JPH04360156A - Color developing toner - Google Patents

Abstract

PURPOSE:To enhance heat resistance, independency of environmental conditions, and electric charging stability and resolution by providing a coating layer of thermosetting resin on the surface of carrier core and incorporating a conductive filler on the outermost layer. CONSTITUTION:The surface of each carrier core is coated with a thermosetting resin, such as silicone, epoxy, alkyd, phenol-formaldehyde, and urea-formaldehyde resins, and the outermost layer contains a conductive filler, such as magnetic powder like ferrite and magnetite, NiO, CrO2, MnO2, and conductive ZnO, thus permitting the coating with the thermosetting resin to contribute to enhancement of heat resistance and durability, and addition of the conductive filler to contribute to elevation of stability against environment conditions, especially, that of charging stability under high temperature and high humidity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to resin-coated carriers used as developers in combination with toners.

0002

[Prior Art] Conventionally, as an electrostatic latent image development method for electrophotography, an insulating non-magnetic toner and carrier particles are mixed to triboelectrically charge the toner, and a developer is conveyed. A two-component development method is known in which the image is developed by contacting the image.

[0003] The granular carrier used in such a two-component development system has the following functions: prevention of toner filming on the carrier surface, formation of a uniform surface of the carrier, prevention of surface oxidation, prevention of deterioration of moisture sensitivity, and extension of the life of the developer. It is usually coated with a suitable resin material for the purpose of extension, protection from scratches or abrasion of the photoreceptor by the carrier, control of charge polarity, or adjustment of charge amount (for example, JP-A-58-108548).
.

[0004] Thermosetting resins are known to be used as one such resin material, but they still have problems with durability or heat resistance, and they also have problems with toner being spent on the surface of the carrier, and This causes problems such as destabilization of the amount of charge and occurrence of toner fog. Furthermore, there is a need to improve environmental resistance. Particularly in a high-temperature, high-humidity environment, a good image can be obtained initially, but as printing is continued, the amount of charge decreases, toner fog and carrier streaks occur, and the quality of the copied image deteriorates.

[0005]

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and is capable of forming images with excellent heat resistance, environmental resistance, and charging stability, and with no toner fog. The purpose is to provide a career.

[0006]

[Means for Solving the Problems] The present invention provides an electrostatic image development method characterized in that the surface of the carrier core particle has a coating layer made of a thermosetting resin, and the outermost shell coating layer contains a conductive filler. Regarding carriers for

The carrier of the present invention comprises at least a carrier core material, a thermosetting resin coating layer covering the core material, and a conductive filler contained in the outermost shell of the thermosetting resin coating layer.

[0008] The thermosetting resin coating contributes to improving the heat resistance and durability of the carrier, and the addition of a conductive filler greatly contributes to the environmental stability of the carrier, especially the charging stability under high temperature and high humidity. . As a result, the carrier of the present invention can form images with excellent texture and no toner fog.

The core material of the carrier should be at least 20% in order to prevent the carrier from adhering (scattering) to the electrostatic latent image bearing member.
To prevent deterioration of image quality such as carrier streaks, use particles with a particle size of at least 1 μm (average particle diameter).
00 μm is used. Specific materials include those known as two-component carriers for electrophotography, such as metals such as ferrite, magnetite, iron, nickel, and cobalt, and these metals and zinc, antimony, aluminum, lead, tin, bismuth, beryllium, and manganese. , alloys or mixtures with metals such as selenium, tungsten, zirconium, and vanadium; metal oxides such as iron oxide, titanium oxide, and magnesium oxide; nitrides such as chromium nitride and vanadium nitride; and carbides such as silicon carbide and tungsten carbide. and ferromagnetic ferrites, as well as mixtures thereof can be applied.

