JPH0296189A - Developing method - Google Patents

Abstract

PURPOSE:To obtain a preferable image by using specific carbon black of which DBP oil absorption for toner in starting developer is different from that for replenishing toner. CONSTITUTION:When the DBP oil absorption of the carbon black in the toner in the starting developer is A(ml/100g), and that in the replenishing toner is B(ml/100g), the carbon black is selected so that 1.1<=B/A<=2.0. Generally, the large the DBP oil absorption is, the higher structure can be formed. Therefore, since the toner is produced by using carbon black different in DBP oil absorption, the electrical resistance of the toner can be effectively controlled without changing the compounding ratio of constituents such as fixing resin and charge controller. Thus, a distinct image of high density can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a developing method using a two-component developer, and more specifically to a method for producing high-density, clear fixed images without causing toner scattering or background fog over a long period of time. The present invention relates to a developing method for obtaining.

(Prior art and its problems) Conventionally, a developing method using a two-component developer has been widely used in the field of electrophotography, and when this is used, the developer is usually placed on the surface of a sleeve that has a magnet inside. The developer is used in the form of a so-called magnetic brush that supports the photoconductive layer.During development, the developer is mixed and stirred in the developing device, and in a mutually frictionally charged state, the rotation of the sleeve or magnet causes the developer to spread on the photoconductive layer. The toner particles are transported to the electrostatic latent image bearing surface, and due to the electrostatic attraction between the triboelectric charge of the toner and the electrostatic latent image, the toner particles are transferred to the latent image, and development is performed.

Furthermore, when making a large number of copies, it is necessary to keep the toner concentration in the developer constant, so a method is used in which only toner is replenished.

However, due to repeated development operations, the developer in the developing device gradually deteriorates, and the carrier surface in particular becomes contaminated with the toner composition, resulting in high resistance of the entire developer and uneven triboelectric charging. , and the bias development efficiency decreases. As a result, image density may decrease or background fog may occur during running copying.

The present applicant previously wrote in Japanese Patent Application No. 58-75429,
By making the volume resistance of the replenishing toner lower than that of the toner in the starter agent, it prevents the decrease in image density caused by the high resistance of the developer due to continuous copying, and the occurrence of background fog due to the edge effect. proposed a method to do so. In this method, the volume resistivity of the toner in the start developer and the replenishment toner is controlled by particularly changing the content of carbon black contained in the toner.

On the other hand, in recent years, high-resistance ferrite carriers with rich gradation and less characteristic change due to environmental changes have been used in order to obtain higher-quality copies, and With the development of high-speed copying systems that can obtain high-speed printing, development conditions have become stricter, and it has become necessary to further improve toner properties. Therefore, when the developing method of the above-mentioned Japanese Patent Application No. 58-75429 was applied under such conditions, it was possible to prevent background fogging and a decrease in image density to some extent during running copying, but the carbon black content of the replenishment toner Due to the large amount of carbon black, there were defective particles mainly composed of carbon black, and it was observed that toner scattering and background smearing occurred immediately after toner replenishment.

Furthermore, during toner production, it is difficult to control the degree of dispersion because the content of carbon black varies.
The drawback is that the image quality of the formed image varies slightly, and
Due to the large amount of carbon black in the replenishment toner, the fixing performance deteriorates, and a drawback has been recognized that fixing failure occurs particularly in high-speed copying machines.

Therefore, the present invention has been made in view of the above points,
The purpose of this is to maintain good image quality and fixability over a long period of time without significantly changing the formulation of the toner in the starting developer and the replenishment toner, and to prevent fogging not only during running copying but also immediately after toner replenishment. It is an object of the present invention to provide a developing method capable of forming a clear image with high density without causing toner scattering.

(Means for Solving the Problems) According to the present invention, a starting developer made of a mixture of a magnetic carrier and a toner is brought into contact with an electrostatic latent image bearing surface, and the amount of the toner consumed for development is In an electrophotographic development method in which replenishment toner is supplied according to the D of carbon black in the toner in the starting developer,
The BP oil absorption amount is A (ml/100g), and the DBP oil absorption amount of carbon black in the refill toner is B (ml/100g).
), the object of the present invention can be achieved by selecting carbon black in the relationship of 1.1≦B/A≦3.

