JPH04308855A - Electrostatic image developer - Google Patents

Abstract

PURPOSE:To offer an electrostatic image developer which can prevent production of black stripes or black spots, reduction of picture density, and fogging, and also prevent image failure due to transfer of toner from a fixing roller. CONSTITUTION:The electrostatic image developer consists of color particles comprising at least a binder resin and a coloring agent and contains composite fine particles comprising inorg. fine particles fixed to the surface of resin fine particles. The resin which constitutes the composite fine particles has 30-120 deg.C glass transition point.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic image developer applied to, for example, electrophotography, electrostatic recording, electrostatic printing, and the like.

0002

BACKGROUND OF THE INVENTION For example, in electrostatic image developers for electrophotography, in order to improve triboelectric charging properties and cleaning properties, conventionally, in order to improve triboelectric charging properties and cleaning properties, an average particle diameter of 0.05 is used, which is smaller than binder resin particles.
A technique has been proposed in which a developer is constructed by adding and mixing composite fine particles, which are composed of inorganic fine particles fixed to the surface of resin particles of ~3.0 μm, with binder resin particles (Japanese Patent Application Laid-Open No. 1986-9).
(See Publication No. 1143).

0003

[Problem to be solved by the invention] However, JP-A-64-
In the developer of Publication No. 91143, when the glass transition point of the resin constituting the composite fine particles is low, the stress and heat generated during the cleaning process, especially in non-image areas, may cause the composite to develop on the photoreceptor during repeated image formation. The fine resin particles tend to stick together, making it impossible to obtain sufficient abrasiveness.On the contrary, the stuck composite fine particles become nuclei, to which toner constituents adhere, resulting in black streaks or black spots on the image. In addition, with two-component developers, as development is repeated, composite fine particle resin adheres to the carrier surface and contaminates the carrier, which gradually deteriorates the triboelectric charging properties of the toner, making it difficult to obtain images with stable image density over many cycles. There is a problem that it is difficult to form. On the other hand, it is known that the fixing roller used in thermal roller fixing has a more or less temperature distribution. In particular, the temperature at the edges tends to be lower than that at the center, which is particularly noticeable when images are repeatedly formed and in high-speed machines with high line speeds. In such a fixing method, if the resin constituting the composite fine particles has a high glass transition point,
This causes the following inconveniences. When toner particles with composite fine particles interposed therein are fixed at the edge of the fixing roller where the temperature has become low, the heat transmitted from the fixing roller is insulated by the composite fine particles, which inhibits the melting of toner particles especially near the transfer material, and prevents the composite particles from melting. The toner layer is discontinuous due to the interface of the fine particles, and the upper layer adheres to the fixing roller and is transferred to the transfer material when the fixing roller makes one revolution, resulting in a so-called cold offset, which tends to cause image defects.

The present invention was made based on the above-mentioned circumstances, and its objects are to prevent the occurrence of black lines and black spots, to prevent a decrease in image density and the occurrence of fog, and to prevent the formation of a fixing roller. An object of the present invention is to provide an electrostatic image developer that can prevent image defects caused by toner transfer from the toner.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the electrostatic image developer of the present invention has colored particles consisting of at least a binder resin and a colorant, and inorganic fine particles fixed to the surface of the resin fine particles. The electrostatic image developer containing the composite fine particles is characterized in that the resin constituting the composite fine particles has a glass transition point of 30 to 120°C.

[0006]

[Function] As a result of extensive research by the present inventors, by defining the glass transition point of the resin constituting the composite fine particles within a specific range as described above, it is possible to prevent the occurrence of black streaks and black spots, and improve image density. The present invention was completed based on the discovery that it is possible to prevent a decrease in image quality and the occurrence of fog, and to prevent the occurrence of image defects due to toner transfer from the fixing roller. That is, in the present invention, since the lower limit of the glass transition point of the resin constituting the composite fine particles is set to 30° C., there is no fear that the resin of the composite fine particles will stick to the photoreceptor. Therefore, no black streaks or black spots appear on the image. Also,
Even in a two-component developer, since adhesion of the resin of the composite fine particles to the carrier surface is prevented, the triboelectric charging properties of the toner are stabilized, and image density does not decrease and fogging does not occur. In addition, since the upper limit of the glass transition point of the resin constituting the composite fine particles is set at 120°C, the transfer of toner to the fixing roller during fixing of the toner image is prevented, and the image due to the transfer of toner from the fixing roller is prevented. No defects will occur.

