JPS6371860A - Dry carrier - Google Patents

Abstract

PURPOSE:To stabilize the amt. of toner charge even if a continuous copying is executed by dispersing at least magnetic powder, and colloidal silica in a binder resin. CONSTITUTION:Magnetic powder (e.g. magnetite powder), colloidal silica, and if necessary, an electroconductivity regulator or a charge controller, etc., are dispersed in a binder resin (e.g. styrenic copolymer). By this constitution, a stable charge characteristic is obtd. when the binder resin is mixed with toner. Particularly, adhesion of toner or carrier to a back ground part of a picture image is prevented, and a carrier having superior resolution, gradation, etc., as well as durability for the use for a long time, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a developer, particularly a dry carrier, for developing transparent TM images.

Conventional techniques include methods for obtaining copies by electrophotography or electronic recording. 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, a friction zone t is created between the carrier and the toner, and the toner is charged with a polarity opposite to that of the electrostatic latent image, causing it to adhere to the m image and develop it. .

Conventionally, such a developer is toner! The appearance was gradually incorporated using a carrier with a large particle size.

However, when a carrier whose particle size is larger than that of the toner is used, the reproducibility of the pif tonality is poor and the toner tends to adhere to the W1 portion. 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 the particle size of the toner. For example, a developer used in the fine brush development method is a mixture of a small particle carrier having an average particle size of 5 to 50 μm and consisting of a binder resin and magnetic powder, and a toner having an average particle size of 5 to 20 μm.・Such developers can solve the above-mentioned drawbacks, but the tolerance range for the amount of band required for the toner to adhere to the latent image is narrow, and the amount of charge is too large. If the amount of charge is too small, toner scattering or toner adhesion to the background will occur, and the tolerance range is narrow. Therefore, such a phenomenon occurs even under normal development conditions.

In addition, in recent years, organic photoreceptors have come to be used as photoreceptors, and in this case, the latent image polarity must be negative, and the toner must be positively charged, that is, the carrier must be configured to be negatively charged. As one such attempt, a method of attaching colloidal silica to the surface of toner is known. L$t,
2: m, the photoreceptor may be scratched due to the abrasive action of silica, and the charging speed during the frictional charging process between the toner and carrier is slow and the charge distribution is wide9, resulting in toner charged with the opposite polarity. Toner adhesion to the background area occurs. Furthermore, if used for a long time, silica will adhere to the carrier, the carrier will be contaminated with silica, the chargeability of the carrier will change, and the carrier agent will be provided to the background area. Therefore, a small particle size carrier is used for subsequent development. reduction in image density in agents,
An object of the present invention is to provide a developer that prevents adhesion to background areas. Furthermore, the present invention can be achieved by providing a dry carrier characterized in that the carrier is a mixture of a stably negatively chargeable developing agent and rhoidal silica.

(1) Carrier (a) Binder Resin The binder resin of the carrier used in the present invention determines the content in the carrier or the magnitude of the saturation magnetic flux density of the carrier. Usually, the blending ratio of alcohol binding resin and magnetic powder in the carrier is 2Q:80 to 60:40, preferably 20:8.
0-40:6a. This means that the binder resin content is 2
If the amount is less than 0 tfi parts, there will be problems such as the binder becomes too small and binding ability cannot be obtained, the carrier particles become brittle, and manufacturing is difficult; if the amount exceeds 60 parts by weight, sufficient magnetic properties may not be obtained. This is because the binder resins include polyethylene, polyacrylate, polymethacrylate, vinyl resin, streamer ester,
Polyethylene, polypropylene, polyvinyl chloride, I-reacrylonitrile, polyether, polycar? Nate,
Cellulosic resins, polyamides and monomer copolymers thereof can be used. Among these, it is preferable to use a resin that is close in charge series to the binder resin used in the toner. This is because a binder resin with the same charge series is used for the binder resin of the carrier and toner, and the colloidal silica contained in the carrier gives the carrier negative chargeability, and the toner adheres to the latent image. This is because it is possible to easily reach the allowable range of the amount of cold charging required for this purpose.

