JP2870833B2 - Electrophotographic developer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developer for electrophotography used in the field of copying machines and the like.

More specifically, the present invention relates to a reliable electrophotographic developer having excellent copy quality.

(Prior Art and Problems to be Solved by the Invention) Conventionally, as a developer for developing an electrostatic image formed on a latent image holding surface such as an electrophotographic photosensitive member, a developer comprising a carrier and a toner is used. A one-component developer which does not require a component developer and a carrier is known. The two-component developer includes toner particles containing a resin and a colorant as main components,
It contains a magnetic carrier with a relatively large particle diameter that transports the toner particles to the vicinity of the photoreceptor while holding it on the surface with electrostatic force.However, only toner particles are consumed during development. It is necessary to keep the content ratio between the magnetic carrier and the toner particles constant. In the case where development using a two-component developer such as PPC (plain paper copier) or the like with a large amount of black background and consuming a large amount of toner particles is performed, in the subsequent development, fog of a white background called background stain increases. The line image becomes unnecessarily thick and undesired development occurs.
In many PPCs, the bulk density of the developer changes when the replenished toner particles adhere to the carrier surface or penetrate into the space between the carriers, or the magnetic permeability of the developer changes with the change in the bulk density. The toner content in the developer is controlled by replenishing the toner so as to keep the constant. However, when it is necessary to replenish the developer with a large amount of toner particles, for example, after performing development with a large amount of black background, the change in the toner particle content in the developer due to the replenishment of the large amount of toner causes the bulk density of the developer or Since the change in the magnetic permeability cannot catch up and replenish the toner particles more than necessary, so-called over toner occurs, and the above-mentioned undesired development occurs. In particular, this tendency is likely to occur when a spherical ferrite carrier is used, which has a small frictional force inside the developer and is excellent in durability, but does not easily cause triboelectric charging.

In addition, a toner having a small particle size capable of obtaining a high-resolution image is
Since the surface of the carrier is covered with a small amount, triboelectric charging is also difficult.

In order to improve the response speed of the change in the bulk density or the magnetic permeability of the developer to the change in the content of the toner particles in the developer, and to improve these disadvantages, conventionally, the type and amount of the colorant, the particle size of the carrier, Improvements have been made by selection of the distribution, selection of the carrier coating material, and a combination thereof, but at present, satisfactory results have not always been obtained.

(Means for Solving the Problems) Accordingly, the present inventors have provided a developer with a high response speed to the change in the toner particle content of the bulk density and the magnetic permeability of the developer, and have intensively studied to solve the above problems. As a result, it was found that the above performance was satisfied by mixing magnetic fine particles subjected to a specific treatment with toner particles, and the present invention was reached.

That is, the gist of the present invention is to adhere a toner particle; a magnetic carrier; a fine powder of TiO ₂ , Al ₂ O ₃ or SiO ₂ and a substance having a charge polarity opposite to that of the toner particle with respect to the magnetic carrier to the surface. This is easily achieved by an electrophotographic developer characterized by containing magnetic fine particles.

(Operation) Hereinafter, the present invention will be described in detail.

The toner particles used in the present invention are a powder having an average particle diameter of 5 to 20 μm obtained by kneading and dispersing a colorant and, if necessary, a charge control agent in a binder resin by a kneader or the like, pulverizing after cooling, and classification. Various known materials can be used as these toner components.

The binder resin for the toner can be selected from a wide range including known ones, for example, polystyrene, chloropolystyrene, poly-α-methylstyrene,
Styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid Ester copolymers (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-phenyl acrylate copolymer, etc. ), Styrene-methacrylate copolymers (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-phenyl methacrylate copolymer, etc.), styrene -Α-chloromethyl acrylate copolymer and Styrene - acrylonitrile - styrene resins such as acrylic acid ester copolymer (including styrene or styrene substituents homopolymer or copolymer),
Vinyl chloride resin, rosin-modified maleic resin, phenol resin, epoxy resin, saturated or unsaturated polyester resin, low molecular weight polyethylene, low molecular weight polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer , A xylene resin, a polyvinyl butyral resin, and the like, and particularly preferred resins for use in the present invention include a styrene resin, a saturated or unsaturated polyester resin, and an epoxy resin. In addition, the above resins are not limited to being used alone, and two or more resins can be used in combination.

Colorants used for toner include carbon black, lamp black, iron black, gun blue, nigrosine dye,
Aniline blue, phthalocyanine blue, phthalocyanine green, Hanza Yellow G, rhodamine dyes and pigments,
Chrome yellow, quinacridone, benzidine yellow,
Any conventionally known dyes and pigments such as rose bengal, triallylmethane dyes, monoazo and disazo dyes and pigments can be used alone or in combination.

The amount of the colorant added to the toner is preferably 0.1 to 30 parts by weight, and particularly preferably 0.5 to 10 parts by weight, per 100 parts by weight of the binder resin. If the amount is too small, the coloring effect will be poor, and if it is too large, the fixability will be poor, which tends to be undesirable.

