JPH06202381A - Developer for electrostatic latent image - Google Patents

Abstract

PURPOSE:To provide a two-component developer excellent in heat resistance, environmental resistance and electrostatic charge stability and capable of forming a clear image free from toner fogging. CONSTITUTION:This developer consists of a carrier having resin coating layers on the surfaces of the core particles and contg. inorg. fine powder of silica, titania, alumina, zinc oxide, tin oxide or carbon black in the outermost coating layers and a toner contg. the practically same inorg. fine powder as the inorg. fine powder contained in the carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for an electrostatic latent image for electrophotography, which contains a specific toner and carrier.
More specifically, it has a coating layer on the surface of the carrier core particles,
The present invention relates to a developer composed of a carrier containing an inorganic fine powder in the outermost shell coating layer and a toner containing substantially the same inorganic fine powder as the carrier.

[0002]

2. Description of the Related Art Conventionally, as an electrostatic latent image developing method for electrophotography, by mixing an insulating non-magnetic toner and carrier particles, the toner is triboelectrically charged, and a developer is conveyed to cause electrostatic latent image development. A two-component developing method is known in which the image is contacted with an image and developed.

The granular carrier used in such a two-component developing system prevents the filming of the toner on the surface of the carrier, the formation of a uniform surface of the carrier, the prevention of surface oxidation, the prevention of deterioration of moisture sensitivity, and the life of the developer. For the purpose of extension, protection from scratches or abrasion by the carrier of the photoconductor, control of charge polarity or adjustment of charge amount, it is usually coated with a suitable resin material (for example, JP-A-58-108548). Further, a technique of adding various additives to the coating layer is known (for example, Japanese Patent Laid-Open No. 54-155048).
JP-A-57-40267, JP-A-58-
108549, JP-A-59-166968, JP-B-1-19584, JP-B-3-628, etc.).

However, there is still a problem in durability or heat resistance, and there is a problem that the toner is spent on the carrier surface, the charge amount becomes unstable accordingly, and toner fogging occurs. Furthermore, it is necessary to improve the environmental resistance.

Particularly in a high temperature and high humidity environment, a good image can be obtained in the initial stage, but as printing is performed, the charge amount decreases, toner fogging and carrier streaks occur, and the image quality of the copied image deteriorates. To do.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and is capable of forming a textured image which is excellent in heat resistance, environment resistance and charge stability and is free from toner fog. It is an object to provide a two-component developer.

[0007]

That is, the present invention has a resin coating layer on the surface of carrier core particles, and the outermost shell coating layer is an inorganic oxide selected from silica, titania, alumina, zinc oxide or tin oxide. The present invention relates to a developer comprising a toner containing a carrier containing a fine powder and an inorganic oxide fine powder substantially the same as the inorganic fine powder contained in the carrier.

According to the present invention, the resin-coated carrier and the toner treated with substantially the same inorganic fine powder prevent the toner external additive from migrating to the carrier surface and stabilize the charge level. Is effectively prevented. Therefore, even if the printing durability running is performed for a long period of time, the charge amount does not decrease and good image quality is maintained. It also extends the life of the developer.

The developer of the present invention comprises at least a resin-coated carrier and a toner. First, the toner will be described.

The toner is not limited to black toner, and various color toners can be applied. After mixing and kneading a thermoplastic resin, a colorant and / or a charge imparting agent,
A pulverized toner obtained by pulverizing and classifying, or a suspension polymerization toner obtained by dispersing a colorant and / or a charge-imparting agent in a monomer and polymerizing this, or a low softening point substance such as a colorant and wax or fixing. It is possible to use encapsulated toner in which a liquid containing resin for use is wrapped with a wall material (capsule shell) having a higher softening point than these, or a photoconductive toner whose surface is coated with a photoconductive substance. it can.

Inorganic oxides such as silica, titania, alumina, zinc oxide or tin oxide are generally added to such toners as fluidizing agents. The addition may be carried out by a method that is usually carried out according to the purpose and the purpose of use such as a method of internally adding the toner particles, a method of externally attaching the toner particles to the surface of the toner particles.

