JP2859637B2 - Black toner for color image formation - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner, and more particularly, to a black toner for forming a color image useful for full-color copying.

[Prior art] In electrophotography, a latent image is formed by uniformly applying an electrostatic charge to a photoconductive layer by corona discharge and exposing it to a light image corresponding to a document, thereby extinguishing the charge in an exposed portion. Do.
The development is carried out by attaching toner onto the obtained electrostatic latent image. The toner is attracted to the electrostatic latent image according to the amount of charge on the photoconductive layer, and forms a toner image having a density. This toner image is transferred to the support surface, and is permanently fixed to the support surface by using an appropriate fixing means such as heating, pressing, solvent treatment, or overcoating treatment.

Examples of the developing method include a cascade developing method, a magnetic brush method, and a touch-down method. In addition, a bias electric field including an AC component and a DC component is applied between the developer carrier (developing sleeve) and the photoconductive layer. And develop
It is disclosed in JP-A-62-63970. There is a so-called J / B development method.

The most widely used method is a magnetic brush method. This method uses magnetic particles such as steel and ferrite as a carrier. The developer including the toner and the magnetic carrier is held by a magnet, and the developer is arranged in a brush shape by the magnetic field of the magnet. When the magnetic brush comes into contact with the electrostatic latent image surface on the photoconductive layer, only the toner is attracted from the brush to the electrostatic latent image to perform development.

However, this method has extremely low development efficiency because the ratio of the consumable toner in the magnetic brush in the developing section is small. For example, only 1% to 5% of the total developer may be used. If a large amount of developer is used to increase the development efficiency, the size and weight ratio of the developing device are reduced, which is not suitable for reducing the size and weight of the copying machine.

Also, in terms of image quality, traces of rubbing by the magnetic brush are generated on the developed image as in the case of sweeping, and strong mixing of the toner and the carrier inside the developing device tends to cause charging deterioration. There is a problem in that so-called fogging is likely to occur.

In the J / B development method, as shown in FIG. 1, a bias electric field composed of an AC component and a DC component is applied between the developing sleeve 13 and the photosensitive drum 1 having an electrostatic latent image. The volume occupied by the carrier in the developing section of the developing sleeve 13 is 1.5 to 40% of the volume of the space formed by the developing sleeve 13 and the photosensitive drum 1 in the developing area. 3000 Hz, the peak-to-peak voltage is adjusted to a voltage that does not destroy the electrostatic latent image and moves the carrier between the developing sleeve 13 and the photosensitive drum 1 in the developing area.
This is a method of developing the latent image by transferring the toner on the developing sleeve 13 and the toner to the photosensitive drum 1 attached to the carrier surface.

In recent years, along with the demand for colorized copy images, the development from black-and-white copiers to full-color copiers has been rapidly progressing, and two-color copiers and digitized full-color copiers have also been released. It is taking place in the market.

Color image formation by full-color electrophotography generally reproduces all colors using three primary colors of yellow, magenta, and cyan color toners and four colors including black.

In the general method, first, an electrostatic latent image is formed on a photoconductive layer by passing light from an original through a color separation light transmission filter having a complementary color relationship with the color of the toner. Next, the toner is held on a support through development and transfer steps. Next, the above-described steps are sequentially performed a plurality of times, and while the registration is being performed, the toner is superimposed on the same support, and the final full-color image is obtained by performing the fixing only once. The black toner used here is, like the black ink for inking in printing, the black toner is partially overlapped on the upper or lower layer of the toner image composed of the three primary colors, and the function of drawing the copied image and the function of drawing It has important functions such as obtaining an image having a certain color and enhancing the reproducibility of a halftone in a gray portion.

The present applicants have proposed a toner and a developer that produce black by combining three chromatic colorants other than black. However, the black toner has a subtle color change due to a production lot of the colorant and a coloring power. The height of the black toner or the kneading of the black toner is different. Depending on the difference in the height, the undertone of the black toner is significantly different, and the difference in dispersibility of the used colorant during kneading causes the charging characteristics and fluidity, and thus the overall electrophotographic characteristics. It has problems such as the need for extreme care in the selection of the colorant and the manufacturing process, such as adverse effects on

As the colorant conventionally used as a black toner for electrophotography, carbon black is first mentioned.
However, the selection of carbon black for full color is based on the selection criteria in the case of the conventional mono-color black-and-white copying machine, as well as the halftone reproducibility, the bottom color of the halftone portion, A great deal of caution is required due to the wide variety of performances, such as high image density and fog removal on white paper.