佽）Magnetic powder The carrier magnetic powder used in the present invention has an average particle size of 0.1 to 3μ. The blending ratio of magnetic powder and binder resin is 40:60 to 80:20, preferably 6
0:40-80:20. As the magnetic powder, fine powders of magnetite, ferrite, iron, nickel, cobalt, r-hematite, chromium dioxide, etc. can be used. Among them, magnetite is preferred because it is inexpensive and can be used stably.

The carrier colloidal silica used in the present invention has an average particle size of 0.1 μm or less, preferably 0-005
~0*05 Jgm of commercially available colloidal silica may be used. The blending ratio of colloidal silica is 0.1 to 10 wt%, preferably 0.5 to 10 wt%, based on the mixture of magnetic powder and binder resin. 5 wt% - Silica imparts appropriate negative chargeability to the carrier, and when silica is added to the toner surface, they electrostatically repel each other and prevent the silica on the toner surface from adhering to the carrier. If Oe is less than 1wt%, the above effect cannot be expected, and if it exceeds 10wt%, the above effect can be achieved, but the image quality will deteriorate and manufacturing will be difficult. 8 emsl I 200 as commercially available colloidal silica
, Aerosll R-972, etc. may be used.

If necessary, carbon black or a charge control agent may be added as a 25 charge control agent.

The carrier of the present invention can be mixed with toner to obtain stable negative chargeability, and in particular, does not adhere to the toner or carrier background area, and can withstand long-term use with excellent image quality such as resolution and gradation. It's watery. The average particle size of the carrier is 10
~4 Q Bm tFf”! or 20 to 504 m. This means that if the magnetic force is less than 10 μm, the magnetic force per gear is small and the carrier tends to adhere to the photoreceptor, and if it exceeds 40 μm This is because the sharpness of the image is lost, the image quality is deteriorated, and when the toner concentration is increased, toner adhesion to the background area, so-called fog, tends to occur.

(C) Manufacturing method of carrier The carrier of the present invention can be manufactured by mixing, crushing and then classifying, and by dissolving agglomerates in a solvent and spray drying a suspension in which magnetic powder and colloidal silica are dispersed. Either a method of granulating and then classification, or a method of dispersing magnetic colloidal silica in the monomer layer when paging the binder tree PI'g may be used.

Gi) Toner: The toner used by tribocharging with the carrier of the present invention is:
Constructed so that it can be positively charged. Although the binder resin used in the toner is quite limited depending on the fixing method, the same binder resin as the carrier can be used. As the coloring agent for the toner, any suitable pigment or dye is used in an amount sufficient to color the binder resin, generally 25 wt% of the toner, preferably 1 to 20 wt%. used in quantity. In order to impart positive chargeability to the toner, it is preferable to add a charge control agent such as a quaternary ammonium salt or a nigrosine dye. The average particle size of toner is 5-20
μm is preferable because if it is less than 5 μm, the fluidity of the toner deteriorates and the toner adheres to the background area, and if it exceeds 20 μm, 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.

The carrier of the present invention exhibits stable negative chargeability when mixed and stirred with the above-described toner.@The carrier of the present invention contains colloidal silica. This means that the magnetic powder on the surface of the magnetic carrier is less exposed, and the binder resin coats the magnetic powder with a thickness of at least several 1 OA.
Because colloidal silica is uniformly dispersed in the binder resin, when it comes into contact with the toner and is rubbed, it provides effective positive charging to the toner, and it also provides the necessary amount of charge for the toner to adhere to the m-image. This is because a permissible range can be given. An even more significant feature is that colloidal silica is sometimes added to the toner surface for the purpose of a lubricant and toner fluidity in the cleaning method, but when colloidal silica is added to the positively chargeable toner surface, the charge of the toner increases. When the toner density is significantly shifted to the negative side, the charge distribution is widened, and the toner concentration is increased, development occurs in which toner and carrier adhere to the background area. However, such problems can be prevented by including colloidal silica in one carrier as in the present invention. This is because a part of the colloidal silica added to the toner surface migrates to the carrier, preventing the charge distribution from expanding and imparting effective positive chargeability to the toner. The developer is scd'5sZnO
1 Preferably used for negative polarity m-images formed on organic photoreceptors.Se%Se can also be used as a reversal developer for positive polarity latent images on alloy-based photoreceptors.The present invention An example of a developing method using a carrier according to the present invention is to develop an electrostatic latent image formed on a photoreceptor or an electrostatic recording medium using a magnetic brush developing device.
Since the carrier is negatively charged and the toner is positively charged, the toner is attracted to the negative polarity ftI image and developed, and after the toner image is transferred to the transfer paper, it is fixed.

