JP3113367B2 - Electrophotographic carrier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 applied with an electrostatic charge by a means such as corona discharge, and is exposed to a light image corresponding to a document, thereby eliminating the electrostatic charge of the exposed portion.
An electrostatic latent image is formed. On the other hand, by mixing the insulating toner and the carrier particles, the toner is frictionally charged, and at the same time, the developer is conveyed, brought into contact with the electrostatic latent image on the photoconductor, and the contact latent image is developed.

[0003] 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 a developing device, adjusting electric resistance, and providing environmental stability. (Eg, JP-A-47-13954, JP-B-58-9946, JP-A-60-57352, JP-A-62-262057, etc.).

JP-A-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 discloses a carrier coated with a crosslinked resin containing at least 5% by weight of a melamine resin. 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. JP-A-62-262057 discloses a carrier obtained by curing and coating an unreacted thermoplastic resin having a hydroxyl group and an alkoxylated melamine resin.

[0005] However, conventional resin-coated carriers still have problems in durability, heat resistance and environmental resistance, and improvements in their 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 copied image having excellent image quality and having excellent durability, heat resistance and environmental resistance. With the goal.

[0007]

That is, the present invention relates to an electrophotographic carrier in which carrier particles are coated with an acrylic resin crosslinked by a melamine formaldehyde resin composition, wherein the melamine formaldehyde resin composition has the following general formula [ The present invention relates to a carrier for electrophotography, which comprises at least 50 mol% of a melamine formaldehyde compound represented by I).

Embedded image [Wherein, among R _{1 to} R ₆ , one to four groups are hydrogen atoms, and the other groups are CH ₂ OH or CH ₂ OR ′ (R ′
Represents an alkyl group), and the ratio of (number of CH ₂ OR ′ groups) / (number of CH ₂ OH groups + number of CH ₂ OR ′ groups) is 0.7 to
1.0].

[0008] The carrier particles of the present invention comprise at least carrier core particles and an acrylic resin covering the core particles. Then, the acrylic resin is treated together with a melamine formaldehyde resin composition containing a melamine formaldehyde compound represented by the above general formula [I].

In the general formula [I], at least one and at most four of R _{1 to} R ₆ are hydrogen atoms, and one to four free NH groups that 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 formed melamine resin with the solvent or the acrylic resin used in combination becomes poor, and the melamine resin is precipitated. The possibilities increase. 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] includes CH ₂ OH and CH ₂ O
CH ₂ O having an alkyl group based on the total number of R ′ groups
The ratio of the number of R 'groups is 0.7 to 1.0, that is, at least 70% or more of the number of methylol groups bound to the melamine skeleton is alkoxy-modified, and the ratio of free methylol groups is 30%.
Less than. When the ratio 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 at least 50 mol% of the melamine formaldehyde compound specified above. If the amount of the melamine formaldehyde compound is less than 50 mol%, the OH groups remaining as unreacted groups of the crosslinking agent deteriorate the environment.

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

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

Embedded image

In the alkyl etherification reaction in this case, alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, 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, se
c-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; or ketone alcohols; For example, acetonyl methanol, diacetone alcohol, pyruvyl alcohol, or the like 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.

[0015] In determining the structure of the melamine resin according to the present invention, a field desorption mass spectrometry (Field Desorption Mass Spectrometry) is used.
s Spectrometry) (hereinafter abbreviated as “FD-MS method”). Although this analysis method is known as a means for simultaneously performing separation and identification, it is particularly effective for analyzing thermally unstable non-volatile substances. The feature is that molecular ions or pseudo-molecular ions are easily observed and the number of fragment ions is small, so the molecular weight can be determined from the spectrum, and the molecular weight distribution and molecular species distribution can be obtained from oligomers and polymers which are a mixture of homologues. Structural analysis can be easily performed (thermosetting resin Vol.1.18.198
0 Saito et al.).