The amount of the inorganic oxide added is 1 to 15% by weight, preferably 2 to 10% by weight, based on the toner binder resin. If the addition amount is less than 1% by weight, the image density will be low. If it is more than 15% by weight, the amount of electrification becomes low and problems such as toner scattering and background fog occur.

Next, the resin-coated carrier used in combination with the above toner will be described.

The resin-coated carrier is composed of at least a carrier core material, a coating resin and an inorganic oxide fine powder.

The core material of the carrier is at least 20 μ from the viewpoint of preventing carrier adhesion (scattering) to the electrostatic latent image carrier.
Use a size of m (average particle size), and at the most 100 points from the viewpoint of preventing deterioration of image quality such as occurrence of carrier stripes etc.
Use the μm one. As a specific material, a well-known one as a two-component carrier for electrophotography, for example, ferrite, magnetite, iron, nickel, etc. may be appropriately selected and used according to the use and purpose of use of the carrier.

In the resin-coated carrier, the above-mentioned carrier core material is a thermoplastic resin such as polystyrene resin or poly (meta).
Acrylic resin, polyolefin resin, polyamide resin, polycarbonate resin, polyether resin,
Various thermoplastic resins such as polysulfinic acid type resin, polyester type resin, epoxy type resin, polybutyral type resin, urea type resin, urethane / urea type resin, silicone type resin, polyethylene type resin, Teflon type resin and thermosetting Resins and mixtures thereof, as well as copolymers, block polymers, graft polymers and polymer blends of these resins are used.

The above coating resin is used for the carrier core particles.
The coating amount is 0.5 to 10% by weight, preferably 1 to 5% by weight. If the proportion is less than 0.5% by weight, the carrier core material cannot be uniformly coated and the environment resistance is deteriorated. On the other hand, if it exceeds 10% by weight, the particle size of the obtained carrier becomes too large and the image quality deteriorates.

In the present invention, silica, titania, alumina, zinc oxide,
It contains an inorganic fine powder selected from tin oxide or carbon black.

Silica, titania, alumina, zinc oxide,
Inorganic oxides such as tin oxide are generally added to the toner as toner fluidizing agents (internal addition, external addition), and the carrier is substantially the same as that added to the toner. . Here, "substantially the same" means that the difference between the isoelectric point of the inorganic fine powder added to the carrier and the isoelectric point of the inorganic fine powder added to the toner is 5 or less, preferably 3 or less. The most preferable case is that the carrier and the inorganic fine powder used in the toner are the same. If the difference between the isoelectric points is larger than 5, the effect of the present invention is not obtained.

In the present invention, the isoelectric point is JIS.
The value measured by Z8802.

The amount of the inorganic oxide added to the outermost shell layer of the carrier is 0.0001 to 1% by weight, preferably 0.001 to 0.5% by weight, based on the carrier core particles. If the added amount is less than 0.0001% by weight, the effect of the present invention is not obtained. If it exceeds 1% by weight, the resistance of the carrier is lowered and the image quality is deteriorated.

In the present invention, carbon black may be added as an inorganic fine powder to the outermost shell layer portion of the resin-coated carrier. In this case, substantially the same carbon black as the colorant added to the toner is used as the carrier. In the present invention, the carbon blacks are substantially the same when the difference between the pHs of the two carbon blacks (the pH of the carbon black used for the carrier)-(the pH of the carbon black used for the toner) is 3 or less. The most preferred is to use the same carbon black for the toner and carrier. pH
If the difference is larger than 3, the effect of the present invention cannot be obtained.

In the present invention, carbon black
pH means a value measured according to JIS Z8802.

The amount of carbon black added to the outermost shell layer of the carrier is 0.0005 to 1 with respect to the carrier core particles.
%, Preferably 0.001 to 0.5% by weight.
If the added amount is less than 0.0005% by weight, the effect of the present invention is not obtained. If it exceeds 1% by weight, the resistance of the carrier is lowered and the image quality is deteriorated.

In order to incorporate the inorganic fine powder into the outermost shell layer of the carrier, for example, the thermosetting resin as the outer shell layer is applied to the carrier core particles as follows. That is, first, a thermosetting resin to be used is dissolved in an appropriate solvent to use a resin solution, and a dipping method, a spray drying method, or the like is applied. When using a monomer alone or a mixture of monomers as the thermosetting resin, in order to secure the amount of adhesion to the surface of the core particles, it is necessary to cure the monomer mixture solution to some extent to give viscosity. preferable.

