JPH08314182A - Toner for forming electrophotographic image and electrophotographic image forming method - Google Patents

Abstract

PURPOSE: To provide a toner capable of ensuring a stable quantity of electric charges over a long period of time in an image forming method by which devel opment is carried out with a developer layer kept in noncontact with a photoreceptor and capable of maintaining stable electrostatic chargeability independently of an environmental change and to provide an electrophotographic image forming method. CONSTITUTION: In this toner obtd. by adding at least fine resin particle and inorg. fine particles to colored particles consisting essentially of a resin and a colorant, the fine resin particles are made of a melamine-formaldehyde condensation polymer and have 0.01-1.0μm vol. average particle diameter and the inorg. fine particles have 0.01-0.20μm vol. average particle diameter. The standard deviation of the vol. average particle diameter distribution of the inorg. fine particles is 10-30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming toner and an electrophotographic image forming method, and more particularly to an electrophotographic image forming toner and an electrophotographic image forming method which provide excellent images.

[0002]

2. Description of the Related Art Conventionally, as a technique for forming a good multi-color development without color misregistration by using a compact and low-cost multi-color image forming apparatus, the surface of an image forming body uniformly charged. Is subjected to spot exposure with a laser beam or the like to form an electrostatic latent image, and the electrostatic latent image of the image forming body is repeatedly developed in a non-contact manner with a two-component developer containing color toner, A method is known in which a plurality of color toner images of different colors are superposed on an image forming body, and then the plurality of color toner images are collectively transferred and fixed to form a multicolor image. .

However, the technique for forming a multicolor image as described above has the following problems. That is,
In order to form a multicolor image by developing a plurality of images on the surface of the photoreceptor, it is necessary to develop in a non-contact state. In this non-contact developing method, since it is necessary to widen the gap between the photoconductor and the surface of the developer carrying member in the developing section, there is a problem that a minute change in the charge amount has a great influence on the development. There is.
The change in the charge amount also changes the amount of the developing toner that is governed by the change in the amount of the charge, and the ratio of the amount of the developing toner in each of the plurality of color toner images to be superimposed changes with time. As a result, the color tone of the formed multicolor image changes with time.

Therefore, it is necessary to maintain the toner charge amount of each color within a certain range, and conventionally, addition of inorganic fine particles and resin fine particles has been proposed for the purpose of stabilizing the charge amount.

However, in a system in which only inorganic fine particles are added, under high temperature and high humidity, the charge amount is apt to decrease when left as it is due to the leakage of charges due to the adsorption of water to the toner, and the image density increases. However, contamination of the machine occurs due to toner scattering. In addition, in a system in which only resin fine particles are added, although the charge retention of the resin fine particles is high, it is possible to prevent a decrease in the charge amount under high temperature and high humidity, but on the contrary, it causes excessive charging under low temperature and low humidity, and In the durability test, there arises a problem that the charge amount increases.

Further, even in a system in which resin fine particles and inorganic fine particles are used in combination, when the resin fine particles described in Japanese Patent Publication No. 2-60179 are used, the stability of the charge amount is surely secured to some extent. Since the absolute value difference between the charge amounts under high temperature and high humidity and under low temperature and low humidity becomes large, the image density does not change stably with environmental changes.

When inorganic fine particles having a sharp particle size distribution are used, the inorganic fine particles are apt to be embedded in the toner in the non-contact development system, and particularly, 3
If a material having a sharp particle size distribution in a region of 0 nm or less is used, the amount of charge is greatly reduced due to this embedding phenomenon. Further, if a toner having a sharp particle size distribution in a region of 100 nm or more is used, it becomes difficult to adhere to the surface of the colored particles, so that a uniform toner cannot be obtained and the charge amount cannot be stabilized.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a stable charge amount over a long period of time in an image forming method of developing a developer layer in a non-contact state with a photoreceptor. Another object of the present invention is to propose an electrophotographic image forming toner and an electrophotographic image forming method capable of maintaining stable chargeability even under environmental changes.

Further, in the present invention, a plurality of color toner images of different colors are superposed on the photoconductor by repeatedly developing the electrostatic latent image formed on the photoconductor in a non-contact state. When applied to a multicolor image forming method in which a plurality of color toner images that are formed by overlapping are transferred together, they have stable triboelectrification ability that is not affected by the environment for a long period of time and always have good characteristics. It is to provide a developer capable of exhibiting the above.

