JPS59223458A - Dry type carrier - Google Patents

Abstract

PURPOSE:To prevent the decrease in image density in a developer and sticking thereof on a background part by using a small grain-size carrier mixed with a binder resin and needlelike magnetic powder. CONSTITUTION:The compounding ratio by weight of the binder resin and magnetic powder in a carrier is made (20:80)-(40:60). Polystyrene, polyacrylate, polyamide, etc. and a copolymer of monomers constituting said polymers are usable as the binder resin. The amt. of the magnetic carrier to be compounded in the carrier is 40-80wt% and at least 10% needlelike magnetic powder is used for the magnetic powder. The needlelike magnetic powder having 0.1-3mu average grain size and >=2 ratio between the long axis/short axis is used and pulverous powders of needlelike magnetite, needlelike ferrite, gamma-Fe2O3, etc. are usable. The average grain size of the carrier is 10-40mum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a developer for developing an electrostatic latent image, and in particular to a dry carrier used in a dry development method.

2. Description of the Related Art Methods of obtaining copies by electrophotography or electrostatic recording are known. In this method, an electrostatic latent image formed on a photoreceptor or an electrostatic recording medium is developed with a developer, and the toner image is transferred and fixed on a transfer paper to obtain a copy.

As this developer, a developer consisting of two components, carrier and toner, is generally used.

By stirring the developer in the developing device, frictional charging is generated between the carrier and the toner, and the toner is charged with a polarity opposite to that of the electrostatic latent image, so that the toner adheres to the latent image and is developed.

Conventionally, as such a developer, a carrier having a particle size larger than that of the toner (60 to 500 μm) has been used for development. However, when a carrier having a particle size larger than that of the toner is used, there are disadvantages in that gradation reproduction is poor and the toner tends to adhere to the background area. In recent years, in order to solve these drawbacks, developers have been proposed in which the particle size of the carrier is approximately the same as that of the toner.

For example, as a developer used in the magnetic brush development method, a small particle carrier having an average particle size of 3 to 308 m and consisting of a binder resin and magnetic powder, and a small particle carrier having an average particle size of 5 to 308 m. A developer mixed with a toner having a particle size of 20 μm is known. Although such a developer can solve the above-mentioned drawbacks, the tolerance range for the amount of charge required for the toner to adhere to the latent image is narrow, and if the amount of charge is too large, the image density will decrease and the carrier will be damaged. +J adhesion to the background area occurs, and if the amount of charge is too small, toner scattering or toner adhesion to the background area will occur, and the tolerance range is narrow, so under normal development conditions However, this kind of phenomenon was the first to occur.

Furthermore, in recent years, organic photoreceptors have come to be used as photoreceptors, and in this case, the latent image polarity is negative and the toner must be positively charged, that is, the carrier must be configured to be negatively charged. In this case, as an attempt to narrow the allowable range of the amount of charge mentioned above, a method is known in which the same binder resin is used for the toner and the carrier. In this method, the charging speed in the frictional charging process between the toner and the carrier is slow, and the charge distribution of the static charge is widened, resulting in the formation of oppositely charged toner, which causes the toner to adhere to the background area. Furthermore, when used for a long time, the toner with a low charge amount is consumed during development because the charge distribution is wide, and the charge distribution gradually changes to a higher side, causing carrier adhesion to the background area, causing the image to deteriorate. It had an impact on

OBJECTS OF THE INVENTION The purpose of the present invention is to provide a developer which solves the above-mentioned drawbacks, and which prevents the reduction in image density and the adhesion of background areas in developers using small particle diameter carriers. This is what we provide. A further object of the present invention is to provide a developer with a narrow charge distribution in which the carrier can be stably negatively charged.

Structure of the Present Invention The object of the present invention can be achieved by a dry carrier characterized in that at least a binder resin and acicular magnetic powder are mixed.

(i) Carrier a) Binder Resin The content of the binder resin in the carrier used in the present invention determines the saturation magnetic flux density of the carrier. Usually, the blending ratio of the binder resin and magnetic powder in the carrier is 2o:go~otsuO:1i-o, preferably 2. o:go-7g0:60. , this means that when the binder resin content is less than 0 parts by weight, the binder is small (
If it exceeds 60 parts by weight, it will not be possible to obtain binding ability, the carrier particles will become brittle, and it will be difficult to knead. This is not preferable because the carrier adheres to the latent image or background. Binder resins include polystyrene, polyacrylate, polymethacrylate, vinyl resin, polyester resin, polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, polyether,
Precarbonates, cellulosic resins, polyamides, and copolymers of these monomers constituting the polymer can be used.

