JPH03170953A - High-density development method to prevent toner splashing - Google Patents

Abstract

PURPOSE:To form images having a high density, more particularly a high density in a solid part while preventing toner splashing by specifying developing conditions and maintaining the flow state of a developer in a good range. CONSTITUTION:The developing conditions are so set as to satisfy equation I to maintain the adequate flow state of the developer in the development method for transporting the two-component type developer from a developing device to a developing area by a sleeve, developing the electrostatic latent image on a photosensitive drum in the developing area and circulating the developer used for the development to the developing device. In the formula I, M is a coating amt. (g/cm<2>) of the developer per unit area of the sleeve; H is the distance cm on the line connecting the centers of the photosensitive drum and the sleeve; T/D is the weight fraction of the concn. of the toner in the developer; C/D is the weight fraction of the concn. of the carrier in the developer; rhot is the true density g/cm<3> of the toner; rhoc is the true density g/cm<3> of the carrier. The toner splashing is prevented in this way and the high-density images and more particularly the solid part images are formed.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a high-density development method that prevents toner scattering in electrophotography, and in particular to a high-density development method that prevents toner scattering during color copying. Concerning a two-component developing method suitable for (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 charged image, the developer's magnetic brush is internally connected to a magnetic pole. The toner image is formed on a developing sleeve equipped with a magnetic brush, and the toner image is formed by rubbing this magnetic brush against a photoreceptor carrying a charged image. In this two-component developer, sufficient image density is {
The requirements for obtaining and maintaining these properties over a long period of time without toner scattering are determined by the compatibility between the toner and the carrier. - As a V trend, as the toner density increases, a high image density can be obtained, but the frictional charging of the toner tends to be insufficient, the ability to combine with the carrier decreases, and moreover, the toner movement in and out of the developing device becomes difficult. , a tendency for toner scattering to increase is observed. For this reason, in conventional two-component developing methods, the toner density is kept low, but the developing efficiency is generally low and the density of toner particles, etc., tends to be low. To prevent this drawback, Japanese Patent Application Laid-Open No. 62-6397
Publication No. 0 proposes forming an alternating electric field between the drum and the sleeve, and setting the volume occupied by the magnetic carrier per volume between the drum and the sleeve in the range of 1.5 to 30%. ．． (Problem to be solved by the invention) If the charging characteristics of the toner and carrier in the two-component developer are sufficient, even when the toner concentration is high, the image density will be high and the toner jump will be low. However, this is almost impossible to achieve with commercial toners and developing methods. In other words, during toner production, defective toner particles that do not contain or contain a small amount of charge control agent are bound to be produced, and during development, the charge control agent is removed due to mechanical forces inside and outside the developing device. This occurs frequently, resulting in toner particles that have lost or have a reduced content. In addition, toner scattering does not necessarily occur because it includes uncharged toner particles that have temporarily not been charged due to a change in the area ratio of the document or a change in the environment. This can lead to contamination of the inside of the copying machine and contamination of copies. The present inventors have discovered that in a developer using a two-component developer consisting of a magnetic carrier and a toner, the key point is the flow state of the developer through the development area, and the development conditions are adjusted in relation to this flow state. It has been found that by setting the toner within a certain range, it is possible to effectively prevent toner scattering when a toner with a relatively high toner concentration and containing defective charged particles is used6. An object of the present invention is to provide a developing method that can prevent toner scattering when using a two-component developer consisting of a magnetic carrier and toner, and can form a high-density image, especially a solid image. ．． (Means for Solving the Problem) According to the present invention, a two-component developer consisting of a magnetic carrier and a toner is conveyed from the developing device to the developing area 1 by a sleeve, and in the developing area, the static 1! In the developing method consisting of developing a latent image and discharging the developed developer into a developing device, the developing conditions are expressed in the formula, where M is the amount of developer applied per unit area of the sleeve (g
/cm"!, H is the distance H feel on the line connecting the centers of the photosensitive drum and the snowb.T/D
is the toner concentration weight fraction in the developer. C/D is the carrier concentration weight fraction in the developer, pt is the true density of the toner (g/cm"l), and ρc is the true density of the carrier [g/cm3]. There is provided a high-density image developing method that prevents toner scattering. According to the present invention, in the above-mentioned development, the vertical direction between the opening edge of the developer circulation side of the developing device and the sleeve is provided. Provided is a method characterized in that the developing device is arranged so that the expression B > H - (2) is satisfied, where B is the projection distance seen in the image. Development conditions are set so that formula +11 is satisfied,
That is, developer application per unit area of sleeve 11 (M:
g/c+w2), the distance li on the line connecting the centers of the photosensitive drum and the sleeve? (}lies...also called D-S distance), toner weight fraction in developer (T/D)
and toner true density 1ρt: g/cvs2), carrier weight fraction (C/D) in the developer, and carrier true density (ρc: g/cm31), the flow of the two-component developer in the development area This is based on the knowledge that toner scattering is effectively suppressed even under development conditions where the condition is significantly improved and the image density becomes high. That is, the following formula R=M X (T/DX 1/ p t 10C/D
l/ρc)=IIXIO ro...(lal) R is a dimensionless number that indicates the volume ratio occupied by the two-component developer in the developing area volume,
By maintaining the value of H at a value greater than 33% and less than 40%, toner scattering can be effectively prevented. First, if this developer occupancy (R) becomes 33% or less.
