JP2002244335A - Electrophotographic developer and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developer excellent in low temperature fixability, to further provide a developer capable of giving an image having high image density, excellent in thin line reproducibility and gradation and free from surface stain, capable of ensuring high image density with low consumption and free of a change of performance due to environmental variation and long-time use and even in use in a toner recycling system and to provide an image forming method. SOLUTION: In the developer having a carrier and a toner containing at least resin particles containing a bonding resin and a colorant and a fluidity imparting agent, (a) the particle size distribution of the toner has 30-70 number % content of toner particles of 2.0 to <4.0 μm particle diameter and <=60 number % content of toner of 4.0-8.0 μm particle diameter, (b) the acid value of the toner is >=10.0 and (c) the quantity of electric charges of the developer is <=-30 μC/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a developer for visualizing a latent electrostatic image in an image forming method such as electrophotography and electrostatic recording, and to an image forming method.

[0002]

2. Description of the Related Art In a heat fixing method, toner must be melted at a temperature as low as possible and fixed on a medium such as paper.
In recent years, there has been an increasing demand for low-temperature fixability of toner, particularly from the viewpoint of energy saving. It is effective to use a binder resin containing a polyester resin in the toner as a means for satisfying such a requirement of low-temperature fixability. To achieve low-temperature fixability, toner and transfer material (paper, O
HP and the like). Improving the adhesion to paper can be easily achieved by increasing the number of carboxylic acid groups in the toner component. On the other hand, as the versatility of the copier increases, the copier is often installed under severe conditions such as high temperature and high humidity or low temperature and low humidity, and even under such severe conditions, even in a normal environment. It is indispensable to obtain a clear image similar to the above. Although the toner has electrical characteristics such as a preferable charge amount or insulation resistance under normal conditions, the toner may significantly fluctuate under high-temperature high-humidity or low-temperature low-humidity conditions, resulting in image deterioration. Not a few. For example, under low temperature and low humidity, the image density decreases, and under high temperature and high humidity, the image density increases. When the image density is remarkable, a phenomenon occurs in which almost all of the solid black portions become white.
Polyester resins having a hydrophilic carboxyl group or hydroxyl group at the polymer terminal may be susceptible to the above-described environment if their concentration, that is, the acid value or the hydroxyl value is too high. Accordingly, there is a demand for a toner which has a sufficient low-temperature fixing property and can obtain a clear image which is completely the same as ordinary environmental conditions under any environment.

[0003]

An object of the present invention is to provide a developer having excellent low-temperature fixability. In addition, high image density, excellent fine line reproducibility, excellent tonality, images without background contamination can be obtained, high image density can be obtained with low consumption, and performance can be obtained even in environmental fluctuations and long-term use. It is an object of the present invention to provide a developer and an image forming method which are not changed and whose performance is not changed even when the toner recycling system is used.

[0004]

Means for Solving the Problems The above problems are as follows:
It is solved by the invention of 5). 1) In a toner containing at least resin particles containing a binder resin and a colorant and a fluidity-imparting agent, and in a developer having a carrier, (a) the particle size distribution of the toner is as follows. 0.0 μm
The content of toner particles having a particle size of less than 30 to 70% by number and the content of toner particles having a particle size of 4.0 to 8.0 μm being 60% by number
(B) the toner has an acid value of 10.0 or more, and (c) the developer has a charge amount of −30 μC / g or more.
A developer, characterized in that: 2) The developer according to 1), wherein the toner has a weight average particle size of 7 μm or less. 3) The binder resin is a polyester resin and / or a styrene-acryl resin, and the acid value of the toner is 2
The developer according to 1) or 2), which is 0.0 or more. 4) The developer according to any one of 1) to 3), wherein the charge amount of the developer is −40 μC / g or more. 5) The latent image formed on the latent image holding member is developed with toner of a developing unit to form a toner image, and the formed toner image is transferred from the latent image holding member to a transfer material by a transfer unit applying a bias, An image forming method comprising: cleaning a latent image holding member after a toner image is transferred, collecting toner on the latent image holding member, supplying the collected toner to the developing unit, and reusing the toner in a developing step. An image forming method using the developer according to any one of 1) to 4).