(Function) A feature of the present invention is that each toner is prepared by determining the DBP oil absorption amount of the carbon black used according to the above-mentioned relational expression, without changing the formulations of the starter toner and replenishment toner. That's true. If you select carbon black that satisfies the above relational expression to create the toner in the starting developer and the replenishment toner, a high-density image can be obtained from the beginning, and replenishment occurs due to carbon black agglomerations caused by the replenishment toner. There is no immediate toner scattering or background fog, and the durability of the developer is also good, effectively preventing high resistance due to developer deterioration, and reducing image density due to edge effects during running copying.
It is possible to prevent a decrease in bias development efficiency and keep toner developability (transferability) constant. Furthermore, the fixability of the toner remains good, and the number of sheets to be printed can be increased without causing fixing failure, and furthermore, it is possible to suitably cope with high-speed copying.

The carboblack dispersed in the binder resin forms more paths for electrons to flow as it tends to form a highly strangled structure in the binder resin, that is, a net-like, chain-like, or cluster-like aggregated structure. and exhibits high electrical conductivity. Generally, the larger the DBP oil absorption, the higher the structure can be formed. Therefore, by creating toners using carboblacks with different DBP oil absorption, it is possible to improve colorability, fixability, durability, etc. without significantly changing the blending ratio of other constituent materials such as fixing resin and charge control agent. The electrical resistance of the toner can be effectively controlled while keeping the toner properties constant. Furthermore, D used here
BP oil absorption is the minimum amount of dibutyl phthalate required to make 100 g of carbon black into a paste.

When B/A > 3 outside the above relational expression, the resistance of the developer decreases, especially immediately after replenishment, and the charge retention ability of the toner decreases, making it easy to cause image blurring and image deletion. Furthermore, when B/A<1°1, the resistance of the developer increases, resulting in a decrease in image density.

The present invention will be explained in detail below.

Examples of the binder resin in which the carbon black of the starting developer toner and the replenishing toner used in the present invention are dispersed include styrene polymers, acrylic polymers, styrene-acrylic polymers, chlorinated polyethylene, Olefin polymers such as polyprolene and ionomers, polyvinyl chloride, polyester, polyamide, polyurethane, epoxy resin, diallyl phthalate resin, silicone resin, phenol resin, rosin modified phenolic resin, xylene resin, rosin modified maleic acid resin, rosin ester,
Examples include various polymers such as petroleum resins.

These polymers generally have a glass transition point (Tg) of 40 to 80°C, particularly 50 to 75°C, and a weight average molecular weight of generally 30,000 to 200,000, particularly 500°C.
00 to 150,000 is preferable, and one type or a mixture of two or more types is used.

Among the above polymers, rosin esters, rosin-modified phenolic resins, rosin maleic acid resins, epoxy resins, polyesters, cellulose polymers, polyester resins, etc. are useful in improving the triboelectric properties of toner. .

In addition, when the toner is a pressure fixable toner, olefin polymers such as polyethylene and polypropylene, etc.
Polymers that are easily plastically deformed are mainly used. This polymer can be used with other polymers, such as polyvinyl acetate, ethylene-vinyl acetate copolymer, hydrogenated polystyrene, hydrogenated rosin ester, aliphatic, alicyclic or aromatic petroleum It may also contain a resin or the like.

The carbon black used in the present invention has a DBP oil absorption that satisfies the above relational expression in the toner during start development and the replenishment toner, and in particular, the DBP oil absorption of the toner used in the start developer is 40 to 40. 100 (m
ml/100g) is preferable, and the specific surface area of the toner used for replenishment is 80 to 500 (ml/100g).
g) is preferred. The carbon black is preferably used in an amount of about 2 to 30 parts by weight per 100 parts by weight, although it varies depending on the binder resin used.

