JP2742082B2 - Negatively chargeable electrophotographic developer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developer for developing a latent image in electrophotography, electrostatic recording, electrostatic printing, magnetic recording and the like. More specifically, the present invention relates to an electrophotographic developer which is uniformly charged to a negative charge in a direct or indirect electrophotographic developing method, visualizes a positive electrostatic image, and gives a high quality image.

[Conventional technology]

Conventionally, many methods are known as electrophotography, such as U.S. Pat.No. 2,297,691.However, generally, a photoconductive substance is used to form an electric latent image on a photoreceptor by various means. And then developing the latent image with developing powder (hereinafter referred to as toner)
And then, if necessary, transferring the toner image to a transfer material such as paper, followed by fixing by heating, pressure or solvent vapor to obtain a copy. In the case where a step of transferring a toner image is provided, a step for removing residual toner on the photoconductor is usually provided.

A developing method for visualizing an electric latent image using toner is as follows.
For example, the magnetic brush method described in U.S. Pat.No. 2,874,063, the cascade developing method described in U.S. Pat. A method using a conductive magnetic toner described in the specification is known.

Conventionally, fine powders obtained by dispersing dyes and pigments in natural or synthetic resins have been used as toners applied to these developing methods. For example, particles obtained by finely pulverizing a dispersion of a colorant in a binder resin such as polystyrene to about 1 to 30 μm are used as the toner. A magnetic toner containing magnetic particles such as magnetite is used. In the case of a system using a so-called two-component developer, the toner is usually used by being mixed with carrier particles such as glass beads and iron powder.

Generally, a charge control agent is used in such a dry developing toner. Organic compounds such as metal-containing complex salts and dyes are mainly used as the charge control agent. These are usually added to a thermoplastic positive resin, melt-dispersed under heating, finely pulverized, and adjusted to an appropriate particle size as required to produce a toner. However, these charge control agents have complicated structures, inconsistent properties, and poor stability. Further, it is easily decomposed or deteriorated due to dispersion at the time of heat kneading, mechanical impact, friction, change in temperature and humidity conditions, and the like, and a phenomenon that charge controllability is likely to be reduced.

Therefore, when a toner using such a charge control agent is developed in a copying machine, the charge control agent may be decomposed or deteriorated with an increase in the number of times of copying, which may cause deterioration of the toner during running.

In addition, many of the charge control agents have a polarizer, so that they are poorly dispersed in the resin, and when melted and kneaded, the control agents are exposed on the toner surface. Therefore, when the toner is used under high humidity conditions, there is a drawback that high quality images cannot be obtained because these control agents have polar groups.

As described above, when the conventional charge control agent is used in toner, the amount of charge generated on the surface of toner particles varies between toner particles, between toner and carrier, or between toner carrier and toner carrier. And problems such as fogging, toner scattering, and carrier contamination are likely to occur. Further, this obstacle appears as a remarkable phenomenon when a large number of copies are made, resulting in a result which is practically unsuitable for a copying machine.

Further, under high humidity conditions, the transfer efficiency of the toner image is remarkably reduced, and many of them are not usable. Also,
Even at normal temperature and normal humidity, when the toner is stored for a long period of time, deterioration occurs due to the instability of the charge control agent used,
It may become unusable.

Further, many developers cannot retain desirable properties for faithfully reproducing a latent image over a long period of time. Even those that initially exhibit desirable performance will not retain their initial properties over long periods of continuous use and will not be usable. In addition, fogging occurs, and toner is scattered around edges in copying a line drawing, and the image density is also reduced. Other disadvantages include a decrease in image density, scattering of line drawings, white spots, fog, and the like when development and transfer are performed under environmental conditions of high temperature and high humidity.

As a method for solving such a disadvantage, Japanese Patent Application Laid-Open No. 55-12
No. 0041 and JP-A-59-34539 disclose a method in which hydrophobic colloidal silica is added to impart high fluidity to a toner and make the chargeability uniform. Specifically, for example, silica fine powder was reacted with an organic silicon compound such as dimethyldichlorosilane, hexamethyldisilane, silicone oil, etc., and the silanol group on the surface of the silica fine powder was replaced with an organic group, and the surface was hydrophobized. Silica fine powder is used. Among these, silicone oil treatment is preferred as the hydrophobizing treatment, and shows sufficient hydrophobicity, and gives excellent properties to the toner when contained in the toner. Has a drawback that the charge amount of the toner becomes excessively large in repeated copying for a long time due to high electric resistance, resulting in a decrease in density. This tendency is particularly remarkable under low humidity.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a negatively chargeable electrophotographic developer which does not change its charging characteristics even when copying is repeated for a long time under low humidity.

