JPH07104513A - Developer for developing electrostatic charge image - Google Patents

Abstract

PURPOSE:To obtain a developer having satisfactory flowability, giving a high density image almost free from unevenness in density, giving an image liule in deterioration even after the developer is allowed to stand for a long time or at the time of continuous copying repeated many times and having a long service life. CONSTITUTION:This developer consists of a toner with fine particles stuck to the surface and a carrier and alpha value calculated by an equation [Tc/(100-Tc)](rho2/rho1)(gamma2/4gamma1) is 0.35-0.80 [where Tc is the concn. (wt.%) of the toner, rho1 is the true specific gravity of the toner, rho2 is the true specific gravity of the carrier gamma1 is the volume average particle diameter (mum) of the toner and gamma2 is the volume average particle diameter (mum) of 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 used in electrophotography, electrostatic recording, electrostatic printing and the like.

[0002]

2. Description of the Related Art Electrophotographic methods are USP2,
Many proposals have been made as described in Japanese Patent Publication No. 297,691, Japanese Patent Publication No. 42-23910 and Japanese Patent Publication No. 43-24748. Then, an electrical latent image is usually formed on the photoconductor by various methods using a photoconductive substance, and after the latent image is developed with toner, the toner image is transferred to a transfer material such as paper as necessary. After that, it is fixed by heating, pressurizing, pressurizing under heating, solvent vapor or the like to obtain a desired copy. That is, the toner first adheres to the photoconductor from the developing device and is then transferred from the photoconductor to the transfer material. Therefore, in addition to fluidity and releasability from the contacted object, the toner
Various performances such as prevention of aggregation in the developing device are required. In order to satisfy such problems, fine particles having a smaller particle diameter than the normal toner particles are internally or externally added to ordinary toner particles.

The method of internally adding fine particles to the toner is disclosed in JP-B-44-18995, JP-A-51-81623 and JP-A-56-1946. However, when a large amount of fine particles are made to exist on the toner surface or in the vicinity thereof by the above-mentioned disclosed method to obtain the internal addition effect,
Since it is necessary to add a large amount of fine particles at the time of melting and kneading in the toner manufacturing process, there arises a problem such as deterioration in fixing property. The method of externally adding the fine particles is generally a simple addition method or a mixing method using a mixer in which the peripheral speed of the stirring blade is several m/sec to 40 m/sec. In this method, the fine particles are present between the toner particles due to the physical attraction and the electric attraction, and the fine particles contribute to the improvement of the fluidity of the toner particles. Moreover, since the fine particles are present only on the surface of the toner, which is involved in the fluidity, the effect is greater than that at the time of internal addition.

In the electrostatic image development method, a carrier formed of magnetic particles is used in order to give an appropriate amount of charge to the toner and form a magnetic brush that slides on the developing surface.
A developer in which a carrier and toner are mixed and frictionally charged is put into the developing device. In this mixing of the developers (premixing of the carrier and the toner), the carrier having a large specific gravity collides with or rubs against the surface of the toner, so that the surface of the toner is exposed to a severe impact, but copying is repeated. Since the developer is subjected to sleeve mixing, paddle stirring, etc., this phenomenon is accelerated. Therefore, the fine particles adhered to the surface of the toner before forming the developer are often buried in the toner, and in the developer having many buried particles, the fine particles are interposed between the toner particles to improve the fluidity. The amount of The embedding phenomenon of such fine particles in the toner is more remarkable in a relatively soft toner having a glass transition point of 72° C. or less, and the externally added fine particles are buried so that they cannot be seen by an electron microscope observation at a magnification of 30,000. There is also.

When the amount of fine particles contained in the developer during copying decreases due to the phenomenon of burial or the like, the fluidity of the toner particles decreases as the copying progresses, resulting in a decrease in copy density or a solid image portion. Image quality deterioration such as density unevenness (lack of uniformity) increases. In particular, a small particle size toner having a volume average particle size of 10 μm or less has poor fluidity of the toner itself, and thus the above-mentioned deterioration of image quality is severe. Further, in full-color copying, a solid image having a high copy density is often formed, and in this case, the deterioration of image quality is conspicuous. In addition to the above, the blocking phenomenon is likely to occur due to the decrease in the fluidity of the developer. This phenomenon is a solidification phenomenon due to a decrease in fluidity. If the solidification becomes stronger, the toner particles will agglomerate. If the blocking phenomenon progresses, the toner will become difficult to use.

