JPS5934538A - Manufacture of electrophotographic developing magnetic particle - Google Patents

Abstract

PURPOSE:To disperse uniformly fine magnetic particles into a resin, to reduce the number of holes, to reduce substantially voids of the magnetic particles, to raise binding force with a binder, and to enhance durability, by impregnating said particles with a monomer lower in hydrophobic property as compared with the resin, and polymerizing it. CONSTITUTION:One or more kinds of radically polymerizable monomers, such as acrylic, vinyl, or styrene type monomer are mixed in a prescribed ratio, a prescribed amt. of polymn. initiator is added and dissolved therein, and a prescribed amt. of fine magnetic particles is added, and dispersed with stirring. The present magnetic particles usable as a toner or as a carrier is obtained by heating with stirring the obtd. liquid dispersion, prepolymerizing it to form gel, polymerizing it in an inert atmosphere, pulverizing the obtd. solid product by an ordinary method, and classifying it.

Description

DETAILED DESCRIPTION OF THE INVENTION Specifically, the present invention relates to a method for producing magnetic particles used as a toner or carrier in an electrophotographic developer used to visualize an electrostatic latent image.

Electrophotographic developers include one-component magnetic developers consisting of a magnetic toner (average particle size 5 to 50 μm) in which fine magnetic powder is dispersed in a binder, and one-component magnetic developer consisting of a magnetic toner (average particle size 5 to 50 μm) in which fine magnetic powder is dispersed in a toner and binder. Magnetic carrier obtained by dispersing (average particle size 5 to 150
Dry type developers such as two-component magnetic developers made of a mixture with .mu.m] are mainly used. The magnetic toner or magnetic carrier (collectively referred to as magnetic particles) in these developers usually contains thermoplastic or thermosetting resin as a binder, iron powder as magnetic fine powder,
It is manufactured by kneading and dispersing magnetite, ferrite, etc., pulverizing it, and classifying it. However, with this method, it is difficult to uniformly disperse the magnetic fine powder in the resin due to the poor wettability of the magnetic fine powder to the resin, and the porosity inside the magnetic particles is large. In addition to the problem of weak binding force between the magnetic particles and the resin, since magnetic particles contain resin, their fluidity or magnetic transportability is poorer than that of magnetic fine powder alone.In order to improve this, the content of magnetic fine powder is If the number is increased, the porosity increases further, and the magnetic particles themselves become opaque. Although techniques for improving wettability have been proposed, the current situation is that they are not yet satisfactory.

The present invention has been made in view of these problems, and provides magnetic particles for electrophotographic developers that can obtain magnetic particles with substantially small porosity and in which fine magnetic powder is uniformly dispersed in a resin. The purpose is to provide a method for producing , the gist of which is to disperse magnetic fine powder in a radically polymerizable monomer, prepolymerize the monomer to gel it, and then polymerize and assimilate it under pressure. It is in.

In other words, the present invention takes into account that the poor wettability between magnetic fine powder and resin as a binder is due to the fact that the former is hydrophilic, whereas the latter is hydrophobic. By moistening the magnetic fine powder with nanatsumer, which has less hydrophobicity than the
This was done based on the knowledge that if this was made into a polymer, the magnetic fine powder would be uniformly dispersed in the resin, and the binding strength between the two would also increase.

