JP3493473B2 - Developer for developing electrostatic images - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for developing an electrostatic charge image used in electrophotography and the like.

[0002]

2. Description of the Related Art Electrophotography generally uses a photoconductive material to form an electrical latent image on a photoconductor by various means, and then develops the latent image with a toner. The toner image is transferred onto a transfer material such as paper according to the requirements, and then fixed by heating, pressure, heat pressure, or solvent vapor to obtain a copy.

As described above, since the toner is first transferred from the developing device to the photoconductor and then from the photoconductor to the transfer material, the toner must maintain the fluidity between the toners and the releasability from the contacted object. I won't. Further, it is necessary to prevent aggregation of toner particles in the developing device. Conventionally, in order to solve such a problem, a method of internally or externally adding particles having a smaller particle size than toner particles has been used.

A method of internally adding fine particles to a toner is disclosed in Japanese Patent Publication No. 44-18995, Japanese Patent Laid-Open No. 51-81623, Japanese Patent Laid-Open No. 56-1948, and the like. In order to allow the fine particles to exist on the surface of the toner and in the vicinity thereof and to obtain a sufficient effect of internal addition, a large amount of fine particles must be added at the time of melt-kneading. In addition, it has been a cause of lowering the fixing property.

On the other hand, as a method of externally adding the fine particles, the peripheral speed of the stirring blade by a simple addition or a mixer is several m / m.
Mixing of about 2 to 40 m / sec is general. in this case,
The fine particles are present between the toner particles by the physical attraction force and the electric attraction force, 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 particles relating to the fluidity, the effect is larger than the internal addition.

In a general electrostatic image developing method, magnetic particles called a carrier are used in order to give a proper amount of charge to toner and form a magnetic brush that slides on a developing surface. Is mixed with a carrier and toner and charged with a frictionally charged developer. But in this mixing process,
The surface of the toner, which repeatedly collides with and has friction with a carrier having a large specific gravity, is exposed to a severe impact. Even in the developing device, the developer is subjected to the same stress as described above due to the rotation of the sleeve and the paddle. Therefore, the fine particles that had adhered to the toner surface before the developer was often embedded in the toner, and were observed with an electron microscope (magnification: 30,000).
In some cases, it was buried so that the externally added fine particles could not be seen at all. Then, due to this embedding, the fluidity of the toner and the developer is greatly reduced.

If the developer or process is prone to the embedding phenomenon, the fluidity of the toner is deteriorated as the copying progresses, the image density is lowered (developing ability is lowered), and the density unevenness of the solid image portion (transfer Deterioration of image quality).
In the worst case, problems such as developer blocking and toner aggregation may occur.

The toner in which the embedding phenomenon is likely to occur is a relatively soft toner having a glass transition point of 72 ° C. or less, and particularly, a small particle size toner having a particle size of 10 μm or less has poor fluidity of the toner itself, and thus is described above. The image quality was severely degraded. In full-color copying, the image quality is also markedly deteriorated because there are many solid images with high image density.

In order to solve the above problem, Japanese Patent Laid-Open No. 61-
Japanese Patent No. 228460 discloses a method of compensating for the shortage of silica in the developing device by increasing the content of silica (fine particles) in the toner supplied to the developing device. Further, Japanese Patent Publication No. 63-65701 and Japanese Patent Application Laid-Open No. 2-167561 specify the amount of silica that is embedded in the surface of the toner and the amount of silica that is not embedded in the toner necessary for maintaining the fluidity of the developer. However, it has been pointed out that the silica in the buried state does not contribute to the fluidity of the toner and also causes the fixing property to be significantly impaired. Japanese Patent Application Laid-Open No. 4-177258 proposes, as a method for producing a developer, that the toner and the externally added fine particles are mixed in two stages. That is, here, the fine particles for maintaining the initial fluidity and the fine particles for the purpose of improving the fluidity over time are made to coexist by different mixing methods, but it is necessary to mix the fine particles twice. The complexity of the manufacturing process is a problem.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a developer for developing an electrostatic charge image, which solves the above problems. Another object of the present invention is to provide a developer for developing an electrostatic charge image, which has good fluidity, high image density, no unevenness, and a good image can be obtained without deterioration even when a large number of sheets are continuously copied. It is in. Further, it is an object of the present invention to provide a developer for developing an electrostatic charge image, which has little deterioration of an image even when left for a long time and is excellent in long-term storability. Still another object of the present invention is to provide a developer for developing electrostatic charge images, which is stable and has sufficient triboelectrification properties, which is less affected by environmental changes.