The volume occupied by the developer in the D-S development area decreases, and the magnetic brush in this area draws in air from above the D-S valley and carries it below the D-SH valley.
There is a tendency for the toner to generate airflow and scatter the toner outside the developing unit and into the machine. On the other hand, when this developer occupancy rate (R) exceeds 40%, the developer is too clogged in the valley between D and S, and the developer does not flow smoothly, resulting in a considerable load on the developer sleeve. , the sleeve does not rotate smoothly and the developer is disturbed, making it more likely that the toner will fly away above the valley.
On the other hand, within the range defined by the present invention, D
While the developer flows smoothly through the valley between -S, the generation of the aforementioned air current is also prevented, effectively preventing toner scattering or even when the toner concentration is high. In the present invention, the relationship between the developer occupancy (R) and various factors of the development conditions is clear from the above formula (lal). That is, the larger the amount M of developer applied to the sleeve, the more R
increases, and the larger the distance H between D and S, the more R
becomes smaller. In addition, since ρ and <ρ1 (3) are generally satisfied, the higher the toner concentration (weight fraction) in the two-component developer, the higher the developer occupancy. More specifically, M is generally between 0.06 and 0.25 g/
cm". Particularly from the range 0.1 to 0.2 g/cva", H generally ranges from 0.04 to 0. 16cm. Especially 0
．． 06 to ro. 14c+s and the toner weight fraction in the developer is from 0.03 to 0.08, especially from 0.03 to 0.08. 0
35 to 0. From the range of 075, R when these are combined is determined so as to satisfy the formula (11). Toner scattering during development can be
It turns out that it is affected. In the developing method used in the present invention, the two-component developer is transferred from the developing device to the D-
After being transported to the S-interval development area and used for developing the electrostatic latent image on the photoreceptor drum, it is circulated to the developing device. In order to perform this circulation smoothly without toner scattering, in a preferred embodiment of the present invention, when the projected distance in the vertical direction between the opening edge of the developer circulation side of the developing device and the sleeve is 8, the above formula is used. (2)
Arrange the developing device so that the following conditions are satisfied. That is, even if the scattering of the toner in the developer due to the centrifugal force is greatest, in this embodiment of the present invention, there is a gap larger than the drum-sleeve distance H outward from the vertical projection line of the edge of the sleeve. By providing a developer receiver that opens at , it is possible to prevent toner from scattering outside the developer. (Preferred Embodiment of the Invention) In FIG. 1 for explaining the magnetic brush developing method used in the present invention, a large number of magnetic poles 10. N. A magnet roll 1l equipped with S is housed in a developing sleeve 12 made of a non-magnetic material such as aluminum. With a minute gap 2, ie H, from this developing sleeve l2, the base l3
A photosensitive drum 15 is provided, which includes a photosensitive drum 15 and an electrophotographic photosensitive layer 14 provided thereon. The developing sleeve l2 and the photosensitive drum l5 are rotatably supported by a machine frame (not shown), and are driven so that the moving directions (arrows) at the nib position are the same (the rotating directions are opposite to each other). The developing sleeve l2 is located at the opening of the developing device 16, and a mixing agitator l7 for a two-component developer (i.e., a mixture of toner and magnetic carrier) l8 is provided inside the developing device 16. A horizontal toner supply machine 20 for supplying toner l9 is provided above it.The two-component developer l8 is mixed by an agitator 17 and the toner is abraded.
*After obtaining an electric charge, it is supplied to the developing sleeve l2, and a magnetic brush 2l is formed on its surface. This magnetic brush 2l
The stand length of the panicle is adjusted by a horizontal panicle cutter 22, and the grain is conveyed to a nip position with the electrophotographic photosensitive layer l4, and an electrostatic latent image is formed on the photosensitive layer l4 as a visible image using toner l9. The developing sleeve I2 is located at the opening of the developing device shown as 23 as a whole, and the above-mentioned ear cutter side 22 is arranged on the supply side to the developing sleeve 5, and the tli'lii from the sleeve to the developing device is arranged. A developer receiver 25 having an opening edge 24 is arranged on the side. The developer application amount M can be adjusted by changing the circumferential speed of the sleeve l2.
