JPH03186858A - Developing method with high image quality - Google Patents

Abstract

PURPOSE:To obtain high-quality images by specifying the relation of the resistivity in a dynamic state between a carrier and a developer and the frequencies of the contact of a magnetic brush with a photosensitive body. CONSTITUTION:The developer has the dynamic resistivity Rd lower than the dynamic resistivity Rc of the carrier and the rubbing between the magnetic brush and the photosensitive body is so set as to have 100 to 300 frequencies k defined by equation I. In the equation I, n denotes the number of the carrier contacts (piece/mm<2>) per area of the photosensitive body determined from a scanning type electron microscopic photograph concerning the collodion fixed magnetic brush; L is expressed by equation II. In the equation II, Nip denotes the nip width (mm) of the developer on the surface of the photosensitive body; Vs denotes the moving speed (mm/sec) of a developing sleeve; Vd denotes the developing length regulated by the moving speed (mm/sec) of the surface of the photosensitive body. The excellent reproducibility of the line images and the higher density of the solid images are simultaneously attained in this way.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a developing method using a two-component developer used in electrophotography and electrostatic printing, and more specifically, it relates to a developing method using a two-component developer used in electrophotography and electrostatic printing. The present invention relates to a high-quality image developing method in which character images are good, and the density of vector images is sufficiently reproduced.

(Prior Art) A two-component developer containing a magnetic carrier and a toner is widely used in commercial electrophotographic copying machines, and when developing a charge image, the developer's magnetic brush is equipped with an internal magnetic pole. The toner image is formed by rubbing this magnetic brush against a photoreceptor carrying a charged image.

Spherical ferrite sintered particles and those coated with resin on their surfaces have recently come into wide use as magnetic carriers, and in order to improve the quality of reproduced images, it is common practice to increase the resistance of magnetic carriers. It is being done.

When the resistance of the carrier is increased, the reproducibility of line images becomes better, but on the other hand, the density of the solid image tends to decrease due to the edge effect in the solid image area.

As described above, the electrical characteristics of the developer due to the increased resistance of the carrier have not yet been fully understood, and it is still difficult to obtain images that can satisfy both high-density solid images and line images with little bias. We are in a difficult situation.

Furthermore, if we are aiming for high-quality images, not only the electrical characteristics of the developer but also the state of the developer in the development area (rubbing state) are important, but this is not fully understood. It is difficult to say, but no proposal has been made that comprehensively captures the electrical characteristics of the developer and the dynamic rubbing condition in the developing area.

Therefore, the present invention has been made in view of the above points,
The purpose is to provide a developing method that can achieve both excellent reproducibility of line images and high density of dark images at the same time.

A further object of the present invention is to provide a developing method that has less bias when reproducing dense thin lines and has excellent reproducibility of Chinese characters and reproducibility when copying from copy to copy is repeated.

Another object of the present invention is to provide a developing method using a dry two-component developer in which the toner charge amount remains stable, toner scattering is small, and the durability is excellent.

(Means for Solving the Problems) According to the present invention, a magnetic brush of a two-component developer containing magnetic carrier J and toner is formed on a developing sleeve, and this magnetic brush is transferred to a photoreceptor having a charge image. In a developing method in which a toner image is formed by rubbing with a magnetic brush, the developer has a dynamic resistivity (Rd) lower than the carrier dynamic resistivity (Rc), and the developer has a dynamic resistivity (Rd) lower than the carrier dynamic resistivity (Rc), is expressed by the following formula, k = L - n... (1) In the formula, n is the number of carrier contacts per photoreceptor area (pieces/mm2) determined from a scanning electron micrograph of the collodion fixed magnetic brush. Yes, L is the formula % formula % (2) (N i p is the nip width of the developer on the surface of the photoreceptor (
mm), and ■5 is the moving speed of the developing sleeve (mm/
s e c ), and Vd indicates the development length defined by the moving speed (mm/sec) of the photoreceptor surface.The frequency (k) defined by is set to be 100 to 300. A characteristic high-quality image development method is provided.

In the present invention, the ratio of the dynamic resistivity of the developer to the dynamic resistivity of the carrier (Rd/Rc) is preferably in the range of 0.20 to 0.99.