The present invention will be explained in detail below. In the present invention, an electrostatic image developer is constructed using colored particles made of at least a binder resin and a colorant, and composite fine particles made of fine inorganic particles fixed to the surface of fine resin particles.
The resin constituting the composite fine particles has a glass transition point of 3.
Select one having a temperature of 0 to 120°C, preferably 40 to 100°C. The glass transition point of the resin of the resin fine particles constituting the composite fine particles was determined by heating 10 mg of a sample at a constant heating rate (10°C/mi) according to differential scanning calorimetry (DSC).
This is the value determined from the intersection of the baseline when heated at 100 nm and the slope of the endothermic peak.

[0008] When the glass transition point of the resin constituting the composite fine particles is lower than 30°C, when the developer is repeatedly stressed in the cleaning process, the resin constituting the composite fine particles adheres to the photoreceptor and generates electricity. Black streaks or black spots occur due to changes in the optical characteristics. Also, especially 2
In component-based developers, as the image forming process is repeated, the surface of the carrier gradually becomes contaminated by the resin from the resin particles that make up the composite particles, making it difficult to form images with stable image density over multiple cycles. Become. On the other hand, the glass transition point of the resin constituting the composite fine particles is 12
When the temperature exceeds 0° C., there is a problem that the toner is transferred to the fixing roller during fixing of the toner image, and this transferred toner is transferred from the fixing roller to the paper, resulting in image defects.

[0009] Furthermore, the softening point of the resin constituting the composite fine particles is set at 100% from the viewpoint of ease of manufacture and prevention of transfer to paper.
~200°C is preferred. That is, the softening point is 200
If the temperature is higher than 0.degree. C., it becomes difficult for inorganic fine particles to stick, and sufficient cleaning performance may not be obtained. Further, if the softening point is lower than 100° C., the molten composite fine particles act as nuclei and induce toner to adhere to the fixing roller, and may further transfer from the fixing roller to the paper, staining the paper. However, in the present invention, a 1 cm2 sample was heated at a heating rate of 6°C using a Koka type flow tester (manufactured by Shimadzu Corporation).
20k using a plunger while heating at /min.
Applying a load of g/cm2 and pushing out a nozzle with a diameter of 1 mm and a length of 1 mm, this draws a plunger drop-temperature curve (softening flow curve) of the flow tester, and determines the height of the S-curve. When h is h, the temperature corresponding to h/2 is defined as the softening point.

[0010] The fine resin particles constituting the composite fine particles preferably have an average particle size of 0.1 to 7 μm, particularly 0.2 to 5 μm, from the viewpoint of improving cleaning properties and stability of triboelectric charging properties. is preferred. Note that the average particle size of resin fine particles refers to the average particle size on a volume basis, and is a laser diffraction particle size distribution measuring device equipped with a wet dispersion machine "HELOS" (SYMPATE).
(manufactured by C) Co., Ltd.). However, before the measurement, several 10 mg of resin fine particles were dispersed in 50 ml of water together with a surfactant, and then an ultrasonic homogenizer (output 150 W) was used to prevent reaggregation due to heat generation.
A pretreatment of dispersion for 10 minutes was performed.

[0011] As the resin material constituting the composite fine particles,
As mentioned above, various resins can be used without particular limitation as long as the glass transition point is in the range of 30 to 120°C. For example, styrene resins such as styrene, α-methylstyrene, divinylbenzene, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-
Ethylhexyl methacrylate, methyl acrylate,
Acrylic resins such as ethyl acrylate and butyl acrylate; styrene monomers such as styrene, α-methylstyrene, and divinylbenzene; methyl methacrylate, ethyl methacrylate, butyl methacrylate;
Nitrogen-containing styrene-acrylic copolymers that are copolymers with acrylic monomers such as 2-ethylhexyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, dimethylamino methacrylate, diethylamino methacrylate, vinylpyridine, etc. Examples include resin, nylon resin, urethane resin, urea resin, and the like.

[0012] Means for obtaining resin fine particles composed of the above resin include a method of synthesizing the resin by a polymerization reaction such as emulsion polymerization or suspension polymerization using monomers, and a method of melting the resin itself by heat or the like. Examples include a method of atomizing the resin by spraying, and a method of dispersing a molten resin in water to obtain a predetermined particle size. In addition, when producing resin fine particles by a polymerization method, a so-called soap-free polymerization method is preferably used in order to stabilize chargeability and prevent surfactants etc. from remaining on the surface of the resin fine particles.
A method may also be used in which the suspension stabilizer is removed after suspension polymerization.

