JPH05216282A - 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 the surface of carrier particles with an acrylic resin having specific physical property and then cross- linking them. CONSTITUTION:The carrier consists of carrier core particles and the acrylic resin applied on the carrier core particle. The acrylic resin is formed by cross- linking an acrylic resin having 15-120KOHmg/g hydroxide value, 5-40KOHmg/g acid value and 5000-30000 number average molecular weight. Acrylic acid or methacrylic acid is preferably used as a monomer having an acid group and used for acrylic resin. Hydroxyethylmethacrylate, hydroxypropylmethacrylate, hydroxybutylmethacrylate or the like is used as a monomer having hydroxyl group. A well-known material as the electrophotographic two-component carrier is used as the carrier core particles.

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-60-208767, 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 5% by weight or more of a melamine resin. This resin is inferior in heat resistance because of its low molecular weight and softening point. JP-A-60-208767 discloses a carrier coated with a methyl methacrylate copolymer having a number average molecular weight of 1 to 50,000. Since this coating resin is thermoplastic, it has poor durability.

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 has a hydroxyl value of 15 to 120 KOHmg / g and an acid value of 5 to 40 KOH.
The present invention relates to an electrophotographic carrier coated and crosslinked with an acrylic resin having a mg / g and a number average molecular weight of 5,000 to 30,000.

The carrier particles of the present invention are composed of at least carrier core particles and an acrylic resin coating the core particles. Then, the acrylic resin has a hydroxyl value of 15 to 120.
It is formed by crosslinking an acrylic resin having a KOH mg / g, an acid value of 5 to 40 KOH mg / g and a number average molecular weight of 5,000 to 30,000. 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, more preferably a monomer having an acid group, and is a methylolamide group, an alkoxymethylolamide group, an amino group or a glycidyl group. It may be a copolymer of monomers containing at least one kind of a thionyl group or the like.

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 acrylic resin has an acid value of 5 to 40 KOHmg / g, preferably 5 to 35. 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, unreacted acid groups remain, resulting in poor charge stability and environmental resistance. The acid value is the m of KOH required to neutralize 1 g of resin.
It is represented by the number of g and the unit is KOH mg / g.

As the monomer having a hydroxyl group, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 1,4-butanediol mono (meth) acrylate, hydroxyethyl (meth) Ε of acrylate
Caprolactone adducts, ethylene and propylene adducts of hydroxyethyl (meth) acrylate and the like can be mentioned, 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 15 to 120 KOHmg / g, preferably 15 to 100. If the hydroxyl value is less than 15, the crosslinking reaction will not be sufficiently carried out, and if the copying is repeated, the carrier coating resin will be abraded and the environment stability of charge stability will be deteriorated. When the hydroxyl value exceeds 120, the charge stability and environmental resistance are poor.

As copolymerizable monomers, 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 (meth) acrylate, diethylaminoethyl (meth)
Esters of acrylic acid and methacrylic acid such as acrylates can be used. Note that, for example, methyl (meth) acrylate means methyl methacrylate and methyl acrylate. Other copolymerizable monomers include styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide, vinyl chloride, propylene. , Ethylene, C
Α- olefin, etc. ₄ -C ₂₀ and the like.

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 obtained carrier has poor durability and 3000
When it exceeds 0, the adhesion between the carrier core material and the coating resin is poor. In the present invention, the number average molecular weight is shown by the value measured by gel permeation chromatography (GPC).

More preferably, the acrylic resin is
15 to 80 ⁰ C as glass transition point (Tg), preferably prepared to have a 20 to 75 ° C.. If the glass transition point of less than 15 0 ^C, the resin after crosslinking becomes inferior in heat resistance. If exceeding 80 0 ^C, becomes adhesiveness to the carrier core coating resin is poor.

The glass transition point was measured by thermal analysis.

The acrylic resin obtained as described above is applied to carrier core particles together with a crosslinking agent containing a triazine ring to form a coating resin. As the cross-linking agent containing a triazine ring, a methylolated melamine resin etherified with a C1 to C8 alcohol is suitable. It is also possible to use guanamine resin. The amount of the crosslinking agent containing a triazine ring used is acrylic resin / crosslinking agent = 95 /
It is desirable to be 5 to 65/35 (weight ratio).

Carrier core particles coated with an acrylic resin are those known as two-component carriers for electrophotography, such as ferrite, magnetite, iron, nickel,
Metals such as cobalt, these metals and zinc, antimony,
Alloys or mixtures with metals such as aluminum, lead, tin, bismuth, beryllium, manganese, selenium, tungsten, zirconium, vanadium, metal oxides such as iron oxide, titanium oxide, magnesium oxide, nitriding of chromium nitride, vanadium nitride, etc. It is possible to use a substance, a mixture with a carbide such as silicon carbide or tungsten carbide, and a ferromagnetic ferrite.

As the size of the carrier core particles, one having a particle size of at least 20 μm (average particle diameter) is used from the viewpoint of preventing carriers from adhering (scattering) to the electrostatic latent image carrier, and preventing the occurrence of carrier stripes, 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 prepared by dissolving the above-mentioned acrylic resin and a crosslinking agent containing a triazine ring in a suitable solvent is used, and a dipping method, a spray drying method or the like is used. You can apply. 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 to obtain a carrier having a desired particle size. In order to increase the thickness of the resin film, the above coating,
The firing and crushing may be repeated.