[0011]

According to the present invention, firstly, the toner and the carrier are composed of a toner having fine particles adhered to the surface thereof and a carrier, and the fine particles are titania having a particle diameter of at least 16 nm or less. An electrostatic charge image developing developer having an α value calculated from the following formula (1) from the respective concentration, specific gravity and volume average particle diameter of 0.35 to 0.80 is provided. It

## EQU1 ## α = [Tc / (100-Tc)] (ρ ₂ / ρ ₁ ) (r ₂ / 4r ₁ ) ... (1) (where Tc is toner concentration (% by weight) and ρ ₁ is True specific gravity of toner, ρ ₂ is true specific gravity of carrier, r ₁ is volume average particle diameter (μm) of toner, r ₂ is volume average particle diameter of carrier (μ
m)) Secondly, in the developer described in the first item, there is provided a developer for developing an electrostatic charge image, characterized in that silica is used in combination as fine particles. Thirdly, in the developer described in the first or second, there is provided a developer for developing an electrostatic charge image, characterized by using a dispersion polymerization toner as a toner.

The present invention will be described in detail below. The developer according to the present invention has an α value of 0.35 to 0.80,
It is preferably adjusted to be in the range of 0.35 to 0.60 and set higher than that of the conventional product. As a result, the surface of the toner particles is less likely to be impacted in any process, so that the fine particles are prevented from being embedded in the toner particles, and stable fluidity is maintained over time.

That is, the impact of the carrier or the like on the surface of the toner particles during the processes of loading the surface of the toner particles, mixing with the carrier at the time of preparing the developer, mixing the sleeve in the developing device, stirring the paddle, etc. is mitigated. be able to.

The equation (1) can be rewritten as the following equation (2). In the latter half of this equation, the volume of the toner and the carrier to which the fine particles adhere is divided by the volume average particle diameter of each. Therefore, the value can be said to be one of the indexes showing the ratio of the surface areas.

## EQU2 ## α = 1/4 [(Tc / ρ ₁ ) / r ₁ ] / [{(100-Tc) / ρ ₂ } / r ₂ ] ... (2) α value is less than 0.35 As can be seen from the equation (2), the ratio of the toner to the total surface area of the carrier in the developer is small, and the impact force from the carrier per one toner seems to be increased. Therefore, starting from the mixing at the time of developing the developer, the embedding of the fine particles in the toner is accelerated by the sleeve mixing and the paddle stirring even in the developing device, and the fluidity of the developer and the toner is deteriorated as the copying is repeated. The resulting image also has low density and uneven density, resulting in lack of clarity. On the other hand, when the α value exceeds 0.80, an excessive amount of toner is present in the gap between the carriers, and it is difficult for the toner to obtain sufficient charge, and fogging easily occurs. Further, at the time of development, the carrier may be attached to the photoconductor together with the toner.

The developer of the present invention has an α value of 0.35 to
Fine particles of 0.1 to 2.0 parts by weight, preferably 0.25 to 1.
In addition to adding 2 parts by weight, a carrier having a particle size of 2 to 20 times, preferably 6 to 16 times, of the toner is added to the toner.
˜99 times by weight, preferably 12 to 39 times by weight. The developer of the present invention may have an α value in the range of 0.35 to 0.80 by the above-described method or other methods, and it is equivalent even if the α value is in the above range by any method. The effect can be obtained.

In the developer of the present invention, if the carrier is a metal or metal oxide having the same strong magnetism as the conventional product, or a magnetic substance dispersion type carrier in which ferromagnetic fine powder is dispersed in an adhesive, good. The performance of these carriers can be further improved by coating them with a silicone resin or the like as in the conventional products.

Conventionally, various inorganic fine particles have been used as a fluidity improver. Among them, titania fine particles have a small triboelectric property with respect to a carrier, so that they have environmental dependence in the triboelectric charge of toner. Can be made smaller.

However, the conventional fine titania particles are inferior to the fine silica particles in terms of improving the fluidity. The present inventor has conducted various studies on the performance of the titania fine particles as a fluidity improving agent, and found that particles having a primary particle diameter (volume average) of 16 nm or less have the same fluidity improving ability as silica fine particles. The present invention has been reached. That is, by making the titania fine particles also small in particle size, the dispersed state on the toner surface becomes good, and the same fluidity as silica fine particles can be obtained. And by controlling this and the range of α value mentioned above,
The fluidity is further improved, and the developer has excellent chargeability, image density and image quality both at the initial stage of copying and after continuous copying, and has little environmental dependence.