Furthermore, in the present invention, the dynamic resistivity of the magnetic carrier is 5
It is preferably in the range of X109 to 5×1011 Ω·cm.

(Function) The present invention uses a component developer containing a magnetic carrier and a toner that has a dynamic resistivity (Rd) lower than the dynamic resistivity (RC) of the carrier, and satisfies the above formula (1).
Contact frequency of carriers (k, number/m m
) is set to ioo to 300, it achieves excellent reproducibility of line images and high density of solid images at the same time, and also prevents bias during development of dense fine lines and reproduces character images such as kanji. This is based on the new knowledge that it is possible to produce high-quality copied images that have good properties and do not cause toner scattering or image blurring.

In this specification, dynamic resistivity refers to the resistivity when the carrier or developer forms a magnetic brush on the developing sleeve and is moving, and is different from the resistivity conventionally measured statically. The measurement means and meaning are completely different.

This dynamic resistivity is measured using the measuring device shown in FIG. 1 as follows.

That is, as shown in FIG. 1, a carrier (developer) 3 is introduced into a developing device 2 equipped with an agitating roller 1, and the carrier (developer) 3 is carried on a sleeve 4, and at the same time, it is , the carrier (developer) 3 is transported with the three carrier (developer) layers adjusted to a predetermined thickness. Also,
A detection section 8 having a predetermined surface area is arranged along a surface imaginary line 6 of the photoreceptor facing the sleeve 4 at a predetermined distance using a micromake 7 as an inter-electrode distance adjusting means,
Applying an alternating current voltage of a predetermined wavelength to the sleeve 4, supplying the detection signal y from the detection section 8 to the parallel circuit of the door and the oscilloscope 9, and reading the waveform data on the oscilloscope 9 with the reading means 10, The electrical resistivity is calculated by the calculation unit 11.

In the figure, reference numeral 12 denotes a cleaning blade as a 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 detection part 8, that is, the distance between the electrodes d = 1.2 mm, the surface area of the detection part 8, that is, the electrode area s = 0.785 cm2, and an AC voltage with a frequency of 50 Hz was set. use By using the carrier as a magnetic brush, the dynamic resistivity Rc is determined, and by using the two-component developer as the magnetic brush, the dynamic resistivity Rd is determined.

In the developer of the present invention, the fact that the dynamic resistivity Rd of the developer is lower than the dynamic resistivity Rc of the carrier means that when the carrier contains an electroscopic toner, it is more electrostatic than when the carrier is used alone. This shows the surprising fact that the resistance is low, making it easier for the developing current to flow. Therefore, in the present invention, when the formula % formula % (3) is satisfied, there is no bias in the fine lines (no chipping at the leading edge or chipping at the trailing end in the rotational direction of the photoreceptor drum) when reproducing densely packed fine lines. ) The fact that the density of solid images can be improved at the same time has been obtained through many experiments, and although the theoretical basis cannot be said to be fully clarified, it is possible to improve the density of solid images at the same time. Since the developer has a lower resistance than this, it is recognized that development proceeds under conditions where the edge effect of the electrostatic latent image is large but the relaxation time of the charge is relatively small. That is, with respect to the reproduction of fine lines, it is recognized that while faithful reproduction of fine lines is performed due to the edge effect, during development of a solid image, charge relaxation occurs relatively quickly, leading to an increase in the density of the solid image. In the present invention, a developer having the above-mentioned electrical characteristics is used, and the contact frequency (k) expressed by the above formula (1) is set to 100 to 300 to determine the rubbing state of the developer against the photoreceptor drum in the development area. Configure the settings so that

Since the contact frequency (k) expressed by the above formula (1) is expressed as the product of the number n of carriers in contact per photoreceptor area and the development length L, one or both of n and L can be expressed as By adjusting it, it can be set within a predetermined range.

FIG. 3 is a sketch of a scanning electron micrograph of a collodion-fixed magnetic brush for a two-component developer suitable for the present invention, from which the number of contacts per unit area can be easily determined.