The firing treatment is carried out at 130 to 200 ° C. and 0.5 to
Three hours is sufficient, and this treatment almost completes the crosslinking of the acrylic 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 charge on the toner, and the addition of conductive fine particles is
It is effective for controlling the electric resistance of the carrier.

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.

As the conductive fine particles, carbon black such as carbon black and acetylene black, 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 average particle size of the fine particles is 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 based on 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.

Reference Example 1 (Preparation of Crosslinking Agent) Paraformaldehyde (containing 80% by weight of formaldehyde) 150.0 g, n-butanol was added to a reactor equipped with a thermometer, a stirrer, a reflux condenser and a solvent by-product recovery device. 7
40 g and melamine 126 g were added, and the pH of the reaction liquid was adjusted to 4.0 by adding a 10 wt% aqueous solution of oxalic acid while stirring. After that, the mixture was heated, and water was removed from the system under the reflux temperature condition of the reaction solution while continuing for 5 hours.
After cooling to 0 ° C., the pH was adjusted to 7.0 with a 10 wt% aqueous solution of caustic soda. Then, while keeping the temperature in the system at 50 ° C. or lower under heating and depressurization, the heating residue (JISK-
Excess butanol was removed to the outside of the system so that the content thereof was 60% by weight (according to the measuring method of 5400). The viscosity of the resin obtained at this time was 20 poise (20 ° C.).

The measurement of electrolytic desorption mass spectrometry (FD-MS spectrum) was carried out by a JEOL-JMS-300 type double-focusing mass spectrometer. The sample is coated on the carbon emitter, the cathode voltage is 5.5KV, and the emitter current is 0m.
The magnetic field was swept up from 2 A at 2 mA / min (100-20
0 or 100-1000 / 10 seconds), and the spectrum was measured. Data processing was performed with JEOL-JMA-3500. The spectrum output is the average of all scans. The resin obtained as a result of the measurement is a compound (a) in which R _{1 to} R ₆ are shown in Table 1 in the following general formula,
It was a butylated methylolmelamine resin containing 53.8 mol% in total of (b), (c) and (d).

[0033]

[Chemical 1]

[0034]

[Table 1]

Reference Example 2 (Synthesis of acrylic resin) After purging nitrogen into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen introduction tube, 70 parts of xylene and 30 parts of n-butanol were added to the flask. Charge 1
The temperature was raised to 00 ° C. Next, the mixture of the raw materials shown in Table 2 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-13) 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), glass transition point (Tg) (° C), number average molecular weight (Mn)) are summarized in Table 2.

[0036]

[Table 2]

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, with respect to the resin solids of the acrylic resins (a-1) to (a-13) obtained in Reference Example 2, a crosslinking agent (butylated methylolmelamine resin obtained in Reference Example 1) was used. To 20 wt% and further dilute the mixture with xylene and n-butanol to give 3 wt%
A coating solution of was prepared.

While keeping the coating solution at 50 ° C., the ferrite powder (2) was sprayed at 35 ml per minute 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 2 hours. By this treatment, the acrylic resin coated on the ferrite powder is further crosslinked by the crosslinking agent and cured. The obtained bulk was taken out, crushed with a crusher, and classified with a 90 μm sieve to obtain a resin-coated ferrite carrier having an average particle size of 50 μm. Film thickness of coating resin of the obtained carrier (μm)
Table 3 shows the electric resistance (Ω · cm).

[0040]

[Table 3]

The film thickness was measured from the difference between the particle size of the carrier core material and the particle size of the carrier after coating. For electrical resistance, a sample was placed on a circular electrode made of metal so that the thickness was 1 mm and the diameter was 50 mm, and the mass was 895.4 g, the electrode had a diameter of 20 mm, and the inner diameter was 38.
A guard electrode having an outer diameter of 42 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 specific resistance (ρ) value of the sample was converted. The measurement environment was a temperature of 25 ± 1 ° C. and a relative humidity of 55 ± 5%, the measurement was repeated 5 times, and the average was taken.

[0042] Toner Production Example [(-) chargeable toner] Component Parts by weight Polyester resin 100 (softening point, 135 ° C.; glass transition point, 62 ° C.), pigment (Lionol Blue SM-7) 8 ( Toyo Ink Charge control agent 3 (Hodogaya Chemical Co., Ltd .; Spiron Black TRH)

After thoroughly mixing the above materials with a ball mill,
The mixture was kneaded on a triple roll heated to 110 ° C. The kneaded product was left standing and cooled, coarsely pulverized, and then finely pulverized by a jet mill. Next, air classification was performed to obtain a toner having an average particle size of 8 μm. This toner was treated with 0.2% of hydrophobic silica R-974 (manufactured by Nippon Aerosil Co., Ltd.).

A developer was prepared by mixing the toner 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 4.

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. For toner scattering, only the developing device is removed from the copying machine, and the toner scattered from the developing device when it is operated for a certain period of time is received on a white paper, and the amount of toner is visually observed and evaluated. "○" indicates that there is no problem in use “X” 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.

[0046]

[Table 4]

[0047]

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. A hydroxyl value of 15 to 120 KOHmg / g,
Acid value 5-40 KOHmg / g and number average molecular weight 5000
A carrier for electrophotography, which is coated and crosslinked with an acrylic resin having a viscosity of ˜30,000.