JP2000172002A - Toner for reversal development and developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a toner for reversal development which ensures sufficient image density and slight surface fog and causes no problem even after printing repeated many times by sticking magnetite particles to toner matrix particles containing a bonding resin, a colorant and magnetite particles. SOLUTION: Magnetite particles are stuck to toner matrix particles containing at least a bonding resin, a colorant and magnetite particles. The amount of the magnetite particles contained in the toner matrix particles is preferably 3-10 pts.wt. per 100 pts.wt. bonding resin. The bonding resin is, e.g. a styrene resin or a polyacrylic ester resin. An arbitrary pigment or dye such as a carbon black or a nigrosine dye may be used as the colorant and the carbon black is preferably used because it contributes toward the stability of the quantity of triboelectric charges on the resulting toner for reversal development. The shape of the magnetite particles stuck to the surfaces of the toner matrix particles is preferably octahedral or hexahedral.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversal developing toner and a developer used for developing an electrostatic image formed by an electrophotographic method, an electrostatic recording method, an electrostatic printing method or the like.

[0002]

2. Description of the Related Art Generally, in a copying machine for electrophotography, a normal rotation developing method for forming an image same as an original image on a photosensitive member is used. However, in recent years, a reversal development method for forming a reversal image on a photoconductor, which is a reversal image of a document image, has also been used, and this method is mainly employed in printers. Generally, the negative polarity toner using the reversal development method is developed as follows. First, the surface of the photoreceptor is uniformly charged with a negative charge by the main charger, and the surface of the photoreceptor is irradiated with laser light or the like in a streak shape to remove the charge on the irradiated part and reduce the latent image potential. Let it. In this way, a latent image having a well potential is formed, and a negative toner is developed on the exposed latent image portion of the well potential by applying a negative developing bias to the developing device.

In a reversal printer based on such a principle, it is difficult to obtain a large developing potential on the photosensitive member, so that image density is hardly obtained, and a portion corresponding to a non-image portion of the original image is also formed on the photosensitive member surface. In this case, the toner is developed in the first place, and as a result, a printed image having a lot of background fog is caused. In particular, this problem is conspicuous when a large number of prints are made. Conventionally, in order to solve the above-mentioned problem, the content of carbon black and a charge control agent contained in the toner is adjusted, or the state of dispersion of the compound in the toner using a means for uniformly dispersing such a compound in the toner. It has been studied to keep the charge amount constant by optimizing the image quality, but it has not been possible to stably obtain an image having a sufficient image density and a small amount of background fog when printing many sheets.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a novel reversal developing method which has a sufficient image density, has little background fog, and has no problem even when printing a large number of sheets. It is an object of the present invention to provide a toner and a developer.

[0005]

The summary of the present invention is a reversal developing toner characterized in that magnetite particles are adhered to toner base particles containing at least a binder resin, a colorant and magnetite particles. Also, a reversal developing developer containing a carrier and a carrier for reversal development in which magnetite particles are attached to toner base particles containing at least a binder resin, a colorant and magnetite particles.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The toner for reversal development of the present invention has magnetite particles adhered to toner base particles containing at least a binder resin, a colorant and magnetite particles as described above. The reversal developing toner having such a configuration can obtain an image with a good balance between image density and background fog, and can obtain a stable and good image even when printing a large number of sheets. In this case, it is preferable that the magnetite particles contained in the toner base particles be contained in an amount of 3 to 10 parts by weight based on 100 parts by weight of the binder resin. When the amount is less than 3 parts by weight, there is no problem at the initial stage, but an image having a large amount of background fogging tends to be formed when printing a large number of sheets.

Further, it is preferable that the adhesion amount T (% by weight) of the magnetite particles adhering to the toner base particles satisfies the following equation (1). The adhesion amount T in this case is a weight ratio of the magnetite particles to the total weight of the toner base particles and the magnetite particles.

0.35−0.028C ≦ T ≦ 1.1−0.028C (1) where C is the content of magnetite particles contained in the toner base particles, and 100 parts by weight of the binder resin Parts by weight. When the above expression is not satisfied, the image density is low and an image having a lot of background fog is liable to occur, and the surface of the photoreceptor is easily damaged or filmed by magnetite particles adhered to the surface of the toner base particles.

Next, another configuration of the present invention will be described in detail.
As the binder resin, for example, styrene resin, polyacrylate resin, styrene-acrylate copolymer resin, polyvinyl chloride resin, polyvinyl acetate resin, polyvinylidene chloride resin, phenol resin, epoxy resin, polyester resin, etc. These resins are not limited to one type and may be used as a mixture of two or more types depending on the purpose.

