrostatic latent image is large, but the development proceeds under the condition that the charge relaxation time is relatively short. Is recognized. In other words, when reproducing a fine line, faithful reproduction of the fine line by the edge effect is performed.On the other hand, when reproducing a solid image, the charge is relaxed relatively quickly, and the amount of adhered toner is increased. It is considered that this leads to an increase in the density of the solid image. Therefore, if the lower limit of the ratio of dynamic resistivity (R _D / R _C ) is less than 0.20, the edge effect becomes too large, causing the deviation of fine lines, the density unevenness of a solid image, and the like. Is recognized.

Therefore, from the viewpoint of improving the image density of the solid portion and the balance between the fine line reproducibility and the solid portion density, it is desirable that the dynamic resistivity ratio (R _D / R _C ) is sometimes in the range of 0.3 to 0.7. The dynamic resistivity of the resin-coated ferrite carrier should have a _RC in the range of 5 × 10 ^{9 to} 5 × 10 ¹¹ Ω · cm.

In FIG. 2 for explaining the leading edge and trailing edge defects that occur during the development of dense fine lines, the horizontal axis represents the distance in the feed direction, and the vertical axis represents the density of the reflected fine line copy image reflected by the microdensitometer. And plots the relationship between the two. The curve (i) in FIG. 2 has a constant line width for each line and does not have chipping at the front end or the rear end.
Curve (iii) shows that the rear end chipping is remarkable. Regarding the reproduction of each line width, the deviation (δ) in the feed direction is expressed by the following formula, where the image density of each peak in the feed direction is A, B, C in order. Given by When the value of δ is at or near 100, each line width is constant, there is no bias, and when it is considerably larger than 100, there is a chipped tip, and more than 100,
If it is quite small, it indicates that there is a rear end chipping.

When the dynamic resistivity of the resin-coated ferrite carrier to be used is smaller than 5 × 10 ⁹ , the value of δ is generally 80 or less, and it is recognized that rear end chipping occurs. 5 × 10
When it is larger than ¹¹ Ωcm, the value of δ is generally 120 or more, and the tendency for chipping to occur is recognized,
Whereas the chemical concentration of the solid portion becomes 1.2 or less and the concentration is remarkably reduced, according to a preferred embodiment of the present invention, the δ value is reduced by using a magnetic carrier having a dynamic resistivity in the above range. Is generally in the range of 80 to 120, especially 90 to 110, so that the reproducibility of the diagram can be remarkably improved.

In the present invention, the static conductivity of the toner is set in the range of 6 × 10 ^{−10 to} 4 × 10 ⁻⁹ s / cm so that the relationship between R _D and R _C satisfies the above expression (1). To do that. The reason why the conductivity is static is that the dynamic resistivity cannot be measured by the toner alone.

The conductivity and the dielectric constant of the toner used in the present invention were measured using a parallel plate electrode type measuring device having an electrode area of 2.27 cm ² and a distance between the electrodes of 0.5 mm. , Peak to peak are measured by applying an AC voltage of +1 V to -1 V.

Also, the reason that the dielectric constant (ε) of the toner is defined to be in the range of 2.7 to 3.9 is that when the dielectric constant is large, the electric field intensity during development is emphasized, the development stop potential is reduced, and the amount of toner to be developed is increased. However, if the size is too large, the edge effect is emphasized, and fogging occurs due to induced polarization.

(Preferred Embodiment of the Invention) Magnetic Carrier In the present invention, a ferrite carrier provided with a resin coating and having a dynamic resistance _RC adjusted to the above-described range is used as the magnetic carrier. Of course, the dynamic resistance R _C must be such that the dynamic resistance ratio is within the above-described range according to the conductivity of the toner mixed with the carrier.

Spherical ferrite particles are preferred,
The particle size is desirably in the range of 20 to 140 μm, especially 50 to 100 μm.