Hereinafter, the present invention will be described in detail. Table 1 shows specific examples of the polyester resin used as the binder resin in the present invention. Table 2 shows the physical properties of these polyester resins.

[Table 1]

[Table 2] In the table, the weight ratio between (R-1) and (R-4) is 1: 1.

First, regarding the acid value of the toner of the present invention,
It is required to be 0.0 or more. This was determined from the following experiment. {Acid value measurement} The acid value was measured by the acid value measurement method of JIS K-0070. The numerical values in Table 2 are mg of potassium hydroxide required to neutralize 1 g of the resin. {Measurement of Molecular Weight Distribution} The number average molecular weight Mn of the toner is G
PC (gel permeation chromat
(Ography) under the following conditions.・ Apparatus: GPC-150C (manufactured by Waters) ・ Column: KF801 to 807 (manufactured by Shodex) ・ Temperature: 40 ° C. ・ Solvent: THF (tetrahydrofuran) ・ Flow rate: 1.0 ml / min ・ Sample: concentration: 0.05 ０．６0.6% by weight of the sample
From the molecular weight distribution of the toner resin measured under the above conditions, the number average molecular weight Mn of the toner was calculated using a molecular weight calibration curve prepared from a monodisperse polystyrene standard sample.

<Preparation of Toner A> 100 parts of polyester resin R-2 3 parts of carnauba wax (melting point 82 ° C., acid value 2) 3 parts of carbon black (# 44: manufactured by Mitsubishi Kasei Co., Ltd.) 8 parts 2 parts of a zirconium compound

Embedded image (In the formula, L1 represents 3,5-di-t-butylsalicylic acid.) The mixture having the above composition was sufficiently stirred and mixed in a Henschel mixer, and heated at a temperature of 130 to 140 ° C. for about 30 minutes using a roll mill. After melting, it was cooled to room temperature. The obtained kneaded material is pulverized and classified by a jet mill, and has a volume average particle size of 9.
A 6 μm toner was obtained. 0.5 parts by weight of an additive (R972 manufactured by Nippon Aerosil Co., Ltd.) was added to 100 parts by weight of the toner, and the mixture was stirred and mixed by a Henschel mixer, and then passed through a mesh to remove particles having a large particle diameter, thereby obtaining a final toner. .

<Preparation of Toner B> 100 parts of polyester resin R-1 + R-4 (weight ratio of R-1 to R-4 is 1: 1) 100 parts Carnauba wax (melting point 82 ° C., acid value 2) 3 parts 8 parts of carbon black (# 44: manufactured by Mitsubishi Kasei Co., Ltd.) 2 parts of the zirconium-based compound of the above [Chemical Formula 1] The mixture of the above composition is sufficiently stirred and mixed in a Henschel mixer, and at a temperature of 130 to 140 ° C. using a roll mill. After heating and melting for about 30 minutes, it was cooled to room temperature. The obtained kneaded material is pulverized and classified by a jet mill, and has a volume average particle size of 9.
4 μm toner was obtained. 0.5 parts by weight of an additive (R972 manufactured by Nippon Aerosil Co., Ltd.) was added to 100 parts by weight of the toner, and the mixture was stirred and mixed by a Henschel mixer, and then passed through a mesh to remove particles having a large particle diameter, thereby obtaining a final toner. .

<Preparation of Toner C> 100 parts of polyester resin R-3 3 parts of carnauba wax (melting point 82 ° C., acid value 2) 3 parts of carbon black (# 44: manufactured by Mitsubishi Kasei Co., Ltd.) 8 parts 2 parts of the zirconium-based compound of the above) was sufficiently mixed by stirring in a Henschel mixer, heated and melted at a temperature of 130 to 140 ° C. for about 30 minutes using a roll mill, and then cooled to room temperature. The obtained kneaded material is pulverized and classified by a jet mill, and has a volume average particle size of 9.
A 5 μm toner was obtained. 0.5 parts by weight of an additive (R972 manufactured by Nippon Aerosil Co., Ltd.) was added to 100 parts by weight of the toner, and the mixture was stirred and mixed by a Henschel mixer, and then passed through a mesh to remove particles having a large particle diameter, thereby obtaining a final toner. .