[0010]

In order to achieve the above-mentioned problems, the present inventor has made various investigations, and as a result, has solved the problems as follows.

1) In a toner for electrophotographic image formation, wherein at least resin fine particles and inorganic fine particles are added to colored particles comprising at least a resin and a colorant, the resin fine particles have a volume average particle diameter of 0.01 to 1.0 μm melamine
Resin fine particles composed of formaldehyde condensation polymer,
The volume average particle size of the inorganic fine particles is 0.01 to 0.20 μm, and the standard deviation (σ) of the volume average particle size distribution is 10 ≦.
An electrophotographic image forming toner characterized by being inorganic fine particles having σ ≦ 30.

2) A developer layer containing the electrophotographic image forming toner described in 1 above, which is formed on the surface of a developer bearing member, is conveyed to develop the electrostatic latent image formed on the surface of the photosensitive member. And an electrophotographic image forming method.

3) The developer layer having at least the electrophotographic image forming toner described in the above 1 formed on the surface of the developer carrying member is conveyed in a state where the developer layer is thinner than the gap between the surface of the photoreceptor and the developer carrying member. 3. The electrophotographic image forming method as described in 2 above.

The present invention will be described in more detail. The electrophotographic image forming toner (hereinafter, also simply referred to as a toner) used in the present invention is used in combination with specific resin fine particles and inorganic fine particles having a specific particle diameter to prevent a decrease in charge amount under high temperature and high humidity. At the same time, it is possible to prevent the increase of the charge amount under low temperature and low humidity, so that the stability of the charge amount in the environment can be obtained.

By using the melamine-formaldehyde condensate of the present invention as the resin fine particles, it is possible to prevent excessive charging under low temperature and low humidity while maintaining the charge retention performance peculiar to organic substances, so that a stable charge amount can be obtained regardless of the environment. can get.

The volume average particle diameter of the resin fine particles in the present invention is 0.01 to 1.00 μm, preferably 0.0.
It is 5 to 0.50 μm. Volume average particle size is 0.01 μm
If it is smaller than the above range, the toner tends to be buried in the toner, so that the long-term stability of the charging property cannot be maintained. On the other hand, when the volume average particle diameter is larger than 1.0 μm, the toner does not uniformly adhere to the toner, so that the charge amount distribution is widened and an image defect such as toner scattering occurs. The addition amount is 0.1 to 5.0% by weight.
Is preferable, and 1.0 to 3.5% by weight is preferable. If the addition amount is small, the charge amount will drop under high temperature and high humidity,
When the added amount is large, the charge amount increases under low temperature and low humidity.

By using the inorganic fine particles having a specific particle size distribution, it is possible to prevent the external additive from being buried, so that stable chargeability can be obtained. As a result of various studies by the present inventor, it was found that the volume particle size distribution of the inorganic fine particles to be added is largely due to the stabilization of the charge amount. When the inorganic fine particles of the present invention are used, the inorganic fine particles on the small particle size side are superior in the fluidity imparting effect and the burial resistance of the inorganic fine particles on the large particle size side, and the stress received by the inorganic fine particles on the small particle size side. Has a relaxing effect. Therefore, the time until burial is significantly increased, and the charge amount is stable over a long period of time.

In the present invention, the inorganic fine particles are preferably composed of a single type of inorganic fine particles. In the present invention, since the inorganic fine particles have a wide distribution compared with the case where they are used in combination, the inorganic fine particles on the large particle size side are buried, and the inorganic fine particles on the small particle size side contribute to the charging property. This is because the amount of charge applied to the toner does not change much even if it starts. In this case, when different kinds of inorganic fine particles are used in order to widen the particle size distribution, the change of the charging property due to the burying of the inorganic fine particles due to the embedding phenomenon becomes excessive and the object of the present invention cannot be achieved. .