The main factors that influence the number n of carrier contacts per unit area are the physical properties of the developer, especially the magnetic carrier.
In addition, the distance between the developing sleeve and the photoreceptor drum (dc+-s
). Generally dD-! As l increases, n decreases; conversely, as aO-S decreases, n increases. d
Assuming that D-3 is constant, n depends on the characteristics of the developer, especially the magnetic carrier, especially the saturation magnetization; when the saturation magnetization increases, n increases, and when it decreases, n decreases.

The development length L in the formula (1) has the following meaning. In FIG. 2, which schematically shows the developing section, the drum 21 has a circumferential speed of V
, the developing sleeves 22 are moving at a peripheral speed V0 such that their moving directions become the same at the position of the nip width Nip. A magnetic brush of a magnetic carrier 23 is formed on the developing sleeve 22 . For example, negatively charged toner 24 is placed on the magnetic carrier 23.
On the other hand, the carrier has a positive counter charge, and the toner 24 is attracted to the electrostatic latent image (positive) of 1 on the drum and is developed, and the counter charge on the carrier 23 passes through the magnetic brush onto the developing sleeve 22. run away to

The time t for a latent image point to pass through the dip is expressed by the formula % (4), and the length L of the toner passing over the latent image point is calculated by multiplying the above t by the speed difference between the two. That is, it is expressed by the formula % formula % (2). This development length has a dimension of length and is a value proportional to the amount of development toner.

Thus, the nip width (Nip), drum peripheral speed (■,,)
The contact frequency (k) of the carrier can also be set by selecting the developing sleeve circumferential speed (V5).

- If the frequency of contact is reduced as a tendency for boat fishing, tip chipping of multiple thin wires tends to occur, as well as uneven density in solid areas. ) occurs more frequently, and toner dust and fog density around the image area tend to increase. Increase contact frequency from 100 to 30
If the developer is adjusted to a specific range of 0 and has electrical characteristics that satisfy the above formula (3), a uniform image with high density can be obtained in the base area without fogging or dust, and there will be no multiple fine lines. is reproduced without any bias (lack of front and rear edges), and in particular, it is possible to faithfully reproduce character manuscripts such as kanji characters.

The dynamic resistivity (Rc) of a magnetic carrier is generally 5×10
A range of 9 to 5×10 11 Ω, cm is good in terms of fine line reproducibility, while the ratio of the dynamic resistivity (Rd) of the developer to the dynamic resistivity (Rc) of the magnetic carrier is Rd / R
It is preferable that c is in the range of 0.20 to 0.99, particularly 0.3 to 0.7, from the viewpoint of balance between improvement of image density in solid areas and fine line reproducibility, and prevention of image fogging and toner scattering.

(Preferred Embodiment of the Invention) In the present invention, as the magnetic carrier, dynamic resistivity (
Any material can be used as long as Rc) is within the above-mentioned range. Generally, ferrite particles are used whose surfaces are coated with a high-resistance resin so that the dynamic resistivity is within the above range.

Spherical ferrite particles are preferred, and the particle size is 20 to 140 μm, particularly 50 to 100 μm.
It is desirable that it be within the range of .

Conventionally, for example, iron zinc oxide, (ZnFe
Ju, iron cadmium oxide (CdFe504), iron gadolinium oxide (CdFe50,2), iron yttrium oxide (YaFesO+z), iron nickel oxide (NiFe
204), barium iron oxide, (Babe + zo 1
9), sintered ferrite particles with a composition consisting of one or more types of iron oxide magnesium (MgFe03), etc. are used, and in particular Cu, Z
Soft ferrite containing one, preferably two or more selected from the group consisting of n, Mg and N1, such as copper-zinc-magnesium ferrite, is used.

The dynamic resistivity of ferrite particles depends on the type and coating amount of resin provided on the surface of the ferrite particles. Coating resins for surface coating include one or more of silicone resins, fluorine resins, acrylic resins, styrene resins, styrene acrylic resins, olefin resins, ketone resins, phenol resins, xylene resins, diallyl phthalate resins, etc. can be used. Among these resins, straight silicone resins, ie, silicone resins made of organopolysiloxanes such as dimethylpolysiloxane, diphenylsiloxane, and methylphenylpolysiloxane, and having a network structure are most preferred.