After coating, it is dried and baked if necessary. 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 obtain the desired thickness and uniformity of the resin film, the above coating, firing and crushing may be repeated as necessary. It is preferably performed 2 to 3 times. By doing so, the carrier core particles are uniformly coated with the thermosetting resin.

Then, in the last application step, the resin liquid is applied by incorporating the above-mentioned inorganic fine particles. The inorganic fine particle coating layer can be formed with good adhesion on the thermosetting resin coating layer formed in the previous step.

When a thermoplastic resin is used as the outermost shell layer of the carrier, the resin may be coated by a conventional method, and the resin liquid may be coated with the inorganic fine particles in the final coating step.

When a thermoplastic resin is used, a method may be employed in which a resin-coated carrier is first prepared and then the above-mentioned inorganic fine particles are attached and fixed to the surface of the carrier.

The present invention will be described below with reference to examples. In the following examples, "parts" means "parts by weight" unless otherwise specified.

Toner Production Example 1 400 parts of 2.2 mol adduct of bisphenol A ethylene oxide, 192 parts of 2.2 mol adduct of bisphenol A propylene oxide, 232 parts of terephthalic acid and 0.8 part of dibutyric acid oxide were added. The flask was placed in a one-necked flask, a thermometer, a stainless stir bar, a cooler and a nitrogen introducing tube were attached, and the reaction was carried out at 200 ° C. under a nitrogen stream. The acid value of the obtained polyester was 2.7 KOH mg / g, the hydroxyl value was 47 KOH mg / g, and the glass transition temperature by DSC (differential calorimeter) was 58 ° C.

The GPC measurement result shows that the number average molecular weight is 2,2.
00, weight average molecular weight 6,200, peak molecular weight 5,60
It was 0.

Parts by weight Polyester resin obtained above 100 Silica (isoelectric point: 1.8) 1 Copper phthalocyanine pigment 4 Charge control agent (Bontron E-84; manufactured by Orient Chemical Co., Ltd.) 3 The above materials are sufficiently mixed with a Henschel mixer. After mixing and kneading with a twin-screw extruder, it was cooled. The mixture was roughly pulverized with a feather mill, and then a jet pulverizer and an air classifier were used to obtain a toner having a particle size of 5 to 25 μm (average particle size 10.5 μm).

Toner Production Example 2 Exactly the same as Toner Production Example 1 except that 2 parts by weight of titania (isoelectric point 6.5) was used in place of 1 part by weight of silica used in Toner Production Example 1. Got toner.

Toner Production Example 3 Except for using 2 parts by weight of alumina (isoelectric point 9.0) in place of 1 part by weight of silica used in Toner Production Example 1, the same procedure as in Toner Production Example 1 was carried out. , Toner was obtained.

Toner Production Example 4 Instead of 1 part by weight of silica used in Toner Production Example 1, carbon black (pH: 3.0, MA # 100;
The same procedure as in Toner Production Example 1 was carried out except that 3 parts by weight of Orient Chemical Co., Ltd.) was used to obtain particles having a particle size of 5 to 25 μm (average particle size 10.5 μm).

Next, hydrophobic titanium (manufactured by Nippon Aerosil Co., Ltd .:
1.0 wt% of T-805 and 0.2 wt% of hydrophobic silica (H2000 / 4 manufactured by Wacker Co.) were added and mixed with a Henschel mixer to obtain a toner.

Toner Production Example 5 Carbon Black M used in Toner Production Example 4
A toner was obtained in the same manner except that 5 parts by weight of carbon black (pH: 6.0, # 50; manufactured by Mitsubishi Kasei) was used in place of 3 parts by weight of A # 8 (manufactured by Mitsubishi Kasei).

Toner Production Example 6 Carbon Black MA # 8 in Toner Production Example 4
(Made by Mitsubishi Kasei) Carbon black (p
H: 8.4, # 55; manufactured by Mitsubishi Kasei Co., Ltd.) Toner was obtained in the same manner except that 8 parts by weight was used.