For example, JP-A-59-187353, JP-A-59-102250, and JP-A-53-33151 disclose the use of carbon having a specified particle size or oil absorption range.
In the following, as the particle size decreases, the dispersibility in the binder resin worsens, the uneven distribution of carbon increases the toner,
It will increase fog. In particular, when the J / B developing method is used, it becomes more remarkable. However, as the particle size of the carbon decreases, the tinctorial strength increases and the maximum image density increases with decreasing particle size. This development is intended to increase the density of a line image for a mono-color copying machine, and is a preferable tendency.However, considering full-color copying, if it is intended to satisfy both the line image density and the gradation in halftone, The use of this small particle size carbon is inevitable. The reason is that the toner using this is a graph of contrast potential (V) versus image density (D),
This is because the slope of the curve obtained from the so-called VD curve becomes very steep, and almost no gradation in halftones.

The amount of oil absorption in carbon black indicates the length of the structure of the carbon particles, and serves as a measure of electric resistance. For example, as the oil absorption becomes smaller, the dispersibility of carbon becomes easier and the electrical insulation of the toner increases. In Japanese Patent Application Laid-Open No. 57-181553, only the amount of oil absorption is specified, but if various other characteristics such as the charging characteristics and environmental resistance characteristics of the electrophotographic toner are taken into consideration, carbon should be selected based on these items. Can not.

JP-A-54-151648 discloses that 5 to 15 parts by weight of a fornes type carbon is added. According to the study of the present inventors, when using the J / B developing method, 5 parts by weight or more is used. It has been obtained that the addition of a high density gives a high image density, but tends to cause fogging under high temperature and high humidity.

On the other hand, as described above, in a color electrophotographic method in which a plurality of toner layers are superimposed on the same support to obtain a copy image by one-time fixing, the fixing property is a very important element even for a black toner. . A color copy image in which four color toners are fixed needs to have an appropriate glossiness and gloss to suppress irregular reflection by toner particles. Further, since the black toner is generally present in the uppermost layer of the three primary color toner layers, more attention must be paid to the offset resistance to the fixing roller than to toners of other colors.

For a normal color toner, a binder resin having a sharp melt property is used in consideration of gloss and color mixing. The same applies to the black toner. However, in order to exhibit the offset resistance more than other color toners by using the same binder resin, it is necessary to preferably select carbon black mixed and dispersed. That is, as the particle size of carbon becomes smaller, the hot melt viscosity of the black toner during fixing becomes higher due to the filler effect, and the offset resistance increases. Conversely, when the particle size is large, the dispersibility of carbon is easy, but the offset resistance due to the filler effect is reduced.

[Problems to be Solved by the Invention] An object of the present invention is to provide a high image density in a dark portion when inking,
An object of the present invention is to provide a black toner for forming a color image having a good gray gradation in a halftone portion.

Another object is to provide a black toner for forming a color image having good offset resistance.

Another object is to provide a black toner for forming a color image having a sufficient triboelectric charging property.

It is another object of the present invention to provide a black toner for forming a color image having high gloss, which enhances image quality.

Another object of the present invention is to provide a black toner for forming a color image having excellent durability, which is less likely to cause carrier spent due to repeated copying.

[Means and Actions for Solving the Problems] The above object is achieved by the present invention described below.

That is, the present invention relates to a black toner for forming a color image for forming a color image in combination with a color toner containing a chromatic colorant, wherein the black toner comprises at least carbon black as a colorant and a binder resin. The carbon black has an average particle size of 50 to 80 mμ, an oil absorption of 50 to 90 cc / 100 g,
It has pH 6.0-9.0 and electrical resistance 0.5-10Ωcm,
The black toner has an apparent viscosity at 90 ° C. in the range of 10 ⁴ to 10 ⁶ poise and an apparent viscosity at 100 ° C. in the range of 5 × 10 ³ to 10 ⁵ poise. Related to toner.

 Hereinafter, the present invention will be described in detail.

The range of the average particle size of the carbon black used in the present invention is
It is 50 to 80 mμ, preferably 55 to 75 mμ. If it is less than 50 μm, the dispersibility of carbon becomes extremely difficult, and fog due to poor dispersion is likely to occur.

Although it is possible to produce toner and improve dispersion of carbon by using an advanced dispersing device or passing through a dispersing device many times, all of these are unfavorable because they increase the production cost. . If it exceeds 80 μm, the coloring power is low, so that even if the content in the toner is increased, a significant effect cannot be expected.