In order to solve the above-mentioned problems, Japanese Patent Laid-Open No. Sho 61-61
JP-A-228460 discloses a method of increasing the content of silica fine particles in the toner replenished in the developing device to eliminate the shortage of silica fine particles in the developing device. Also,
JP-B-63-55701 and JP-A-2-16756.
Although Japanese Patent Laid-Open No. 1-91 specifies the amount of embedded silica fine particles and the amount of non-embedded silica fine particles necessary for maintaining the fluidity of the developer, the embedded silica fine particles do not contribute to the fluidity of the toner. It has also been pointed out that it will cause a significant decrease in fixability. Japanese Unexamined Patent Publication No. 4-177258 proposes a method for producing a developer in which toner particles and the fine particles are mixed in two steps. This method is characterized in that the fine particles for maintaining the initial fluidity and the fine particles for improving the fluidity for a long period are made to coexist, but it is necessary to increase the number of production steps such as two fine particle mixing steps.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in a developer for developing an electrostatic charge image which comprises a carrier and a toner, and the fluidity of the image is high and the density of the image is high. An object of the present invention is to provide a developer for developing an electrostatic charge image, which has little unevenness in density and has little deterioration of an image obtained even when left standing for a long time or when a large number of sheets are continuously copied.

[0008]

[Where Tc is the toner concentration (wt %), ρ ₁ is the true specific gravity of the toner, ρ ₂ is the true specific gravity of the carrier, γ ₁ is the volume average particle size (μm) of the toner, and γ ₂ is the Represents volume average particle size (μm)]

The developer of the present invention has the above α value of 0.35 to 0.80, which is larger than less than 0.35 obtained by the conventional product.
It is preferably adjusted to be in the range of 0.35 to 0.60 and is characterized in that the adhered state is maintained for a long time because the fine particles on the toner surface are difficult to be embedded in the toner. Therefore, it is a particularly preferable developer for a full-color image forming toner or a toner having a sharp image with a small particle size. According to a detailed study by the present inventor, it is recognized that the fine particles embedded in the toner do not contribute to the increase of fluidity at all, and the smaller the adhesive force between the fine particles and the toner is, the higher the fluidity becomes. Further, when the equation (1) is rewritten, it is represented by the following equation (2). Since the latter half of this equation is a value obtained by dividing the volumes of the toner and the carrier to which the fine particles are attached by the respective volume average particle diameters, The α value can be said to be one of the indexes showing the particle number ratio. α=(γ ₂ /4γ ₁ )(Tc/ρ ₁ )/{(100-Tc)/ρ ₂ }=1/4 [(Tc/ρ ₁ )/γ ₁ ]/[{(100-Tc)/ ρ ₂ }/γ ₂ ] (2)

The developer of the present invention has an α value of 0.35.
The amount of fine particles is 0.1 to 2.0 parts by weight, preferably 0.25 to 100 parts by weight, per 100 parts by weight of toner particles.
1.0 to 20 parts by weight of the toner particles are added.
Carrier particles having a particle size of 6 times to 16 times, preferably 11 to 99 times the weight of toner particles, preferably 19 to
I use 39 times the weight.

As described above, in the developer of the present invention, the addition ratio of fine particles or carriers may be adjusted, or the α value may be adjusted within the range of 0.35 to 0.80 by other methods.
The same effect can be obtained by setting the α value in the above range by any method. By setting the α value in the above range higher than that of the conventional product, the toner is less likely to be impacted, which prevents the fine particles from being embedded in the toner particles, thereby maintaining good fluidity. become. That is, mixing the carrier and the toner during the preparation of the developer, which places a load on the surface of the toner particles during the electrostatic charge image development using the toner and the carrier, mixing the sleeve in the developing device,
In various processes such as paddle stirring, it is possible to prevent the impact of the carrier particles on the surface of the toner particles. The reason why the effect is manifested due to the change in the α value is not clear, but it is surprising that a large effect can be obtained only by changing the composition ratio.