Conventionally, as ferrite, for example, zinc oxide (ZnFe
₂ O ₂ ), yttrium iron oxide (Y ₃ Fe ₅ O ₁₂ ), cadmium iron oxide (CdF ₁₂ O ₄ ), gadolinium iron oxide (CdFe
₅ O ₁₂ ), Lead iron oxide (PbFe ₁₂ O ₁₉ ), Nickel iron oxide (NiF
e ₂ O ₄ ), iron neodymium (NdFeO ₃ ), barium iron oxide (BaFe ₁₂ O ₁₉ ), magnesium iron oxide (MgFeO ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ), etc. In particular, sintered ferrite particles having a composition of one or more of the following are used. In particular, at least one, preferably two, of metal components selected from the group consisting of Cu, Zn, Mg, Mn and Ni Soft ferrite containing the above, for example, copper-zinc-magnesium ferrite is used.

The dynamic resistivity of the ferrite particles depends on the type and coating amount of the resin provided on the surface of the ferrite particles. As the coating resin for surface coating, one or two of silicone resin, fluorine resin, acrylic resin, styrene resin, styrene-acrylic resin, olefin resin, ketone resin, phenol resin, xylene resin, sialyl phthalate resin, etc. More than one species can be used. Among these resins, a straight silicone resin, that is, a silicone resin composed of an organopolysiloxane such as dimethylpolysiloxane, diphenylsiloxane and methylphenylpolysiloxane and having a network structure is most preferable. The reticulation (cross-linking) of the silicone resin is carried out by allowing a hydrolyzable functional group such as a trimethoxy group or a functional group such as a silanol group to exist in an organopolysiloxane unit. This is done by acting. The coating amount of the resin is generally selected from the range of 0.5 to 3 parts by weight, particularly 0.8 to 1.5 parts by weight per 100 parts by weight of ferrite, so that the value of _RC is within the above range.

Electrostatic Toner As the electroconductive toner, any toner can be used as long as the static conductivity and the dielectric constant are within the above ranges. In order to keep the characteristic value of the toner within the above range, a carbon black having particularly excellent conductivity is selected as the carbon black: the amount of the conductive carbon black is increased: a resin having a low electric resistivity is also selected as the resin. : Etc.

As a resin having a relatively small electric resistivity, a resin containing a polar group is suitable, and in particular, an acrylic resin or an acrylic resin
Styrene copolymer resins are suitable. Make up these resins.

As acrylic monomers, In the formula, R ₁ is a hydrogen atom or a lower alkyl group, R ₂
Is a hydrogen atom or an alkyl group having up to 18 carbon atoms.

Such as ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, acrylic acid, and methacrylic acid. As the acrylic monomer, in addition to those described above, other ethylenically unsaturated carboxylic acids or anhydrides thereof, for example, maleic anhydride, crotonic acid, itaconic acid and the like can also be used.

Further, as the styrene monomer constituting the copolymer resin, the following formula In the formula, R ₃ is a hydrogen atom, a lower alkyl group (having 4 or less carbon atoms) or a halogen atom; R ₄ is a substituent such as a lower alkyl group or a halogen atom;
Is an integer greater than or equal to.

And styrene, vinyltoluene, α-methylstyrene, α-chlorostyrene, vinylxylene, vinylnaphthalene, and the like. Among them, styrene is preferred.

The acid value of the resin used is suitably in the range of 0 to 25, particularly 5 to 10.

The conductive carbon black to be blended in the toner preferably has a high ability to form a structure in terms of conductivity and a high surface purity. Struture formation ability means that the resin easily forms a chain structure or a tufted structure in the resin, and has a fine particle size and a large oil supply amount and a large BET specific surface area. Generally, those having a BET specific surface area of 50 m ² / g or more are preferred.

The amount of the conductive carbon black is preferably 2 to 20 parts by weight, more preferably 5 to 10 parts by weight per 100 parts by weight of the resin.

The toner may contain a toner compounding agent known per se, for example, a charge control agent. For example, as the charge control agent, any charge control agent known per se, for example, nigrosine base (CI 50415), oil black (CI 2
6150), oil-soluble dyes such as spiron black, 1: 1 type or 2: 1 borrowed metal complex dyes, metal salts of naphthenic acid, fatty acid soaps and resin acid soaps.