[0010] Fixability was evaluated using toners A to C having different acid values. Table 3 shows the evaluation results.

[Table 3] The results in Table 3 show that the correlation between the acid value of the toner and the fixability is high. That is, it was found that when the acid value of the toner was increased, not only the low-temperature fixing property (cold offset resistance) but also the hot offset resistance were improved. It is considered that the effect of improving the low-temperature fixability is based on the adhesion between the carboxyl group derived from the acid value of the toner and the paper component. In the present invention, since excellent low-temperature fixability of the toner is required, good adhesion to paper is required. In order to maintain good adhesion to paper, the acid value of the toner must be 10.0 or more, and preferably 20.0 or more. If the acid value of the toner is 20.0 or more, low-temperature fixing can be sufficiently performed even with a high-speed machine (linear speed: 160 mm / sec or more). However, the acid value is 50.0
If it exceeds, the adsorbability with moisture in the environment will increase, and the environmental dependence of triboelectricity will increase,
As a result, the image quality becomes unstable, which is not preferable.

<Evaluation of Fixing Property> Ricoh type 6200 paper was manufactured by using a device in which the fixing unit of a copier Imagio MF-4570 manufactured by Ricoh Co., Ltd. was modified using a Teflon (registered trademark) roller as a fixing roller. Was set and a copying test was performed. The fixing roller has a thickness of 2.5 mm and a roller load / contact area of 2.5 × 10 ⁵ Pa on the side in contact with the toner image supporting surface. Is 1.2 × 1
Used was a 0 ⁵ Pa. By changing the fixing temperature, the low-temperature fixing property and the hot offset occurrence temperature were determined. The evaluation conditions for the low-temperature fixability are as follows: linear velocity of paper feed: 140 to 150 mm / s
The evaluation conditions of ec and hot offset were set to a linear speed of paper feeding of 50 mm / sec. First, a copy image having an image density of 1.2 by a Macbeth densitometer was obtained. The low-temperature fixability was evaluated by rubbing the copy image at each temperature with a clock meter equipped with an eraser 10 times, measuring the image density before and after the rubbing, and calculating the fixation rate (%) by the following formula.

## EQU1 ## Fixing rate = (image density after 10 times of sand eraser / previous image density) × 100 Assuming that a temperature at which a fixing rate of 70% or more is attained is a fixing lower limit temperature, the fixing lower limit temperature of the conventional toner is 150 to 170. Table 3 shows the toners A to C evaluated on the basis of the following criteria, while the temperature was on the order of ° C. The hot offset was evaluated based on the following criteria by setting the OK level at which no paper was wound around the fixing roller when the fixing temperature was increased.

Evaluation criteria for low-temperature fixability and hot offset were evaluated in the following five steps. (Low-temperature fixability) good ：: less than 125 ° C .: 125-135 ° C. □: 135-145 ° C. Δ: 145-155 ° C. bad X: 155 ° C. or more (hot offset) Good ：: 220 ° C. or more ○: Less than 220 ° C to 200 ° C or more □: Less than 200 ° C to 180 ° C or more △: Less than 180 ° C to 170 ° C or more Poor ×: Less than 170 ° C Insufficient stability in environmental changes such as humidity was observed in the following experiments.

Preparation method of carrier coating liquid a 600 parts of dimethyl silicone resin S of the following [Chemical formula 2] (toluene solution having a solid content of 20%) 600 parts of toluene γ- (2-aminoethyl) aminopropyltrimethoxy Silane 8.2 parts SH6020 (manufactured by Dow Corning Toray Silicone Co., Ltd.) Carbon black, BP-2000 (Cabot) 10.2 parts

Embedded image The above material was sufficiently dispersed with a homomixer to obtain a carrier coating liquid a.

