JPH0426862A - Production of magnetic toner - Google Patents

Abstract

PURPOSE:To prevent deterioration of the magnetic toner even due to long-time friction by heat fusing a mixture of a magnetic powder and a binder resin and kneading it, and crushing it to form base particles, mixing conductive particles with them, and exerting external force to firmly attach a number of fine conductive particles to the surfaces of the base particles or to bury them into the surfaces. CONSTITUTION:The fine magnetic toner particles are formed by mixing the binder resin and the magnetic powder in a mixer, kneading the mixture in a kneader, classifying the obtained powder mixture with a sieve or a wind classifier, then, mixing the fine conductive particles with the obtained base particles, exerting compression and friction forces on the obtained mixture to firmly attach the numerous fine conductive particles to the surfaces of the base particles or to bury them into the surface, thus permitting the magnetic toner to be enhanced in rigidity, consequently, sufficiently endure stirring during storage or development, friction during conveyance, and further heat due to friction or heat emission in an apparatus and to maintain the primary form and function of the toner.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a magnetic toner for developing electrostatic images formed in electrophotography, electrostatic printing, electrostatic recording, etc. .

<Prior art> In the general electrophotographic method, an electrical latent image is formed on a photoreceptor made of a photoconductive material by utilizing its photoconductivity, and then the latent image is developed using toner. After the toner image is transferred to a transfer material such as paper if necessary, it is fixed by heating, pressure, etc. to obtain a copy. Among the developers for this purpose, the two-component developing method is an excellent method for obtaining relatively stable and good images, but in order to keep the amount of charge of the toner constant, the mixing ratio of carrier and toner must be adjusted. It needs to be constant. However, the two-component developing method has the problem that the mixing ratio of toner and carrier fluctuates during the copying process, requiring constant control of toner concentration, and that the carrier itself deteriorates, resulting in limited durability.

On the other hand, one-component development methods, in which the toner has a carrier function, do not have these problems and only replenish the amount of toner that has been consumed.In particular, development methods using magnetic toner particles can maintain a constant image. There are many advantages in this respect.

However, toner can withstand mechanical pressure during transportation to the latent image surface, or heat from heat generating parts such as the fixing system and drive system in the developing system, without changing its developing characteristics.
It is also necessary to maintain its performance during storage.

Such magnetic toner has a volume resistivity of 102 to 10"0.
The conductive magnetic toner has a volumetric resistance of 109 to 10
It is broadly classified into 14Ω insulating magnetic toner.

Conventionally, the method for manufacturing such magnetic toner involves tri-blending magnetic powder, binder resin, and other additives added as necessary in a predetermined ratio, and melting this mixture using an extruder, roll mill, etc. The resulting agglomerates are pulverized by a mechanical pulverizer such as a jet mill to disperse them into particles of a predetermined particle size, and then a carbon blank or the like is externally added to the toner using a mixer such as a Henschel mixer. It was attached.

<Problems to be Solved by the Invention> However, with magnetic toner manufactured using conventional techniques, carbon black easily separates from the surface of the magnetic toner due to stirring in the developer tank, and the carbon blank adheres to copy paper. This caused stains on the copy paper. In addition, in the case of magnetic toner with white powder such as titanium oxide or zinc oxide attached to the surface instead of carbon black, the separated white powder adheres to the developing sleeve, causing development defects and also causing damage to the photoreceptor. This caused so-called filming, where carbon black or white powder adhered to the surface.

To solve these problems, the conventional technology involves attaching a carbon blank, etc. to the surface of magnetic toner, and then passing the magnetic toner through a hot air stream to fix carbon black, etc., but this method is very expensive. Also, since magnetic toner was processed at high temperatures, there was a risk of dust explosion.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic toner that overcomes the above-mentioned drawbacks, and in particular, provides a magnetic toner that is less susceptible to deterioration even under long-term friction.

<Means for Solving the Problems> In the method for producing a magnetic toner of the present invention, in the first step, magnetic powder is dispersed in a binder resin to create mother particles. That is, a binder resin and magnetic powder, which will be described later, are mixed in a mixer such as a ball mill, a V-type mixer, or an S-type mixer, and the resulting mixture is passed through an extruder, a double-arm kneader - 1 three rolls, a co-kneader, The mixture is kneaded using a pressurized kneading machine such as a pressurized niegu, and then this kneaded material is pulverized using a pulverizer such as a hammer mill, jet mill, or ball mill, and the resulting powder is classified using a sieve or a wind classifier to determine the average particle size. 5-30μm
This is the process of obtaining mother particles.

A charge control agent, a coloring agent, a fluidity modifier, and a fixing aid may be added to the above-mentioned base particles as necessary.
The fluidity modifier may be externally added to the magnetic toner. Examples of the charge control agent include metal-containing dyes and nigrosine dyes. As the coloring agent, conventionally known dyes and pigments can be used. As the fluidity modifier, colloidal silica, fatty acid metal salts, etc. Fixing aids include low molecular weight polypropylene and the like.

In order to produce a conductive magnetic toner having a volume resistivity of 10@2 to 10@Ωl, a conductive substance such as carbon black may be contained in the base particles. Next, in the second step, the base particles obtained in the first step and conductive fine particles are mixed,
A compressive force and a frictional force are applied to the base particles and the conductive fine particles to fix a plurality of conductive fine particles to the surface of the base particles, thereby creating fine particles of magnetic toner.

At this time, by changing the amount of conductive fine particles added to the base particles and fixing them depending on the purpose, conductive magnetic toner or insulating magnetic toner with controlled volume resistivity of the magnetic toner can be obtained. It will be done.

Hereinafter, the constituent elements of the present invention will be explained in detail.

i) About the base particle The base particle, which is one of the constituent elements of the present invention, is composed of magnetic powder, a binder resin, and as necessary, a charge limiting agent, a coloring agent, a fluidity modifier, and a fixing agent. be done.

As for the fine powder of the binder resin constituting the mother particles, a general thermoplastic resin is used. Binder resins include polystyrene, polyp-chlorostyrene, polyvinyltoluene,
Homopolymers of styrene and its substituted products, such as styrene-p-chlorostyrene copolymers and styrene vinyltoluene copolymers, and copolymers thereof; styrene-methyl acrylate copolymers, styrene-ethyl acrylate copolymers ,
Copolymers of styrene and acrylic esters such as styrene-n-butyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-n-butyl methacrylate copolymer Copolymers of styrene and methacrylic esters such as; multi-component copolymers of styrene and acrylic esters and methacrylic esters; other styrene-acrylonitrile copolymers, styrene vinyl methyl ether copolymers, styrene butadiene copolymers Styrenic copolymers of styrene and other vinyl monomers such as styrene vinyl methyl ketone copolymer, styrene acrylonitrile indene copolymer, styrene-maleic acid ester copolymer; polymethyl methacrylate, polybutyl methacrylate ,
Polyvinyl acetate polyester, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid phenol resin, aliphatic or alicyclic hydrocarbon resin, petroleum resin, chlorinated paraffin, etc. can be used alone or in combination.

Furthermore, low molecular polyethylene, low molecular polypropylene,
Ethylene vinyl acetate copolymers, ethylene acrylate copolymers, higher fatty acids, polyamide resins, polyester resins, etc. can be used alone or in combination.

li) [About magnetic powders] Magnetic powders include metals such as cobalt, iron, and nickel, aluminum, cobalt, copper, iron, nickel, magnesium, tin, zinc, gold, silver, selenium, titanium, tungsten, zirconium, and other Mention may be made of metal alloys, metal oxides such as aluminum oxide, iron oxide, nickel oxide, ferromagnetic ferrite, magnetite or mixtures thereof. This magnetic powder has an average particle size of 0.05 to 3μ
m is preferably used, and its proportion to the total magnetic toner is usually 10 to 90% by weight, preferably 35 to 65% by weight.

iii) About conductive fine particles Conductive fine particles include carbon black, zinc oxide,
Examples include titanium oxide, tin oxide, antimony oxide, magnetite, and ferrite. Among these, carbon black is particularly preferably used because it is easy to control the volume resistivity of the magnetic toner. These conductive fine particles having an average particle diameter of 0.05 to 10 μm are preferably used.

The amount of conductive fine particles adhering to the base particles is as follows. That is, in the case of an insulating magnetic toner, the amount is 0.01 to 0.5% by weight, preferably 0.1 to 0.2% by weight based on the base particles.
Weight%. In addition, in the case of conductive magnetic toner, 0.0
It is 5 to 5% by weight, preferably 1 to 2% by weight.

In this way, the volume resistivity of the magnetic toner can be controlled by the amount of conductive fine particles fixed to the base particles.

iv) About fixation As a means of fixing conductive particles to the surface of base particles using the above-mentioned materials, there is a "Nara Hybridization System" made by Nara Kikai Seisakusho Co., Ltd., which is known as a surface modification machine, and a "Nara Hybridization System" made by Hosokawa Micron Co., Ltd., which is known as a surface modification machine. “Ong Mill” can be preferably used.

<Function> By using the above-mentioned mixing means, it is possible to mix the base particles and the conductive fine particles in a state where they are not substantially crushed. Compressive force and frictional force can be applied between the two particles, and if necessary, impact force can be applied between the two particles.

This phenomenon occurs when the mother particles and conductive fine particles come into point contact during mixing, and compressive force, force, and sometimes impact force are applied at the contact point, and at least one of the two particles temporarily acts at the contact point. This is thought to be because heat exceeding the melting point of one of the particles is instantaneously generated, causing a sticking phenomenon due to fusion.

As mentioned above, the magnetic toner obtained by the method of the present invention has conductive fine particles embedded in the surface of the spherical base particles, which improves the rigidity, so it is difficult to use during storage or development. It can withstand friction during stirring or conveyance processes, as well as frictional heat and heat generated from equipment.
The original form and function of the toner can be maintained.

Generally, in the case of insulating magnetic toner, the volume resistivity is 10
``Since there are more than 9 ports, the charge opposite to the charge on the photoreceptor induced by the charge on the photoreceptor during development is carried from the developing sleeve to the toner particles in contact with the photoreceptor, but at this time, the electrical resistance of the toner is Because the charge is high, the toner particles that are in contact with the photoreceptor are transferred to the toner surface, so when the toner particles themselves are moving freely, such as during development, the conductive parts of the toner surface are The apparent electrical resistance of the toner is 10'3Ω due to contact between
The charge is easily induced even to the toner particles that are in contact with the photoreceptor, thereby preventing deterioration of developability. Furthermore, during transfer, the toner particles developed on the photoreceptor are in a stationary state on the photoreceptor, and there is no contact between the toner particles, so there is no contact between the conductive parts on the surface of the toner particles, and the electrical resistance is 10'3 Ω. ■That's all. Therefore, the charge of the toner developed on the photoreceptor is not transferred to the photoreceptor but is retained by the toner. Therefore, since the toner is transferred to the paper by electrostatic force due to the opposite charge to that of the toner attached to the back surface of the paper in the transfer process, deterioration of transferability due to a decrease in the amount of charge of the toner on the surface of the photoreceptor does not occur. On the other hand, if conductive fine particles are simply externally added to the toner surface using a Henschel mixer or the like, the conductive fine particles will separate from the toner surface, and in the case of carbon black, they will cause burr, titanium oxide, zinc oxide, etc. on the copy. In this case, a phenomenon of fusion to the photoreceptor occurs.

Examples will be described in detail below.

[In the case of conductive magnetic toner] <Example 1> The above toner composition was kneaded in a pressure kneader, and then pulverized and classified to obtain base particles with an average particle size of 15 μm.

Next, using "Nara Hybridization System" manufactured by Nara Kikai Seisakusho Co., Ltd., 1% by weight of carbon blank was adhered to the surface of the base particles to obtain a conductive magnetic toner having a volume resistivity of 103 ΩC.

<Example 2> 1% by weight of titanium oxide was adhered to the surface of the mother particles used in Example 1 using the "Nara Hybridizer System" to obtain a volume resistivity 10S magnetic toner.

<Example 3> Magnetite (FezO:+) Conductivity of Ω1 (Prioride AC manufactured by Gutdeyer) The above toner composition was kneaded in a pressure kneader, and base particles with an average particle size of 13 μm were obtained by pulverization and classification. Obtained.

This base particle is manufactured by Micron Co., Ltd. “Mechanofusion”
0.8% by weight of carbon black was adhered to the surface of the base particles to obtain a conductive magnetic toner having a volume resistivity of 10"0.

<Comparative Example 1> 1% by weight of carbon black was attached to the mother particles obtained in Example 1 using a Henschel mixer manufactured by Mitsui Miike Co., Ltd.
A conductive magnetic toner having a volume resistivity of 3Ω was obtained.

Comparative Example 2> 1% by weight of titanium oxide was attached to the base particles obtained in Example 1 using a Henschel mixer manufactured by Mitsui Miike Co., Ltd., and 10 sQa
A conductive magnetic toner having a volume resistivity of n was obtained.

<Evaluation> The conductive magnetic toners obtained in Examples and Comparative Examples were evaluated by a live copy test using a commercially available copying machine "900 D manufactured by Sanda Kogyo Co., Ltd.". The toners of Example 3 and Comparative Example 2 were for hot roll fixing, so after copying with 900D, fixing was performed using an external hot roll fixing device.

The results are listed in Table 1. At this time, a "Macbeth densitometer" (Macbeth) was used to measure the image density, and a "Hunter brightness meter" (Macbeth) was used to measure the Capri density.
Nippon Denshoku Kogyo) was used.