In the present invention, the binder resin used for the carrier and the toner can be used even if they are separated from each other in terms of triboelectric series. this is,
When the acicular magnetic powder of the present invention is mixed to obtain a carrier with a small particle size, a part of the acicular magnetic powder is exposed on the surface of the carrier, and the amount of negative charge on the carrier is kept low due to the electricity consumption with the toner. This is because the variation in distribution is reduced.

b) Acicular Magnetic Powder The acicular magnetic powder of the carrier used in the present invention has an average particle size θ of 3 μm and a long axis/short axis ratio of 1 or more. Acicular magnetic powders include acicular magnetite, acicular Fe, light, and γ-Fe 20z.

Fine powder such as can be used. Among them, acicular magnetite is preferred because it is inexpensive and can be used stably. The mixing ratio of the magnetic powder in the carrier is 4tθ~goJt%, but it is not necessary that all the magnetic powder be acicular magnetic powder (it is necessary to use at least 70% of the magnetic powder as acicular magnetic powder). This is because if less than 70% of the magnetic powder is acicular powder, it will not be possible to suppress the amount of charge and narrow the charge distribution, which is the objective of the present invention, resulting in a decrease in image density and
This is because the carrier adheres to the background area.

In the carrier of the present invention, carbon black, a surfactant, and a charge control agent may be added as conductivity modifiers, if necessary.

C) Particle size of carrier The carrier of the present invention has a stable 41 band property when mixed with toner; in particular, there is no adhesion of the toner or carrier to the background area, and it improves resolution, gradation, etc. .

It has excellent image quality and can withstand long-term use.

The average particle diameter of the carrier is preferably 10 to 30 μm. If the carrier particle size is less than 10 μm, the magnetic force per carrier/piece is small, and the carrier tends to stick to the photoreceptor (if it exceeds 1708 m, the sharpness of the image will be lost and the image quality will deteriorate). This is because when the toner concentration is increased, toner adhesion to the background area, so-called capri, tends to occur.

d) Method for producing carrier The carrier of the present invention may be produced by any method in which magnetic powder is dispersed in a monomer during crosstalk and polymerization.

(ii)) The toner to be triboelectrically charged with the carrier of the present invention is:
It is best to configure it so that it can be positively charged. The binder resin used in the toner is quite limited depending on the fixing method, but the same binder resin as the carrier can be used. Any suitable pigment or dye may be used as the coloring agent for the toner in an amount sufficient to color the binder resin, generally less than 2 t % of the toner, preferably 20 t % or less of the toner. %
It is used in one of the following. In addition, in order to impart positive chargeability to the toner, a charge control agent such as a basic dye such as nigrosine dye, a q-class ammonia salt, or a 1um salt may be added, or a binding agent such as 1SL may be added.
It is preferable to chemically contain nitrogen in the fat. The average particle size of the toner is preferably 5-20μ. This is because if it is less than Sμ, the fluidity of the toner will deteriorate and the toner will adhere to the background area, and if it exceeds 20μ, the sharpness of the image will be lost and the image quality will deteriorate. The method for manufacturing the toner is the same as the method for manufacturing the carrier described above.

Effects of the Present Invention The carrier of the present invention exhibits stable negative chargeability when mixed and stirred with the above-mentioned toner.

In the present invention, the carrier contains acicular magnetic powder.

This is due to the fact that the oblique magnetic powder on the surface of the magnetic carrier is often exposed, and the acicular magnetic powder is uniformly dispersed in the binder resin, so when it comes into contact with the toner and rubs, it has a positive charge that is effective for the toner. Moreover, it is possible to provide a tolerance range for the amount of charge necessary for the number of toners to be deposited on the n-image. Therefore, even if the device is used for a long time, the charge amount of the carrier does not increase and remains constant, and the charge distribution is narrow, so that the carrier does not adhere to the background portion. In particular, in the fringe electric field area of the latent image on the photoconductor, carriers are prevented from being attracted by the fringe electric field with a force stronger than the magnetic force of the magnetic brush than in the normal background area, and the carrier is not attached to the background area near the latent image area, making it clearer. image quality.

The carrier of the present invention has a small particle size, is lightweight, has a small amount of charge, and has little variation in charge distribution, so the torque required to stir the developing device is small, and there is no contamination on the carrier surface, so it can be used for a long time. However, a highly reliable developer can be obtained.

The developer using the carrier of the present invention is CdS.