In the present invention, the volume average particle diameter of the inorganic fine particles is 0.01 to 0.20 μm, but 0.03 to 0.
15 μm is more preferable. Volume average particle size is 0.01 μm
If it is smaller, the toner tends to be buried in the toner, so that the long-term stability of the charging property cannot be maintained. On the other hand, if the volume average particle diameter is larger than 0.20 μm, the particles are not evenly attached to the toner, so that the charge amount distribution is widened and an image defect such as toner scattering occurs. Furthermore, the addition amount is 0.1 to 5.0% by weight.
Is preferable, and 2.0 to 3.5% by weight is preferable. When the addition amount is small, the burying of the external additive progresses rapidly, so that the charge amount decreases, and when the addition amount is large, the charge amount decreases remarkably under high temperature and high humidity.

In the volume particle size distribution of the inorganic fine particles, the standard deviation (hereinafter referred to as σ) is 10 to 30, preferably 10 to 25. When the standard deviation is smaller than 10, the particle size distribution becomes sharp, and the embedding of the external additive easily proceeds in the region where the particle size is small (100 nm or less). Although the burial is alleviated in the region where the particle size is large (100 nm or more), a large amount must be added to obtain the fluidity imparting effect and the burial suppressing effect. Occurs, the distribution of the amount of charge spreads, and image defects such as toner scattering occur. On the contrary, when the standard deviation is larger than 30, the volume particle size distribution of the inorganic fine particles becomes too wide, so that the charge amount distribution is widened and an image defect such as toner scattering occurs.

The addition weight ratio (A / B) of the resin fine particles (A) and the inorganic fine particles (B) is preferably 0.2 to 2.0.
If it is less than 0.2, the effect of the inorganic fine particles is increased, and the charge amount is reduced under high temperature and high humidity. If it is larger than 2.0, the effect of the resin fine particles becomes large, and the charge amount is increased under low temperature and low humidity.

Further, the resin fine particles and the inorganic fine particles of the present invention may be fixed to the toner surface. Since the transfer of the external additive does not occur by fixing the external additive to the toner, carrier contamination does not occur, the charge amount changes stably, and a stable image can be obtained for a long period of time.

Whether or not the external additive was adhered was determined by measuring the surface area of the toner by the BET specific surface area measuring method, and from this, the adhesion degree Fd was defined by the following equation.

Fd = [1- (fixed toner Sw-untreated toner Sw) / added external additive Sw)] × 100 Fd: fixing degree (%) fixed toner Sw: BET specific surface area (m ^{2 of} fixed toner)
/ G) Untreated toner Sw: BET specific surface area of untreated toner (m
² / g) Added external additive Sw: BET specific surface area of added external additive (m ² / g) The BET specific surface area is Flow manufactured by Shimadzu Corporation.
It is measured by the BET one-point method using sorb 2300.

As a method of fixing, Tg-20≤ (stirring / mixing temperature) ≤Tg + 2 for preventing the detachment of the external additive.
It is preferable to stir and mix the resin particles and the external additive under the condition of 0 and uniformly fix the external additive to the surface of the resin particles while applying mechanical impact force.

The Tg referred to here is the glass transition temperature of the toner or the binder resin. Glass transition temperature is DSC7
The measurement was performed using a differential scanning calorimeter (manufactured by Perkin Elmer). The measuring method is to elevate the temperature from 0 ° C to 200 ° C at 10 ° C / min, and then to 200 ° C at 10 ° C / min.
10 ℃ / mi after cooling from ℃ to 0 ℃ and erasing the previous history
The temperature was raised from 0 ° C. to 200 ° C. with n, the endothermic peak temperature of the second heat was determined, and it was defined as Tg. When there were a plurality of endothermic peaks, the temperature of the main endothermic peak was taken as Tg.

The Tg of the toner or binder resin is 40
~ 70 ° C is preferably used. If the temperature is lower than 40 ° C, the toner has poor storage stability and agglomerates. If it is higher than 70 ° C., it is not preferable from the viewpoint of fixability and productivity.

Specific devices for immobilization include Henschel mixer, Ledige mixer, TURBO SPHE
An RE mixer or the like can be used. Among them, the Henschel mixer can be preferably used from the viewpoints that the mixing processing of the external additive and the fixing processing can be performed by the same apparatus, and that the mixing and stirring are easy and the heating from the outside is easy.