Further, in the present invention, as the toner,
Toners obtained by various production methods can be used, but particles obtained by dispersion polymerization are true spheres and have no irregularities, and all externally added fine particles come into contact with the outside, so the fluidity is remarkably improved by adding a small amount. Since it is possible to obtain the replenishment property and transfer property more than those of the conventional pulverized toner, it is preferably used.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples. All parts and percentages shown below are based on weight.

<Toner Preparation Example 1> Styrene-methyl acrylate copolymer (50:50) 100 parts 3,5-di-tertiary butyl salicylic acid chromium complex 2 parts carbon black 3 parts The above composition was used as a Henschel mixer ( HENSCHEL FM20B remodeling machine manufactured by Mitsui Miike Seisakusho Co., Ltd.) was premixed, heat-kneaded for 30 minutes in a roll mill (100 ° C.), cooled, and then finely pulverized in a jet mill. Particle size 6.8 μm, number average particle size 5.2
A classified product having a glass transition point of 62 ° C. in μm was obtained.

<Toner Preparation Example 2> A sealable reaction container equipped with a stirring blade, a cooling condenser, and a nitrogen gas introduction tube was installed in a constant temperature water tank, and the reaction container was charged with the following composition. Methanol 90 parts Polyvinylpyrrolidone 4 parts The stirring blade was rotated to completely dissolve polyvinylpyrrolidone, and the following composition was charged in a container. Styrene 22 parts Methyl acrylate 18 parts Ethylene glycol dimethacrylate 0.2 parts tert-Dodecyl mercaptan 0.1 parts While continuing to rotate the stirring blade, nitrogen gas was blown into the container and oxygen was completely expelled. 65
The temperature was raised to ± 0.1 ° C., and the following were added to initiate polymerization. Azobisisobutyronitrile 0.6 part Methanol 10 parts 6 hours after the initiation of polymerization, the following was added with a syringe. Thioglycerin 0.4 parts Methanol 1 part Then, after continuing the reaction for 15 hours, it was cooled to room temperature. Next, 80 parts of this dispersion was placed in a flask, and 20 parts of ion-exchanged water was mixed and the following dye powder was added little by little over 30 minutes while stirring with a stirrer. Oil black 860 1.8 parts Oil orange 201 0.45 parts After adding the dye, the mixture was stirred as it was at room temperature for 10 hours, and this dyeing solution was passed through a 75 μm filter. Then, this dyeing solution is spun down by centrifugation, the supernatant is removed, and methanol 70
Part, and a step of redispersing in a mixed solvent of 30 parts of ion-exchanged water was performed twice, and finally redispersed in a mixed solvent of 50 parts of methanol and 50 parts of ion-exchanged water. After separation by filtration, it was air-dried to obtain particles having a volume average particle diameter of 5.5 μm, a number average particle diameter of 4.9 μm and a glass transition point of 60 ° C.

Example 1 Classification product 10 of toner preparation example 1
Titania A (primary particle size 15 nm) 0.8 against 0 part
Parts were added and mixed by a high speed mixer to obtain a toner.
To 95 parts of carrier a (commercially available silicon-coated ferrite carrier having a volume average particle size of 70 μm and a true specific gravity of 5.0), 5 parts of the above toner was mixed to obtain a developer having an α value of 0.56 at Tc of 5%. The above developer is applied to our copier IMAGIO 4
When a copy test (20 ° C., 60% RH) was carried out with No. 20, a good image density of 1.39 (Macbeth densitometer) was obtained with an initial charge amount of -18.3 μC / g. Further, when 20,000 sheets were continuously copied, the α value fluctuated in the range of 0.39 to 0.75 during that period, a solid image was not uneven, and an excellent image free from fogging or stains due to poor cleaning was obtained. was gotten. High temperature and high humidity (30 ℃,
When 5,000 sheets were continuously copied under the condition of (90% RH), the average charge amount was stable at -17.9 μC / g, and almost no change in image quality was observed.