Reticulation (crosslinking) of silicone resin involves the presence of hydrolyzable functional groups such as trimethoxy groups and functional groups such as silanol groups in organo-4 polysiloxane units, and if necessary, after hydrolysis treatment, silanol condensation. This is done by applying a catalyst.

The coating amount of the resin is generally selected from the range of 0.5 to 5 parts by weight, particularly 0.8 to 3 parts by weight per 100 parts by weight of ferrite, so that the RcO value is as described above. Also,
From the point of view of contact frequency, when the saturation magnetization is small, the number of carrier contacts per photoconductor area decreases, and the contact frequency (K) tends to decrease accordingly. becomes. The saturation magnetization of the carrier is preferably in the range of 40 to 7 Qemu/g, particularly 45 to 60 emu/g.

In the present invention, the electrodetectable toner has a static conductivity of 6.
The range of X 10-10 to 4X10-9 S/cm is preferable, in order to satisfy the above formula (1).

Furthermore, the reason why the electrical conductivity is static is that dynamic resistivity cannot be measured using toner alone. Furthermore, the dielectric constant (ε) of the toner is 2°7 to 3.9
It is preferable that the developing electric field is emphasized and the development stop potential is adjusted to a preferable level.

The conductivity and dielectric constant of the toner used in the present invention were measured using a parallel plate electrode type measuring device with an electrode area of 2.27 cm2 and an interelectrode area of 0°5 mm, and the toner was filled to a porosity of 25%. The vehicle peak was measured by applying an AC voltage of -1 from the river.

In order to keep the characteristic values of the toner within the above range, select a colorant with particularly good conductivity as the colorant: Increase the amount of conductive colorant mixed: Select a resin with low electrical resistance. :Means such as adding a conductivity regulator are adopted. As the resin having relatively low electrical resistance, a resin containing a polar group is suitable, and acrylic resins, acrylic-styrene copolymer resins, polyester resins, epoxy resins, etc. are preferably used. The resin conductivity is generally lX
l0-” to 1.X 10-9S/cm, especially 3x
In the present invention, it is preferable that the length is in the range of 1 Q-10 to 37 cm.In addition, in the case of black toner, carbon black, which is a coloring agent, is likely to form chain stractures in the resin. Therefore, it is best to use particles with a fine particle size and large oil absorption and BET specific surface area. Generally, those with a BET specific surface area of 50 m2/g
The above is good.

In this case, the amount of carbon black blended is preferably in the range of 2 to 20 parts by weight, particularly 5 to 10 parts by weight, per 100 parts by weight of the resin. Further, in the case of chromatic toner, it is preferable to use a coloring agent having high conductivity among known colorants per se, but it is better to use one whose resin itself has high conductivity.

In addition, in order to control the charge of the toner, the toner may contain charge control agents such as oil-soluble dyes such as nigrosine dye, oil black, and spirone black, naphthoic acid, salicylic acid, alkylsalithicylic acid, fatty acids, and resin acids. 0.1 parts by weight of metal salts or complex salts such as manganese, iron, cobalt, nickel, lead, zinc, cerium, calcium, aluminum 7, etc., metal-containing azo dyes, pyrimidine compounds, etc. per 100 parts by weight of the binder resin. The preferred amount may be adjusted from a range of 10 to 10 parts by weight.

In addition, an anti-offset agent may be added, such as low molecular weight polypropylene, low molecular weight polyethylene, various waxes such as paraffin wax, low molecular weight olefin polymers of olefin monomers having 4 or more carbon atoms, fatty acid amide, silicone oil. etc. per 100 parts by weight of binder resin
．． It is used in a content of 5 to 15 parts by weight.

The particle size of the toner particles is preferably a volume-based median diameter of 8 to 14 μm, particularly 9 to 12 μm, as measured by a coulter counter. It may be an amorphous material obtained through Step G or a spherical material produced by suspension polymerization, dispersion polymerization, or the like.

Furthermore, the toner is surface-treated with well-known surface treatment agents such as resin particulate components such as acrylic polymers, silicone resins, and fluorine resins, and inorganic particulate components such as silica, alkali, titanium oxide, and tin oxide. It can also be used as

Development In the present invention, the magnetic carrier and toner are mixed to form a two-component developer such that the Rd value falls within the above range. Carrier and toner are generally 9921 to 80:
20, particularly preferably in a weight ratio of 98:2 to 90:10.