It is preferably used for a negative latent image formed on a ZnO+organic photoreceptor. It is also used as a reversal developer for positive latent images on Se and Se alloy photoreceptors.

As an example of a developing method using the carrier of the present invention, an electrostatic latent image formed on a photosensitive member or an electrostatic recording member is developed by a magnetic brush developing unit. The developer according to the present invention is
Since the carrier is negatively charged and the toner is positively charged, the toner is attracted to the negative latent image and developed, and after being transferred to the transfer paper, the toner is fixed.

The developer using the carrier of the present invention can be applied to a developing method with a narrow charge amount tolerance range by containing acicular magnetic powder in the carrier. Another effect is that even if continuous copying is performed, the amount of charge on the toner is stable, and image quality comparable to that of printing can be maintained. If a carrier that does not contain acicular magnetic powder is used, the carrier will have a lid with a background part, making it unusable.

The carrier of the present invention does not have to be a small particle size carrier.
Even if a carrier with a particle diameter of 0 μm is used, the toner concentration can be lower than that of a small particle carrier (1), the developer layer can be made lighter, and the developer can be agitated.

Torque can be reduced.

Example The present invention will be specifically explained below using examples.

Example/ Styrene/n-butyl methacrylate copolymer 3
0 parts by weight (styrene: n-butyl-63 methacrylate
:3! ; weight average molecular weight = go, oθ0, number average molecular weight = 29,00θ) acicular magnetite (long axis diameter θSμ, short axis diameter % 3μ) 31 parts by weight granular magnetite (d
=0.3μ) 35 parts by weight 0 Carbon black 3 parts by weight (Black Pearls ggg: Cabot M)? After mixing, melting and mixing, finely pulverize and classify at °C.
Average grain size 2'1. A magnetic carrier of gμm was obtained.

Example costyrene-coethylhexyl acrylate copolymer 3
0 weight sound μ (styrene: coethylhexyl acrylate = gO: 20. Weight average molecular weight = 720,000° Number average molecular weight = 4'pu0θ0) Carbon black 3 weight sound l
5 (Black Pear, IS goo: manufactured by Cat Cat Co., Ltd.) in the same manner as in Example/1 to obtain an average particle size of 2! ;,'
A carrier of 1 μm was obtained.

Comparative example/Except that the sample did not contain acicular magnetite but was changed to 70 parts by weight of granular magnetite at °C.
: Same composition, average particle size 2 by the same method as Example/
A carrier of 5.0 μm was obtained.

Comparative Example: Granular magnetite 70 without containing acicular magnetite
Same composition as Example Ω except for changing parts by weight,
A carrier having an average particle size of 2 da and 3 μm was obtained in the same manner as in Example.

Toner Example Styrene/n-butyl methacrylate copolymer 92
Parts by weight (styrene: n-butyl methacrylate-65:3
Left, weight average molecular weight = 7 leak θoo, number average molecular weight = 2 mm. oo) Carbon black
6 parts by weight (Reagal 330: manufactured by Cavit)
2 parts by weight of quaternized ammonium salt (cetylpyridinium chloride) were mixed, melt-kneaded, and pulverized to an average particle size of 2.7 μm.
I got the toner.

Preparation of Developer 70 parts by weight of toner was added to 90 parts by weight of the carriers of the Examples and Comparative Examples and mixed for about /θ minutes in a V-type mixer to prepare a developer.

The distance between the photoreceptor coated with organic photoreceptor and the developing sleeve is 0 mtn K L/, XEROX 7 A O
When I put DA type of developer into the θ modified machine, developed it, and made a copy, the image quality shown in Table 1 was obtained.

(Peta black area density is determined by Macbeth densitometer) Comparative example in which carrier adhesion to the background area occurred In a developer using the carrier shown in the box, when the bias voltage applied to the developing sleeve is increased, carrier adhesion increases significantly. It has also been found that the increase occurs when the copying environment is made low temperature and low humidity.

Therefore, when we measured the environmental changes in the amount of charge, we obtained the values shown in Table 1.

As can be seen from Table 2, it was found that when a carrier containing no acicular madanetite was used, the amount of charge was high and the change depending on the environment was large, and the chargeability was particularly high at low temperature and low humidity.

Next, while replenishing toner with the developer using the carrier of Example/ and Ω, an image with excellent gradation without a decrease in fog density was obtained even after 100,000 copies.

Claims (1)

[Claims] A dry carrier used in a dry development method, characterized in that at least a binder resin and acicular magnetic powder are mixed.