[0010] As the thermosetting resin to be coated on the carrier core material, a resin known as a resin that hardens (insolubilizes) when heated can be used. For example, silicone resin, epoxy resin, alkyd resin, phenol-formaldehyde resin, urea-formaldehyde resin, melamine-formaldehyde resin, resin obtained by curing acrylic polyol with isocyanate, resin obtained by curing polyester polyol with isocyanate, acrylic polyol with melamine or resins made by curing acrylic acid with melamine. Further, monomers that are constituent components of the thermosetting resin may be used in combination. In addition, thermoplastic resins are included in the thermosetting resin of the present invention as long as they are cured by crosslinking and have heat resistance. especially,
When the constituent resin of the toner used in combination with the carrier is composed of polyester resin, the toner is negatively chargeable, and in order to make the carrier more positively chargeable, a thermosetting acrylic resin is used. It is preferable. Thermosetting acrylic resin is a product obtained by crosslinking at least one acrylic monomer or a copolymer obtained by polymerizing an acrylic monomer and a styrene monomer with a melamine compound or an isocyanate compound. It is. Examples of acrylic monomers include methyl methacrylate,
Methacrylic acid alkyl esters such as butyl methacrylate, octyl methacrylate, stearyl methacrylate;
Acrylic acid alkyl esters such as ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate; acrylonitrile, acrylamide; or dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethyl acrylate Vinyl monomers containing amino groups such as aminopropyl methacrylic acid amide can be used, and as styrene monomers,
Styrene, α-methylstyrene, vinyltoluene, p-
Ethyl styrene etc. can be used.

In the present invention, the above thermosetting resin is added in an amount of 0.5 to 10% by weight, preferably 1 to 5% by weight, more preferably 2 to 3% by weight based on the carrier core particles. Coat the carrier. If it is less than 0.5% by weight, the core material cannot be coated uniformly and environmental resistance deteriorates, and if it is more than 10% by weight, the particle size becomes too large and there are problems such as deterioration of image quality. This is because it occurs.

The outermost shell layer of the carrier-coated thermosetting resin layer contains a conductive filler. As the conductive filler, fillers having an electrical resistance (specific resistance) of 1010 Ω·cm or less can be used, such as magnetic powder (ferrite, magnetite), NiO, CrO2, MnO.
2. Conductive ZnO, conductive carbon black, etc. can be used.

The content of the conductive filler should be appropriately selected depending on the type of filler, but when ferrite is used, it is 0.01 to 10% by weight, preferably 0.05 to 5% by weight, based on the carrier core particles. % by weight, more preferably from 0.1 to 2% by weight. This is because if the content is less than the above range, the effects of the present invention cannot be fully achieved, and if the content is more than the above range, the amount of charge will decrease and toner fog will occur.

[0014] In order to apply the thermosetting resin to the carrier core particles, a dipping method, a spray drying method, etc. may be applied using a resin solution in which the above-mentioned thermosetting resin is dissolved in an appropriate solvent. When using a monomer alone or a mixture of monomers as a thermosetting resin, in order to ensure the amount of adhesion to the core particle surface, it is necessary to cure the monomer mixture solution to some extent to give it viscosity. preferable.

After coating, drying and baking are performed as necessary. After the firing, the carrier particles are aggregated to form a bulk, so the bulk is crushed and passed through a sieve to obtain a carrier having a desired particle size.

[0016] In order to obtain the desired thickness and uniformity of the resin film, the above-described coating, baking, and crushing may be repeated as necessary. Preferably it is carried out 2 to 3 times. By doing so, the carrier core particles are uniformly coated with the thermosetting resin.

In the final coating step, a resin liquid containing the above-mentioned conductive filler is applied. The filler-containing coating layer can be formed with good adhesion on the thermosetting resin coating layer molded in the previous step.

To apply a thermosetting resin containing a conductive filler to the resin-coated carrier, add a predetermined amount of the conductive filler to a resin solution prepared by dissolving the above-mentioned thermosetting resin in a suitable solvent, and then mix thoroughly. A dipping method, a spray drying method, etc. may be applied using a dispersed resin liquid. The conductive filler can be effectively dispersed in the resin liquid using an ultrasonic homogenizer. As a result, a uniform dispersion can be obtained in a short time without contamination with impurities.