The electrical resistance of carbon black is closely correlated with the physical properties of the carbon, and its factors include particle size, oil absorption, specific surface area, structure, pH, volatile content, and the like.

Toners used in electrophotography must have an appropriate balance between tribocharging properties and leakage properties.

That is, if only the charging characteristics are excellent, the charge-up phenomenon is liable to occur.Especially under low temperature and low humidity, the electrostatic force due to the excessive charge accumulated by the repeated triboelectric charge causes the toner and the carrier to adhere very strongly, and the toner It hinders flying to the photosensitive drum and causes a low image density.
Therefore, in addition to stably maintaining a preferable charge amount,
The charge leakage property of the toner is important. The electric resistance of the carbon black contained in the toner is a factor that affects the charge leakage characteristics of the toner. If the electric resistance is too low, only the electric leakage characteristics are exhibited, and only a low charge amount can be obtained. It causes fogging and image scattering due to insufficiently charged toner that is not controlled to be charged under moisture.

However, the range of the electrical resistance of the carbon black is 0.5 to 10 Ω · cm, preferably 0.6 to 7 Ω · cm.

It has moderate gloss and color mixing to enhance the quality of color copied images, and is located on the uppermost layer of the toner layer as black toner for inking.In order to maintain the offset resistance to the fixing roll, 90 ° C, It is necessary that the apparent viscosity at 100 ° C. is 10 ⁴ to 10 ⁶ poise and 5 × 10 ^{3 to} 5 × 10 ⁵ poise, respectively. It is important that the viscosities at 90 ° C. and 100 ° C. are in the above-mentioned range, and it is not possible to satisfy both the color mixing property and the anti-offset property even above or below the range.

It is necessary to use oil having an oil absorption of 50 to 90 cc / 100 g and a pH of 6.0 to 9.0, preferably 6.5 to 9.0.

In the present invention, as the binder resin for toner, the following can be used, for example, polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, Styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylate copolymer (styrene-methyl acrylate copolymer,
Styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-phenyl acrylate copolymer, etc., styrene-methacrylic ester copolymer (styrene-methacrylic) Methyl acrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-phenyl methacrylate copolymer), styrene-α-methyl methacrylate copolymer, styrene-acrylonitrile A styrene resin such as an acrylate copolymer (a homopolymer or a copolymer containing styrene or a styrene substituent), a vinyl chloride resin,
Styrene-vinyl acetate copolymer, rosin-modified maleic resin, phenolic resin, epoxy resin, polyester resin, low molecular weight polyethylene, low molecular weight polypropylene,
Examples include an ionomer resin, a polyurethane resin, a silicone resin, a ketone resin, an ethylene-ethyl acrylate copolymer, a xylene resin, and a polyvinyl butyral resin. Particularly preferred resins in the practice of the present invention include styrene-acrylate resins and polyester resins.

In particular, (Wherein R is an ethylene or propylene group, x and y are each an integer of 1 or more, and the average value of x + y is 2
~ 10. A) a carboxylic acid component comprising a dicarboxylic acid or its anhydride or a lower alkyl ester thereof, such as fumaric acid, maleic acid, and weightless maleic acid; A polyester resin obtained by at least co-condensation polymerization of phthalic acid, terephthalic acid, trimellitic acid, promellitic acid and the like is particularly preferable because it has sharp melting characteristics.

As the carrier used in the present invention, known materials can be used without departing from the scope of the present invention. For example, surface-oxidized or unoxidized iron, nickel, copper, zinc, cobalt, manganese, chromium, rare earth elements And ferrites containing two or more metals selected from zinc, copper, nickel, and cobalt. There is no particular restriction on the manufacturing method.

It is also possible to coat the surface of the carrier with a resin or the like. As the method, any conventionally known method such as a method of dissolving or suspending a coating material such as a resin in a solvent, coating and adhering to a carrier, and a method of simply mixing with a powder can be applied.

The fixing substance on the carrier surface varies depending on the toner material. Examples thereof include polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal complex of di-tert-butylsalicylic acid, and styrene resin. It is appropriate to use acrylic resin, polyacid, polyvinyl butyral, nigrosine, amino acrylate resin, basic dyes and lakes thereof, silica fine powder, alumina fine powder or the like alone or in plurals, but it is not necessarily limited thereto. .