The charge control of the toner may be carried out by the binder resin or the dye / pigment itself, but if necessary, a charge control agent which does not cause a problem in color reproduction may be used in combination. As the positive charge control agent, a basic / electron donating substance such as a nigrosine dye or a quaternary ammonium salt, and as the negative charge control agent, an acid / electron withdrawing substance such as a metal chelate or a contained dye may be appropriately selected. Good to use.

The amount of the charge control agent to be added may be determined in consideration of the chargeability of the binder resin, the production method including the amount of the colorant added and the dispersion method, and the conditions such as the chargeability of other additives. The appropriate amount is 0.1 to 10 parts by weight.

In addition, inorganic particles such as a metal oxide or an inorganic substance surface-treated with the organic substance may be used.

These charge control agents may be used by mixing and adding to the binder resin, or may be used in the form of being attached to the surface of toner particles.

In addition, auxiliary agents such as various plasticizers and release agents can be added to the toner for the purpose of adjusting thermal characteristics, physical characteristics, and the like. The addition amount is suitably from 0.1 to 10 parts by weight.

Furthermore, fine particles of TiO ₂ , Al ₂ O ₃ or SiO ₂ are added to the toner particles, and the surface of the toner particles is coated with the fine powder to improve the fluidity and the aggregation resistance of the toner. The addition amount is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the toner particles.

As a method for producing toner particles, various conventionally used toner production methods can be applied. For example, the following examples are given as typical production methods.

First, a resin and a colorant (optionally an additive such as a charge controlling agent may be added) are uniformly dispersed by a ball mill, a V-type mixer, an S-type mixer, a Henschel mixer, or the like. Next, the dispersion is melt-kneaded with a double-arm kneader, a pressure kneader, an extruder, a roll mill, or the like. The kneaded material is pulverized by a pulverizer such as a hammer mill, a cutter mill, a jet mill, and a ball mill, and the obtained powder is classified by an air classifier or the like.

The magnetic carrier that can be used in the developer of the present invention has a particle size of 30.
Conventionally known materials such as iron powder, ferrite powder, magnetite powder, and magnetic resin carrier of about 200 μm can be used. Further, those obtained by coating these surfaces with a silicone resin, an acrylic resin, a fluorine-based resin, or the like, or a mixture of these resins can be suitably used. The content ratio of the carrier and the toner in the developer is preferably 100: 1 to 10.

The magnetic fine particles used in the present invention are ferromagnetic substances exhibiting ferromagnetism or ferrimagnetism at a use environment temperature such as PPC (around 0 ° C. to 60 ° C.), for example, magnetite (Fe ₃ O ₄ ), Maghemite (γ-Fe ₂ O ₃ ), ferrite (MxFx _3-x O ₄ is M for Mn, Fe, Co, Ni, Cu, Mg, Z
n, Cd, etc. or spinel ferrite or _{BaO · 6Fe 2 O 3, SrO} · 6Fe 2 O 3 or the like hexagonal ferrite of the mixed crystal) or the like, Y ₃ F
Garnet-type oxides such as e ₅ O ₁₂ and Sm ₃ Fe ₅ O ₁₂ , rutile-type oxides such as CrO ₂ , metals such as Fe, Mn, Ni, Co, and Cr, and other ferromagnetic alloys. Those exhibiting ferromagnetism or ferrimagnetism in a temperature range from about 60 ° C. to about 60 ° C. are preferred. Among them, fine particles having an average particle size of 3 μm or less, more preferably about 0.01 to 1 μm, such as magnetite, ferrite, and chromium dioxide are preferable.

In the present invention, one characteristic of the magnetic fine particles is that a substance having a charge polarity opposite to that of the toner particles with respect to the magnetic carrier is adhered. The aspect may be any as long as the surface of the magnetic fine particles can be surely charged in the opposite direction to the toner by friction with the magnetic carrier, and for example, it is preferable to merely coat particles of a smaller particle size on the surface of the magnetic fine particles. Although the effect can be obtained, it is preferable to coat the surface of the magnetic fine particles with various resins. In this case, preferable resins that can be used include, for example, an olefin-based resin, an epoxy-based resin, a polyester-based resin, a styrene-acryl-based resin, and a fluorine-based resin for a positively charged toner. For the negatively charged toner, a polyamide resin, a styrene acrylic resin containing an amino group, and the like are used. The weight ratio between the magnetic fine particles and the substance to be attached to the surface is not particularly limited, but is preferably 100: 0.5 to 100: 10.
It is. It is sufficient to add 0.1 to 2 parts by weight of the magnetic fine particles having the specific substance adhered to the surface thereof to 100 parts by weight of the toner particles.