After coating, firing and crushing are performed to obtain a carrier having a desired particle size. In the carrier of the present invention finally obtained, it is desirable that the thermal decomposition peak temperature of the coating layer is 275° C. or higher. When the thermal decomposition peak temperature is lower than 275° C., the heat resistance of the carrier decreases and blocking tends to occur. The carrier of the present invention is used in combination with a toner as a two-component developer. The present invention will be explained below using examples.

Production of toner (Binder resin: Production of vinyl-modified polyester resin) 68 parts by weight of polyoxyethylene (2)-2,2-bis(4-hydroxyphenyl)propane, 1 part by weight of isophthalic acid.
6 parts by weight, 16 parts by weight of terephthalic acid, 0 maleic anhydride
．． A flask was charged with 3 parts by weight of dibutyltin oxide and 0.06 parts by weight of dibutyltin oxide, and the reaction was continued at 230° C. for 24 hours under a nitrogen atmosphere, and then taken out to obtain a polyester resin containing unsaturated polyester. The weight average molecular weight of the obtained polyester resin was 10,600.

50 parts by weight of this polyester resin and 50 parts by weight of xylene were charged into a flask and dissolved. Raise the temperature until the xylene refluxes, and add 1 styrene under the xylene reflux.
A solution of 0.4 parts by weight of azobisisobutyronitrile dissolved in 3 parts by weight and 2 parts by weight of methyl methacrylate was added dropwise under a nitrogen atmosphere over about 30 minutes. After dropping, the temperature was kept for 3 hours, the xylene was distilled under reduced pressure, and the resin was taken out.The weight average molecular weight was 13,100, and the melt viscosity at 100°C was 6
A binder resin having a poise and glass transition temperature of 63°C was obtained.

However, the melt viscosity is a value measured using a Shimadzu flow tester CFT-500 under the conditions of a nozzle diameter of 1 mm, a nozzle length of 1 mm, a load of 3 kg, and a temperature increase rate of 3° C./min.

[0023]

Part by weight: Styrene acrylic modified polyester resin obtained above 100
・Carbon black MA#8 (manufactured by Mitsubishi Chemical Corporation)
3. Charge control agent (Bontron E-84, manufactured by Orient Chemical Co., Ltd.)
3 The above materials were thoroughly mixed using a Henschel mixer, kneaded using a twin-screw extruder, and then cooled. The mixture is roughly pulverized with a feather mill, and then a jet pulverizer and an air classifier are used to reduce the particle size to 5 to 25 μm (average particle size 10.
5 μm) particles were obtained.

Next, 1.0% by weight of hydrophobic titanium (manufactured by Nippon Aerosil Co., Ltd.: T-805) and 0.2% by weight of hydrophobic silica (manufactured by Wacker Company: H2000/4) were added and mixed in a Henschel mixer. And got toner.

Example 1 80 parts by weight of a styrene-acrylic copolymer (1.5:7:1.0:0.5) consisting of styrene, methyl methacrylate, 2-hydroxyethyl acrylate, and methacrylic acid and butylated melamine. 20 parts by weight of the resin was diluted with toluene to prepare a styrene acrylic resin solution having a solids ratio of 2% by weight.

[0026] Calcined ferrite powder (F-300
; Average particle size: 50 μm, bulk density: 2.53 g/cm3;
The styrene acrylic resin solution was applied using a spiller coater (manufactured by Okada Seiko Co., Ltd.) so that the amount of coating resin to the core material was about 1% by weight.
Dry. The obtained carrier was left to stand at 170° C. for 2 hours in a hot air circulation type open chamber and fired. After cooling, the ferrite powder bulk was crushed using a sieve shaker equipped with screen meshes with openings of 210 μm and 90 μm to obtain resin-coated ferrite powder. This ferrite powder was subjected to the above coating, firing and crushing process three more times to obtain a resin-coated carrier.

