JPH05216283A - Electrophotographic carrier - Google Patents

Abstract

PURPOSE:To provide an acrylic resin coated carrier capable of forming a copying image having excellent picture quality and excellent in durability, heat resistance and environmental resistance by coating a carrier core material with an acrylic resin having hydroxyl group and N-alkoxyalkylamide group and then cross-linking it. CONSTITUTION:The carrier consists of carrier core particles and the acrylic resin applied on the carrier core particles. The acrylic resin is formed by cross- linking an acrylic resin having hydroxyl group and N-alkoxyalkyl amido group. Hydroxyethylmethacrylate, hydroxypropyl-methacrylate or the like is used as a monomer having hydroxyl group. n-Methoxymethylmethacrylamide, n- ethoxymethylmethacryl amide, n-buthoxymethylmethacylamide or the like is exemplified as a monomer having N-alkoxyalkylamide group.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a resin-coated carrier used as a developer in combination with a toner.

[0002]

2. Description of the Related Art Generally, in electrostatic recording and electrophotography, a two-component developing method is known. In this method, a photoconductor having photoconductivity is uniformly given an electrostatic charge by means such as corona discharge, and an optical image corresponding to the original is exposed to this to eliminate the electrostatic charge in the exposed portion,
Form an electrostatic latent image. On the other hand, by mixing the insulating toner and the carrier particles, the toner is triboelectrically charged, and the developer is conveyed to be brought into contact with the electrostatic latent image on the photoconductor to develop the contact latent image.

The granular carrier used in such a two-component developing system is coated with an appropriate material for the purpose of controlling the charging polarity of the carrier surface by stirring in the developing device, adjusting the electric resistance, imparting environmental stability, and the like. (For example, JP-A-47-13954 and JP-B-58-).
9946, JP-A-60-115948, etc.).

Japanese Unexamined Patent Publication No. 47-13954 discloses a carrier coated with a thermoplastic styrene-acrylic resin having a specific composition ratio, molecular weight and glass transition point. Since this resin is thermoplastic, the coating resin may be abraded during repeated copying. Japanese Patent Office Sho 5
JP-A-8-9946 discloses a carrier coated with a cross-linking resin containing a cross-linking agent such as melamine resin in an amount of 5% by weight or more. Unreacted melamine resin remains in this resin, and there is a problem in environmental stability. Further, the constitution is completely different from that of the present application which does not contain a crosslinking agent. JP-A-60-115948 discloses a carrier coated with a copolymer of a polyfunctional acrylic monomer and a monofunctional acrylic monomer. Since this coating resin is thermosetting, it is excellent in abrasion resistance, but unreacted monomers remain, so that the environmental resistance is insufficient and the developer agglomerates or the like.

As described above, conventional resin-coated carriers still have problems in durability, heat resistance and environment resistance, and improvements in these properties are desired.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a carrier capable of forming a copy image with excellent image quality and excellent in durability, heat resistance and environment resistance. With the goal.

[0007]

That is, the present invention relates to an electrophotographic carrier obtained by coating a carrier core material with an acrylic resin having a hydroxyl group and an N-alkoxyalkylamide group and heating and self-crosslinking.

The carrier particles of the present invention are composed of at least carrier core particles and an acrylic resin coating the core particles. The acrylic resin is formed by crosslinking an acrylic resin having a hydroxyl group and an N-alkoxyalkylamide group. In the following, in the present invention, when simply referred to as an acrylic resin, it means an acrylic resin before crosslinking.

The acrylic resin is a (co) polymer of a monomer having at least a hydroxyl group, a monomer having an N-alkoxyalkylamide group, and more preferably a monomer having an acid group. Group, amino group,
It may be a copolymer of monomers containing one or more kinds of glycidyl groups, thionyl groups and the like.

Examples of the monomer having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 1,4-butanediol mono (meth) acrylate and hydroxyethyl (meth) acrylate. And an ethylene and propylene adduct of hydroxyethyl (meth) acrylate, etc., and one or more of them can be used.

The amount of the monomer having a hydroxyl group is adjusted so that the hydroxyl value of the acrylic resin is 20 to 100 KOHmg / g, preferably 20 to 95. If the hydroxyl value is less than 20, the crosslinking reaction will not be sufficiently carried out, and if the copying is repeated, the carrier coating resin will be worn and the environment resistance of charge stability will be poor. If the hydroxyl value exceeds 100, the hydroxyl groups will remain unreacted, resulting in poor environmental stability of charge stability.