Production Example 1 of Carrier 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 20 parts by weight of a butylated melamine resin were diluted with toluene to prepare a styrene acrylic resin solution having a solid ratio of 2% by weight.

Fired ferrite powder (F-300;
Using an average particle size: 50 μm, bulk density: 2.53 g / cm ³ ; manufactured by Powder Tech Co., Ltd., a spira coater (Okada Seiko Co., Ltd.) is used so that the coating resin amount of the styrene acrylic resin solution with respect to the core material is about 1% by weight. (Manufactured by the company) and dried. The carrier obtained is heated at 170 ° C. in a hot air circulation oven for 2 hours.
It was left to burn for a period of time. After cooling, the ferrite powder bulk was crushed using a sieve shaker equipped with screen meshes of 210 μm and 90 μm to obtain resin-coated ferrite powder. The ferrite powder was subjected to the above-mentioned coating firing and crushing three more times to obtain a resin-coated carrier.

Next, 10% by weight of silica (isoelectric point 1.8) was added to the resin solid content of the styrene-acrylic resin solution and sufficiently dispersed with an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd.). Then, an inorganic oxide-dispersed styrene acrylic resin solution was prepared.

Using the above resin-coated carrier as a core material,
The above inorganic oxide-dispersed styrene acrylic resin solution was applied by a Spira coater (made by Okada Seiko Co., Ltd.) so that the coating resin amount with respect to the core material was about 1% by weight, dried, and further 170 It was left to burn at ℃ for 2 hours and baked.

Next, after cooling, the product was crushed using a sieve shaker equipped with screen meshes of 210 μm and 90 μm to obtain an inorganic oxide-containing resin-coated carrier.

The average particle size of the obtained carrier is 55 μm.
m, resin coverage (Rc) is 2.81%, thermal decomposition temperature is 280
The temperature and electrical resistance were 3 × 10 ¹⁰ Ωcm.

The coating resin amount (Rc) was determined as follows. Resin coated carrier about 5g, weight W _{0 in} advance
(g) is placed in a precisely weighed 10 cc magnetic crucible, and the total weight W ₁ (g) is precisely weighed. The crucible is placed in a muffle furnace, heated to 900 ° C. at a speed of 15 ° C./min, left at 900 ° C. for 3 hours to burn the coating resin, and then allowed to cool to room temperature. Immediately after reaching the room temperature, the weight W ₂ (g) of the crucible containing the carrier is precisely weighed. Amount of coating resin
(Rc) is calculated by the following formula.

[0048]

[Equation 1]

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

The bulk density of the carrier was measured according to JIS Z2504 using a bulk specific gravity measuring instrument manufactured by Kuramochi Kagaku Kikai Seisakusho.

The thermal decomposition peak temperature was determined from the DSC curve by a thermal analyzer (Seiko Denshi Co., SSS-5000).

Carrier Production Example 2 The same operation as in Example 1 was conducted except that the titania (isoelectric point: 6.5) was 20% by weight based on the resin solid content of the styrene acrylic resin solution. A resin-coated carrier containing ferrite filler was obtained.

The average particle size of the borrowed carrier is 56 μ.
m, resin coating amount Rc is 2.83% by weight, thermal decomposition temperature is 28
0 ° C., the electrical resistance was 2 × ¹⁰ 10 Ω · cm.

Carrier Production Example 3 In Example 1, 2 parts by weight of inorganic oxide alumina (isoelectric point 9.0) was added to the resin solid content of the styrene-acrylic resin solution.
A ferrite filler-containing resin-coated carrier was obtained in the same manner as in Example 1, except that the amount of coating resin was about 0.5% by weight based on the carrier core particles.

The average particle size of the obtained carrier is 53 μm.
m, resin coating amount Rc is 3.45% by weight, thermal decomposition temperature is 28
The electrical resistance was 1 × 10 ¹⁰ Ω · cm at 3 ° C.

Carrier Production Example 4 Carbon black was contained in the same manner as in Example 1 except that carbon black (pH 3.0, MA # 100; manufactured by Mitsubishi Kasei Co.) was added in place of the silica used in Example 1. A resin-coated carrier was obtained.