[0016] That is to say, the RCI (Recountructed Ion Cu) obtained by FD-MS spectrum measurement of each sample.
from Rrent) chromatogram and calculate the amount relationship each melamine nucleus number, -CH ₂ OH generation molecular species from each MS spectrum molecular species analysis, -NH, to measure the ratios, etc. of the -CH ₂ OR ' it can.

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

The acrylic resin is a (co) polymer of at least a monomer having a hydroxyl group, more preferably a monomer having an acid group, and is a methylolamide group, an alkoxymethylolamide group, an amino group, a glycidyl group. And a copolymer of a monomer containing at least one kind of a thionyl group or the like. Particularly preferred is a hydroxyl value (OHV) of 15
~ 120KOHmg / g and acid value (AV) is 5-40KOHmg / g,
Number average molecular weight is 5,000 to 30,000 and glass transition point is 15 to 80
° C.

In the present invention, preferred examples of the monomer having an acid group used in the acrylic resin include acrylic acid and methacrylic acid, and furthermore, maleic acid,
Maleic anhydride, itaconic acid and their monoesters are listed, and one or more of these can be used.

The monomers having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 1,4-butanediol mono (meth) acrylate, and hydroxyethyl (meth) acrylate. Acrylate ε-
Examples include adducts of caprolactone and ethylene and propylene of hydroxyethyl (meth) acrylate, and one or more of these 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. In addition, for example, methyl (meth) acrylate indicates 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, and propylene. ,ethylene,
Α- olefins such as the C 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, 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, if necessary, dodecyl mercaptan, mercaptoethanol, α-methylstyrene dimer and the like can be used as a chain transfer agent.

As carrier core particles coated with an acrylic resin, those known as two-component carriers for electrophotography, for example, 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, and vanadium; metal oxides such as iron oxide, titanium oxide, and magnesium oxide; and nitrides such as chromium nitride and vanadium nitride , A mixture with a carbide such as silicon carbide and tungsten carbide, and a ferromagnetic ferrite can be used.

As for the size of the carrier core particles, particles having a size of at least 20 μm (average particle size) from the viewpoint of preventing the carrier from adhering (scattering) to the electrostatic latent image carrier are used. At least from the viewpoint of preventing deterioration in image quality
Use the one with 150 μm. Those having a thickness of 30 to 100 μm are preferred.

In order to apply the acrylic resin to the carrier core particles, a resin solution obtained by dissolving the acrylic resin in a suitable solvent may be used, and a dipping method, a spray drying method, or the like may be applied. After the application, the coating is dried and, if necessary, a firing treatment is performed. After the calcination, the carrier particles are aggregated into a bulk, so the bulk is crushed and sieved,
A carrier having a desired particle size is obtained. Baking process 130 ~ 200 ℃,
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, baking, and crushing may be repeated.

The coating resin thus formed has a film thickness of 0.1.
It is 1-5 μm, preferably 0.5-4 μm. Its thickness is 0.1
If it is less than μm, environmental stability is poor. On the other hand, if the thickness is more than 5 μm, the coating layer becomes too thick, and when applied to a developer, the thickness increases due to the accumulation of the amount of charge and the like, causing problems such as a decrease in image density.

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 to the toner, and the addition of conductive fine particles is effective for controlling the electric resistance value of the carrier.

The fine particles having a charge imparting function include Cr
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 a charge control agent such as Spiron Black TRH.

Examples of the conductive fine particles include carbon black such as carbon black, acetylene black and Ketchin black, carbides such as SiC, TiC, MoC and ZrC, nitrides such as BN, NbN, TiN and ZrN;
Examples include magnetic powders such as ferrite and magnetite.

The fine particles have an average particle size of about 2 to 0.01 μm, preferably about 1 to 0.01 μm.

As described above, the addition amount of the two fine particles cannot be unequivocally defined as described above. However, the addition amount is 0.1 wt% to 200 wt%, preferably 1.0 wt% to 60 wt%, based on the coated acrylic resin. % Is appropriate.