[0009] Any appropriate pigment or dye can be used as the colorant. For example, carbon black, nigrosine dye, aniline blue, calcoil blue, chrome yellow, ultramarine blue, quinoline yellow, methylene blue, phthalocyanine blue, malachite blue and the like can be mentioned. Among them, carbon black is particularly preferred because it contributes to the stability of the triboelectric charge of the reversal developing toner. More preferably, DBP oil absorption of a 70~120cm ³ / 100g, and PH is 8
Ten carbon blacks are preferred. DBP oil absorption is 7
0 cm ³ / If 100g smaller than, the quantity of triboelectricity becomes high image density of the toner tends to decrease while going to a large number printed, it tends to become and fogging of many images. On the other hand, it tends image density triboelectric charge increases in the toner tends to deteriorate even greater than 120 cm ^3/100 g. Also, when the PH is less than 8, the amount of triboelectricity of the toner is likely to be high, so that the image density is reduced, and an image with a lot of background fog is likely to be formed. On the other hand, if it is larger than 10, the amount of triboelectricity tends to decrease, and the toner develops on the photoreceptor portion corresponding to the non-image portion of the original image, and the image tends to have a lot of background fog. Commercial products of carbon black having such specific physical properties include, for example, product names of Cabot Corporation:
BLACK PEARLS430, also available under the trade name: REGAL330 manufactured by Cabot Corporation.

Next, the magnetite particles will be described. The magnetite particles described below can be used for both the magnetite particles contained in the toner base particles and the magnetite particles adhered to the surface of the toner base particles. The shape of the magnetite particles is not particularly limited, but octahedral or hexahedral magnetite particles to be adhered to the surface of the toner base particles are effective in preventing the adhesion of the toner component and the paper powder component on the surface of the photoreceptor. preferable. The shape in this case can be confirmed by taking a photograph with an electron microscope and analyzing the shape. The magnetite particles are neutralized by adding an aqueous solution of caustic soda to an aqueous solution of iron sulfate, and after obtaining a hydroxide of iron by a neutralization reaction, air is injected into this suspension to be oxidized to obtain a precipitate of magnetite. . The precipitate is filtered, dried, and crushed and granulated to obtain magnetite particles. The magnetite particles have an average primary particle diameter of 15 to 40 nm, and the surface thereof is hydrophobized by a titanium-based coupling agent such as a silane-based coupling agent, an alkylchlorotitanium coupling agent, or an alumina-based coupling agent. It may be something.

As a method for attaching the magnetite particles to the toner base particles, a method using a general stirrer such as a turbine type stirrer, a Henschel mixer, a super mixer, or a device called a surface reformer (manufactured by Nara Machinery Co., Ltd.) Nara Hybridization System, Ongmill manufactured by Hosokawa Micron Corporation, etc.). The magnetite particles on the surface of the toner base particles are:
The toner base particles may be formed in a weak adhesion state called a glare, or the magnetite particles may be formed in an adhesion state in which a part of the magnetite particles is buried in the toner base particles, and may be fixed. In addition, magnetite particles and a fluidizing agent such as hydrophobic silica can be mixed and used according to the purpose. The reason why the magnetite particles adhere to the surface of the toner base particles to obtain the effect of suppressing the increase in image density and the background fog, etc. is not necessarily clear, but the triboelectric charging between the toner particles is promoted by the magnetite particles. It is presumed that it is.

The toner base particles may contain a charge controlling agent, a lubricant, an abrasive, a fixing agent, and the like, if necessary. For example, as the charge control agent, a conventionally used charge control agent can be used. Examples thereof include nigrosine dyes, quaternary ammonium salts, triphenylmethane dyes, and monoazo metal complex dyes. Examples of the lubricant include polytetrafluoroethylene powder, metal salts of higher fatty acids, and the like.Examples of the abrasive include cerium oxide, titanium oxide, and zinc oxide.Examples of the fixing agent include low-molecular-weight polyethylene and low-molecular-weight polypropylene. No. The toner for reversal development of the present invention is obtained by dry-mixing each raw material composition such as the binder resin and kneading with hot melt and then pulverizing and classifying, or a polymerization method such as a suspension polymerization method and an emulsion polymerization method. Can be obtained by