Examples of the monomer having an N-alkoxyalkylamide group include n-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide,
N-butoxymethyl (meth) acrylamide etc. can be mentioned, and 1 or more types of these can be used.

The N-alkoxyalkylamide group-containing monomer has an N-alkoxyalkylamide group amount of 0.5 to 2.0 mg / calculated from the charged amount for resin synthesis.
g, preferably 0.5 to 1.5.
If the amount is less than 0.5 mg / g, the crosslinking reaction will be insufficient and the coating resin will have poor durability. If the value exceeds 2.0 mg / g, a stable acrylic resin cannot be manufactured.

Preferred examples of the acid group-containing monomer used for the acrylic resin in the present invention include acrylic acid and methacrylic acid, and further maleic acid and
Examples thereof include maleic anhydride, itaconic acid, and monoesters thereof, and one or more of these may be used.

The amount of the monomer having an acid group is adjusted so that the acid value of the acrylic resin is 5 to 40 KOHmg / g, preferably 6 to 37. If the acid number is less than 5,
If the curability is insufficient and the copying is repeated, the carrier coating resin is abraded, resulting in poor durability and poor environmental stability of charge stability. On the other hand, when the acid value exceeds 40, the coating resin finally obtained becomes brittle, and the coating resin is cracked. The acid value is expressed in mg of KOH required to neutralize 1 g of resin, and the unit is KOHm.
It is g / g.

Other copolymerizable monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate,
tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate, tridecyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, dimethylaminoethyl ( Esters of acrylic acid and methacrylic acid such as (meth) acrylate and diethylaminoethyl (meth) acrylate can be used. Note that, for example, methyl (meth) acrylate means methyl methacrylate and methyl acrylate. As other copolymerizable monomers, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile,
Examples thereof include vinyl acetate, vinyl propionate, acrylamide, methacrylamide, methylol acrylamide, methylol methacrylamide, vinyl chloride, propylene, ethylene, and C _{4 to} C ₂₀ α-olefins.

The acrylic resin can be synthesized by a conventional method and can be produced by any known polymerization method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method and an emulsion polymerization method. At that time, as a polymerization initiator, azobisisobutyronitrile, 4,4′-azobis (4-cyanopentanoic acid), benzoyl peroxide, t-butylperoxy-2-
Ethyl hexanoate, cumene hydroperoxide, potassium persulfate, hydrogen peroxide, 2,2'-
Azobis [2-methyl-N- (2-hydroxyethyl)
Propioamide] and the like, and if necessary, dodecyl mercaptan, mercaptoethanol, α-methylstyrene dimer and the like can be used as a chain transfer agent.

In synthesizing the acrylic resin, the number average molecular weight is 5,000 to 30,000, preferably 6,000 to 2
It should be 5000. When the number average molecular weight is less than 5,000, the coating resin is soft and the obtained coated carrier is poor in durability, and when it exceeds 30,000, the adhesion between the carrier core material and the coating resin is poor, and the coating resin is mixed and agitated in a developing machine. Peeling may occur. In the present invention,
The number average molecular weight is shown as a value measured by gel permeation chromatography (GPC).

More preferably, the acrylic resin is
It is prepared so as to have a glass transition point (Tg) of 15 to 90 ° C, preferably 20 to 80 ° C. When the glass transition point is lower than 15 ° C., the resin after crosslinking becomes inferior in heat resistance. If it exceeds 90 ° C, the adhesion between the carrier core material and the coating resin will be poor.

In the present invention, the glass transition point was measured by thermal analysis.

The acrylic resin obtained as described above is applied to carrier core particles and crosslinked and cured to form a coating resin. As the carrier core particles coated with an acrylic resin, those known as a two-component carrier for electrophotography,
For example, ferrite, magnetite, iron, nickel, cobalt and other metals, alloys or mixtures of these metals with metals such as zinc, antimony, aluminum, lead, tin, bismuth, beryllium, manganese, selenium, tungsten, zirconium, vanadium, It is possible to use metal oxides such as iron oxide, titanium oxide and magnesium oxide, nitrides such as chromium nitride and vanadium nitride, mixtures with carbides such as silicon carbide and tungsten carbide, and ferromagnetic ferrite.

The size of the carrier core particles should be 20 μm (average particle size) at least in order to prevent the carrier from adhering (scattering) to the electrostatic latent image carrier, and prevent the occurrence of carrier streaks, etc. From the viewpoint of preventing the deterioration of image quality, a material with a maximum size of 150 μm is used. It is preferably 30 to 100 μm.