Examples of radical polymerizable monomers include (meth)acrylic acid, methyl (methacrylate), ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, propyl (meth)acrylate, n-octyl (meth)acrylate, dodecyl (meth)acrylate, 2-ethylhexyl (meth)acrylate-stearyl (meth)acrylate, 2-chloroethyl (meth)acrylate, phenyl (meth)acrylate, α-chlor (
(Meth)acrylic acid esters such as methyl metacoacrylate, dimethylaminoethyl (meth)acrylate, and diethylamine ethyl (meth)acrylate; (meth)acrylic acid derivatives such as (meth)acrylonitrile and (meth)acrylic acid amide; Acrylic monomers containing; vinyl ethers of lower alcohols having 1 to 8 carbon atoms such as vinyl methyl ether, vinyl ethyl ether, and vinyl isophthyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isobutyro π-nyl ketone; N-vinyl pyrrole; N-vinylcarbazole, N-
Vinyl monomers including N-vinyl compounds such as vinyl indole and N-vinylpyrrolidone, vinyl halides such as vinyl bromide and vinyl fluoride, and vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate, styrene, 0-lm - or P-methylstyrene, 0-1m-1P
-ethylstyrene, 2,4-dimethylstyrene, P-n
-butylstyrene, p-tert-butylstyrene,
Examples include styrenic monomers including 01 to C1o lower alkylstyrenes such as P-n-hexylstyrene and p-n-octylstyrene, P-chlorostyrene, 3I4-dichlorostyrene, etc., but are limited to these monomers. It is not something that will be done.

In addition, in this specification, the term "(meth)acrylic acid" means acrylic acid and methacrylic acid, whether it is itself or a larger group.

The monomers may be used alone or in combination of two or more,
By being polymerized in the presence of a radical polymerization initiator,
It functions as a binder, but if necessary, unsaturated carboxylic acids having 3 to 5 carbon atoms such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid may be used in combination with other monomers as a subcomponent. Good too. In this case, the amount of unsaturated carboxylic acid in the total monomers is suitably in the range of 01 to 20% by weight.

Further, when polymerizing, the polymerization may be carried out in the presence of a crosslinking agent to generate a crosslinked polymer, if necessary. Examples of crosslinking agents include compounds having two or more polymerizable double bonds, such as divinylbenzene, divinylnaphthalene, and derivatives thereof, such as ethylene glycol dimethacrylate, diethylene glycol methacrylate, triethylene glycol methacrylate, trimethylolpropane triacrylate, and allyl methacrylate. , [-butylaminoethyl methacrylate, tetraethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, N,N-divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone, ethylene glycol, triethylene glycol, 1.2- Propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butynediol, 1,4-bis(hydroxymethyl)cyclohexane, bisphenol A, fl, etc. may be used alone or in combination of two or more. Bye.

As the magnetic fine powder, iron powder or other ferromagnetic metal powder, magnetite, γ-ferric oxide, ferrite, etc. may be used (the proportion thereof in the magnetic particles is 1 to 85% by weight, preferably , 30 to 85% by weight is suitable.

Since magnetic fine powder is hydrophilic, simply dispersing it in a monomer may not allow the monomer to wet the pore walls of the magnetic fine powder sufficiently.
It is preferable that the magnetic fine powder be impregnated with the 7-mer by stirring and dispersing them under reduced pressure, or by dispersing in the atmosphere and then further stirring under reduced pressure.

When magnetic fine powder particles are impregnated with monomer in this way,
The pores are reduced and the porosity of the magnetic particles is substantially reduced, and at the same time, the binding force with the binder can be increased, and the durability can be greatly improved.

In addition, the wettability (or wettability, or infiltration ability) of the magnetic fine powder with respect to the monomer is smaller than that of the polymer (compared to that of the polymer), so it can be uniformly dispersed, but if necessary, in order to further improve the wettability, it is necessary to The magnetic fine powder may be mixed with a silane coupling agent and subjected to a coupling reaction to impart lipophilicity, or the magnetic fine powder may be added to a monomer together with a silane coupling agent to cause a coupling reaction. Silane Cup As a ring agent, the general formula: %Formula%0In the formula, k is a C1 to C1o alkyl group, a phenyl group,
A group having a vinyl group, an epoxy group, or an amine group, Y represents an alkyl group or a hydrolyzable group, and X represents a hydrolyzable group. ) can be used, and commercially available ones may be used as they are. The hydrolyzable group of this silane coupling agent undergoes a coupling reaction with the magnetic fine powder, and the group k protrudes from the surface of the powder particle, giving lipophilicity to the magnetic fine powder. The wettability to any binder can be improved by selecting . The content of silane coupling agent is 0 for magnetic fine powder.
The content is preferably 0.01 to 2% by weight. This is because if the silane coupling agent is less than 0.01% by weight, almost no effect can be expected from the addition, and if it exceeds 2% by weight, when mixed directly with the magnetic fine powder and then kneaded with the binder, This is because it causes agglomeration of powder particles, and when kneaded together with magnetic fine powder in a binder, residues of hydrolyzable groups and active groups remain, reducing moisture resistance and stability.