As a mixing method at the time of the fixing treatment, it is desirable that the peripheral speed of the tip of the stirring blade is 5 to 50 m / s. It is desirable that the treatment is performed at 10 to 40 m / s. Further, it is preferable to carry out pre-mixing to uniformly attach the external additive to the surface of the resin particles, and as a method of controlling the temperature, it is preferable to adjust the temperature to the required temperature by using warm water or the like from the outside. The method of measuring the temperature is to measure the temperature of a portion where the toner is flowing while the toner is being stirred and mixed. Further, it is preferable to carry out cooling and crushing steps by circulating cold water after the fixing treatment.

In the present invention, it is possible to fix two or more kinds of fine particles at the same time or separately. Further, a fluidity imparting agent or the like may be added and mixed after the fixing treatment.

The constituent components and component examples of the present invention will be described below.

<< Toner >> Colored Particles The colored particles contain a binder resin, a colorant, and other additives used as necessary, and the average particle size thereof is usually a volume average particle size of 1 to 1. 30 μm, preferably 5-20 μm
m.

The binder resin constituting the colored particles is not particularly limited, and various conventionally known resins can be used. For example, styrene resin, acrylic resin, styrene / acrylic resin, polyester resin, etc. may be mentioned. The Tg (glass transition temperature) of these binder resins is preferably 40 to 70 ° C.

The colorant is not particularly limited, and various conventionally known materials can be used. For example, black toner uses carbon black, nigrosine dye, etc., yellow,
The pigments required for magenta and cyan toners are C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 1
5, C.I. I. Pigment Blue 15: 6, C.I. I. Pigment Blue 68, C.I. I. Pigment Red 48-
3, C.I. I. Pigment Red 122, C.I. I. Pigment Red 212, C.I. I. Pigment Red 57-
1, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 81, C.I. I. Pigment Yellow-154
Pigments such as can be preferably used.

Other additives include, for example, salicylic acid derivatives, charge control agents such as azo metal complexes, low molecular weight polyolefins, and fixability improving agents such as carnauba wax.

External Additive <Resin Fine Particles> The resin fine particles used in the present invention have a volume average particle diameter of 0.01 to 1.00 μm. This volume average particle diameter is one observed by a transmission electron microscope and measured by image analysis. The material forming the resin fine particles is a substantially spherical material composed of a condensation reaction product of melamine and formaldehyde.

The term “substantially spherical” means that the ratio of the major axis diameter to the minor axis diameter of the particles measured using an image analyzer is 0.8 or more.

<Inorganic Fine Particles> The inorganic fine particles used in the present invention have a volume average particle diameter of 0.01 to 0.20 μm. This volume average particle diameter is one observed by a transmission electron microscope and measured by image analysis. Further, the standard deviation (σ) was calculated from each measurement data according to the following formula.

Σ = [{Σ (χi−χ) ² } / n] ^2/1 χi: each sampling data value χ: volume average particle diameter n: sampling number Various inorganic oxides are used as a material for forming the inorganic fine particles. ,
Nitride and boride are preferably used. For example, silica, alumina, titania, zirconia, barium titanate, aluminum titanate, strontium titanate,
Magnesium titanate, zinc oxide, chromium oxide, cerium oxide, antimony oxide, tungsten oxide, tin oxide, tellurium oxide, manganese oxide, boron oxide, silicon carbide, boron carbide, titanium carbide, silicon nitride, titanium nitride, boron nitride, etc. can give. Further, the inorganic fine particles may be subjected to a hydrophobic treatment. When performing the hydrophobic treatment, it is preferable to perform the hydrophobic treatment with various silane coupling agents such as dimethylchlorosilane and hexamethyldisilazane, and further, higher fatty acid metal salts such as aluminum stearate, zinc stearate and calcium stearate. It is also preferably used to carry out a hydrophobic treatment.

<< Carrier >> The carrier may be any of iron powder, ferrite, magnetite, and resin-coated ones, but in view of uniformity of spikes and stress resistance, low magnetization, low specific gravity, and small particles are used. Diameter carriers are preferred.

Carrier Core As the carrier core (magnetic particles), magnetic particles having a specific gravity of 3 to 7 and a weight average diameter of 30 to 65 μm are used. For example, ferrite particles and magnetite particles falling within the above range can be preferably used.