The toner for reversal development of the present invention is as it is.
It can also be used as a non-magnetic one-component developer
However, in order to obtain the effect of the present invention more,
Carrier and used as a two-component developer.
No. The carrier has an average particle size of 20 to 1000 μm.
Use iron powder, ferrite powder, magnetite powder, etc. as they are
Carrier or granulation of resin coated with such powder
Granulated carriers that have been used can also be used. in this way
The carrier mixed with the reversal developer toner of the present invention is particularly limited.
Although not specified, iron powder, ferrite powder,
Carriers coated with magnetite powder etc. are preferred, and furthermore
Many carriers with ferrite powder coated with silicone resin
It is preferable because it can improve the durability of several prints.
New Ferrite powder is Fe_Two O_Three And a divalent metal oxide
Is a compound of _Two O_Three The molecular formula of
It has a pinel lattice structure. However, in the above, M
Is Mn, Mg, Cu, Co, Ni, Zn, Cd, etc.
You. As the silicone resin used in the present invention,
Any silicone resin known from
However, especially silicone containing methyl silicone compound
Resin is preferred because of the excellent durability of the developer.
Resin containing methyl silicone compound
Is used in combination with a negatively chargeable reversal developing toner.
The image density, reduce ground fog and durability
It is preferable because of its excellent properties. In this case, silico
The content of methylsilicone compound in the epoxy resin is 30
% To 90% by weight, preferably less than 30% by weight and 90% by weight.
If the amount is more than% by weight, the image will be
Since image characteristics such as density and image quality are likely to change,
No. Commercially available silicone resins include Shin-Etsu Chemical
KR-271, KR-255, KR-152
The product name is SR2400 manufactured by Toray Silicone Co., Ltd.
SH840, SR2406 (both are trade names)
Can be

[0014]

The present invention will be described below based on examples and comparative examples. However, the present invention is not limited to these. The following parts are parts by weight. <Example 1> 100 parts of styrene-acrylate copolymer resin (trade name: CPR-100, manufactured by Mitsui Chemicals, Inc.) 10 parts of carbon black (trade name: MA-100, manufactured by Mitsubishi Chemical Corporation) 3 parts of metal-containing dye ( 3 parts of magnetite particles (trade name: TRH, manufactured by Hodogaya Chemical Co., Ltd.) (Average primary particle diameter: 30 nm, shape: hexahedron) Raw materials having the above mixing ratios are mixed by a super mixer, and hot-melted at 120 ° C. by a pressure kneader. After kneading, the mixture was pulverized with a jet mill and then classified with a dry air classifier to obtain toner base particles having a volume average particle diameter of 10 μm. Next, the ratio with the toner base particles is 0.3% by weight of magnetite particles (average primary particle diameter: 30 nm, shape: hexahedron) and hydrophobic silica (trade name: R-972, manufactured by Nippon Aerosil Co., Ltd.).
The magnetite particles and hydrophobic silica were adhered to the surface of the toner base particles by mixing with a Henschel mixer so as to be 0.5% by weight to obtain a toner for reversal development of the present invention. The amount T of magnetite particles adhered to the toner for reversal development satisfies the expression 1, and the calculated T is in the range of 0.266% by weight to 1.016% by weight.
Next, 6 parts of the above-mentioned toner for reversal development and 100 parts of a carrier composed of ferrite particles (average particle diameter: 90 μm) coated with a silicone resin (containing 85% by weight of a methylsilicone compound) were mixed. The developer for reversal development of the invention was obtained.

<Example 2> A reversal developing toner of the present invention was obtained in the same manner as in Example 1 except that the amount of magnetite particles attached was 1.0% by weight. The amount T of magnetite particles adhered to the toner for reversal development satisfies the expression 1, and the calculated T is in the range of 0.266% by weight to 1.016% by weight. Next, a carrier 1 composed of 6 parts of the reversal developing toner and ferrite particles (average particle diameter: 90 μm) coated with a silicone resin (having a methyl silicone compound content of 85% by weight).
And 100 parts thereof to obtain a developer for reversal development of the present invention. Example 3 A toner for reversal development of the present invention was obtained in the same manner as in Example 1 except that the content of the magnetite particles was 10 parts by weight and the amount of the magnetite particles attached was 0.1% by weight. . The amount T of the magnetite particles adhered to the toner for reversal development satisfies the expression 1, and the calculated T is in the range of 0.07% by weight to 0.82% by weight. Next, 6 parts of the toner for reversal development and a silicone resin (a content of a methyl silicone compound is 85% by weight)
Particles coated with ferrite particles (average particle size: 9)
0 μm) to obtain a developer for reversal development of the present invention.

Example 4 The toner for reversal development of the present invention was prepared in the same manner as in Example 1 except that the content of the magnetite particles was 10 parts by weight and the amount of the magnetite particles attached was 0.8% by weight. I got The amount T of magnetite particles adhered to the toner for reversal development satisfies the expression 1, and the calculated T is 0.07% by weight to 0.8%.
It is in the range of 2% by weight. Next, 6 parts of the above-mentioned toner for reversal development and 100 parts of a carrier composed of ferrite particles (average particle diameter: 90 μm) coated with a silicone resin (containing 85% by weight of a methylsilicone compound) were mixed. The developer for reversal development of the invention was obtained. Example 5 A toner for reversal development of the present invention was obtained in the same manner as in Example 1, except that the content of magnetite particles was 2 parts by weight and the amount of magnetite particles attached was 1.1% by weight. . The amount T of magnetite particles attached to the toner for reversal development does not satisfy Equation 1, and the calculated T
Ranges from 0.294% to 1.044% by weight. Next, ferrite particles (average particle diameter: 90 μm) coated with 6 parts of the toner for reversal development and a silicone resin (containing 85% by weight of a methyl silicone compound) are coated.
m) was mixed with 100 parts of the carrier to obtain a developer for reversal development of the present invention.