The amount of the compound to be treated may be appropriately determined so that the carrier satisfies the above conditions, but is generally desirably 0.1 to 30% by weight (preferably 0.5 to 20% by weight) based on the carrier of the present invention.

In the present invention, a particularly preferred embodiment is Cu-Zn-
Fe ternary ferrite, the surface of which is a combination of a resin such as a fluorine resin and a styrene resin, for example, polyvinylidene fluoride and styrene-methyl methacrylate resin; polytetrafluoroethylene and styrene-methyl methacrylate resin; 90: 10-20: 80, such as a fluorine-based copolymer and a styrene-based copolymer, preferably 70: 30-30:
A mixture of 70 to 70% by weight, preferably 0.1 to 1% by weight, is a coated ferrite carrier. Examples of the fluorine-based copolymer include vinylidene fluoride-tetrafluoroethylene copolymer (10:90 to 90:10), and examples of the styrene-based copolymer include styrene-2-ethylhexyl acrylate (20:80 to 90%). 80:20), styrene-2-ethylhexyl acrylate-methyl methacrylate (20-60: 5-30: 10-50)
Is exemplified.

When preparing a two-component developer by mixing with a color toner, the mixing ratio is 2.5% as the toner concentration in the developer.
Good results are usually obtained at levels of up to 15% by weight, preferably 3.0 to 13% by weight. When the toner concentration is less than 2.5% by weight, the image density is low and it is not practical to use. When the toner concentration is more than 15% by weight, fog and scattering in the machine are increased, and the useful life of the developer is easily shortened.

In the measurement of the average particle diameter in the present invention, the carbon particle diameter is directly measured from a transmission electron micrograph of carbon black, and the average particle diameter is determined from the distribution degree based on 100 measurement data.

The oil absorption is measured using an absorbometer in accordance with ASTM, D-24.

 The pH value is measured according to the following method.

1 to 10 g of carbon black is measured in a beaker, water is added at a ratio of 10 ml per 1 g of the sample, and the mixture is boiled for 15 minutes. To make the sample wet easily, a few drops of ethyl alcohol may be added. After boiling, the mixture is cooled to room temperature, and the supernatant is removed by a gradient method or a centrifugal separation method to leave a muddy substance. An electrode of a glass electrode pH meter is put into the mud and the pH is measured. In this case, the measured value may change depending on the insertion position of the electrode, so move the beaker to change the position of the electrode,
Take care that the electrode surface and the muddy surface make sufficient contact,
Read the value at which the pH value becomes constant.

The electric resistance of carbon black is measured by an ohmmeter using an apparatus as shown in FIG.

The apparatus comprises a cylindrical glass container filled with carbon 17 to be measured in the center, and a plunger having conductivity above and below it.
16, 16 'preferably a metal plunger is set, and leads are connected to the ohmmeter 15 from the upper and lower plungers. At this time, a load 18 of 5 kg is applied to the upper plunger.

The measurement of the apparent viscosity is performed using a flow tester CFT-500 type (manufactured by Shimadzu Corporation). A sample weighs about 1.0 to 1.5 g of a 60 mesh pass product. Using a molding machine,
Press for 1 minute with a load of 00 kg / cm ² .

Perform a flow tester measurement at a temperature of about 20 to 30 degrees and a humidity of 30 to 70% RH to obtain a temperature-apparent viscosity curve. From the obtained smooth curve, the apparent viscosities at 90 ° C. and 100 ° C. are determined and are defined as the apparent viscosities for the temperature of the sample.

RATE TEMP 6.0 D / M (° C for 1 minute) SET TEMP 70.0 DEG (° C) MAX TEMP 200.0 DEG INTERVAL 3.0 DEG PREHEAT 300.0 SEC (seconds) LOAD 20.0 KGF (kg) DIE (DIA) 1.0 MM (mm) DIE (LENG) 1.0 MM PLUNGER 1.0 CM ² (cm ² ) [Example] Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 The black powder having a weight average particle diameter of 8 μm having the above configuration is used as a toner classified product.

The production method is that the above-mentioned formulation amounts are sufficiently preliminarily mixed with a Henschel mixer, melt-kneaded at least twice with a three-roll mill, cooled, roughly crushed using a hammer mill to about 1-2 mm, and then air-cooled. It was pulverized to a particle size of 40 μm or less by a jet-type pulverizer. Further, the obtained finely pulverized product was classified, and 2 to 20 μm was selected so as to have the particle size distribution of the present invention.

