JPH05216281A - Electrophotographic carrier - Google Patents

Abstract

PURPOSE:To provide an acrylic resin-coated carrier contributive to form a copying image having excellent picture quality and excellent in durability, heat resistance and environmental resistance. CONSTITUTION:In the acrylic resin-coated carrier, the acrylic resin is cross-liked with a melamine-formaldehyde resin composition containing a melamine- formaldehyde compound expressed by the formula. In the formula, 1-4 groups of R1-R6 are hydrogen atom and the other groups are CH2OH or CH2OR' (R' is alkyl group) and the ratio of (number of CH2OR' group)/(number of CH2OH group+number of CH2OR') is 0.7-1.0.

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 a suitable material for the reason of controlling the charging polarity of the carrier surface by stirring in the developing device, adjusting the electric resistance, and imparting environmental stability. (For example, JP-A-47-13954 and JP-B-58-).
9946, JP-A-60-57352, JP-A-62-262057).

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. JP-B-58-9946 is 5% by weight.
A carrier coated with a cross-linking resin containing the above melamine resin is disclosed. JP-A-60-57352 discloses a carrier coated with an acrylic resin having a hydroxyl group cross-linked by a derivative containing a triazine ring.
It differs from the present application in the composition of the triazine ring system of the crosslinking agent.
Japanese Unexamined Patent Publication No. 62-262057 discloses a carrier in which a thermoplastic resin having an unreacted hydroxyl group and an alkoxylated melamine resin are cured and coated.

However, conventional resin-coated carriers still have problems with respect to 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 provides an electrophotographic carrier in which the surface of carrier particles is coated with an acrylic resin crosslinked with a melamine-formaldehyde resin composition, wherein the melamine-formaldehyde resin composition has the following general formula: I] is contained in at least 50 mol% of the melamine formaldehyde compound.

[Chemical 2] [Wherein, in R _{1 to} R ₆ , 1 to 4 groups are hydrogen atoms, and the other remaining groups are CH ₂ OH or CH ₂ OR '(R'
Represents an alkyl group), and the ratio of (CH ₂ OR ′ group number) / (CH ₂ OH group number + CH ₂ OR ′ group number) is 0.7.
~ 1.0].

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 treated with a melamine formaldehyde resin composition containing the melamine formaldehyde compound represented by the general formula [I].

In the general formula [I], at least one or more and four or less of R _{1 to} R ₆ are hydrogen atoms, and 1 or more and 4 or less free NH groups which are not methylolated are present. R _{1 to} R ₆
When 5 or more of them are H, that is, when the number of bound formalin is 1 or less, the compatibility of the produced melamine resin with the solvent or the acrylic resin used in combination becomes poor and the melamine resin is deposited. The possibility increases. When all of R _{1 to} R ₆ are CH ₂ OR ', the low temperature curability deteriorates. The melamine formaldehyde compound represented by the general formula [I] is CH ₂ OH and CH ₂ O.
CH ₂ O having an alkyl group based on the total number of R's
The ratio of the number of R'groups is 0.7 to 1.0, that is, at least 70% of the number of methylol groups bonded to the melamine bone nucleus
The above is alkoxy-modified, and is characterized in that the proportion of free methylol groups is less than 30%. When the proportion of free methylol groups is 30% or more, the obtained performance becomes poor when used as a crosslinking agent.

The melamine formaldehyde resin composition of the present invention contains 50 mol% or more of the melamine formaldehyde compound specified as described above. When the amount of the melamine formaldehyde compound is less than 50 mol%, the residual 0H group as an unreacted group of the crosslinking agent deteriorates the environmental property.

The melamine-formaldehyde resin of the present invention is produced by reacting melamine with formalin to perform alkyl etherification with excess alcohol. In this case, the amount of formalin to be reacted is appropriately 2 to 5 per 1 melamine nucleus, and the bound formalin needs to be 70% or more alkyl etherified.

The alkyl group R'in the melamine formaldehyde compound represented by the general formula [I] is produced by the following reaction.