The carrier finally obtained has an electric resistance of about 1 × 10 ⁸ to 1 × 10 ¹³ Ω · cm. If the value is smaller than 1 × 10 ⁸ Ω · cm, carrier development occurs.If the value is larger than 1 × 10 ¹³ Ω · cm, developability is poor, sufficient image density cannot be obtained, and an image with a strong edge effect can be 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 ) 150.0 g of paraformaldehyde (containing 80% by weight of formaldehyde) was added to a reactor equipped with a thermometer, a stirrer, a reflux condenser, and a device for recovering a solvent by-product. Add 740 g of butanol and 126 g of melamine.
A 10% by weight aqueous solution was added to adjust the pH of the reaction solution to 4.0. Thereafter, the mixture was heated and continued for 5 hours while removing water out of the system under the reflux temperature condition of the reaction solution, then cooled to 50 ° C., and adjusted to pH 7.0 with a 10% by weight aqueous solution of caustic soda. Thereafter, while maintaining the temperature in the system at 50 ° C. or lower under heating and reduced pressure, excess butanol was removed from the system so that the heating residue of the resin (according to the measurement method of JISK-5400) was 60% by weight. The viscosity of the resin obtained at this time (hereinafter referred to as “M-1”) is 20 boys (2
0 ° C).

The measurement of the FD-MS spectrum was performed with a JEOL-JMS-300 type double focusing mass spectrometer. The sample was applied on a carbon emitter, the cathode voltage was increased to 5.5 KV, and the emitter current was increased from 0 mA to 2 mA / min, and the magnetic field was swept (100-200
Alternatively, the spectrum was measured for 100-1000 / 10 seconds). Data processing was performed with JEOL-JMA-3500. The output of the spectrum is the sum and average of all scans. In the resin obtained as a result of the measurement, in the following general formula, R _{1 to} R ₆ are the total of the compounds (a), (b), (c) and (d) shown in Table 1.
It was a butylated methylol melamine resin containing 53.8 mol%.

[0035]

Embedded image

[0036]

[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 inlet tube, 700 g of xylene and 300 g of n-butanol were charged into the flask. , 100 ℃
And heated. Styrene 400 g, methyl methacrylate
160 g, i-butyl methacrylate 110 g, n-butyl acrylate 200 g, methacrylic acid 30 g, 2-hydroxy methacrylate 100 g and azobisisobutyronitrile 10 g
Was dropped into the flask over 5 hours. Thereafter, the content is further held at 100 ° C. for 6 hours to obtain a solid content of about 50%.
% Acrylic resin was obtained. Various 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) (℃): 50, number average Molecular weight (Mn): 1,2000

Preparation of Coated Carrier The ferrite carrier was coated using the apparatus shown in FIG. First, 3 kg of ferrite particles having an average particle diameter 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 ferrite powder. Was kept mixed. Furthermore, air is sent from the blower (6), and the air is turned into hot air (50 ° C.) by the heater (7), and the ferrite (2) mixed and stirred.
Supplied. The ferrite (2) in the dryer is sowed by the hot air and is in a state of rolling and stirring in the direction of the arrow in the figure.

On the other hand, a crosslinking agent (crosslinking agent obtained in Reference Example 1-1) was mixed with the resin solid content of the acrylic resin obtained in Reference Example 2 so as to be 20% by weight. The mixture was further diluted with xylene and n-butanol to prepare a 3 wt% coating solution.

While maintaining the coating solution at 50 ° C., 35 ml per minute was sprayed onto the ferrite powder (2) from the spray nozzle (3). After completion of the spraying, the temperature was kept at 50 ° C. while maintaining the stirring state, followed by drying for 1 hour. The resulting coated carrier was taken out of the product outlet (8), placed in a hot air drier, and treated at 150 ° for 2 hours. In this process,
The acrylic resin coated on the ferrite powder undergoes a crosslinking reaction further by the crosslinking agent and is 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 (μ) of the coating resin of the obtained carrier was
m) and electrical resistance (Ω · cm) are shown in Table 2.