[0013] The inorganic fine particles constituting the composite fine particles preferably have an average particle size of 5 to 200 nm in terms of primary average particle size, particularly 10 nm.
~100 nm is preferred. Note that the primary average particle size of the inorganic fine particles refers to the number average particle size observed with a scanning electron microscope and measured by image analysis. As the inorganic material constituting the inorganic fine particles, various inorganic oxides, carbides, nitrides, borides, etc. are suitably used. for example,
Silica, alumina, titania, zirconia, barium titanate, aluminum titanate, strontium titanate, magnesium titanate, calcium titanate, zinc oxide, chromium oxide, cerium oxide, antimony oxide, tungsten oxide, tin oxide, tellurium oxide, oxide Manganese, boron oxide, silicon carbide, boron carbide, titanium carbide,
Examples include silicon nitride, titanium nitride, titanium nitride, boron nitride, and the like.

[0014] As a method for fixing inorganic fine particles to the surface of resin fine particles, the resin fine particles and inorganic fine particles are mixed, the inorganic fine particles are electrostatically attached to the surface of the resin fine particles, and then mechanical energy is applied. Examples include a method of fixing inorganic fine particles to the surface of resin fine particles. As a method for electrostatically adhering the inorganic fine particles to the surface of the resin fine particles, there is a method in which the resin fine particles and the inorganic fine particles are placed in a mixer such as a turbular mixer, Lodeige mixer, Henschel mixer, etc., and then stirred. Can be mentioned. Methods for applying mechanical energy include "Hybridizer" (manufactured by Nara Kikai Seisakusho), which is an improved impact crusher, "Ong Mill" (manufactured by Hosokawa Micron), and "Cryptron".
(manufactured by Kawasaki Heavy Industries, Ltd.) and the like. The degree of adhesion changes depending on the magnitude of this mechanical energy, but this mechanical energy is affected by, for example, the circumferential speed of the stirring blade, etc.
It can be adjusted by stirring time, product temperature during processing, etc.

The amount of inorganic fine particles added to the resin fine particles may be any amount that can uniformly cover the surface of the resin fine particles. Specifically, although it varies depending on the specific gravity of the inorganic fine particles, from the viewpoint of more effectively preventing filming on the photoreceptor by the resin constituting the composite fine particles, 5 to 100 parts by weight per 100 parts by weight of the resin fine particles is added. Preferably, 5 to 80 parts by weight is particularly preferable. For example, if the amount of inorganic fine particles added is too small, a large amount of resin portion will be present on the surface of the composite fine particles, and this resin portion may cause filming on the photoreceptor. On the other hand, when the amount of inorganic fine particles added is excessive, the inorganic fine particles tend to exist in a free form, which tends to cause deterioration of the triboelectric charging properties of the colored particles and poor cleaning.

[0016] The amount of composite fine particles added to the colored particles is:
From the viewpoint of improving the cleaning performance due to the polishing effect and not inhibiting the triboelectric charging properties of the colored particles,
．． 0.01 to 5% by weight is preferred, especially 0.01 to 2% by weight
is preferred.

In the electrostatic image developer of the present invention, in addition to the composite fine particles, inorganic fine particles such as hydrophobic silica fine particles may be used as an external additive in order to improve the fluidity of the developer. The primary average particle diameter of the inorganic fine particles is preferably 5 to 20 nm from the viewpoint of improving fluidity and preventing damage to the photoreceptor. In addition, this primary average particle diameter refers to the number average particle diameter observed with a scanning electron microscope and measured by image analysis. Further, the amount of inorganic fine particles added is preferably 0.01 to 3.0% by weight based on the colored particles from the viewpoint of improving fluidity and cleaning properties.

The colored particles contain a binder resin, a coloring agent, and other additives such as a charge control agent used as necessary, and the average particle size is usually 1 to 30 μm. range. The binder resin constituting the colored particles is not particularly limited, and various conventionally known resins can be used. Typical examples include polyester resin, styrene/acrylic resin, and the like. The coloring agent constituting the colored particles is not particularly limited, and various conventionally known coloring agents can be used. For example, carbon black, nigrosine dye, aniline blue, calco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate,
Examples include lamp black and rose bengal.

Examples of other additives include charge control agents such as salicylic acid derivatives, and fixing property improvers such as low molecular weight polyolefins. Further, when obtaining a magnetic toner, magnetic particles are contained as an additive in the colored particles. Such magnetic particles have an average particle size of 0.
Particles of 1 to 2 μm such as ferrite and magnetite are used. The amount of magnetic particles added is usually 20 to 70% by weight of the colored particles excluding external additives such as composite fine particles. The glass transition point of colored particles is 50-65
℃ is preferable, and the softening point is preferably 110 to 160 ℃.