To apply the acrylic resin to the carrier core particles, a resin solution obtained by dissolving the above-mentioned acrylic resin in a suitable solvent may be used, and a dipping method, a spray drying method or the like may be applied. After coating, it is dried and, if necessary, baked. After the firing, the carrier particles are agglomerated into a bulk, so the bulk is crushed and sieved.
A carrier having a desired particle size is obtained. In order to increase the thickness of the resin film, the above application, firing and crushing may be repeated.

The baking treatment is carried out at 130 ° C. to 200 ° C. at 0.5.
Approximately 3 hours is sufficient, and this treatment almost completes the crosslinking of the acrylic resin. Crosslinking is mainly a reaction between a hydroxyl group and an N-alkoxyalkylamide group or between N-alkoxyalkylamide groups. You may add a melamine resin or an isocyanate resin.

The film thickness of the coating resin thus formed is 0.1 to 5 μm, preferably 0.5 to 4 μm. If the thickness is less than 0.1 μm, environmental stability is poor. On the other hand, if it is thicker than 5 μm, the coating layer becomes too thick, and even if it is applied to a developer, it increases due to the accumulation of electric charge and causes a problem that the image density decreases.

Further, in the present invention, fine particles having a charge imparting function or conductive fine particles may be added to the coating resin layer. Fine particles having a charge imparting function are effective for controlling the amount of charge on the toner, and addition of conductive fine particles is effective for controlling the electric resistance value.

As fine particles having a charge imparting function, Cr is used.
O ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , IrO ₂ , MnO ₂ , Mo
O ₂ , NbO ₂ , PtO ₂ , TiO ₂ , Ti ₂ O ₃ , Ti
₃ O ₅ , WO ₂ , V ₂ O ₃ , Al ₂ O ₃ , MgO, SiO ₂ , Z
metal oxides such as rO ₂ and BeO, nigrosine base,
Specific examples include dyes such as Spiron Black TRH.

The conductive fine particles include carbon black, carbon black such as acetylene black, and Si.
Carbides such as C, TiC, MoC, ZrC, BN, Nb
Examples thereof include nitrides such as N, TiN and ZrN, magnetic powders such as ferrite and magnetite.

The fine particles have an average particle diameter of 2 to 0.01 μm,
Preferably, it is about 1 to 0.01 μm.

Further, the addition amount of both the fine particles cannot be unconditionally specified as described above, but is 0.1 wt% to 200 wt% with respect to the coated acrylic resin.
%, Preferably 1.0 wt% to 60 wt% is suitable.

The finally obtained carrier has an electric resistance value of about 1 × 10 ⁸ to 1 × 10 ¹³ Ω · cm. When the value is smaller than 1 × 10 ⁸ Ω · cm, carrier development occurs, and when the value is larger than 1 × 10 ¹³ Ω · cm, the developability is poor, and sufficient image density cannot be obtained, and an image with a strong edge effect is obtained. It is formed. The carrier of the present invention is used as a two-component developer in combination with a toner. Hereinafter, the present invention will be described using examples. In the examples, “parts” means “parts by weight” unless otherwise specified. After purging nitrogen into a four-necked flask equipped with an acrylic resin synthetic stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube, 70 parts of xylene and 30 parts of n-butanol were charged into the flask, and 1
The temperature was raised to 00 ° C. Next, the mixture of the raw materials shown in Table 1 was dropped into the flask over 5 hours. Then, the contents were further held at 100 ° C. for 6 hours to obtain acrylic resins (a-1) to (a-8) having a solid content of about 50%. Physical properties of the obtained resin (acid value (based on solid content) (KOHmg /
g), hydroxyl value (based on solid content) (KOHmg / g), N
-Alkoxyalkylamide group content (based on solid content)
(Mg / g), glass transition point (Tg) (° C.), number average molecular weight (Mn)) are summarized in Table 1. In addition, N in the table
The amount of alkoxyalkylamide group was calculated from the charged amount of the monomer.

[0032]

[Table 1]

Preparation of Coated Carrier A ferrite carrier was coated using the apparatus shown in FIG. First, 3 kg of ferrite particles having an average particle size of 50 μm are charged into the tumbling fluidized bed dryer from the raw material supply port (1), and the tumbling fluidized bed (5) is rotated by the motor (4) to obtain the ferrite powder. Was kept mixed. Further, air was sent from the blower (6), and the air was made into hot air (50 ° C.) by the heater (7) and supplied to the ferrite (2) being mixed and stirred. Ferrite in the dryer (2)
Is agitated by hot air and is in a rolling flow stirring state in the direction of the arrow in the figure.