When the α value is less than 0.35, the abundance ratio of toner particles is smaller than that of the developer of the present invention, as can be seen from the formula (2), and therefore the toner of the present invention is less than that of the developer of the present invention. The impact of the carrier particles on the particle surface seems to increase. As a result, it is presumed that the embedding of the fine particles adhering to the toner surface will increase in the above-mentioned steps 1 to 3. This phenomenon seems to be remarkable in the above processes after the start of copying, and the fluidity of the toner gradually decreases during development, and the quality of the obtained image also deteriorates. Then, only an image having a low density and being unclear and having a large density unevenness can be obtained. On the other hand, when the α value exceeds 0.80, the abundance ratio of the toner particles is higher than that of the developer of the present invention, so that excess toner is present in the carrier gap and the toner is hard to be sufficiently charged. As a result, fogging is likely to occur, and a phenomenon in which a carrier adheres to the photoconductor may occur.

As can be seen from the above description, the developer of the present invention does not need to be formed of a special material different from the conventional product, and the carrier is a metal or metal oxide having the same strong magnetism as the conventional product. Alternatively, a magnetic substance-dispersed carrier in which fine ferromagnetic powder is dispersed in a binder may be used. The performance of these carriers can be further improved by coating them with a silicone resin or the like as in the conventional products.
The toner can be the same as the conventional product, the colorant and the polarity control agent are melted and kneaded with the binder resin, then cooled and solidified, and then pulverized and crushed.
It may be produced by a conventional method such as classification. The raw materials for manufacturing the coloring agent, the binder resin and the like used in this case may be exactly the same as those used for manufacturing the conventional product, or various additives used in the conventional method may be added.

The fine particles used in the present invention may be the same as the conventional ones, and fine particles such as silica, titania, alumina, inorganic oxides other than the above, and organic fine particles can be used. Of these, silica fine particles are particularly preferable because they have a greater effect of improving the fluidity of the toner and the developer than other fine particles. The amount of fine particles added is preferably 0.1 to 2.0 parts by weight, and more preferably 0.25 to 1.0 parts by weight, based on 100 parts by weight of toner. If it is too large, the surface of the photoconductor will be easily damaged.

[0015]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples. The following parts are parts by weight, and the image density was measured with a Macbeth densitometer.

Synthesis Example 1 Styrene-methyl acrylate copolymer (50 parts: 50 parts) 100 parts Chromium complex of 3,5-di-t-butylsalicylic acid (polarity control agent) 2 parts Carbon black (colorant; Mitsubishi Kasei Kogyo Co., Ltd. #44) 3 parts The above composition was mixed with a Henschel mixer (Mitsui Miike Seisakusho:
HENSCHEL-FM20B modified machine) premix,
This was heat-kneaded for 30 minutes in a roll mill at 100° C. and then cooled, and the cooled product was finely pulverized and classified by a jet mill to obtain fine particles having a volume average particle diameter of 5.8 μm. The classified product is a toner body having a glass transition point of 62°C. As a carrier used in combination with the classified product, a commercially available silicon-coated ferrite carrier having a volume average particle diameter of 50 μm and a true specific gravity of 5.0 was used.

Example 1 Hydrophobic titania fine particles T- were added to 100 parts of the classified product of Synthesis Example 1.
805 (manufactured by Nippon Aerosil Co., Ltd.) was externally mixed to obtain a toner, and 4.0 parts of the toner and the carrier 96.0 were mixed.
The two parts were mixed to prepare a two-component developer having an α value of 0.37.
When this developer is put into the developing unit of a Ricoh copy machine IMAGIO 420 and copied on a commercially available copy paper, the image density is 1.38 and there is no density unevenness in the solid part, and a high-quality image with good fine line reproducibility is obtained. It was This result was almost maintained during printing of 10,000 sheets, and the image density after printing 10,000 sheets was 1.30, and a clear image was maintained. There were some scratches that were not a problem. Next, the same copying experiment as above was tried after leaving the developer at 40° C. for 4 weeks, but there was no abnormality in the transportability of the developer in the developing device or the copied image. Further, filming or cleaning failure did not occur on the surface of the photoconductor during copying.

Example 2 Hydrophobic silica fine particles R-9 were added to 100 parts of the classified product of Synthesis Example 1.
72 (manufactured by Nippon Aerosil Co., Ltd.) was externally mixed to prepare a toner, and a two-component developer having an α value of 0.37 was prepared in the same manner as in Example 1. When the same test as in Example 1 was attempted on this developer, a high-quality image having a fine line reproducibility with an image density of 1.89 and no density unevenness in a solid portion was obtained. The image density after printing 10,000 sheets was 1.70, and a clear image was maintained, but the surface of the photoreceptor after the test had the same scratches as in Example 1. Next, the same copying experiment as above was carried out after the developer was left standing at 45° C. for 4 weeks, and the same result as the experiment result of using the long-term storage developer of Example 1 was obtained.