[Table 2] The 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. The electric resistance was measured by placing a sample on a metal circular electrode to a thickness of 1 mm and a diameter of 50 mm.
A 5.4 g electrode having a diameter of 20 mm, a guard electrode having an inner diameter of 38 mm, and an outer diameter of 42 mm were mounted, and the current value one minute after the application of a DC voltage of 500 V 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 five times, and the average was taken.

Production Example of Toner [(-) Chargeable Toner] Component parts by weight styrene-n-butyl methacrylate resin 100 (softening point, 132 ° C .; glass transition point, 60 ° C.) Carbon black (manufactured by Mitsubishi Kasei Corporation) , MA # 8) 8 ・ Charge control agent (Hodogaya Chemical Co .; Spiron Black TRH) 3 ・ Osset inhibitor (Sanyo Chemical Industries Co., Ltd .; Viscol 550P) 3

After thoroughly mixing the above materials with a ball mill,
Kneading was performed on three rolls heated to 110 ° C. The kneaded product was allowed to cool, coarsely pulverized, and further finely pulverized by a jet mill. Next, air classification was performed to obtain a toner having an average particle diameter of 8 μm.
This toner was treated with hydrophobic silica R-974 (manufactured by Nippon Aerosil Co., Ltd.) 0.2% and hydrophobic titanium T-805 (manufactured by Nippon Aerosil Co., Ltd.) 0.8%.

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

NN environment; temperature: 18 ° C. to 22 ° C., humidity: 50
LL environment; temperature: 10 ° C, humidity: 15% HH environment: temperature: 35 ° C, humidity: 85% The charge amount was measured by the method described in JP-A-63-13587. For toner scattering, remove only the developing device from the copier,
The toner scattered from the developing device when the image is formed for a certain period of time is received on white paper, and the amount of the toner is visually observed and evaluated.
“○” indicates that there is no problem in use, and “×” indicates that it cannot be used. The image quality was evaluated by visual observation. "O" indicates that there was no problem in use, and "X" indicates that it could not be used.

[0046]

[Table 3]

[0047]

The acrylic resin-coated carrier of the present invention has excellent durability and environmental resistance.

[Brief description of the drawings]

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

[Explanation of symbols]

 Reference Signs List 1 raw material supply port 2 ferrite 3 spray nozzle 4 motor 5 tumbling fluidized bed 6 blower 7 heater 8 product outlet

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yukio Tanigami 2-3-1 Azuchicho, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Camera Co., Ltd. In-house (72) Inventor Taisaku Kano Sakae-ku, Yokohama-shi, Kanagawa 1190 Kasama-cho Mitsui Toatsu Chemicals Co., Ltd. (72) Inventor Eiichiro Miyazaki 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Mitsui Toatsu Chemicals Co., Ltd. (56) References JP-A-62-262057 ( JP, A) JP-A-62-17863 (JP, A) JP-A-2-108069 (JP, A) JP-A-2-168266 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) G03G 9/113

Claims (1)

(57) [Claims] 1. An electrophotographic carrier in which the surface of carrier particles is coated with an acrylic resin crosslinked by a melamine formaldehyde resin composition, wherein the melamine formaldehyde resin composition comprises a melamine formaldehyde compound represented by the following general formula [I]: An electrophotographic carrier characterized by containing at least 50 mol%; [Wherein, among R _{1 to} R ₆ , one to four groups are hydrogen atoms, and the other groups are CH ₂ OH or CH ₂ OR ′ (R ′
Represents an alkyl group) and the ratio of (number of CH ₂ OR ′ groups) / (number of CH ₂ OH groups + number of CH ₂ OR ′ groups) is 0.7.
~ 1.0].