Example 2 Particles 100 of Toner Preparation Example 2
Toner was added in the same manner as in Example 1 except that 0.5 part of Titania A was added. Carrier b (volume average particle size 60μ
5 parts of the above toner is mixed with 95 parts of a commercially available silicon-coated ferrite carrier having a true specific gravity of 5.0 and a Tc of 5%.
Thus, a developer having an α value of 0.60 was obtained. The above developer is used in Example 1.
When a copy test was performed in the same manner as in, a good image density of 1.25 was obtained with an initial charge amount of −21.0 μC / g. After continuous copying of 20,000 sheets,
During that time, the α value fluctuated within the range of 0.41 to 0.79, a solid image was not uneven, particularly fine line reproducibility was obtained, and a high-quality image free from stains due to fog or cleaning failure was obtained. Further, 5,000 sheets were continuously copied under conditions of high temperature and high humidity, and the average charge amount was stable at -20.5 μC / g, and almost no change in image quality was observed.

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COMPARATIVE EXAMPLE 1 In Example 1, 0.8 part of hydrophobic silica R972 was used in place of 0.8 part of titania A.
A toner was obtained in the same manner as in Example 1 except that the parts were used. 5 parts of the above toner was mixed with 95 parts of carrier a to obtain a developer having an α value of 0.56 at Tc of 5%. When a copy test was conducted on the above developer in the same manner as in Example 1, the image density was 0.9 at an initial charge amount of −26.1 μC / g.
It was as low as 7. Further, when 20,000 sheets were continuously copied, the α value fluctuated in the range of 0.49 to 0.80 during that period, and the solid image had no unevenness, and the excellent image was free from stains due to fog and poor cleaning. was gotten. Further, 5,000 sheets were continuously copied under the condition of high temperature and high humidity, but the average charge amount was greatly reduced to -5.2 μC / g, and stains on the background portion due to fog and poor brush cleaning were conspicuous.

[Comparative Example 2] In Example 1, instead of 0.8 parts of titania A, hydrophobic titania T8050.8 was used.
A toner was obtained in the same manner as in Example 1 except that the parts were used. 5 parts of the above toner was mixed with 95 parts of carrier a to obtain a developer having an α value of 0.56 at Tc of 5%. A copy test was conducted on the above developer in the same manner as in Example 1. The initial charge amount was -16.3 μC / g and the image density was 1.1.
It was 8. During continuous copying of 20,000 sheets, the α value fluctuated in the range of 0.35 to 0.67 during that period, but uneven transfer was partially observed in the solid image, and the portion written in fine print was also observed. It was faint. In addition, some fog was generated and the image was blurred overall. Further, under high temperature and high humidity conditions, the amount of toner dispensed was insufficient, and the image density decreased due to the decrease in toner density. In addition, a lump of toner was generated between the toner box and the developing device.

[Comparative Example 3] 3 parts of the toner used in Example 1 was mixed with 97 parts of the carrier a to obtain a developer having an α value of 0.33 at Tc of 3%. When a copy test was conducted on the above developer in the same manner as in Example 1, the initial charge amount was −2.
The image density was 1.12 at 1.5 μC / g. Further, when continuous copying of 20,000 sheets was carried out, the α value fluctuated in the range of 0.22 to 0.51 at a low level during that period, and there was no stain on the image due to fog or cleaning failure.
Partially uneven transfer was seen in the solid image, and the part written in fine print was faint.

Comparative Example 4 7.5 parts of the toner used in Example 1 was mixed with 92.5 parts of the carrier a to obtain Tc.
A developer having an α value of 0.87 was obtained at 7.5%. When a copy test was conducted on the above developer in the same manner as in Example 1, the image density was as high as 1.57 at an initial charge amount of -14.9 μC / g. During continuous copying of 20,000 sheets, the α value fluctuated a little in the range of 0.68 to 1.00 during that time, and the uniformity of the density was found in the solid image area. The stain on the part was noticeable.

[Comparative Example 5] A toner was obtained in the same manner as in Example 1 except that 0.5 part of hydrophobic silica R972 was used in place of 0.5 part of titania A.
5 parts of the above toner is mixed with 95 parts of the carrier b, and T
A developer having an α value of 0.60 was obtained at c5%. When a copy test was conducted on the above developer in the same manner as in Example 1, the image density was as low as 0.95 at an initial charge amount of -28.4 μC / g. Further, when continuous copying of 20,000 sheets was performed, the α value fluctuated in the range of 0.53 to 0.80,
It was possible to obtain a high-quality image without unevenness in the solid image, particularly excellent in fine line reproducibility, and free from stains due to fog or cleaning failure. Further, continuous copying of 5,000 sheets was performed under conditions of high temperature and high humidity, but the average charge amount was significantly reduced to -6.0 μC / g, and stains on the background due to fog and poor brush cleaning were conspicuous.