It can be set to a predetermined value by adjusting the distance between 2 and the ear cutter side 22.

According to the present invention, the developer, the amount of developer applied, and the D-S distance are set so as to satisfy the above formula (1).

Disaster 1 The magnetic carrier generally has a density ρc of 3.50 to 6.50 g/+a, although it depends on the carrier concentration C/D.
m', particularly 4.00 to 5.50 g/Icm3, is preferred, and ferrite-based magnetic carriers are particularly used. Conventionally, ferrite has been used, for example, iron zinc oxide (ZnFe2
0J, iron yttrium oxide (YsFesO+z), iron cadmium oxide (CdFezOJ), iron gadolinium oxide (GdsFesO+z) % iron copper oxide (CuFe20
4) , iron lead oxide (PbFe+20ts) % iron nickel oxide (NIFezO4), iron neodymium oxide (NdF
eOs), barium iron oxide <BaFe+aO+s+)
, magnesium iron oxide (MgFe204), manganese iron oxide (MnFezOJ), lanthanum iron oxide (LaFeO
Cu. Zn. M
g. at least ill. of a metal component selected from the group consisting of un and Ni. Soft ferrite containing two or more types, for example, copper-zinc-magnesium ferrite, is preferably used, and among these ferrites, one that satisfies the above conditions is used. The saturation magnetization of the carrier is 40 to 65 emu/g.
In particular, it is desirable that it be in the range of 45 to 56 ea+u/g. The magnetic carrier is preferably a ferrite carrier that satisfies the above conditions, especially a spherical ferrite carrier, and its particle size is 20 to 140 μm. In particular, it is desirable that it be in the range of 50 to 100 μ-. The electrical resistance of a ferrite carrier varies not only depending on its chemical composition, but also depending on its grain structure, manufacturing method, and coating type and thickness. Generally, its volume resistivity is between 5X10' and 5X.
10th Ω・C error, especially IXIO” to IXIO”Ω・c
It is better to be in the range of m. The density of the toner generally depends on the density of the magnetic carrier and the toner concentration, but the density ρ is generally 1. B0 to 1.40g
/am'', especially from 1.10 to 1.20 g/mm'. The toner used in the present invention contains a coloring agent and a charge control agent in the fixing resin medium or further toner formulations known per se. The toner used in the present invention also contains I.
XIO' to 3X10"Ω'cm. In particular, it preferably has a volume resistivity of 2X10" to 8X10@Ω'cm, and its dielectric constant is 2.5 to 4.5, especially 3.0.
It is preferable that the fixing resin medium, colorant, charge control agent, and other compounding agents for the toner be selected and combined so as to obtain the characteristics listed in -L. ．． First, as a resin medium for fixing,
Styrene resins, acrylic resins, or styrene-acrylic copolymer resins are generally used. The styrene monomer used in these resins is as follows: In the following formula, R1 is a hydrogen atom, a lower alkyl group (having 4 or less carbon atoms), or a halogen atom, and R2 is a lower alkyl group, a halogen atom, etc. is a substituent, and n is 2 including zero.
Examples of monomers represented by the following integers include styrene, vinyltoluene, α-methylstyrene, α-chlorostyrene, vinylxylene, and vinylnaphthalene. Among these, styrene is preferred. On the other hand, as an acrylic monomer, R3 CH2 ● C C-0-R4 ... (I1) II 0 In the formula, R3 is a hydrogen atom or a lower alkyl group, and R4 is a hydrogen atom or a carbon number up to 18 A monomer represented by, which is an alkyl group of ．． In addition to the above-mentioned acrylic monomers, other ethylenically unsaturated carboxylic acids or their anhydrides,
For example, maleic anhydride, fumaric acid, maleic acid, crotonic acid, itaconic acid, etc. can be used6. Styrene-acrylic copolymer resin is one of the suitable resin media, and the styrene monomer fAl and acrylic monomer tB) are A:B=50:50.