When the magnetic fine particles and toner particles having the specific substance adhered to the surface thereof as described above are replenished to the developer and mixed by stirring, first, the magnetic fine particles adhere to the surface of the carrier particles by electrostatic force and magnetic force, and the toner particles As a result, the toner particles are strongly attracted to the magnetic fine particles, frictional charging of the toner particles is promoted, and the toner particles quickly adhere to the carrier, so that the rise of the bulk density is also promoted. Thereafter, the magnetic fine particles are integrated with the toner particles due to electrostatic force with the toner particles and physical adhesion (dipping into the toner particles) due to agitation, and electrically neutralize and stabilize the charge of the toner particles. That is, it is considered that the magnetic fine particles quickly start charging the toner together with the carrier immediately after the replenishment, and then integrate with the toner to stabilize the charging. It is considered that as the charge of the toner quickly rises and becomes stable, the bulk density and the magnetic permeability of the developer quickly rise and become stable. The developer of the present invention is considered to be a developer having a high response speed to a change in the toner particle content of the bulk density and the magnetic permeability by the mechanism described above, and increases the fog in the development after performing the development with a large amount of black background. Undesirable phenomena such as thickening of line images can be avoided.

Conventionally, the addition of a single magnetic particle to a developer has a polishing effect (JP-B-55-40862), an effect of adjusting the conductivity of the developer (JP-A-58-105236), or a result of both (JP-A-58-105236).
58-118652).

In the case of the developer of the present invention, these polishing effects and conductivity adjusting effects can be naturally obtained, and the above effects can be controlled by selecting the type and amount of the substance to be attached to the surface of the magnetic fine particles.

(Effects of the Invention) The electrophotographic developer of the present invention does not cause undesired development such as an increase in fog and a thick line image in the development after the development with a large amount of black background by PPC or the like, and is not used in a usual manner. It is an electrophotographic developer excellent in various characteristics required as an electrophotographic developer such as image quality and durability at the time of copying and excellent in reliable copy quality, and provides great industrial benefits. .

(Examples) Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples at all without departing from the gist thereof.

In the examples and comparative examples, “parts” indicates “parts by weight”.

Example 1 Styrene-n-butyl acrylate (monomer molar ratio
8:20) Copolymer resin 100 parts Low molecular weight polypropylene 3 parts Carbon black 7 parts Chromium-containing dye 2 parts were blended, kneaded, pulverized and classified to obtain a negatively charged black toner having an average particle size of about 12 μm.

100 parts of magnetite, about 3 parts of a styrene-alkyl acrylate copolymer containing a dimethylamino group having a positive charge in the side chain, and an average particle size of about 0.2
One part of a .mu.m magnetite and 0.2 part of silica fine powder were externally added to 100 parts of the above negatively charged black toner using a Henschel mixer. A developer was prepared by mixing and stirring 2.5 parts of the obtained externally added toner and 100 parts of a spherical resin-coated spherical ferrite carrier having an average particle size of about 90 μm.

Next, 100 parts of the developer and 1 part of the externally added toner are mixed in a V-shaped mixer, and the relationship between the mixing time and the bulk density of the developer is determined. When a simulation test of the bulk density change response was performed, the bulk density change stopped in 2 minutes of mixing time,
After that, it was confirmed that it was stable for up to 20 minutes.

Further, when this developer was subjected to a real-image test using PPC, it was found that the developer operated without problem in development with a black background area of 50% and had excellent reliability.

Example 2 Example 1 was repeated except that the addition amount of the surface-coated magnetite in the external addition treatment in Example 1 was reduced to 0.5 part and the treatment was performed.
A test similar to that in Example 1 was performed using a developer and an externally added toner prepared in the same manner as in Example 1.
The developer was found to be excellent in reliability.

Comparative Example 1 The same test as in Example 1 was performed using the developer and the externally-treated toner prepared in the same manner as in Example 1, except that the surface-coated magnetite was not added during the external addition treatment in Example 1. However, in the simulation test, the bulk density gradually changed even during the mixing time of 20 minutes, and in the actual test, it was found that the toner was overtoner after the development of the black background area of 30% and was an unreliable developer.

Comparative Example 2 A simulation test was performed using a developer and an externally-treated toner prepared in the same manner as in Example 1 except that untreated magnetite was used instead of the surface-treated magnetite of Example 1. The bulk density changed gradually even in 20 minutes, and it was found that the developer was unreliable in which overtoner was expected even in a real-image test.

Comparative Example 3 A developer prepared in the same manner as in Example 1 except that 0.05 parts of silica fine powder having a positive charge and surface-treated with tetradecyldimethylbenzylammonium chloride was used instead of the surface-treated magnetite of Example 1, A simulation test was performed using the externally added toner. The addition amount of the surface-treated positively charged silica fine powder is
The blow-off charge was determined to be approximately the same as the blow-off charge of the developer used in Example 1. The bulk density hardly changed in the simulation test, and it was found that the toner was an unreliable developer in which overtoner was expected even in the actual test. Further, when a real photography test was performed without supplying toner, white fog occurred.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-297561 (JP, A) JP-A-1-229266 (JP, A) JP-A-62-9357 (JP, A) JP-A-58-58 105236 (JP, A) JP-A-63-96665 (JP, A) JP-A-56-43644 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/08

Claims (1)

(57) [Claims] 1. A magnetic material comprising: a toner particle; a magnetic carrier; a fine powder of TiO ₂ , Al ₂ O ₃ or SiO ₂ and a substance having a charge polarity opposite to that of the toner particle based on the magnetic carrier. An electrophotographic developer containing fine particles.