In addition, in order to control the triboelectric charge of the toner, oil-soluble dyes such as nigrosine dye, oil black, spirone black, etc., naphthenic acid, salicylic acid, fatty acids and resin acids such as manganese, iron, cobalt, etc. are added to the binder resin. Metal soaps such as metal salts of lead, zinc, cerium, calcium, nickel, etc., metal alloy azo dyes, pyrimidine compounds, alkyl salicylic acid metal chelates, etc. are added in an amount of 0.1 to 5 parts per 100 parts by weight of the binder resin. Parts by weight, especially 1 to 3 parts by weight, are preferably used.

Further, an anti-offset agent such as wax may be added to the binder resin in order to prevent offset and improve fixing properties. Waxes used include various waxes such as polyethylene wax, polypropylene wax, ethylene-propylene wax, and paraffin wax.
Low molecular weight olefin polymers such as olefin monomers having 4 or more carbon atoms, fatty acid amides, silicone oils, etc. are used.

These anti-offset agents are 0 per 100 parts by weight of binder resin.
．． 1 to 10 parts by weight can be used.

Furthermore, when used as a magnetic toner, it is possible to contain a magnetic substance in the toner, and the magnetic substance may be a material that exhibits magnetism or can be magnetized, such as iron such as ferrite and magnetite, cobalt, etc. , nickel, manganese, and other ferromagnetic metals and alloys are used.

These magnetic substances can be used in an amount of 50 to 200 parts by weight per 100 parts by weight of the fixing resin.

Then, the binder resin, carbon black, and other constituent materials are melt-kneaded, for example, and the kneaded product is cooled, pulverized, and classified to obtain a toner having a particle size of 5 to 20 μm.

In addition, the obtained toner may be used as a toner composition by externally adding fluidity improvers such as hydrophobic silica, aluminum oxide, fatty acid metal salts, electrical resistance regulators, cleaning properties improvers, etc., if necessary. can.

Various carriers can be used for the toner (composition) and developer, including magnetic materials such as iron oxide, reduced iron, copper, silicone, nickel, ferrite,
Magnetic materials such as cobalt, alloys of these with manganese, zinc, aluminum, etc., such as iron-nickel alloys, iron-cobalt alloys, iron-aluminum alloys: High dielectric constant substances, such as titanium oxide , aluminum oxide, copper oxide, magnesium oxide, copper oxide, zirconium oxide, silicon carbide, etc., magnesium titanate,
Ceramics such as barium titanate, lithium titanate, lead titanate, lead zirconate, lithium niobate, A
DP, CNHa H2PO4), KDP (KH2PO
4) Examples include Rochelle salt and magnetic materials such as iron, nickel, cobalt, and ferrite coated with polymers such as acrylic polymers, fluorine polymers, and polyesters.

The above carriers can be used alone or in combination of two or more. The particle size of these carriers is preferably 50 to 150 μm, particularly 80 to 100 μm. Note that among the above carriers, ferrite is preferably used because it is inexpensive, has excellent image characteristics, and has excellent environmental stability.

Then, the toner (composition) and the carrier particles described above are mixed in a weight ratio of 1:99 to 15:85 to form a developer.

The present invention will be explained below with reference to Examples and Comparative Examples.

(Example 1) A toner for a start developer and a toner for replenishment are prepared based on the following formulations.

- 100 parts by weight of styrene-acrylic copolymer as binder resin, DBP oil absorption 90 (m+/100g) (7)
Using 11 parts by weight of carbon black, 1.5 parts by weight of low molecular weight polypropylene as an anti-offset agent, and 1 part by weight of a negative metal-containing monoazo dye as a charge control agent, powder with an average particle size of 5 to 20 μm is prepared by a conventional method. I created a body toner. Hydrophobic silica: Aerosil R972 (manufactured by Nippon Aerosil Co., Ltd., trade name)
A toner composition was prepared by adding and mixing 0.2 parts by weight of aluminum oxide, and 0.2 parts by weight of aluminum oxide C (manufactured by Nippon Aerosil Co., Ltd., trade name).

[To L = In the above-mentioned toner for the start developer, DBP oil absorption amount 10105 (/100g) is used as the carbon black.
) A powder toner was prepared in the same manner except that 11 parts by weight of the powder was used, and the same additives were added to prepare a toner composition.