Example 6 The content of magnetite particles was 7 parts by weight and the amount of magnetite particles attached was 0.1% by weight.
A toner for reversal development of the present invention was obtained in the same manner as in Example 1 except that the following conditions were satisfied. Note that the amount T of magnetite particles attached to the reversal developing toner does not satisfy Equation 1, and the calculated T is in the range of 0.154% by weight to 0.904% by weight. Next, 6 parts of the above-mentioned toner for reversal development and 100 parts of a carrier composed of ferrite particles (average particle diameter: 90 μm) coated with a silicone resin (containing 85% by weight of a methylsilicone compound) were mixed. The developer for reversal development of the invention was obtained. Example 7 A toner for reversal development of the present invention was obtained in the same manner as in Example 1 except that the content of magnetite particles was 7 parts by weight and the amount of magnetite particles attached was 1.0% by weight. . The amount T of magnetite particles attached to the toner for reversal development does not satisfy Equation 1, and the calculated T
Ranges from 0.154% to 0.904% by weight. Next, ferrite particles (average particle diameter: 90 μm) coated with 6 parts of the toner for reversal development and a silicone resin (containing 85% by weight of a methyl silicone compound) are coated.
m) was mixed with 100 parts of the carrier to obtain a developer for reversal development of the present invention.

<Example 8> 6 parts of the toner for reversal development obtained in Example 1 and 100 parts of a carrier composed of ferrite particles (average particle diameter: 90 μm) coated with an acrylic resin were mixed to obtain the reversal of the present invention. A developer for development was obtained.

Comparative Example 1 A comparative reversal developing toner was obtained in the same manner except that no magnetite particles were attached.
Next, 6 parts of the toner for reversal development and 100 parts of a carrier made of ferrite particles (average particle diameter: 90 μm) coated with a silicone resin (containing 85% by weight of a methylsilicone compound) were mixed and inverted. A developer for development was obtained.

Next, the developer for reversal development of each of the above Examples and Comparative Examples was installed in a commercially available digital copying machine (trade name: ED3850, manufactured by Toshiba Corp.) using the reversal development method, and charged to 100,00.
Continuous printing was performed up to 0 sheets. Table 1 shows the initial and 10
The results of image density and background fog after 0000 sheets are shown. Here, the image density was measured on a solid image portion with a Macbeth reflection densitometer RD-914, and the background fog was measured with a colorimeter ZE-2000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0021]

[Table 1]

As is clear from the results shown in Table 1, the developer using the toner for reversal development of the present invention in Examples has an image density of 1.3 or more at the initial stage and after 100,000 sheets.
It was confirmed that printing was possible at a practically acceptable value of 1 or less for background fog. On the other hand, it was confirmed that the toner of Comparative Example 1 was extremely fogged after 100,000 sheets, causing a practical problem. Examples 5 to 5 using a reversal developing toner which does not satisfy the range of the calculated value of the formula 1
In No. 7, it was confirmed that the image density or the background fog after 100,000 sheets was inferior to those of Examples 1 to 4. Further, in Example 5, it was confirmed that filming occurred on the photoreceptor after 100,000 sheets and a white portion was missing in the image area. Furthermore, in Example 8 using a carrier coated with an acrylic resin, it was confirmed that the image density after 100,000 sheets was inferior to Examples 1-4.

[0023]

The toner and the developer for reversal development of the present invention can obtain a sufficient image density even when printing a large number of sheets in a system using the reversal development method in which the development potential on the photoreceptor is low. This has the effect of preventing occurrence of background fogging and filming on the photosensitive member.

Claims (5)

[Claims] 1. A toner for reversal development wherein magnetite particles are attached to toner base particles containing at least a binder resin, a colorant and magnetite particles. 2. The reversal developing toner according to claim 1, wherein the amount of magnetite particles contained in the toner base particles is 3 to 10 parts by weight based on 100 parts by weight of the binder resin. 3. The reversal developing toner according to claim 1, wherein the adhesion amount T (% by weight) of the magnetite particles adhering to the toner base particles satisfies the following expression 1. 0.35−0.028C ≦ T ≦ 1.1−0.028C (1) where C is the content of magnetite particles contained in the toner base particles, and 100 parts by weight of the binder resin Parts by weight. 4. A reversal developer containing a carrier and a carrier for reversal development in which magnetite particles are adhered to toner base particles containing at least a binder resin, a colorant and magnetite particles. 5. The developer for reversal development according to claim 4, wherein the carrier is coated with a methyl silicone resin.