On the other hand, a coating solution was prepared by diluting the acrylic resins (a-1) to (a-8) obtained in Reference Example 2 with toluene so that the resin solid content was 3 wt%.

While maintaining the coating solution at 50 ° C., 35 ml / min of ferrite powder (2) was sprayed from the spray nozzle (3). After the spraying was completed, the temperature was maintained at 50 ° C. while maintaining the stirring state, and the product was dried for 1 hour.
The obtained coated carrier was taken out from the product outlet (8), put in a hot air dryer and treated at 150 ° for 1 hour. By this treatment, the acrylic resin coated on the ferrite powder undergoes a crosslinking reaction and is cured. The obtained bulk is taken out, crushed with a crusher, and classified with a 90 μm sieve to obtain an average particle size of 5
A 0 μm resin-coated ferrite carrier was obtained. The film thickness (μm) of the coating resin of the obtained carrier and the electrical resistance (Ω ・
cm) is shown in Table 2.

[0036]

[Table 2]

The film thickness was measured from the average particle size of the carrier core material and the particle size of the carrier after coating. As for electrical resistance, a sample is placed on a circular metal electrode so that the thickness is 1 mm and the diameter is 50 mm, the mass is 895.4 g, the electrode has a diameter of 20 mm, and the inner diameter is 3
A guard electrode having an outer diameter of 8 mm and an outer diameter of 42 mm was placed, the current value after 1 minute when a DC voltage of 500 V was applied was read, and the volume resistivity (ρ) value of the sample was converted. The measurement environment is temperature 25 ± 1 ℃,
The relative humidity was 55 ± 5%, the measurement was repeated 5 times, and the average thereof was taken.

Production Example of Toner [(-) Chargeable Toner] Component Weight Parts -Polyester Resin 100 (Softening Point: 130 ° C., Glass Transition Point: 60 ° C., AV: 25, OHV: 38) Carbon Black 5 ( MA # 8; manufactured by Mitsubishi Kasei Co., Ltd. ・ Charge control agent 3 (manufactured by Hodogaya Chemical Co., Ltd .; Spiron Black TRH) ・ Offset inhibitor 2 (Viscor TS-200; manufactured by Sanyo Chemical Co., Ltd.)

After thoroughly mixing the above materials with a ball mill,
The mixture was kneaded on a triple roll heated to 140 ° C. After the kneaded product was left standing to cool, it was roughly pulverized using a feather mill and then finely pulverized by a jet mill. Next, air classification was performed to obtain a toner having an average particle size of 13 μm. This toner was treated with 0.2% of hydrophobic silica R-974 (manufactured by Nippon Aerosil Co., Ltd.) as a fluidizing agent.

A developer was prepared by mixing the toner with a carrier so that the evaluation toner would be 8% by weight. The obtained developer is used in a copying machine (EP-550
Z) (manufactured by Minolta Camera Co., Ltd.) and subjected to a durability test under the following environment to evaluate charge amount, toner scattering, and image quality. The results are shown in Table 3.

NN environment; temperature: 18 ° C to 22 ° C, humidity: 50 to 55% ・ LL environment; temperature: 10 ° C, humidity: 15% ・ HH environment; temperature: 35 ° C, humidity: 85% It was measured by the method described in JP-A-63-13587. Toner scattering is obtained by taking out only the developing device from the copying machine and receiving the toner scattered from the developing device on a blank sheet when operating for a certain period of time, and visually observing the toner amount, and "○" indicates that there is no problem in use. , “×” indicates that the item cannot be used. Image quality is evaluated by visual observation,
“O” indicates that there is no problem in use, and “x” indicates that it cannot be used.

[0042]

[Table 3]

[0043]

The acrylic resin-coated carrier of the present invention is excellent in heat resistance, durability and environment resistance.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a carrier coating apparatus.

[Explanation of symbols]

 1 Raw material supply port 2 Ferrite 3 Spray nozzle 4 Motor 5 Rolling fluidized bed 6 Blower 7 Heater 8 Product outlet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Tanigami 2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka, Osaka International Building Minolta Camera Co., Ltd. (72) Inventor Taisaku Kano Sakae-ku, Yokohama-shi, Kanagawa 1190 Kasamacho Mitsui Toatsu Chemicals, Inc. Research Institute (72) Inventor Eiichiro Miyazaki 1190 Kasamacho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemicals Research Institute

Claims (1)

[Claims] 1. An electrophotographic carrier in which a carrier core material is coated with an acrylic resin having a hydroxyl group and an N-alkoxyalkylamide group and heated and self-crosslinked.