This toner for replenishment is filled into a toner cartridge with an internal capacity of 200 g, and as printing progresses, the toner cartridge is attached to a developing device and the toner is replenished.

Copy 3" υ rot electrophotographic copying machine DC-3285 (manufactured by Sanda Kogyo Co., Ltd., trade name) was used.
100μm ferrite carrier and toner density 4.5
%, put the Star L developer into the developing device, started copying, and periodically replenished with replenishment toner to print 50,000 copies.

As a result, a clear image with high density and no fogging could be formed from the initial stage of copying, and the fixability of the toner image on the transfer paper was also good. Immediately after replacing the cartridge and replenishing toner, the image quality remained good without deterioration, and good copies were obtained through 50,000 copies.

The results are shown in Table-1.

(Example 2) In Example 1, 9.5 parts by weight of carbon black with a DBP oil absorption of 90 (ml/100g) was used as the carbon black of the toner for the start developer, and 9.5 parts by weight of carbon black with a DBP oil absorption of 90 (ml/100g) was used as the carbon black of the replenishment toner. 260 (ml
A toner was prepared in the same manner except that 9.5 parts by weight of carbon black (/100 g) was used.

Furthermore, when printing was carried out in the same manner for 50,000 sheets, it was possible to form clear, high-density, fog-free images from the initial stage through 50,000 sheets, with good fixing properties and no stains on copies. Ta.

The results are shown in Table-1.

(Comparative Example 1) In Example 1, 8 parts by weight of carbon black with a DBP oil absorption of 90 (ml/100g) was used as the carbon black of the toner for the start developer, and 8 parts by weight of carbon black with a DBP oil absorption of 90 (ml/100g) was used as the carbon black of the replenishment toner. ml/10
Each toner was prepared in the same manner except that 23 parts by weight of carbon black (0 g) was used.

Further, similar operations were performed to print 50,000 sheets.

At the initial stage of copying, a clear image with high density and no fog was obtained, but immediately after replenishing toner, fog occurred, and just before the end of printing, considerable toner scattering was observed. Also,
The fixability also decreased as the printing cycle progressed.

The results are shown in Table-1.

(Comparative Example 2) In Example 1, the DBP oil absorption amount was 90 (m1/100g) as the carbon black of the toner for the start developer.
Using 11 parts by weight of carbon black, the DBP oil absorption amount was 95 (ml/
Each toner was prepared in the same manner except that 11 parts by weight of carbon black (100 g) was used.

Furthermore, when printing was carried out in the same manner for 50,000 sheets, a clear image with high density and no fog was obtained at the initial stage of copying, but as copying progressed, fog and a decrease in image density occurred.

The results are shown in Table-1.

(Comparative Example 3) DB as carbon black for toner for start developer
Example 1 except that 12 parts by weight of carbon black with a P oil absorption of 80 (ml/100g) was used, and 12 parts by weight of carbon black with a DBP oil absorption of 260 (ml/100g) was used as the carbon black for replenishment toner. Each toner was prepared in the same manner.

Furthermore, when printing was carried out in the same manner for 50,000 sheets, the image quality was stable during running, but immediately after toner replenishment, gabbing and toner scattering occurred, resulting in a decrease in image quality.

The results are shown in Table-1.

In the table, the oil absorption amount represents the DBP (dibutyl phthalate) oil absorption amount. Image density and fog density are values determined by a reflection densitometer. In addition, regarding fixing performance, adhesive tape is applied to the formed fixed image and then peeled off.Before peeling off, the image density of the fixed image after peeling off is measured using a reflection densitometer. The fixing properties are always good, and stable copies can be obtained without greatly changing the image quality.

Claims (1)

[Claims] A starting developer made of a mixture of magnetic carrier and toner is brought into contact with the electrostatic latent image bearing surface, and replenishment toner is replenished according to the amount of the toner consumed for development. In the electrophotographic development method, the D of carbon black in the toner in the starting developer is
The BP oil absorption amount is A (ml/100g), and the DBP oil absorption amount of carbon black in the refill toner is B (ml/100g).
), an electrophotographic developing method that satisfies the following relational expression: 1.1≦B/A≦3.