Preparation of Carrier a ・ Ferrite carrier core material (F-300) 5000 parts ・ Carrier coating liquid a 1220 parts ・ Tin catalyst T (toluene solution containing the following tin compound at 10%) 16.8 parts (C₃H₇)₂Sn (OCOCH₃)₂  Charge the above core material on the rotating bottom plate disk in the fluidized bed,
The rotary bottom plate disk was rotated at 150 revolutions per minute,
A swirling flow of the core material was formed. After this swirling flow has stabilized,
The above coating solution (coating solution a + tin catalyst T) is swirled in a fluidized bed.
Sprayed towards the convection. The co obtained in this way
2 hours in an electric furnace (set at 300 ° C)
For a specific gravity of 5.0 and a weight average particle size of 55 μm.
Rear a was obtained.

Preparation of Carrier b Carrier a except that the temperature of the electric furnace was set to 280 ° C.
The carrier b having a true specific gravity of 5.0 and a weight average particle size of 54 μm was obtained in exactly the same manner as in the preparation of the above.

Preparation of Carrier c Carrier a except that the temperature of the electric furnace was set at 250 ° C.
The carrier c having a true specific gravity of 5.0 and a weight average particle size of 52 μm was obtained in exactly the same manner as in the preparation of Example 1.

Next, the toner C, which exhibited excellent fixability in the object of the present invention, and various carriers were combined to obtain a triboelectric charge (Q / Mstd.) And an image density (ID) under each environment. ) And background stains were evaluated. As the experimental device for evaluation, the same modified Imagio MF-4570 as described above was used. Table 4 shows the experimental results. From the results of Experiments 1 to 3 shown in Table 4, it can be seen that the triboelectric charging property of the toner C is very environment-dependent. For example, in Experiment 1 in combination with carrier a, Q / Mstd. Is large, and the background dirt is broken below the standard. However, from the results of Experiments 2 and 3, it was found that by setting the triboelectric charge amount of the developer higher than usual, the background stain in a high-temperature and high-humidity environment was improved. That is, by setting the triboelectric charge of the developer in a normal environment (normal temperature and normal humidity) as extremely high as −30 μC / g or more, even if the triboelectric charge of the developer decreases in a high-temperature and high-humidity environment, the center Since the amount of triboelectric charge is sufficiently high, it can be said that a slight decrease does not result in an abnormal increase in image density or deterioration of background stain. Further, the more preferable triboelectric charge of the developer of the present invention is -40 μC / g or more. However, in a low-temperature and low-humidity environment, it is rather disadvantageous to set the triboelectric charge of the developer to be high, and in a low-temperature and low-humidity environment, the triboelectric charge of the developer generally sharply increases. It can be seen from Table 4 that the temperature decreases.

[0018]

[Table 4] In the table, high temperature and high humidity are 32 ° C. and 88% Rh, normal temperature and normal humidity are 23 ° C. and 60% Rh, and low temperature and low humidity are 10 ° C. and 20% Rh. Standard of image density (ID): 1.35 or more Standard: 3.5 or higher

{Measurement of triboelectric charge amount} The measurement method will be described with reference to the drawings. FIG. 1 is an explanatory diagram of an apparatus for measuring the charge amount of toner. First, about 3 g of a developer whose frictional charge is to be measured is put into a metal measuring container 12 having a 635-mesh screen 13 at the bottom, and a metal lid 14 is closed. At this time, the weight of the entire measurement container is weighed and defined as W ₁ (g). Next, suction is performed through the suction port 17 by the suction device 11 (at least a portion in contact with the measurement container 12 is an insulator) (the air flow control valve 16 is adjusted to adjust the pressure of the vacuum gauge 15 to 250 mmA).
g). In this state, suction is performed for 0.5 minutes or more, preferably for 1 minute to remove the toner by suction. The potential of the electrometer 19 at this time is set to V (volt). Here, reference numeral 18 denotes a capacitor having a capacity of C (μF). Next, the weight of the whole measuring container after suction is measured and defined as W ₂ (g). The triboelectric charge [Q / M (μC / g)] of this toner is calculated by the following equation.