The developer of the present invention can be used in combination with various conventionally known developing methods. Further, the developer of the present invention can be used for selenium-based photoreceptors, organic photoconductive photoreceptors (OP
It can be used in combination with various conventionally known photoreceptors such as C photoreceptor) and amorphous silicon photoreceptor (a-Si photoreceptor).

[0021]

[Examples] More specific examples will be described below, but the present invention is not limited to these examples. In addition, in the following, "part" represents "part by weight".

Resin fine particles constituting composite fine particles The resin fine particles used in Examples and Comparative Examples are as shown in Table 1 below.

Composite Fine Particles 1 to 9 Resin fine particles and inorganic fine particles in the combinations and amounts shown in Table 2 below are thoroughly stirred and mixed in a V-type blender containing a medium, and the inorganic fine particles are applied to the surface of the resin fine particles by electrostatic force. This mixture was charged into a "hybridizer" (manufactured by Nara Kikai Seisakusho), and a mechanical impact force was applied to the mixture to obtain composite fine particles in which inorganic fine particles were fixed to the surface of resin fine particles. Surface observation using an electron microscope and transmission electron microscope revealed that the inorganic fine particles that had been attached to the surface of the resin fine particles due to electrostatic force were embedded and held in the surface of the resin fine particles. It was confirmed that.

[0024]

[Table 1]

[0025]

[Table 2]

Example 1 60 parts of polyester resin (binder resin), 35 parts of magnetite (magnetic particles), 3 parts of polypropylene, and 1 part of salicylic acid derivative (charge control agent) were mixed in a V-type blender. Thereafter, the mixture was melt-kneaded using two rolls, cooled, coarsely ground using a hammer mill, further finely ground using a jet mill, and then classified using an air classifier to obtain magnetic colored particles 1 with an average particle size of 12 μm. . Hydrophobic silica fine particles “Aerosil R” are added to the magnetic colored particles 1.
-812” (manufactured by Nippon Aerosil Co., Ltd.) 0.4% by weight
, Composite Fine Particles 1 were added in a proportion of 0.9% by weight and mixed using a Henschel mixer to obtain a developer of the present invention consisting of a one-component toner. This toner had a glass transition point of 56°C and a softening point of 125°C.

Example 2 In Example 1, composite fine particles 1 were replaced with composite fine particles 2.
A developer of the present invention was obtained in the same manner except that the amount was changed to 0.8% by weight.

Example 3 In Example 1, composite fine particles 1 were replaced with composite fine particles 5.
A developer of the present invention was obtained in the same manner except that the amount was changed to 0.7% by weight.

Comparative Example 1 In Example 1, composite fine particles 1 were replaced with composite fine particles 6.
A comparative developer consisting of a one-component toner was obtained in the same manner except that the amount was changed to 0.8% by weight.

Comparative Example 2 In Example 1, composite fine particles 1 were replaced with composite fine particles 7.
A comparative developer consisting of a one-component toner was obtained in the same manner except that the amount was changed to 0.5% by weight.

Comparative Example 3 In Example 1, composite fine particles 1 were replaced with composite fine particles 8.
A comparative developer consisting of a one-component toner was obtained in the same manner except that the amount was changed to 1.2% by weight.

Example 4 100 parts of polyester resin (binder resin), 10 parts of carbon black, and 3 parts of polypropylene were treated in the same manner as in Example 1 to obtain nonmagnetic colored particles 2 with an average particle size of 11 μm. Obtained. To the non-magnetic colored particles 2, 0.8% by weight of hydrophobic silica particles "Aerosil R-805" (manufactured by Nihon Aerosil Co., Ltd.) and 1.5% by weight of composite particles 3 were added, and the mixture was mixed using a Henschel mixer. Mix and
A two-component toner was obtained. The glass transition point of this toner is 6
4°C, and the softening point was 135°C. 5 parts of this two-component toner and ferrite core particles (average particle size = 80 μm)
and 100 parts of a resin-coated carrier whose surface was coated with a styrene/acrylic resin (styrene: methyl methacrylate = 3:7) to obtain a two-component developer of the present invention.

Example 5 In Example 4, composite fine particles 3 were replaced with composite fine particles 4.
A developer of the present invention consisting of a two-component developer was obtained in the same manner except that the amount was changed to 0.8% by weight.