Coating resin Fine particles of resin such as styrene resin, acrylic resin, styrene-acrylic resin, etc. can be used.

Coating Method The manufacturing method is not particularly limited, and spray coating, MEC coating and multilayer coating can be used.

<< Photoreceptor >> Generally used selenium-based photoreceptors, amorphous silicon photoreceptors, and OPC-based photoreceptors can be used.

<Development> As the developing method, a method in which the photoreceptor and the developer are developed in a non-contact manner is used. That is, 300 to 600 μm of the developer is provided on the developing sleeve by the layer regulating plate provided on the sleeve and the layer forming rod made of the magnetic rod or the non-magnetic rod.
The layer is regulated to a layer thickness of m and conveyed to the developing area. The gap between the developing sleeve and the photosensitive drum in the developing area is 0.4 to 1.0 mm, which is larger than the developer layer thickness, and is 8 KH during development.
By applying a developing bias superposed with an alternating electric field of z, 1.8 kvp-p, development is performed in a state where the developer does not come into contact with the photoconductor.

[0046]

【Example】

Example Production Example of Colored Particles 100 parts of polyester resin (Tg = 55.1 ° C.), 10 parts of carbon black and 3 parts of polypropylene were mixed,
Kneaded meat, crushed and classified to obtain powder having an average particle size of 8.5 μm,
This was designated as Colored Particle 1.

In the same manufacturing method, yellow particles (CI pigment yellow 17) as a coloring agent were used for coloring particles 2, and magenta pigment (CI pigment red 122) was used for coloring particles 3. Cyan pigment (C.I.
I. Pigment Blue 15: 3) was used as Colored Particle 4.

Example of Production of Inorganic Fine Particles Various particle sizes were obtained by changing the water content and temperature conditions for high-temperature hydrolysis in oxyhydrogen flame of silicon tetrachloride. Further, classification was performed as necessary to adjust the particle size. Hexamethyldisilazane was used for the hydrophobic treatment of the silica fine particles.

As the comparative inorganic fine particles, a mixture of two kinds of inorganic fine particles obtained by mixing equal amounts of titanium fine particles treated with dimethylchlorosilane and silica fine particles treated with hexamethyldisilazane was used as a comparative inorganic fine particle I (volume average particle diameter 70 nm σ = 19). Table 1 shows the volume average particle diameter, the standard deviation and the number of kinds of particles of the adjusted inorganic fine particles of the present invention and comparative inorganic fine particles.

[0050]

[Table 1]

Production Example of Resin Fine Particles Obtained by addition polymerization of melamine and formaldehyde,
Resin fine particles J to L of the present invention having different particle sizes were obtained by changing the reaction time and temperature.

Polymethylmethacrylate (MMA) fine particles (volume average particle size 100 nm) produced by emulsion polymerization were used as the comparative resin fine particles M to give comparative resin fine particles M. Table 2 shows the resin fine particles prepared.

[0053]

[Table 2]

Toner Production Example The toner of the present invention (Examples 1 to 12) was prepared by mixing the above-mentioned colored particles, resin fine particles and inorganic fine particles with a Henschel mixer (FM-10B) and varying the temperature and peripheral speed applied from the outside. And comparative toners (Comparative Examples 1 to 10) were obtained. Table 3 shows the details.

[0055]

[Table 3]

In Table 3, the immobilization conditions are as follows.

Immobilization condition 1: Stirring temperature Tg-30 ° C.
Stirring blade tip peripheral speed 40 m / s Immobilization condition 2: Agitation mixing temperature Tg-15 ° C Stirring blade tip peripheral speed 30 m / s Immobilization condition 3: Agitation mixing temperature Tg ° C Stirring blade tip peripheral speed 30 m / s Immobilization condition 4 : Stirring / mixing temperature Tg + 10 ° C. Stirring blade tip peripheral speed 20 m / s Carrier production example 60 g of copolymer fine particles of styrene / methyl methacrylate = 4/6, specific gravity 5.0, weight average diameter 45 μm, 100
1940 g of Cu-Zn ferrite particles having a saturation magnetization of 62 emu / g when an external magnetic field of 0 Oersted is applied
Is put into a high-speed agitation mixer and mixed at a product temperature of 30 ° C for 15 minutes, then the product temperature is set to 105 ° C and the mechanical impact force is set to 3
It was applied repeatedly for 0 minutes and cooled to prepare a carrier.