Next, fine ferrite powder (manufactured by TDK; M
FP-2) was sufficiently dispersed using an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd.) to prepare a ferrite filler-dispersed styrene acrylic resin solution.

[0028] Using the above resin-coated carrier as a core material,
The above ferrite filler-dispersed styrene acrylic resin solution was applied using the same Spira coater (manufactured by Okada Seiko Co., Ltd.) so that the coating resin amount to the core material was about 1% by weight, dried, and then heated in a hot air circulation oven at 170°C. It was left to stand for 2 hours and fired. Next, after cooling, 210 μm was
It was crushed using a sieve shaker equipped with a μm screen mesh to obtain a resin-coated carrier (2) containing ferrite filler.

[0029] The average particle size of the obtained carrier (■) was 55 μm.
, resin coverage (Rc) is 3.83%, thermal decomposition temperature is 28
At 0°C, the electrical resistance was 3 x 1010 Ωcm.

00
[30] The amount of coated resin (Rc) was determined as follows. Approximately 5 g of resin-coated carrier, weight W0 (
g) is placed in a precisely weighed 10 cc magnetic crucible, and the entire weight W1 (g) is precisely weighed. This crucible was placed in a muffle furnace and heated to 900°C at a rate of 15°C per minute.
The coating resin was left to burn for 3 hours at 0°C, and then allowed to cool to room temperature. Immediately after reaching room temperature, the weight W2 (g) of the crucible containing the carrier is accurately weighed. The amount of coated resin (Rc) is determined by the following formula.

[Math 1]

The carrier particle size was measured using a laser diffraction particle size distribution analyzer manufactured by Microtrac.

The bulk density of the carrier was measured in accordance with JISZ 2504 using a bulk specific gravity meter manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.

The thermal decomposition peak temperature was determined from a DSC curve using a thermal analyzer (Seiko Electronics Co., Ltd., SSS-5000).

Example 2 The same operation as in Example 1 was carried out except that the ferrite fine powder (MFP-2) was used in an amount of 100% by weight based on the resin solid content of the styrene acrylic resin solution. A containing resin-coated carrier (2) was obtained. The average particle size of the obtained carrier (■) was 56 μm, the resin coating amount Rc was 3.80% by weight, the thermal decomposition temperature was 280°C, and the electrical resistance was 2.
×1010Ω·cm.

Example 3 In Example 1, 50% by weight of ferrite fine powder (MFP-2) was added to the resin solid content of the styrene acrylic resin solution.
The same operation as in Example 1 was carried out except that the amount of coating resin was about 0.5% by weight based on the carrier core particles, to obtain a resin-coated carrier (2) containing ferrite filler. The average particle size of the obtained carrier (■) was 53 μm, and the resin coating amount Rc was 3.45.
Weight%, thermal decomposition temperature is 283℃, electrical resistance is 1×101
It was 0Ω·cm.

Comparative Example 1 The same calcined ferrite powder (F-30
0; Average particle size: 45 μm, bulk density: 2.50 g/cm3
The same ferrite filler-dispersed styrene acrylic resin solution as in Example 1 was applied using a spiller coater (manufactured by Okada Seiko Co., Ltd.) so that the amount of coating resin to the core material was about 2% by weight. Dry. The obtained carrier was baked at 160° C. for 2 hours in a hot air circulation oven. After cooling, the ferrite powder bulk was crushed using a sieve shaker equipped with screen meshes with openings of 210 μm and 90 μm to obtain a resin-coated carrier (2) containing ferrite filler. The average particle size of the obtained carrier was 47 μm, and the amount of resin coated (Rc) was 1.90%.
, thermal decomposition peak temperature is 245℃, electrical resistance is approximately 5×10
It was 9Ωcm.