Example 3 A toner was prepared in the same manner as in Example 2 except that the amount of the hydrophobic silica fine particles added was 0.70 parts.
94.5 parts of the above carrier was mixed with 1 part to obtain a two-component developer having an α value of 0.52. When the same test as in Example 1 was attempted with this developer, a high-quality image having a fine line reproducibility with an image density of 1.72 and no density unevenness in a solid portion was obtained. The image density after printing 10,000 sheets was 1.69, and a clear image equivalent to the initial density was maintained. Next, the same copying experiment as above was carried out after the developer was left at 45° C. for 2 weeks. As a result of the experiment using the stored developer of Examples 1 and 2, the transportability of the developer in the developing device and There were no abnormalities in the copied image, and there were no problems such as scratches on the surface of the photosensitive member due to fine particles during use of the developer, and problems such as filming and cleaning failure.

Example 4 A toner was prepared in the same manner as in Example 2 except that the amount of the hydrophobic silica fine particles added was 0.20 part.
93.0 parts of the carrier was mixed with 1 part to obtain a two-component developer having an α value of 0.68. When the same test as in Example 1 was attempted with this developer, a high-quality image with an image density of 1.46 and good density reproducibility in the solid areas was obtained. The image density after printing 10,000 sheets was 1.49, and a clear image above the initial density was maintained, but slight filming was observed on the surface of the photoconductor after the test. next,
When the same copying experiment as above was carried out after the developer was left standing at 40° C. for 2 weeks, there was absolutely no abnormality in the transportability of the developer and the copied image as in the experimental results of using the preservative developer in Examples 1 to 3. And no trouble occurred on the surface of the photoconductor.

Comparative Example 1 3.5 parts of the same toner as used in Example 3 and 96.5 parts of the above carrier were mixed to prepare a two-component developer having an α value of 0.33. When the same test as in Example 1 was tried on this developer, the image density was 1.32, but uneven transfer was observed in a part of the solid part. In addition, the image density after printing 10,000 sheets was reduced to 1.06 and the image was blurred overall. Next, the same copying experiment as described above was carried out after the developer was allowed to stand at 45° C. for 2 weeks. As a result, an image having an image density of 1.08 and some fog was obtained. It was also found that filming occurs on the surface of the photoreceptor during use of the developer.

Comparative Example 2 8.5 parts of the same toner as that used in Example 3 and 91.5 parts of the above carrier were mixed to prepare a two-component developer having an α value of 0.83. When the same test as in Example 1 was attempted with this developer, a high-quality image without image density unevenness was obtained at an image density of 1.88, but some fog was observed in the image. Further, during the printing durability test of 10,000 sheets, the scattering of the developer in the copying machine became severe, and the fiber for detecting the developer was contaminated to make the detection impossible, and the carrier adhered to the photoreceptor.

[0021]

The developer of the present invention is a toner surface generated during development by optimizing the specific gravity, particle size and addition ratio of the toner main body, the particles for improving fluidity and the carrier adhered to the toner surface. It is characterized in that the above-mentioned fine particles are prevented from being buried in the developer, thereby maintaining the developer having high fluidity for a long period of time. Further, because of the characteristics, it is possible to continuously provide an image of high density and excellent quality for a long period of time as compared with the conventional two-component developer, and
Even if stored for a long time under severe conditions, the developer quality does not deteriorate,
Further, the occurrence of troubles such as scratches on the surface of the photoconductor, filming and cleaning failure during development is greatly reduced.

Claims (2)

[Claims] 1. A toner comprising a toner having fine particles adhered to its surface and a carrier, and an α value calculated from the following formula (1) from the concentration, specific gravity and volume average particle diameter of the toner and the carrier is 0.35 to A developer for developing an electrostatic charge image, which is 0.80. α=[Tc/(100−Tc)](ρ ₂ /ρ ₁ )(γ ₂ /4γ ₁ ) (1) [where Tc is the toner concentration (wt %), ρ ₁ is the true specific gravity of the toner, ρ ₂ represents the true specific gravity of the carrier, γ ₁ represents the volume average particle diameter (μm) of the toner, and γ ₂ represents the volume average particle diameter (μm) of the carrier] 2. The toner according to claim 1, wherein at least one of the fine particles adhered to the toner surface is silica fine particles, and the addition amount thereof is 0.25 to 1.0% of the toner weight. Developer for charge image development.