Examples of radical polymerization initiators include diacyl peroxides such as benzoyl peroxide, acetyl peroxide, lauroyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 2,2-azobisisobutyronitrile, 2
．． Azo compounds such as 2-azobis-2,4-dimethylvaleronitrile may be used.

According to the present invention, magnetic particles for electrophotographic developer are specifically manufactured as follows. In other words, one or more of the above radically polymerizable monomers are blended in a predetermined ratio, a predetermined amount of a polymerization initiator is added and dissolved, and a predetermined amount of magnetic fine powder is added and stirred. to disperse. If necessary, the mixture may be stirred under reduced pressure to remove gas from the pores of the fine powder particles to facilitate impregnation of the monomer into the fine powder particles. Alternatively, the magnetic fine powder may be immersed in a silane coupling agent solution in advance, dried, and then dispersed in the monomer. The thus obtained dispersion is heated while stirring to prepolymerize and gel. This prepolymerization is usually carried out at 60 to 100°C for 5 to 120 minutes. Here, it is preferable that the prepolymerization is carried out at a polymerization rate of about 20%, and when the content of magnetic fine powder is large, about 10 to 15%. In this state, the dispersion maintains a gel state. This is because if the polymerization is carried out to the final stage without prepolymerization, not only will the polymer be in a foamed state, but the magnetic fine powder will settle and be difficult to disperse uniformly. Next, the prepolymerized reactants are heated at 70 to 100°C in an inert atmosphere at 30 to 50 Ki9/
Polymerize and solidify under cJ conditions.

The desired magnetic particles are obtained by pulverizing the product according to a conventional method and classifying it.

The magnetic particles produced in this way have a strong binding force between the binder and the magnetic fine powder because the monomer impregnated into the magnetic fine powder particles is polymerized, and the pores are filled with the binder. It has extremely low porosity and exhibits excellent durability. At the same time, the wettability of the monomer to the magnetic fine powder is good, so the dispersibility of the magnetic fine powder is good. Because of this, it exhibits excellent magnetic transport properties and, in some cases, excellent charging properties. In addition, since magnetic particles have excellent durability and do not easily change their physical properties, they are suitable for high-speed development where durability as a developer is particularly required.

Examples of the present invention will be described below. In addition, parts in Examples and Comparative Examples mean parts by weight.

Example 1 187.5 parts of styrene monomer, 1 part of n-butyl methacrylate
50 parts of methacrylic acid, 125 parts of methacrylic acid, and 01 part of n-octyl mercaptan were mixed, and 1.25 parts of benzoyl peroxide was dissolved therein as a polymerization initiator. Magnetite Co., Ltd.)
Add 750 parts and 10 parts of carbon bra 12 ivy, reduce the pressure to lx10g8g,
Impregnate magnetic fine powder with monomer. Next, after mixing in a ball mill for 5 hours, prepolymerization was carried out by heating at 100°C for 20 minutes while stirring at 1000 rpm, and after cooling, using an autoclave for 4 hours in a nitrogen gas atmosphere.
Polymerization was carried out at 85-90° C. for 4 hours under a pressure of 0 Kfl/d. The produced polymer has a weight average molecule it (Mw
) 14,000, and the number average molecular weight was 5,500. This product is crushed in a hammer mill and classified to have a particle size of 10~
Magnetic particles having an average particle diameter of 415 to 20 μm and a volume resistivity of 10 to 100 G were obtained.