Comparative Example 4 In Example 4, composite fine particles 3 were replaced with composite fine particles 7.
A comparative developer consisting of a two-component developer was obtained in the same manner except that the amount was changed to 0.8% by weight.

Comparative Example 5 In Example 4, composite fine particles 3 were replaced with composite fine particles 8.
A comparative developer consisting of a two-component developer was obtained in the same manner except that the amount was changed to 0.5% by weight.

Comparative Example 6 In Example 4, composite fine particles 3 were replaced with composite fine particles 9.
A comparative developer consisting of a two-component developer was obtained in the same manner except that the amount was changed to 1.5% by weight.

Image Formation Test Using the developers obtained in the above Examples and Comparative Examples, the electrostatic latent image formed on the photoconductive photoreceptor was developed to form a toner image. A test was conducted in which a copy image was formed by performing an image forming process that included the steps of transferring the toner image to a transfer material, fixing the transferred toner image, and cleaning the toner remaining on the photoconductive photoreceptor with a cleaning blade after the transfer. Ta. For the image formation test,
An image chart with a pixel rate of 5% only in the central part was used.

However, for one-component developers, a non-contact type developer that applies an oscillating electric field to a selenium-tellurium photoreceptor and a developing area, a cleaning blade, and a hot roller fixing device is used. Using a prototype electrophotographic copying machine, a live copying test was conducted in which a copy image was formed up to 50,000 times under ambient conditions of room temperature and humidity of 20° C. and 50% relative humidity. The heat roller fixing device has an upper roller whose surface layer is coated with fluororesin, a heat-resistant elastic layer made of silicone rubber, and a fixing pad impregnated with silicone oil, and has a surface pressure of 2 kg/cm2 and a nip passage. Fixing is performed at a time of 30 msec and a set temperature of 180°C.

Regarding the two-component developer, an arsenic-selenium photoreceptor, a developing device for the two-component developer, a cleaning blade, and a prototype electrophotographic copying machine for the one-component developer are used. Electrophotographic copying machine "U-Bix 4060" for two-component developer equipped with a heat roller fixing device under the same conditions
Using a modified machine (manufactured by Konica Corp.), a live copying test was conducted in which copy images were formed up to 100,000 times under ambient conditions of room temperature and humidity of 20° C. and 50% relative humidity.

Evaluation (1) Image Density Evaluation was performed by measuring the maximum image density Dmax using a "Sakura Densitometer" (manufactured by Konica Corporation). Evaluation,
When the relative concentration is 1.25 or more, it is ○, and when it is 1.1 or more, it is 1.
A case of less than 25 was marked as △, and a case of less than 1.1 was marked as ×. (2) Black streaks or black spots Evaluation was made by examining the number of times a copy image was formed when black streaks or black spots started to appear in the image area. (3) Fog was determined by measuring the relative density of a white background area with a document density of 0.0 using a "Sakura Densitometer" (manufactured by Konica Corporation). Note that the white background reflection density was set to 0.0. In the evaluation, when the relative concentration was less than 0.01, it was evaluated as ○, when it was 0.01 or more and less than 0.03, it was △, and when it was 0.03 or more, it was evaluated as ×.

(4) Fixability Every time the number of times a copy image is formed reaches 5,000, the copy image is visually observed to determine if image defects start to occur due to the transfer of toner adhering to the fixing roller to the paper. The evaluation was made by examining the number of times a copy image was formed. (5) Cleaning property The surface of the photoreceptor immediately after being cleaned with a cleaning blade was visually observed, and judgment was made based on the presence or absence of deposits on the surface of the photoreceptor. The case where almost no deposits were observed was rated as ○, the case where some deposits were observed but there was no practical problem was rated as Δ, and the case where a large amount of deposits were observed and there was a practical problem was rated as ×. (6) Image stains Evaluation was made by examining the number of times a copy image was formed when stains began to appear on the copied image. The above results are shown in Table 3 below.

[0042]

[Table 3]

[0043]

Effects of the Invention As explained in detail above, the electrostatic image developer of the present invention prevents the occurrence of black streaks and black spots, prevents a decrease in image density and the occurrence of fog, and prevents the fixing roller from forming black lines and black spots. It is possible to prevent the occurrence of image defects due to toner transfer from the toner.

Claims (1)

[Claims] 1. An electrostatic image developer comprising colored particles comprising at least a binder resin and a colorant, and composite fine particles having inorganic fine particles fixed to the surface of the resin fine particles, wherein the composite fine particles are An electrostatic image developer characterized in that a constituent resin has a glass transition point of 30 to 120°C.