As shown in the results in Table 1, the conductive magnetic toners subjected to the surface modification of Examples 1 to 3 have poor image quality such as ground braking, tailing, and uniformity of black spots due to the separation of the conductive powder. is excellent. On the other hand, when the surface of Comparative Examples 1 and 2 was not modified and the conductive powder was simply added externally using a Henschel mixer, the conductive powder was detached during development using an actual machine, resulting in blurring, trailing, and black spots on the copy. There was a problem with uniformity.

[Insulating Magnetic Toner] <Example 4> The above toner composition was kneaded in a pressure kneader, and then pulverized and classified to obtain base particles with an average particle size of 10 μm.

Next, 0.2% by weight of carbon black was fixed to the surface of the base particles using "Nara Hybridizer System" manufactured by Nara Kikai Seisakusho Co., Ltd. to obtain an insulating magnetic toner having a volume resistivity of 10I0Ω.

<Example 5> Titanium oxide 0.2 was added to the base particles used in Example 4 using "Nara Hybridizer System" manufactured by Nara Kikai Seisakusho Co., Ltd.
% by weight was fixed on the surface of the base particles to obtain an insulating magnetic toner having a volume resistivity of 1012Ω.

<Example 6> For the base particles used in Example 4, "Mechanofusion" manufactured by Line Micron Co., Ltd. was used, and 0.5% by weight of magnetite (EP-1000 manufactured by Toda Kogyo Co., Ltd.) was fixed to the surface of the base particles. An insulating magnetic toner having a volume resistivity of 1 oI Ω■ was obtained.

Comparative Example 3 Using the base particles obtained in Example 4 as is, an insulating magnetic toner having a volume resistivity of 1011 Ωcm was obtained.

<Comparative Example 4> 0.2% hydrophobic adhesive was applied to the base particles of Comparative Example 3 using a Henschel mixer manufactured by Mitsui Miike Co., Ltd. to obtain an insulating magnetic toner having a volume resistivity of 10''Ω■.

<Comparative Example 5> 0.2% by weight of titanium oxide was adhered to the base particles of Comparative Example 3 using a Mitsui Miike Co., Ltd. Nshell mixer to obtain an insulating magnetic toner having a volume resistivity of 1012 Ωcm.

Comparative Example 6> Magnetite (EP manufactured by Toda Kogyo Co., Ltd.) was used as the base particle of Comparative Example 3.
-1000) was deposited in a Mitsui Miike Henschel mixer to give a volume resistivity of 10"Ω.
0 insulating magnetic toner was obtained.

<Evaluation> The insulating magnetic toners obtained in the Examples and Comparative Examples were evaluated by a live copy test using a commercial copying machine 'U-BIXT manufactured by Konica Corporation'.The results are shown in Table 2. Macbeth densitometer for measuring image density
(Macbeth), and a "Hunter Whiteness Meter" (Nippon Denshoku Kogyo) was used to measure the fog density.

As shown in the results in Table 2 and above, the toners in which conductive fine particles were fixed to the surface of the toner particles as in Examples 4 to 6 had good image density and ground blur, and showed no abnormality even after continuous copying of 10,000 sheets. Good quality was obtained. Furthermore, in Comparative Example 3, the image density was poor. In Comparative Examples 4 to 6, troubles such as blurring and filming occurred in copies due to detachment of the conductive particles.

<Effects of the Invention> As described above, the magnetic toner obtained by the method of the present invention has conductive fine powder particles on the surface of the spherical base particles.
By fixing or embedding, the toner's rigidity improves, so it can withstand friction during storage or during the stirring or transportation process for development, as well as frictional heat and heat generated from equipment, and maintains the toner's original form and function. be able to.

Agent Patent Attorney Mamoru Takeuchi

Claims (4)

[Claims] (1) Heat melting a mixture consisting of magnetic powder and binder resin,
After kneading and pulverizing to create base particles, conductive fine particles are mixed with the base particles, and compressive force and frictional force or impact force is applied to the resulting mixture to form a base particle on the surface of the base particle. A method for producing a magnetic toner for electrophotography, which comprises fixing or embedding a plurality of conductive fine particles. (2) The method for producing a magnetic toner for electrophotography according to claim 1, characterized in that 0.01 to 5% by weight of the conductive fine particles are fixed to or embedded in the base particles. (3) Conductive fine particles are added to the base particles by 0.01 to 0.
2. The method for producing an electrophotographic insulating magnetic toner according to claim 1, wherein 5% by weight of the insulating magnetic toner is fixed or buried. (4) The method for producing a conductive magnetic toner for electrophotography according to claim 1, characterized in that 0.05 to 5% by weight of the conductive fine particles are fixed to or embedded in the base particles.