[Number 2] triboelectric charge of toner _{= (C × V) / (} W 1 -W 2) Next, the _W 3 weighed after wiping off the dirt of the entire measurement container Toner (g). The toner concentration (TC) of this developer is calculated by the following equation.

TC = [(W ₁ −W ₃ ) / W ₁ ] × 100 (%) The triboelectric charge of the developer [Q / Mstd. (Μ
C / g)] is calculated by the following equation.

## EQU4 ## Q / Mstd. = (Q / M) × (TC) / (T
Cstd. )

(Equation 5) In the formula, ρc: true specific gravity of carrier (g / cm ³ ) ρt: true specific gravity of toner (g / cm ³ ) Dc: weight average particle size of carrier (μm) Dt: weight average particle size of toner (μm)

Next, the present inventors have studied a configuration in which even if the amount of triboelectric charge of the developer sharply increases, there is a margin for lowering the image density. As a result, the following experiment has revealed that the image density and the particle size distribution of the toner have a very high correlation. Here, the toners D and E were prepared by changing the pulverization and classification conditions for the toner C. Table 5 summarizes the particle size distribution of each toner.

[Table 5]

{Measurement of Toner Particle Size Distribution} The toner particle size distribution can be measured by various methods. In the present invention, the measurement was performed using a Coulter counter. That is, using a Coulter Counter TA-II type (manufactured by Coulter) as a measuring device, an interface (manufactured by Nikkaki) for outputting a number distribution and a volume distribution, and a CX-1 personal computer (manufactured by Canon Inc.) were connected. . As an electrolytic solution, an approximately 1% NaCl aqueous solution was prepared using primary sodium chloride. Examples of the electrolytic solution described above include, for example, ISOTONR-
II (manufactured by Coulter Scientific Japan) can be used. The measuring method is as follows:
0.1 to 5 ml of a surfactant (sodium alkylbenzenesulfonate) was added as a dispersant to each ml, and 2 to 20 mg of a measurement sample was further added. The electrolytic solution in which the measurement sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and 100 μm was measured using the Coulter Counter TA-II.
The volume and number of the toner were measured using an aperture, and the volume distribution and the number distribution of the particles having a particle size of 2 to 40 μm were calculated. Then, the number-based fine powder (particle size: 2.0
To less than 4.0 μm, and 4.0 to 8.0 μm).

The toners D and E were combined with various carriers to set a high triboelectric charge at room temperature and normal humidity (combinations in Table 6). As an experimental machine for evaluation, the same Imageio as described above was used.
An MF-4570 modified machine was used. Table 6 shows the experimental results.

[Table 6] In the table, high temperature and high humidity are 32 ° C. and 88% Rh, normal temperature and normal humidity are 23 ° C. and 60% Rh, and low temperature and low humidity are 10 ° C. and 20% Rh. Standard of image density (ID): 1.35 or more Standard: 3.5 or more According to the results in Table 6, the same level of Q / Mstd. This indicates that the larger the number of particles having a particle diameter of 2.0 to less than 4.0 μm, the easier the image density is to be obtained. The reason will be described with reference to FIG. FIG. 2 shows that even when the development amount is the same level, if the particle size distribution of the toner is different, the image density will be different. Specifically, the particle size is 2.0 to
As the number of particles having a particle size of less than 4.0 μm increases, the image density tends to be easily obtained even when the development amount is the same. Table 6 and FIG.
From the results, it is found that the content of toner particles having a particle diameter of 2.0 to less than 4.0 μm is necessary to always obtain a sufficient image density even under a low-temperature and low-humidity environment while the triboelectric charge amount of the developer is -30 μC / g or more. Is required to be 30% by number or more. From another viewpoint, it is considered that the average particle diameter of the toner needs to be 7 μm or less. However, if it exceeds 70% by number, the amount of fine powder becomes too large, and it becomes impossible to provide an appropriate amount of triboelectric charge to individual toner particles, so that an image having a lot of background stains tends to be formed. Therefore, the particle size of the present invention is 2.0 to 4.
By combining a toner having a toner particle content of less than 0 μm and a content of 30 number% or more, the triboelectric charge amount of the developer is −70 μm.
It was confirmed that a sufficient image density could be obtained within the range of C / g.