Preparation of Developer 558 g of the carrier obtained as described above and 42 g of each of the toners shown in Table 3 were mixed for 20 minutes using a V-type mixer to prepare a developer for an actual copying test. The sample numbers of the obtained developers correspond to the corresponding toner numbers. For example, the developer of Example 1 is a developer obtained from the toner of Example 1 of Table 3 as a toner.

<< Evaluation apparatus and conditions >> 9028 manufactured by Konica was used after being modified as follows.

Development conditions Photoconductor surface potential = -850V DC bias = -750V AC bias = 1.8kVp-pf = 8KHz Dsd = 500 .mu.m Pressing control force = 10 gf / mm Pressing control rod = SUS416 (magnetic stainless steel) /
Diameter 3 mm Developing sleeve = 20 mm Developer layer thickness = 150 μm << Evaluation items, method >> Using the above-prepared developer, the developer of the present invention, Examples 1 to 12 and Comparative developers, Comparative Examples 1 to 10 were prepared. A live-action test was conducted using a modified Konica 9028 machine.

As the test, a live-copy test of 20,000 sheets was conducted under the environment of 30 ° C./80% (H.H.) and 10 ° C./20% (LL). At that time, changes in charge amount and occurrence of image disturbance (character dust) were evaluated.

Further, the developer was allowed to stand for 48 hours in an environment of 30 ° C./80%, and the decrease in the charge amount at that time was measured.

Charge Amount The charge amount was measured using a blow-off type charge amount measuring device.

Reduction of charge amount after leaving Q1 is the charge amount before leaving, Q2 is the charge amount after leaving for 48 hours
Then, the ratio of Q2 / Q1 was calculated and classified into the following 4 ranks and judged.

◎; Q2 / Q1 ≧ 0.95 ○; 0.95> Q2 / Q1 ≧ 0.80 Δ; 0.80> Q2 / Q1 ≧ 0.60 ×; 0.60> Q2 / Q1 Image Distortion 200 μm A chart in which five lines each having a width of 200 μm and a length of 1 cm were arranged at intervals was copied, and the dust situation of the portion was observed both visually and with a microscope (500 times), and classified into the following four ranks and judged.

A: Dust around the line is not observed even with a microscope B: Dust is not visible by the visual observation, but dust is observed around the microscope C: Dust around the line is visually observed D: Distinction between lines is difficult Table 4 shows the evaluation results.

[0067]

[Table 4]

From Table 4, the developer of the present invention can obtain a stable charge amount over a long period of time, and can maintain a stable chargeability even under environmental changes, and give a good image. I understand.

[0069]

According to the present invention, a stable charge amount can be obtained over a long period in an image forming method of developing a developer layer in a non-contact state with a photoreceptor, and further, environmental fluctuations can be obtained. In this regard, an electrophotographic image forming toner and an electrophotographic image forming method capable of maintaining stable chargeability have been proposed.

Claims (3)

[Claims] 1. A toner for electrophotographic image formation, comprising at least resin fine particles and inorganic fine particles added to colored particles comprising at least a resin and a colorant, wherein the resin fine particles have a volume average particle diameter of 0.01 to Resin fine particles of 1.0 μm melamine-formaldehyde condensation polymer, the inorganic fine particles have a volume average particle diameter of 0.01 to 0.20 μm, and a standard deviation (σ) of the volume average particle diameter distribution is 10 ≤ σ
An electrophotographic image forming toner, characterized in that it is an inorganic fine particle having a particle size of ≦ 30. 2. The toner according to claim 1, which is formed on the surface of the developer carrying member.
A method of forming an electrophotographic image, which comprises transporting a developer layer containing the toner for forming an electrophotographic image, and developing the electrostatic latent image formed on the surface of the photoreceptor. 3. The developer having at least the toner for electrophotographic image formation according to claim 1, which is formed on the surface of the developer carrying member rather than the gap between the photosensitive member and the surface of the developer carrying member, is conveyed in a thin state. The electrophotographic image forming method according to claim 2, wherein: