JPH06100844B2 - Dry developer - Google Patents

Description

The present invention relates to a dry developer for developing an electrostatic latent image, particularly 2
Component dry developer.

[Prior Art] In the electrophotographic method or the electrostatic recording method, the electrostatic latent image formed on the photoconductor or the electrostatic recording material is developed with a developer, the toner image is transferred onto a transfer paper, and then fixed and copied. The thing is obtained.

In these methods, as a developer, a dry developer composed of two components, a carrier and a toner, is generally used. Two
In the component dry type developer, triboelectrification is generated between the carrier and the toner by stirring in the developing device, and a charge having a polarity opposite to that of the electrostatic latent image is applied to the toner to adhere to the latent image for development.

As such a developer, for example, as a carrier used in the magnetic brush developing method, iron powder having an average particle diameter of 50 to 500 μm, ferrite powder, or those obtained by coating them with a specific polymer is often used. Further, in recent years, a carrier in which at least magnetic powder and a binder resin are mixed and granulated is also proposed.

In any of these two-component developers, it is necessary to adjust the polarity and charge amount generated between the carrier and the toner so as to be suitable for development.

Conventionally, such a two-component developer has been used for image density of a copy,
Toner density that satisfies the required characteristics such as fog,
A carrier and a toner are mixed and used. However, the charge amount changes depending on the environment in which the carrier and toner are mixed (humidity conditions, etc.), and the quality of the obtained copy changes, and when the charge amount is high, the image density of the obtained copy is low. Or, the carrier adheres to the fringe electric field portion around the image. Further, when the charge amount is low, there are disadvantages that the image density is too high, and fog and toner scattering occur.

[Problems to be Solved by the Invention] In particular, in the case of a developer which has been proposed in recent years and comprises a mixture of at least magnetic powder and a binder resin and has an average particle size of 20 to 50 μm, the charge amount Since it has a drawback that the allowable width is narrow, there is a problem that it is difficult to match the narrow charge amount allowed when adjusting the developer by mixing the carrier and the toner. This is because the carrier having such a small particle size and composed of the binder resin and the magnetic powder has a low saturation magnetic flux density per carrier, and therefore the carrier easily attaches to the fringe electric field portion and the background portion around the image. This is due to the tendency.

Since the carrier adhesion to the background portion is likely to occur when the charge amount is increased, the charge amount cannot be increased so much, and it is necessary to reduce the charge amount with such a small particle size carrier. When the toner is used for a long time and when the humidity is high, the charge amount decreases with time, causing fog and toner scattering.

Further, when a small particle size carrier and toner are mixed to prepare a developer, the charge amount is likely to change under the influence of the environment at the time of mixing, particularly humidity. It is considered that this is because the carrier has a small particle size and thus has a large effective surface area.

Therefore, it is desired that the charge amount of at least the two-component developer obtained by mixing the carrier and the toner is stable even if the environment during mixing changes.

Therefore, an object of the present invention is to solve the drawbacks of the conventional small particle size carrier and to provide a developer having a stable charge amount even if the environment at the time of mixing the carrier and the toner is changed. .

Further, it is an object of the present invention to provide a developer which is stable even after being used for a long period of time or when the environment in which it is used changes.

[Means for Solving the Problems] That is, the present invention provides (1) a dry developer obtained by mixing a carrier and a toner, in which magnetic powder and a binder resin are melt-kneaded and pulverized. A dry developer characterized by containing a carrier obtained by classifying particles into particles having an average particle size of 20 to 50 μm and then subjecting them to a humidity control treatment, (2) humidity controlling treatment at a temperature of 10 to 40 ° C. and a humidity of 40 to The dry developer according to the above (1) is provided under the condition of 80% RH (relative humidity).

Examples of the raw magnetic powder that can be used in the present invention include fine powders of magnetite, ferrite, iron, nickel, chromium dioxide, γ-hematite, cobalt and the like having an average particle size of 0.1 to 3 μm. Among them, magnetite is preferable because it is inexpensive and can be used stably.

As the binder resin, vinyl resin, phenol resin,
Condensation-type resins such as urea resins, melamine resins, polyester resins, polycarbonate resins, polyamide resins, polyurethane resins, epoxy resins and copolymers of these monomers can be used. Conventional components can be used as these monomers. Examples of vinyl-based monomers include styrene-based monomers such as styrene, α-methylstyrene, p-chlorostyrene, and p-methylstyrene; methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2 -Acrylic acid and methacrylic acid ester monomers such as ethylhexyl methacrylate, lauryl methacrylate, dimethylaminoethyl acrylate and dimethylamino methacrylate; amide monomers such as acrylamide and methacrylamide; nitrile monomers such as acrylonitrile and methacrylonitrile; ethylene and propylene. , Butylene, isobutylene, and other olefinic monomers; vinyl acetate, vinyl propionate, and other vinyl ester-based monomers Nomar; vinyl chloride, vinyl bromide, include halogenated vinyl monomers such as vinyl fluoride, and vinyl resins by polymerizing one or two or more thereof.

If necessary, the carrier may be added with a carbon black as a conductivity control agent or a charge control agent as described below for the toner. The carrier is manufactured by kneading and pulverizing, dissolving the binder resin in a solvent and spray-drying a suspension in which the magnetic powder is dispersed, and granulating it.When polymerizing the binder resin, the magnetic powder is used as a monomer. Any of the methods of obtaining by dispersing it inside may be used.

The toner in the present invention includes a resin, a colorant, a charge control agent,
And additives and the like. As the resin used for the toner, polystyrene, styrene-propylene copolymer,
Styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, acrylic resin, polyester resin, vinyl chloride resin, epoxy resin, etc. Resins may be mentioned. Examples of the colorant used in the toner include carbon black, aniline black, nigrosine dye, aniline blue, chrome yellow, ultramarine blue, oil red, phthalocyanine blue, lamp black, rose bengal, and mixtures thereof. It is necessary to add these colorants in such a proportion that a visible image having a sufficient density is formed, and it is usually used in the toner in a proportion of about 1 to 20% by weight.

As the charge control agent, a nigrosine dye, a chromium-containing complex,
Quaternary ammonium salts and the like are used, and it is necessary to use them properly depending on the polarity of the toner. Further, as the additive used in the toner, silica, alumina, magnesia, titania, oxides such as zirconia, molybdenum disulfide, sulfides such as tungsten disulfide, boron nitride, nitrides such as silicon nitride, carbon black, Examples thereof include fatty acid metal salts, fluorine resin fine powder such as polyvinylidene fluoride, resin fine powder such as polystyrene and polymethylmethacrylate, and the like.

The toner manufacturing method includes a method of kneading and pulverizing, a method of dissolving and dispersing a resin, a colorant and the like in a solvent and spray-drying a granulation, and a colorant and a charge control agent when polymerizing the resin. And the like may be obtained by dispersing them in a monomer.

The developer of the present invention is manufactured by mixing a carrier and a toner. The mixing ratio of toner and carrier is 1:99 by weight.
A range of up to 30:70 is suitable. This mixing ratio is determined by the specific gravity of the carrier and the toner, the particle size, the charge amount, and the like.

In the present invention, the humidity control method can be carried out by a method of leaving it in an environmental chamber, a method of introducing humidity control air into a fluidized bed type or a swirling airflow type mixer and treating it.

The purpose of the humidity control of the present invention is to control the amount of water in the carrier, and after erasing the history that it has undergone before the humidity control processing, that is, after the influence received from the environment placed before the humidity control processing is erased. It is preferable to perform humidity control treatment. That is, the amount of water in the carrier can be easily made constant by performing moisture conditioning treatment after removing water present on the surface of the carrier by drying.

The humidity control treatment is preferably carried out in a humidity controlled air under the conditions of a temperature of 10 to 40 ° C. and a humidity of 40 to 80% RH (relative humidity). This is because the condition of the carrier after humidity adjustment is selected so as to be compatible with the environmental conditions in which the developer is actually used, and normal copying conditions are included in the above temperature and humidity ranges. Further, the humidity control treatment time is required to reach the equilibrium moisture content when the humidity is controlled in the humidity controlled air. Whether or not the equilibrium water content has been reached can be known by measuring the water content over time. As the method for measuring the water content, any method such as Karl Fischer water content measurement method and thermogravimetric analysis may be used.

The developing method using the developer of the present invention is a method of developing an electrostatic latent image formed on a photoconductor or an electrostatic recording body by a magnetic brush developing device or the like. For example, if the carrier is negatively charged, the toner is positively charged. Therefore, the toner is attracted and adhered to the negative latent image for development, and the toner image is transferred to a transfer paper and then heated. Establish.

[Examples] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1 Styrene-butyl methacrylate (n-BMA) -acrylic acid (AA) copolymer (styrene: n-BMA: AA = 80: 15: 5, Mw =
80,000) 30 parts by weight and 70 parts by weight of magnetite are mixed, melt-kneaded, finely pulverized, and classified to have an average particle size of 35.6 μm.
Got a career.

Separately from the above carrier, styrene-butyl methacrylate-
Dimethylaminomethacrylate (DMAM) copolymer (styrene: n-BMA: DMAM = 65: 30: 5, Mw = 10,000) 94 parts by weight and 6 parts by weight of carbon black were melt-kneaded and then finely pulverized to obtain an average particle size. A toner of 10.8 μm was obtained. 0.5 parts by weight of alumina fine powder was mixed with 100 parts by weight of the obtained toner by a container fixed blade rotary type mixer to obtain a toner to be used.

The humidity control treatment operation of the carrier was carried out by the swirl flow type humidity control apparatus shown in FIG. In this device, the air sucked by the blowers 6 and 7 is adjusted to 28 ° C. and 65% RH in the humidity control air generation chamber 1 through the intake filter 5, and the humidity control air is supplied from the lower part of the humidity control treatment tank 3. The humidity of the sample 8 which is placed on the screen 2 and swirled and fluidized is adjusted, and only air is discharged from the processing tank through the exhaust filter 4.

A sample was taken every 5 minutes to measure the water content of the carrier (measured by the Karl Fischer method) and the charge amount of the developer mixed with the toner. The results are shown in FIGS. 2 and 3.
Shown in the figure. Since the equilibrium moisture content has been reached after 20 minutes of humidity control and the charge amount is stable, the carrier
By weight, 8 parts by weight of toner were mixed with a V-type blender to prepare a developer.

Comparative Example 1 A developer was obtained in the same manner as in Example 1 except that the carrier was not subjected to humidity control treatment.

Development Test As a test method, a magnetic brush developing device equipped with a developer stirring device was used, and the negative electrostatic latent images of the developers obtained in Example 1 and Comparative Example 1 were continuously developed to obtain the charge amount. The maintainability of image quality was observed.

The results of observation of image quality are shown in Table 1, and the results of measurement of charge amount are shown in FIG. As is apparent from the table and the figure, when the developer of Comparative Example 1 which is not subjected to the humidity control treatment is used, the charge amount is high at the initial stage, the image density is lowered, and the fog (adhesion of toner to the background portion) occurs. In contrast to the toner scattering, when the developer of the present invention (Example 1) was used, there was no problem even after copying 200,000 sheets, and excellent image quality was maintained.

Charge amount measurement test The carrier and toner of Example 1 are left in a low humidity environment (20 ° C, 30% RH) and a high humidity environment (20 ° C, 85% RH) for 24 hours separately, and both are kept in a low humidity environment. And then conditioned,
A test developer was prepared by combining one of which was conditioned under high humidity and conditioned, and one which was conditioned under high humidity to prepare a test developer with a toner concentration of 10% by weight. It was measured. The results are as shown in Table 2.

From these results, in the developer of the present invention which uses the small particle size carrier obtained by kneading and pulverizing the fine magnetic material into the binder resin, the largest influence on the charge amount of the developer is It can be seen that the carrier water content is determined by the humidity of the environment in which it is placed.

[Advantages of the Invention] According to the developer of the present invention, stable chargeability is obtained, and when used for development, there is no carrier adhesion or toner adhesion to the background portion, and image quality such as resolution and gradation is improved. Excellent and can withstand long-term use. So, for example, 20
The toner charge amount is stable even after copying 10,000 sheets, and image quality equivalent to printing is maintained. Further, since the humidity adjustment may be performed on the carrier, the processing amount is small compared to the case where the toner consumed by copying is adjusted, which is economical.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an example of a humidity control treatment apparatus, and FIG. 2 is a graph showing the results of time-dependent measurement of the water content of a carrier in the example of the present invention by the apparatus of FIG.
FIG. 4 is a graph showing the charge amount of a developer using a carrier having a water content corresponding to FIG. 2, and FIG. 4 is a graph showing the relationship between the number of copies and the charge amount for the developers of the present invention and comparative examples. is there. The symbols in the figure have the following meanings. 1 ... Humidity control air generation chamber 2 ... Screen 3 ... Humidity control tank 4 ... Exhaust filter 5 ... Intake filter 6 ... Push blower 7 ... Exhaust blower 8 ... Processing sample

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoshi Hashimoto 1600 Takematsu, Minamiashigara City, Kanagawa Fuji Xerox Co., Ltd., Takematsu Plant (72) Inventor Hiroyuki Moriya 1600 Takematsu, Minamiashigara City, Kanagawa Fuji Xerox Co., Ltd. Takematsu Business In-house (72) Inventor Toshiaki Murofushi 1600 Takematsu, Minamiashigara-shi, Kanagawa Fuji Xerox Co., Ltd. Takematsu Works (56) References Japanese Patent Publication No. 52-33496 (JP, B1)

Claims (2)

[Claims] 1. A dry developer prepared by mixing a carrier and a toner, wherein magnetic powder and a binder resin are melt-kneaded, and this is crushed and classified into particles having an average particle size of 20 to 50 μm. A dry developer containing a carrier obtained by post-humidification treatment. 2. The humidity control treatment is performed at a temperature of 10 to 40 ° C. and a humidity of 40 to 80% RH.
The dry developer according to claim 1, which is formed under the condition of (relative humidity).