Next, Image MF used for evaluation
-4570 was improved as follows. That is, in order to cope with the toner of the present invention having excellent low-temperature fixability, the control temperature of the fixing machine was set to be lower by 20 ° C. than usual. Under these conditions, a paper passing test of 300,000 sheets was performed for the combination of Experiment 5 to evaluate the quality at the time of toner recycling. As a result, even after paper passing, both the fixing property and the image quality (image density, background stain) maintained excellent quality as in the initial stage. As shown in Tables 7 to 9, the stability of the fixability and the image quality over time is small because the variation in the particle size distribution of the toner is small (the variation is small because the content of the original fine powder is large). )

[0024]

[Table 7]

[Table 8]

[Table 9]

[0025]

According to the present invention, a developer having excellent low-temperature fixability can be provided. Also, the image density is high,
Excellent in fine line reproducibility and gradation, it is possible to obtain an image without background stain, high image density can be obtained with little consumption, and there is no change in performance even with environmental fluctuations and long-term use, and a toner recycling system It is possible to provide a developer and an image forming method that do not change in performance during use.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an apparatus for measuring a charge amount of a toner.

FIG. 2 is a diagram illustrating a relationship between a development amount and an image density for toners C, D, and E;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Suction machine 12 Measurement container 13 Screen 14 Metal lid 15 Vacuum gauge 16 Air volume control valve 17 Suction port 18 Condenser 19 Electrometer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/00 326 (72) Inventor Fumihiro Sasaki 1-3-6 Nakamagome, Ota-ku, Tokyo RICOH Company, Limited (72) Inventor Yasutaka Iwamoto 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Naoto Shimada 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Hiroshi Nakai 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Hiroto Higuchi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Zhu ICE Ricoh Co., Ltd. 1-3-6 Nakamagome, Ota-ku, Tokyo (72) Inventor Maiko Kondo Rico Co., Ltd. 1-3-6 Nakamagome, Ota-ku, Tokyo The internal F-term (reference) 2H005 AA01 CA04 CA08 EA01 EA05 EA10 2H077 AA37 AC16 AD06 DB14 EA03 GA02 GA03 2H134 GA01 GB02 JA11 KG07 KH11

Claims (5)

[Claims] In a toner having at least resin particles containing a binder resin and a colorant and a fluidity-imparting agent, and a developer having a carrier, (a) the particle size distribution of the toner is as follows. The content of toner particles having a particle size of 0 to less than 4.0 μm is 30 to 70% by number, the content of toner particles having a particle size of 4.0 to 8.0 μm is 60% or less, and (b) the acid value of the toner. Is not less than 10.0, and (c) the charge amount of the developer is not less than −30 μC / g. 2. The developer according to claim 1, wherein the toner has a weight average particle diameter of 7 μm or less. 3. The method according to claim 1, wherein the binder resin is a polyester resin and / or
Or a styrene-acrylic resin, and the toner has an acid value of 20.0 or more.
Or the developer according to 2. 4. The developer according to claim 1, wherein the charge amount of the developer is −40 μC / g or more. 5. A latent image formed on the latent image holding member is developed with a toner of a developing unit to form a toner image, and the formed toner image is transferred from the latent image holding member to a transfer material by a transfer unit to which a bias is applied. An image forming method in which the latent image holding member after the transfer and transfer of the toner image is cleaned to collect the toner on the latent image holding member, and the collected toner is supplied to the developing unit and reused in a developing process An image forming method using the developer according to claim 1.