In order to investigate the characteristics of these magnetic particles, 100 parts of styrene-acrylic resin (consisting of 7Qwt% styrene and 3Qwt% n-butyl methacrylate) and 5 parts of carbon black were used.
After kneading and solidifying the parts, crush them in a hammer mill,
An insulating toner (positively charging toner) with a particle size of 10 to 20 μm5 (average particle size 14 μm) and a volume resistance of 10 Ω was prepared by classifying the toner, and this toner was mixed with the magnetic particles at a weight ratio of 10:90. A two-component magnetic developer was prepared by mixing.This developer was used as a developer in an electrophotographic copying machine equipped with a photoreceptor that forms a negative electrostatic latent image, and 70,000 sheets of A4 size were continuously copied. The amount of charge and average particle size of the magnetic particles were measured every time a predetermined number of copies were made.

The results are shown in Table 1. The electrophotographic copying machine has a built-in magnetic brush developing device equipped with a developing sleeve having a rotationally driven magnetic roller, and the toner is positively charged by frictional contact with magnetic particles functioning as a carrier. Ru. Further, when the copied images after 70,000 continuous copies were examined, the image quality was good and no image fogging was observed.

As is clear from the results in Table 1, when the magnetic particles produced by the method of the present invention are used as a carrier,
It can be seen that the charge amount and average particle size hardly change even after 30,000 copies are continuously made, indicating excellent charging characteristics and durability.

Comparative Example 1 A polymer was produced by polymerizing raw materials having the same composition as in Example 1 under the same conditions as in Example 1, except that the addition of magnetic fine powder RB-BL and carbon black was omitted. Then, 250 parts of this polymer was added with magnetic fine powder RB-BL7.
50 parts of carbon black and 10 parts of carbon black were added, kneaded for 30 minutes with three rolls, assimilated, crushed with a hammer mill, and classified to obtain magnetic particles with an average particle size of 20 μm and a volume resistance of 5×100.

The weight ratio of these magnetic particles to the toner prepared in Example 1 was 90.
: A two-component magnetic developer was prepared by mixing at a ratio of 10:
When continuous copying was performed as a developer for the electrophotographic copying machine used in Example 1, the image quality of the copied images began to deteriorate after 10,000 copies were made, and when the number of copies exceeded 30,000 copies, it became unusable.

Further, when the amount of charge and average particle size of the magnetic particles were measured every time a predetermined number of copies were made, the results shown in Table 2 were obtained.

Table 2 From the results in Table 2, even if magnetic particles have the same composition, when used as a carrier, the amount of charge and average particle size of magnetic particles manufactured by the conventional method decrease as the number of copies increases. However, it can be seen that the binding force between the magnetic fine powder and the binder is small, and the binder peels off or crumbles due to friction, resulting in loss of triboelectric charging properties and lack of durability. It has also been confirmed that the chargeability of the magnetic particles deteriorates, leading to a decrease in the amount of charge on the toner, resulting in a decrease in the density of the copied image and an increase in fog.

Example 2 375 parts of styrene monomer, n-butyl methacrylate-1
2.5 parts of benzoyl peroxide was dissolved in a mixture of -100 parts of acrylic acid, 25 parts of acrylic acid, and 05 parts of n-octyl mercaptan, and 50012 parts of magnetic fine powder MRB-B-450AC manufactured by Toda Kogyo Co., Ltd. was added to the mixture. and impregnated under reduced pressure of 1X10 mmH5' and then mixed in a ball mill for 5 hours - then at 1500 rpm.
35 molecules were prepolymerized at 95° C. with rotational stirring at m, and after cooling, polymerization was carried out at 85 to 90° C. for 4 hours under a pressure of 40 to 9/cd in a nitrogen gas atmosphere using an autoclave.

The molecular weight of the produced polymer is M'w: 33000,
MN: 18,000. This product is crushed in a hammer mill and classified to have a particle size of 10 to 30 μm (average particle size of 2
0 μm) and a volume resistivity of 10145 to 10 Ω· were obtained.