A further object of the present invention is to provide a negatively chargeable electrophotographic developer that reproduces a stable image that is not affected by changes in temperature and humidity, especially when scattered during transfer at high humidity and low humidity, such as transfer omission. Another object of the present invention is to provide a negatively chargeable electrophotographic developer having high transfer efficiency.

It is still another object of the present invention to provide a negatively chargeable electrophotographic developer having excellent storage stability that maintains initial characteristics even after long-term storage.

[Means for solving the problem]

That is, the present invention is an electrophotographic developer having a negatively charged toner and a treated carbon black, wherein the treated carbon black has the following formula (I) (Where R represents hydrogen or a methyl group, and n represents an integer.) Carbon black treated at a temperature of 25 ° C. with a silicone oil having a viscosity of 100 cps or less at a temperature of 25 c. The present invention relates to a negatively chargeable electrophotographic developer which is treated with 5 to 50 parts by weight of silicone oil per part by weight.

In the present invention, carbon black having a particle diameter of 10 to 70 μm can be preferably used as one component of the developer, and among them, conductive furnace black and oil furnace black are particularly preferable.

Among the above silicone oils, those having a viscosity of 100 cps or less at 25 ° C. are suitable for treating carbon black.

In the present invention, the addition amount of silicone oil to carbon black is preferably 5 to 50 parts by weight based on 100 parts by weight of carbon black, and particularly excellent effects can be obtained by treating under heating.

On the other hand, the applied amount of the treated carbon black of the present invention is effective when the amount is 0.01 to 10% by weight, particularly preferably 0.05 to 3% by weight with respect to the developer. Developer is obtained.

Known binder resins for the toner used in the present invention include, for example, polystyrene, poly-P-chlorostyrene, a homopolymer of styrene such as polyvinyltoluene and a substituted product thereof; a styrene-P-chlorosterene copolymer, Styrene-butyl acrylate copolymer, styrene-
Propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-
Methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-octyl acrylate copolymer,
Styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether Copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer Styrene copolymers such as polymers and styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide , Polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin,
Phenol resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins, paraffin waxes and the like can be used alone or in combination.

In the present invention, among these resins, styrene-acrylic copolymers are preferably used, and in particular, styrene-n-butyl acrylate copolymer, styrene-n-butyl methacrylate copolymer, styrene acrylic acid -2
-Ethylhexyl copolymer and the like are preferably used.

Known dyes and pigments as coloring materials used in the toner,
For example, it can be widely used such as carbon black, phthalocyanine blue, indanthrene blue, peacock blue, permanent red, lake red, rhodamine lake, Hansa yellow, permanent yellow and benzidine yellow.

To use the toner as a magnetic toner, a magnetic powder may be included. As such magnetic powder, a substance that is magnetized when placed in a magnetic field is used, and powders of ferromagnetic metals such as iron, cobalt, and nickel or alloys and compounds such as magnetite, γ-iron oxide, and ferrite are used. is there. The content of this magnetic powder is 15 to 70 wt.
%.

It is also possible to add a charge control agent to the toner of the present invention, if necessary. As such a charge control agent, a negative charge such as a metal complex salt of a monoazo dye or a metal complex salt of a salicylic acid compound is used. Control agents are used.

The developer of the present invention can be applied to various developing methods. For example, a magnetic brush developing method, a cascade developing method, a method using a high-resistance magnetic toner described in JP-A-53-31136, JP-A-54-42121, and JP-A-55-42121.
-18656, 54-43027, fur brush developing method, powder cloud method, touch-down developing method, impression developing method and the like.

Further, the developer of the present invention is suitably used in an electrostatic transfer method using an electric field generated by a corona discharge charger, a contact roller charger, or the like.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited thereto.

Example 1 100 parts by weight of a styrene-butyl acrylate (copolymer ratio = 8: 2) copolymer, 60 parts by weight of magnetite as a magnetic material, 4 parts by weight of a polypropylene wax as a release agent, and a monoazo dye as a charge control agent After mixing 2 parts by weight of the chromium complex, the mixture is melt-kneaded in a twin-screw rudder heated to 145 ° C., then cooled, and the cooled product is passed through a wire mesh having an opening diameter of 2 mm by a mechanical grinder. It was coarsely pulverized and then finely pulverized to about 10 μm with a jet mill pulverizer.
The finely pulverized product was pulverized by an air classifier, Alpine 100MZR, so that the volume average particle diameter became 11 to 13μ, and a negatively chargeable black powder (toner) was prepared.