[Chemical 3]

Alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, etc. are used for the alkyl etherification reaction in this case.
iso-butanol, sec-butanol, tert-
Butanol, n-amyl alcohol, iso-amyl alcohol, tert-amyl alcohol, n-hexyl alcohol, sec-hexyl alcohol, 2-methylpentanol, sec-hexyl alcohol, 2-ethylbutyl alcohol, sec-heptyl alcohol, n
-Octyl alcohol, 2-ethylhexyl alcohol, sec-octyl alcohol or cyclohexanol; ether alcohols such as ethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether or triethylene glycol monomethyl ether; Alternatively, ketone alcohols such as acetonylmethanol, diacetone alcohol or pyruvyl alcohol can be used.

The above alcohols can be used alone or in combination of two or more, and the alcohol is also a solvent in the reaction of the present invention.

In determining the structure of the melamine resin according to the present invention, electrolytic desorption mass spectrometry (Field Desorption) is used.
Mass Spectrometry) (hereinafter abbreviated as "FD-MS method"). This analysis method is known as a means capable of simultaneously performing separation and identification, but is particularly effective for the analysis of thermally unstable hardly nonvolatile substances. Its characteristic is that molecular ions or quasi-molecular ions are easily observed, and the number of fragment ions is small, so the molecular weight can be determined from the spectrum, and molecular weight distribution and molecular species distribution can be obtained for oligomers and polymers that are a mixture of homologues. Structure analysis of thermosetting resin V (thermosetting resin V
ol. 1.18.1980 Saito et al.).

That is, the Recountructed obtained by the FD-MS spectrum measurement of each sample
Ion Current) Chromatogram to calculate the quantitative relationship for each number of melamine nuclides, and to measure the ratio of —CH ₂ OH, —NH, —CH ₂ OR ′ of the generated molecular species from each MS spectrum molecular species analysis. You can

The melamine formaldehyde resin of the present invention is usually used in a proportion of 5 to 50% by weight based on the acrylic resin.

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. Particularly preferred is a hydroxyl value (OHV) of 15 to 120 KOHmg / g and an acid value (AV) of 5 to 4.
0 KOHmg / g and number average molecular weight of 5,000 to 30,
000 and a glass transition point of 15 to 80 ° C.

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.

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.

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.

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.

The size of the carrier core particles should be 20 μm (average particle size) at least to prevent carriers from adhering (scattering) to the electrostatic latent image carrier, and to prevent the occurrence of carrier stripes. 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 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. Baking treatment is 130 ~ 20
A temperature of 0 ° C. for 0.5 to 3 hours is sufficient, and this treatment almost completes the crosslinking of the acrylic resin. In order to increase the thickness of the resin film, the above application, firing and crushing may be repeated.

The coating resin thus formed has a film thickness of 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 charges on the toner, and addition of conductive fine particles is effective for controlling the electric resistance value 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 charge control agents such as Spiron Black TRH.

The conductive fine particles include carbon black, acetylene black, carbon black such as Ketchin black, carbides such as SiC, TiC, MoC and ZrC, nitrides such as BN, NbN, TiN and ZrN,
Examples thereof include 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 carrier finally obtained 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.

Reference Example 1-1 (Preparation of Crosslinking Agent) Paraformaldehyde (containing 80% by weight of formaldehyde) 150.0 g, n in a reactor equipped with a thermometer, a stirrer, a reflux condenser and a solvent by-product recovery device. -Butanol 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 (hereinafter referred to as "M-1") obtained at this time is 20 voise (20
℃).

The FD-MS spectrum is measured by JEOL-
The measurement was performed with a JMS-300 type double-focusing mass spectrometer.
The sample was coated on a carbon emitter, the cathode voltage was 5.5 KV, the emitter current was increased from 0 mA to 2 mA / min, and the magnetic field was swept (100-200 or 100-1).
000/10 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 measurement is represented by R _{1 to} R ₆ in the following general formula.
Was a butylated methylolmelamine resin containing a total of 53.8 mol% of the compounds (a), (b), (c) and (d) shown in Table 1.