The particle diameter of the toner particles, as measured by a Coulter counter, is preferably in the range of 8 to 14 μm, particularly 10 to 12 μm in terms of volume-based median diameter, and was produced by a melt-kneading / pulverization method having a particle diameter. It may be amorphous or spherical, produced by a dispersion or suspension polymerization method.

Developer In the present invention, a two-component developer is obtained by mixing the magnetic carrier and the toner such that the value of _RD is within the above range. The carrier and the toner are preferably mixed and used in a weight ratio of generally 99: 1 to 90:10, particularly 98: 2 to 95: 5.

(Effects of the Invention) According to the present invention, as a two-component developer composed of a resin-coated ferrite carrier and an electroconductive toner, the dynamic resistivity _RD of the developer and the dynamic resistivity _{RC of the} carrier are determined. Ratio (R _D
By using the compound having a ratio of (/ R _C ) in the range of 0.20 to 0.99, it has become possible to improve the reproducibility of the line image and to remarkably improve the density of the solid image.

Hereinafter, the present invention will be described in detail with reference to experimental examples and comparative examples.

(Examples 1 to 7, Comparative Examples 1 to 5) A variety of toners having different average particle diameters and electrical characteristics in which carbon black and a negative-polarity dye low molecular weight polypropylene as a charge control agent are dispersed in a styrene-acrylic copolymer. Prepared. The developer was adjusted with various ferrite-based carrier particles having different dynamic resistivity and the toner, and the dynamic resistivity of each of Examples 1 to 7 and Comparative Examples 1 to 5 was measured. Further, an electrophotographic copying machine DC is used depending on the obtained developer.
Images were taken out using a remodeling machine -2585 (trade name, manufactured by Mita Kogyo Co., Ltd.), and image characteristics such as image density (ID) and deviation of line width (δ), image fog, and toner scattering were evaluated. The developing conditions were as follows: the photoconductor surface potential was 800 V, the cutting interval was 1.0 m, the distance between the developing sleeve and the photosensitive layer was 1.2 mm, and the magnetic force of the developing magnet was 800 Ga.
us, the rotation ratio between the developing sleeve and the photoconductor was set to 2.75.

Table 1 below shows the dynamic resistivity of the developer (R _D ), the dynamic resistivity of the carrier (R _C ), the particle size, the saturation magnetization, the dynamic resistivity of the developer and the dynamic resistivity of the carrier. The ratio (R _D / R _C ), the conductivity of the toner, the dielectric constant and the solid of the toner indicate the image density (ID), the deviation (δ) of the line image, the image fog, and the degree of toner scattering. The image density and fog density were measured by a reflection densitometer, and the degree of toner scattering was determined by visually observing the inside of the apparatus after the copying operation.

As is clear from Table 1, the developer adjusted so that the dynamic resistivity (R _D ) of the developer is smaller than the dynamic resistivity (R _C ) of the carrier alone forms a good image. You can see that.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for measuring the dynamic resistivity of a developer and a carrier, and FIG. 2 is a schematic diagram for explaining a chip at a front end and a chip at a rear end which occur in the development of a dense line.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koshi Kuroki 1-2-28 Tamazo, Chuo-ku, Osaka-shi, Osaka Inside Mita Industries Co., Ltd. (72) Inventor Noriaki Tsubota 1-2-2 Tamazo, Chuo-ku, Osaka-shi, Osaka No. 28 Inside Mita Kogyo Co., Ltd. (56) References JP-A-59-139056 (JP, A) JP-A-56-8153 (JP, A) JP-A-62-106475 (JP, A)

Claims (1)

(57) [Claims] 1. A dry two-component developer for electrophotography, comprising a magnetic carrier and an electrophotographic toner, wherein the magnetic carrier is a resin-coated ferrite carrier, and is 5 × 10 ^{9 to} 5 ×. The toner has a dynamic resistivity (R _C ) of 10 ¹¹ Ω · cm, and the toner has a static conductivity of 6 × 10 ^{-10 to} 4 × 10 ^-9 s / cm and a dielectric constant of 2.7 to 3.9. (Ε), and the ratio (R _D / R _C ) of the dynamic resistivity (R _D ) of the developer to the dynamic resistivity (R _C ) of the carrier is in the range of 0.20 to 0.99. A two-component developer.