The present invention will be explained below using experimental examples, but the present invention is not limited thereto.

(Experiment example) Using a modified electrophotographic copying machine D (-2585 (manufactured by Sanda Kogyo Co., Ltd., trade name)), developers with various dynamic resistivity relationships between the carrier and the developer were used. distance(
The frequency (k) was changed and set according to development conditions such as the drum-to-sleeve circumferential speed (S/D), and image formation was performed. The results are shown in Table-1.

The solid density was measured using a reflection densitometer.

9 3 or above was considered a passing level. Regarding fine line reproducibility, the degree of deviation (σ) is measured by measuring the leading edge chipping and trailing edge chipping that occur in the development of dense fine lines using the method shown below, and the degree of deviation falls within the range of 100 ± 15. The item was passed. The fog density was also evaluated using a reflection densitometer and was 0.
A score of 003 or lower was considered a passing level. Furthermore, character reproducibility was evaluated subjectively by visual inspection.

The degree of bias (σ) is measured as follows.

The reflected image density of the copied image of the dense thin lines was read using a microdensitometer, and a curve (
Curve i) shows that each line has a constant line width and no chipping at the leading edge or chipping at the rear end is observed, curve (ii) shows a curve with significant chipping at the leading end, and curve (iii) shows a curve where chipping at the trailing end is significant.

Regarding the reproduction of each line width, the deviation (σ) in the feeding direction changes the image density of Fuyuyama in the feeding direction to A, B, C,
When closed, it is given by the formula. When σ is 100 or around 100, each line width is constant and there is no deviation, when it is larger than 100, there is chipping at the tip, and when it is smaller than 100, there is chipping at the rear end. There is.

In addition, the saturation magnetization in the table refers to the saturation magnetization of the carrier (e m
u/g).

From Table 1, it can be seen that when the ratio of the dynamic resistivity of the carrier and the developer and the frequency k are within the preferable range, the images exhibit high density and faithful reproducibility of fine lines, have extremely little fogging, and have excellent character legibility. I understand that there is something.

1 22 (Effects of the Invention) According to the present invention, the resistivities of the carrier and the developer in a dynamic state have a preferable relationship, and the frequency of contact of the magnetic brush with the photoreceptor is set within a preferable range. It is possible to obtain high quality images.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an apparatus for measuring the dynamic resistivity of a developer (carrier) in the present invention, FIG. 2 is a schematic diagram of a developing section, and FIG. FIG. 4 is a sketch of a scanning electron micrograph of a collodion-fixed magnetic brush as a developer, and FIG. 4 is a diagram showing the relationship between the feeding direction and line temperature of a copied image of a dense fine line in the present invention.

Claims (3)

[Claims] (1) A developing method in which a magnetic brush of a two-component developer containing a magnetic carrier and a toner is formed on a developing sleeve, and a toner image is formed by rubbing this magnetic brush against a photoreceptor having a charged image. The developer has a dynamic resistivity (Rd) lower than the dynamic resistivity (Rc) of the carrier, and the friction between the magnetic brush and the photoreceptor is expressed by the following formula: k=L・n where n is It is the number of carrier contacts per photoreceptor area (pieces/mm^2) determined from the scanning electron micrograph of the collodion fixed magnetic brush, and L is the formula L = (Nip) / (V_d) (V_s - V_d) (Ni
p is the developer nip width (mm) on the surface of the photoreceptor, and V_s is the moving speed of the developing sleeve (mm/sec)
, and V_d is the moving speed of the photoreceptor surface (mm/sec
1. A high-quality image development method, characterized in that the frequency (k) defined by is set to be 100 to 300, indicating the development length defined by ). (2) Ratio of developer dynamic resistivity to carrier dynamic resistivity (R
2. The developing method according to claim 1, wherein d/Rc) is in the range of 0.20 to 0.99. (3) Dynamic resistivity of magnetic carrier is 5×10^9 to 5
3. The developing method according to claim 1, wherein the resistance is in the range of x10^1^1 Ω·cm.