By containing colloidal silica in the carrier, the developer using the carrier of the present invention can be applied to a developing method with a narrow tolerance range for the amount of band 11c. In addition, as another effect,
The toner band weight remains stable even during continuous copying.]
, it is possible to maintain image quality comparable to that of printing. If a carrier that does not contain colloidal silica is used, capri in the background will occur, making it unusable.

Furthermore, even if the carrier of the present invention is used as a carrier of 60 to 150 μm rather than a small particle size carrier, it is sufficient to make the concentration per toner lower than that of a small particle size carrier, and the amount of developer can be quantified. , the stirring torque of the developing machine can be reduced.

The present invention will be specifically explained below using comparative examples and examples.

Example 1 Styrene competition n-butyl methacrylate polymer 30! jif part (styrene "It65 wtX, weight average molecular weight = 80,0
00) Mix 2 parts by weight of Magnemate 70-fold colloidal silica (Degussa Aerosil R-972), melt and mix, then finely pulverize.
Classification was performed to obtain a magnetic carrier with an average particle size of 25 μm. Separately, 90 parts by weight of styrene-n-butyl methacrylate copolymer (styrene content 60 wt%, weight average molecular weight = 50,000) was used as a toner. A toner having an average particle size of 15 μm was obtained by melt-kneading, pulverizing, and classifying 2 parts by weight of carbon black affii (HBLACK PEARLS 880) and 2 parts by weight of nigrosine dye (Orient Chemical Co., Ltd., Gantron No. 3).

A developer was prepared by adding 10 parts by weight of toner to 90 parts by weight of carrier and mixing for about 10 minutes in a type mixer.

Example 2 Styrene-2-ethylhexyl acrylate copolymer 35 negative parts (styrene amount 80 wtX, weight average molecular weight = 1.20. [10
0) Magnemate 65 parts by weight Colloidal silica 1 part (manufactured by Degussa)
eros11 200) carbon black
3 parts by weight (Kiyagatsha! 1! 8LACK
A carrier having an average particle size of 23-m was obtained using the same method as in Example 1.

As a toner, 100 parts by weight of the toner of Example 1 1i (,
Colloidal silica (Aerosll R-9 manufactured by rgusa)
7z) Add parts by weight of o and s and mix in a Henschel mixer.
A toner was obtained by mixing and stirring for 3 minutes.

90 parts by weight of carrier and 10 parts by weight of toner! : A developer was prepared using the same machine as in Example 1 except that part tt was added.

Comparative Example 1 A carrier and toner were obtained and a developer was prepared in the same manner as in Practical Example 1 with the same composition as in Example 1 except that it did not contain colloidal silica.

Comparative Example 2 A carrier was obtained with exactly the same composition as in Example 2, except that it did not contain colloidal silica. The toner of Example 2;
Using the same procedure, add the developer to I! Copies were developed using the above-mentioned four types of developer, and as a result, the image quality as shown in Table 1 was obtained.

(Table 1) (Table 1: C peta part density is measured using a Macchias densitometer) As can be seen from Table 1, when a carrier that does not contain colloidal silica is used, the capri and density drop is so great that it cannot be used.・These developers When the amount of charge was measured, f1g
The results shown in Table 2 were obtained.

Even when 100,000 copies were made using the developers of Examples 1 and 2 while replenishing toner, images with excellent gradation and no decrease in Capri and C degrees were obtained.

Claims (1)

[Claims] A dry carrier used in a dry development method, characterized in that it is composed of a binder resin mixed with at least magnetic powder and colloidal silica.