On the other hand, while vigorously stirring 100 parts by weight of conductive furnace black having a particle diameter of about 30 mμ, a liquid obtained by diluting 15 parts by weight of dimethylpolysiloxane (viscosity at 25 ° C. is 40 cps) with xylene four times is sprayed. While continuing stirring, the temperature of the stirring tank is raised to about 280 ° C. and maintained for 2 hours. Thereafter, the mixture was cooled to obtain dimethylpolysiloxane-treated carbon black.

0.4 wt% of the above-mentioned dimethylpolysiloxane-treated carbon black was added to the black powder to obtain a negatively chargeable electrophotographic developer.

This developer was applied to a commercially available copying machine (trade name, NP-7550, manufactured by Canon Inc.). A clear image without fog was obtained, and the image reflection density was 1.35. Furthermore, in order to examine the durability of the developer at a low temperature, 100,000 sheets were repeatedly copied at 20 ° C. and 5 RH% using an original with an image area ratio of 2% as an original. Although no image was obtained, the charge amount of the developer remained around -8 μc / g, and the triboelectric chargeability was stable. The charge amount of the negatively chargeable electrophotographic developer was measured by absorbing only the toner from a developing machine into a Faraday gauge.

On the other hand, even under a high humidity environment (30 ° C, 90RH%), the image density is
An image free of fog and other problems was obtained with 1.24.

In addition, good transferability was exhibited under various environments, and no white spots or scattering of lines and images were observed.

Example 2 Oil Furnace Black 100 having a particle size of about 13 μm
In parts by weight, methyl hydrogen polysiloxane (25 ° C
The same treatment as in Example 1 was carried out on 20 parts by weight of a solution having a viscosity of 70 cps).

0.6 wt% of the above treated carbon black was added to the black powder of Example 1 to obtain a developer. When this developer was evaluated in the same manner as in Example 1, good results were obtained.

Example 3 Oil Furnace Black 100 having a particle size of about 60 μm
Add dimethylpolysiloxane (viscosity at 25 ° C 20cp
s) 5 parts by weight were processed in the same manner as in Example 1 to obtain a developer. When this developer was evaluated in the same manner as in Example 1, good results were obtained.

Example 4 Styrene-butyl methacrylate (copolymer ratio = 7: 3)
100 parts by weight of copolymer, carbon black 5 as colorant
3 parts by weight of a polypropylene wax as a releasing agent and 2 parts by weight of a chromium complex salt of a salicylic acid compound as a charge control agent were mixed, and black powder was prepared in the same manner as in Example 1.

Conductive furnace black 100 with particle size of about 20mμ
In parts by weight, methyl hydrogen polysiloxane (25 ° C
And a viscosity of 30 cps) using 18 parts by weight.

1.0 wt% of the above treated carbon black to the black powder
% To obtain a toner. 5 parts by weight of this toner and 95 parts by weight of a ferrite carrier were mixed to prepare a developer.

On the other hand, a positive electrostatic latent image is formed on a selenium photoreceptor, developed with the above-described developer, and the resulting powder image is transferred to plain paper using a corona discharger, and then the transferred image on plain paper is printed. The image was fixed with a hot roll fixing device.

When evaluated in the same manner as in Example 1, good results were obtained.

〔The invention's effect〕

As described above, when a developer containing carbon black treated with silicone oil is used, the triboelectrification of the developer is stabilized, and even in various environments,
It shows uniform negative chargeability. In particular, when the surface of the carbon black is coated with the silicone oil represented by the general formula (I), the carbon black exhibits good negative chargeability, and furthermore, the excessive charge accumulation is suppressed by the conductivity of the carbon black inside, and the low humidity It is considered that the composition exhibits stable triboelectrification even below. Therefore, when the developer according to the present invention is used, a clear, high-density image without fogging can be obtained, and even when used repeatedly for a long time, image deterioration does not occur, and high temperature and high humidity or low temperature and low humidity can be obtained. Even under the condition, the transfer characteristics are good, and an image free from problems such as scattering and white spots can be obtained.

Claims (2)

(57) [Claims] An electrophotographic developer comprising a negatively charged toner and a treated carbon black, wherein the treated carbon black has the following formula (I): (Where R represents hydrogen or a methyl group, and n represents an integer.) Carbon black treated at a temperature of 25 ° C. with a silicone oil having a viscosity of 100 cps or less at a temperature of 25 c. A negatively chargeable electrophotographic developer, which is treated with 5 to 50 parts by weight of silicone oil per part by weight. 2. The processed carbon black is added to the developer in an amount of 0.01 to 0.01%.
The negatively chargeable electrophotographic developer according to claim 1, which is contained in an amount of 10 wt%.