[0035]

[Chemical 4]

[0036]

[Table 1]

Reference Example 1-2 (Preparation of Crosslinking Agent) A melamine resin was produced in the same manner as in Reference Example 1-1 except that 300 g of paraformaldehyde was charged in the reactor used in Reference Example 1-1. The obtained resin had a heating residue of 60.0% by weight and a viscosity of 0.2 poise. Reference example 1
As a result of analysis in the same manner as in -1, the total amount of the compounds having the structures (a) to (d) shown in Table 1 was 36.
It was a butylated methylolmelamine resin containing 4 mol% (hereinafter referred to as "M-2").

Reference Example 2 (Synthesis of acrylic resin) A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was purged with nitrogen, and then 700 g of xylene and 300 g of n-butanol were charged into the flask. ,
It heated up and heated up at 100 degreeC. Styrene 400 g, methyl methacrylate 160 g, i-butyl methacrylate 11
0 g, n-butyl acrylate 200 g, methacrylic acid 3
A mixture of 0 g, 100 g of 2-hydroxymethacrylate and 10 g of azobisisobutyronitrile was added dropwise to the flask over 5 hours. Then add 100 more contents
The temperature was kept at 6 ° C for 6 hours to obtain an acrylic resin having a solid content of about 50%. The physical properties of the obtained resin were as follows. Acid value (based on solid content) (KOHmg / g): 20, Hydroxyl value (based on solid content) (KOHmg / g): 43, glass transition point (Tg) (° C): 50, number average Molecular weight (Mn): 1,2000

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, 20% by weight of the crosslinking agent (the crosslinking agent obtained in Reference Example 1-1 or Reference Example 1-2) was added to the resin solid content of the acrylic resin obtained in Reference Example 2. And the mixture was diluted with xylene and n-butanol to prepare a 3 wt% coating solution.

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 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.

The thickness of the coating resin of the obtained carrier (μ
m) and electric resistance (Ω · cm) are shown in Table 2.

[Table 2] The film thickness was measured by measuring the difference between the particle size of the carrier core material and the particle size of the carrier after coating. As 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 diameter was 20 mm, the inner diameter was 38 mm, and the outer diameter was 42.
1 mm when a DC voltage of 500 V is applied with a mm guard electrode
The current value after the minute was read and converted into the volume resistivity (ρ) value of the sample. Measurement environment temperature 25 ± 1 ℃, relative humidity 55 ±
5%, the measurement was repeated 5 times, and the average thereof was taken.

Production Example of Toner [(-) Chargeable Toner] Component by Weight : Styrene-n-butylmethacrylate resin 100 (softening point, 132 ° C .; glass transition point, 60 ° C.) carbon black 8 (Mitsubishi Kasei Co., Ltd.) Made, MA # 8) ・ Charge control agent 3 (Hodogaya Chemical Co., Ltd .; Spiron Black TRH) ・ Osset inhibitor 3 (Sanyo Chemical Co., Ltd .; Viscole 550P)

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. For this toner, 0.2% of hydrophobic silica R-974 (manufactured by Nippon Aerosil Co., Ltd.) and hydrophobic titanium T-805.
It was treated with 0.8% (manufactured by Nippon Aerosil Co., Ltd.).

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. For toner scattering, only the developing device is removed from the copying machine, and the toner scattered from the developing device when an image is formed for a certain period of time is received on a white paper and the amount of toner is visually observed and evaluated, and "○" means 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.

[0047]

[Table 3]

[0048]

The acrylic resin-coated carrier of the present invention has excellent 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 carrier for electrophotography, comprising carrier particles whose surface is coated with an acrylic resin crosslinked with a melamine formaldehyde resin composition, wherein the melamine formaldehyde resin composition contains a melamine formaldehyde compound represented by the following general formula [I]. An electrophotographic carrier characterized by containing at least 50 mol%; [Wherein, in R _{1 to} R ₆ , 1 to 4 groups are hydrogen atoms, and the other remaining groups are CH ₂ OH or CH ₂ OR '(R'
Represents an alkyl group), and the ratio of (CH ₂ OR ′ group number) / (CH ₂ OH group number + CH ₂ OR ′ group number) is 0.7.
~ 1.0].