The weight ratio of these magnetic particles to the toner prepared in Example 1 was 90.
: A two-component magnetic developer was prepared by mixing the two-component magnetic developer in a ratio of The image quality was good until then, and no image fogging was observed.

Example 3 1 part of lauroyl peroxide was dissolved in a mixture of 160 parts of styrene monomer, 35 parts of n-butyl methacrylate, 5 parts of methacrylic acid, and 0.1 part of n-octyl mercaptan, and 800 parts of magnetic fine powder RB-BL was dissolved in the mixture. After adding 10 parts of carbon black and impregnating it under reduced pressure of 12 1 x 10 mmHg,
Mix in a ball mill for 5 hours, then polymerize 15 molecules at 95°C with rotational stirring at soo rpm. After cooling, use an autoclave to polymerize at 40Kq/in nitrogen gas atmosphere.
Polymerization was carried out for 4 hours at 85-90°C under a pressure of dl.

The molecular weight of the produced polymer is MW: 15000, MN
:6500. This product was pulverized in a hammer mill and classified to obtain magnetic particles with a particle size of 10 to 30 μm (Heisei 1415 average particle size of 20 μm) and a volume resistivity of 10 to 10 Ω.

The weight ratio of these magnetic particles to the toner prepared in Example 1 was 90.
: A two-component magnetic developer was prepared by mixing at a ratio of 10:
When this was used as a developer in the electrophotographic copying machine used in Example 1 and 70,000 A4 size sheets were continuously copied, the quality of the copied images was good until the end, and no image fogging was observed.

Example 4 125 parts of benzoyl peroxide was dissolved in a mixture consisting of 700 parts of styrene monomer, 200 parts of n-butyl methacrylate, and 0.1 part of n-octyl mercaptan, and part of magnetic fine powder RB-BL5Q and carfoil were dissolved in the mixture. -y I
50 parts '171I], tTlXl0-12Hri under reduced pressure, mixed in a ball mill for 4 hours, and then heated at 95°C with rotational stirring at 1500 rpm.
After cooling, polymerization was carried out at 95°C under a pressure of 40 to 9/d in a nitrogen gas atmosphere using an autoclave.
Polymerized for hours. The molecular weight of the produced U7-17) is
MW: 13,500-MN: 5800. This product was crushed in a hammer mill and classified to have a particle size of 5 to 1.
Magnetic particles of 2 μm (average particle size 105 Pm) and volume resistivity of 3×10 Ω were obtained.

In order to use this magnetic particle as a magnetic toner, it is used as a one-component magnetic developer used in an electrophotographic copying machine equipped with a built-in magnetic brush developing device equipped with a stainless steel developing sleeve, and is used to print 30,000 sheets of A4 size paper continuously. When I copied it,
The copy image was good until the end, and no image fogging was observed. In addition, the initial charge due to frictional contact of the magnetic particles with the stainless steel developing sleeve, the amount of charge was 138 μC/
It was 7.

Comparative Example 2 A polymer was produced by polymerizing raw materials having the same composition as in Example 4 under the same conditions as in Example 4, except that the addition of magnetic fine powder RB-BL and carbon black was omitted. Then, to 200 parts of this polymer, part of magnetic fine powder RB-BL5Q and 50 parts of carbon black were added, kneaded for 30 minutes with three rolls, solidified, crushed with a hammer mill, and classified to have an average particle size of 13.5 μm. Volume resistivity 5×10 Ω・α
magnetic particles were obtained.

When these magnetic particles were used as a one-component magnetic developer used in the electrophotographic copying machine used in Example 4, and continuous copying was performed, only copied images of poor quality were obtained from the point where copying was started, and Fog was significant and the image density itself was extremely low. The initial charge amount due to frictional contact of the magnetic particles with the stainless steel developing sleeve was only 52 μC/g.

Claims (1)

[Claims] (1) Magnetic particles for an electrophotographic developer characterized in that magnetic fine powder is dispersed in a monomer capable of radical polymerization, the monomer is prepolymerized to gel, and then polymerized and solidified under pressure. Manufacturing method.