to 90:10. In particular, a range of 60:40 to 85:15 is preferable. In addition, the resin used generally preferably has an acid value of 0 to 25. Further, from the viewpoint of fixing properties, it is preferable that the glass transition temperature (Tg) is 50 to 65°C. As the coloring agent to be contained in the s1 fat, the following inorganic or organic pigments and dyes may be used alone or in combination of two or more. Carbon black such as furnace black and channel black Iron black such as triferric oxide; Titanium dioxide such as rutile type or anatase type;
Phthalocyanine blue: phthalocyanine green; cadmium yellow; molybrene orange; virazolonelet; fast violet B, etc. As the charge control agent, any charge control agent known per se may be used, such as nigrosine base (CI50415), oil black (CI20150), etc. Oil-soluble dyes such as Subiron Black, l:1y! ! ! Alternatively, 2:lJJ metal complex dyes, naphthenic acid metal salts, fatty acids, soaps, resin acid soaps, etc. are used. The particle size of the toner particles is 8 to 14 pm on a volume-based median basis as measured by a Coulter counter. Especially 10
The particle shape may be in the range of 12 to 12←■, and the particle shape may be irregular shaped by melt mixing/pulverization method, or spherical shape produced by dispersion or suspension polymerization method. The toner weight fraction T/D in the developer is generally 0.03 to 0.08, particularly 0.03 to 0.08. 035 to 0. [It is best to keep it within the range of l75.] In addition, the electrical resistance of the developer as a whole is lxio' to IXIO"Ω-CIm. Especially, 5X10@ to 5X10
It is preferable for the purpose of the present invention that the amount is within the range of Ω・Ca+.The amount M of developer applied per liter of L is preferably within the range described above, and this depends on the circumferential speed of the developing sleeve and the amount of developer applied. For this reason, the magnetic pole of the developing sleeve is generally 500 to 1000 Gauss, particularly 650 to 850 Gauss, and the circumferential speed of the developing sleeve is 60 to 800 cm/sec
, especially 90 to 450 cm/sec, and the panicle length depends on the magnetic flux density, but it is 0.6 to 1.6 cm/sec, especially 0.6 to 1.6 cm/sec.
A range of 8 to 1.4-1 is appropriate. Further, the distance between D and S (H) is 0.4 to 1.6 ms.
In particular, it is recommended to select from the range of 0.6 to 1.41. As the photoreceptor, photoreceptors conventionally used in electrophotography, such as di-selenium photoreceptors, non-quality silicon photoreceptors, zinc oxide photoreceptors, cadmium selenide photoreceptors, cadmium sulfide photoreceptors, various organic photoreceptors, etc. are all used. As another development condition, the bias voltage applied between the developing sleeve and the photoreceptor conductive substrate has an average electric field strength of 10
0 to 1000 V/mm. Especially 125 to 70
Preferably, it is in the range of 0 V/mm). In the present invention. Toner weight fraction in developer (T/D)
When increasing the toner, it is effective to reduce the developer application amount (M) and increase the D-S distance (11) to prevent toner scattering. (Effects of the Invention) According to the present invention, when developing a two-component developer consisting of a magnetic carrier and a toner with a magnetic brush, the development conditions, that is, the composition and density of the developer, the amount of developer applied, and the drum sleeve. By selecting the distance within a certain range that satisfies the above condition (!), the fluidity of the developer passing through the development area can be maintained within a good range, thereby preventing toner scattering and producing high-density, especially solid areas. This makes it possible to form images with high density. The present invention will be explained below using experimental examples. A 10,000-sheet printing test was conducted under various development conditions using various toner particles in which carbon black was separated into a binder resin mainly composed of polyester and various ferrite carriers. The results are shown in Table 1. From Table 1, it can be seen that if development is performed under conditions that satisfy the above formula (1), a high-density image without density unevenness can be obtained while suppressing toner scattering.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a developing device applied to the developing method of the present invention.

Claims (2)

[Claims] (1) A two-component developer consisting of a magnetic carrier and toner is transported from the developing device to the developing area by a sleeve, the electrostatic latent image on the photoreceptor drum is developed in the developing area, and the developed developer is developed. In the developing method consisting of circulation in the container, the developing conditions are expressed as follows:
)÷H×100<40 In the formula, M is the amount of developer applied per unit area of the sleeve (g
/cm^2), H is the distance (cm) on the line connecting the centers of the photoreceptor drum and sleeve, T/D is the toner concentration weight fraction in the developer, and C/D is the carrier concentration weight fraction in the developer, ρ_t is the true density of the toner (g/cm^3), and ρ_c is the true density of the carrier (g/cm^3). A high-density development method that prevents toner scattering. (2) A claim characterized in that the developing device is arranged so that the formula B>H is satisfied, where B is the projected distance between the opening edge of the developing device on the developer circulation side and the sleeve when viewed in the vertical direction. A high-density development method that prevents toner scattering according to item 1.