Comparative Example 2 Calcined ferrite powder (F-300; average particle size:
45 μm, bulk density: 2.35 g/cm3; manufactured by Powder Tech Co., Ltd.), and coated with the same styrene-acrylic resin solution as in Example 1 using a spiral coater (Okada Seiko Co., Ltd.) and dried. The obtained carrier was heated at 160°C in a hot air circulation oven.
It was left to stand for 2 hours and fired. After cooling, the ferrite powder bulk was crushed using a sieve shaker equipped with screen meshes with openings of 210 μm and 90 μm to obtain resin-coated ferrite powder. For this ferrite powder,
The above coating, firing, and crushing were repeated two more times to obtain a resin-coated carrier (2). The average particle size of the obtained carrier was 48
μm, the coating resin amount (Rc) was 2.85%, the thermal decomposition peak temperature was 245° C., and the electrical resistance was about 8×10 9 Ωcm.

Table 1 summarizes the manufacturing conditions and physical properties of the carrier obtained above.

[Table 1]

[Evaluation of Carrier] 8 parts by weight of the toner produced above and 92 parts by weight of each of the carriers of Examples 1 to 3 and Comparative Examples 1 and 2 were mixed to prepare a developer. Using CF-70 (manufactured by Minolta Camera Co., Ltd.), this developer was used to make 5,000 copies under an environment of 30° C. and 85% for the following items, and the printing durability was evaluated. The results are shown in Table 2.

[0040]

[Table 2]

(Charge amount) Based on the film charge measurement method (
Toner concentration 8% by weight)

(Fog on images) As described above, images were printed using the above-mentioned copying machine using various toner and carrier combinations. Regarding fog on images, toner fog on white background images was evaluated and ranked. A rank of △ or higher is practically usable, but a rank of ○ or higher is desirable.

(Heat resistance) Put 10g of carrier into a container,
The samples were left in an oven at 60° C. for 1 hour, and the presence or absence of carrier aggregation after cooling was determined and ranked as follows. ○: No aggregation △: Aggregation exists, but it can be easily loosened (practical lower limit) ×: Agglomeration is large and cannot be loosened (practical impossibility)

(Environmental variation in charging) The developer was heated at 10°C and 15°C.
% environment after storage for 24 hours (QLL) and 30℃ and 85% environment after storage for 24 hours (QLL)
QHH), the difference ΔQ; ΔQ=QLL−QHH(μC/g) was determined, and the environmental changes in charging were evaluated by ranking them as follows. The following results are summarized in Table 1 below. X is impractical due to large environmental fluctuations.
A rating of △ or higher means that it can be used practically, but a rating of ○ or higher is desirable.

(Texture on the image) Regarding the texture on the image, the texture on the half image was evaluated and ranked. A rank of △ or higher is practically usable, but a rank of ○ or higher is desirable.

(Amount of spent toner) The amount of spent toner is determined by sampling the developer, separating the developer into toner and carrier using a blow-off method, immersing about 1.00 g of the isolated carrier in 20 ml of ethanol for 2 hours, and then filtering it. The absorbance of the filtrate at 500 nm is measured using a spectrophotometer. Separately, a calibration curve is obtained for the dye component in the toner, and the amount of dye in the toner eluted is calculated from the absorbance at 500 nm. From this value and the proportion of dye contained in the toner, the amount of spent toner (mg/1 g of carrier) is determined as the amount of toner fixed on the carrier.

(Amount of toner scattering) This was determined from the amount of toner falling when measuring the amount of charge on the film.

[0048]

Effects of the Invention The carrier of the present invention has excellent heat resistance and durability, and has little environmental fluctuation.In particular, there is no toner fog even under high temperature and high humidity conditions, and it is possible to form fine-grained and excellent copied images.

Claims (1)

[Claims] 1. A carrier for developing an electrostatic image, comprising a thermosetting resin coating layer on the surface of the carrier core particles, and a conductive filler in the outermost shell coating layer.