[Comparative Example 6] In Example 2, instead of 0.5 parts of titania A, hydrophobic titania T8050.5 was used.
A toner was obtained in the same manner as in Example 1 except that the parts were used. 5 parts of the above toner is mixed with 95 parts of the carrier b,
A developer having an α value of 0.60 at a Tc of 5% was obtained. When a copy test was conducted on the above developer in the same manner as in Example 1, the initial charge amount was -17.2 μC / g and the image density was 1.14. During continuous copying of 20,000 sheets, the α value fluctuated in the range of 0.40 to 0.73 during that time, but uneven transfer was partially observed in the solid image, and the portion written in fine print was also observed. It was faint. In addition, some fog was generated and the image was blurred overall. Further, the amount of toner dispensed was insufficient under the conditions of high temperature and high humidity, and the image density decreased due to the decrease in toner concentration. In addition, a lump of toner was generated between the toner box and the developing device.

[Comparative Example 7] 2.5 g of the toner used in Example 2 was mixed with 97.5 parts of the carrier b to obtain Tc.
A developer having an α value of 0.29 was obtained at 2.5%. When a copy test was conducted on the above developer in the same manner as in Example 1, the image density was as low as 0.89 at an initial charge amount of -25.2 μC / g. Further, when continuous copying of 20,000 sheets was performed, the α value fluctuated in the range of 0.17 to 0.47, and there was no stain on the image due to fog or poor cleaning, but partially Transfer unevenness is seen in the solid image,
The part written in fine print was faint.

[Comparative Example 8] 7 parts of the toner used in Example 2 was mixed with 93 parts of the carrier b to obtain a developer having an α value of 0.86 at Tc of 7%. When the above developer was subjected to a copy test in the same manner as in Example 1, the initial charge amount was -1.
The image density was as high as 1.53 at 6.9 μC / g. When continuous copying of 20,000 sheets was performed, α
The value fluctuates in the range of 0.66 to 0.99 and the density is uniform in the solid image area, but the background area is contaminated due to fog.

[Comparative Example 9] 3 parts of the toner used in Example 3 was mixed with 97 parts of the carrier a to obtain a developer having an α value of 0.33 at Tc of 3%. When a copy test was conducted on the above developer in the same manner as in Example 1, the initial charge amount was −2.
The image density was as low as 0.92 at 5.0 μC / g. When continuous copying of 20,000 sheets was performed, α
The value fluctuated in the low range of 0.17 to 0.46, and there was no stain on the image due to fog or poor cleaning, but there was partial transfer unevenness in the solid image and the part written in fine print. It was also faint.

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[0039]

As described above, according to the first and second aspects of the present invention, both have excellent fluidity, good chargeability and image density at the initial stage of copying and after continuous copying, and a solid image quality. It is possible to obtain an image without unevenness and free from stains due to fog and poor cleaning. Further, it is possible to obtain a developer having a small environmental dependency such that the charge amount is stable even under high temperature and high humidity and the image quality hardly changes. According to the invention of claim 3, the effect described above can be obtained by adding a small amount of fine powder.

Continuation of the front page (56) Reference JP-A-3-172860 (JP, A) JP-A-4-204751 (JP, A) JP-A-4-204749 (JP, A) JP-A-6-208241 (JP , A) JP 5-27476 (JP, A) JP 6-19203 (JP, A) JP 7-104513 (JP, A) JP 3-256052 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 9/08-9/10

Claims (3)

(57) [Claims] 1. A toner comprising a toner having fine particles adhered to its surface and a carrier, wherein the fine particles have at least a particle size of 1
Using titania of 6 nm or less, the α value calculated from the following formula (1) from the respective concentration, specific gravity and volume average particle diameter of the toner and carrier is in the range of 0.35 to 0.80. A developer for developing an electrostatic image. ## EQU1 ## α = [Tc / (100-Tc)] (ρ ₂ / ρ ₁ ) (r ₂ / 4r ₁ ) ... (1) (where Tc is toner concentration (% by weight) and ρ ₁ is True specific gravity of toner, ρ ₂ is true specific gravity of carrier, r ₁ is volume average particle diameter (μm) of toner, r ₂ is volume average particle diameter of carrier (μ
represents m)) 2. The developer for developing an electrostatic charge image according to claim 1, wherein silica is used in combination as the fine particles. 3. The developer for developing an electrostatic charge image according to claim 1, wherein a dispersion-polymerized toner is used as the toner.