The average particle size of the obtained carrier is 55 μm.
m, resin coverage (Rc) is 3.80%, thermal decomposition temperature is 280
° C., the electrical resistance was 2 × ¹⁰ 10 Ω · cm.

Carrier Production Example 5 Carbon black (pH: 6.0, # 50; resin solid content of styrene acrylic resin solution in Example 4)
The same procedure as in Example 4 was carried out except that the content was 20% by weight (manufactured by Mitsubishi Kasei Co., Ltd.) to obtain a ferrite filler-containing resin-coated carrier.

The average particle size of the obtained carrier is 56 μm.
m, resin coating amount Rc is 3.75% by weight, thermal decomposition temperature is 28
At 0 ° C., the electric resistance was 1 × 10 ¹⁰ Ω · cm.

Example 1 8 parts by weight of the toner produced above and 92 parts by weight of a carrier were mixed to prepare a developer.

Example 2 As in Example 1, 8 parts by weight of toner and 92 parts by weight of carrier were used as a developer.

Example 3 As in Example 1, 8 parts by weight of toner and 92 parts by weight of carrier were used as a developer.

Comparative Example 1 8 parts by weight of toner and 92 parts by weight of carrier were used as a developer.

The developing agents of Examples 1 to 3 and Comparative Example 1 were treated with CF-
70 (manufactured by Minolta Camera Co., Ltd.)
5000 sheets were copied under N environment (25 ° C., 65%), printing durability was evaluated, and the results are shown in Table 1.

[0065]

[Table 1]

(Charge amount) According to a film charge measuring method (toner concentration 8% by weight)

(Fog on Image) As described above, images were printed by using the above copying machine in the combination of various toners and carriers. Regarding the fog on the image, the toner fog on the white background image was evaluated and ranked. It can be practically used in a rank or more, but is preferably in a rank or more.

(Environmental fluctuation of charging) Developer at 10 ° C., 15%
The amount of charge (Q _LL ) after storage for 24 hours in
Obtain the amount of charge (Q _HH ) after storing for 24 hours in an environment of 85 ° C and 85%, find the difference ΔQ; ΔQ = Q _LL -Q _HH (μC / g), and rank it as follows. , The environmental change of charging was evaluated.

X indicates that there is a large change in the environment and it is not practical. If it is Δ or more, it can be used practically, but ◯ or more is desirable.

(Texture on the image) Regarding the texture on the image,
The texture on the half image was evaluated and ranked. △
It is practically usable with a rank or higher, but ◯ or higher is desirable.

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

(Toner Scattering Amount) It was determined by the amount of toner drop when the film charge amount was measured.

Example 4 Toner prepared above (carbon black pH 3.0)
8 parts by weight and carrier (carbon black pH 3.0) 9
A developer was prepared by mixing 2 parts by weight.

Example 5 Toner (carbon black pH3.
0) 8 parts by weight and carrier (carbon black pH 3.0)
The developer was used in an amount of 92 parts by weight.

Example 6 Toner (carbon black pH3.
0) 8 parts by weight and carrier (carbon black pH 6.0)
The developer was used in an amount of 92 parts by weight.

Comparative Example 2 8 parts by weight of toner (carbon black pH 8.4) and 92 parts by weight of carrier (carbon black pH 3.0) were used as a developer.

The developers of Examples 4 to 6 and Comparative Example 2 were mixed with CF--
70 (manufactured by Minolta Camera Co., Ltd.), about the same items as in Example 1, 5,000 copies were made in an NN environment,
The printing durability was evaluated, and the results are shown in Table 2.

[0078]

[Table 2]

[0079]

The developer of the present invention is excellent in heat resistance, environment resistance and charge stability and is capable of forming an image having a texture without toner fog.

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Claims (2)

[Claims] 1. A carrier having a resin coating layer on the surface of carrier core particles and containing an inorganic oxide fine powder selected from silica, titania, alumina, zinc oxide or tin oxide in the outermost shell coating layer, and the carrier. A developer comprising a toner containing substantially the same inorganic oxide fine powder as the inorganic oxide fine powder contained in. 2. A carrier having a resin coating layer on the surface of carrier core particles and containing carbon black in the outermost shell coating layer, and carbon black and p contained in the carrier.
A developer comprising a toner containing carbon black having a difference of H of 3 or less.