The above carbon black has an average particle size of 60m
μ, an electrical resistance of 1.02 Ω · cm, an oil absorption of 65 cc / 100 g, and a pH value of 8.0 were used. Further, 0.7 parts by weight of a silica fine powder treated with hexamethyldisilazane was added as a fluidity improver to the toner according to the present invention in an amount of 0.7 parts by weight based on 100 parts by weight of the classified product.

On the other hand, resin-coated Cu-Zn-Fe-based ferrite particles were used as the carrier.

5 parts by weight of toner obtained by the above configuration and carrier 95
Parts by weight to prepare a developer having a total weight of 100 parts.
Using this developer, using a commercially available color electrophotographic copying machine (color laser copier, manufactured by Canon Inc.) having a configuration as shown in FIG. As a result of copying, a clear copied image having high image density, no image density unevenness and no fog, and excellent in halftone reproducibility was obtained. Further, in order to examine the durability of the developer, a copy test was repeatedly performed on 10,000 sheets (normal temperature and normal humidity: 23 ° C., 60 ° C.).
% RH) After 10,000 copies, a clear image without fog, similar to the initial image, was obtained. On the other hand, under high temperature and high humidity atmosphere (30 ℃, 8
(0% RH) and under a low-temperature and low-humidity atmosphere (20 ° C., 10% RH), a good visible image without image density unevenness and fog was obtained.

Incidentally, in Example 1, the developing method was
The J / B development method was used. At this time, the application amount of the developer (toner concentration 5%) on the developing sleeve is 34.5 mg / cm ² , the frequency is ² KHz, and the peak to peak is applied.
The development was performed by applying a voltage of 1.8 KV. Also at this time 90
The apparent viscosities at ° C and 100 ° C were 1.2 × 10 ⁵ poise and 2.3 × 10 ⁴ poise, respectively.

Example 2 Carbon black used as a colorant had an average particle size
68mμ, electric resistance 2.04Ω ・ cm, oil absorption 76cc / 100g, and pH
As the carrier particles having a valence of 6.0 and being stirred and mixed with the toner having the carbon black, Cu-Zn-Fe-based ferrite particles coated with a styrene-methyl methacrylate-2-ethylhexyl acrylate copolymer were used.

A developer was prepared according to Example 1 using the toner and carrier obtained by the above-described configuration, and the same evaluation was sequentially performed. As a result, a clear image with a high density and a clear image without fogging or toner scattering was obtained.

The apparent viscosity at 90 ° C and 100 ° C of this toner is 4.8
× 10 ⁵ poise and 32 × 10 ⁴ poise.

Example 3 To 100 parts by weight of a polyester resin obtained by condensing propoxylated bisphenol and fumaric acid, a coloring agent and a charge control agent having the prescribed amounts shown in Table 1 were used.
Magenta and cyan color toners having an average particle size of 8 μm were obtained.

At this time, the developer concentrations of the yellow, magenta, cyan, and black color toners of Example 1 were 5% and 5%, respectively.
%, 6% and 5%.

A full-color copying test was performed using a color electrophotographic apparatus having the OPC photosensitive drum shown in FIGS.

The development and transfer of each color toner were performed in the order of magenta toner, cyan toner, yellow toner, and black toner, and development transfer was performed so that the black toner was on the uppermost layer.

The developer is provided on a developing sleeve 13 with a developer regulating blade.
The amount of the developer becomes a fixed amount due to 14, and the negatively charged toner is transferred onto the photosensitive drum 1 by the reversal development method at the opposite portion of the photosensitive drum 1 having the negatively charged electrostatic latent image.

Using this method, a full-color image that faithfully reproduces the original color chart with little edge effect was obtained after printing 30,000 sheets using a manuscript having an image area of about 20% in the full-color mode. In addition, an image without blurring and density reduction was obtained even during continuous copying, and the conveyance in the copying machine and the detection of the developer density were good and stable. Also, no offset was generated with respect to the fixing roller, and there was almost no contamination on the cleaning web attached to the fixing roller.

Comparative Example 1 A toner was obtained in the same manner as in Example 1 except that the binder resin was styrene-butyl acrylate-methyl methacrylate copolymer and carbon black as the binder resin. As carbon black, average particle size 15 mμ, electric resistance 13.5 Ωcm, oil absorption 125 cc / 100 g-DBP, and pH value 2.5
Was used.

Using this comparative toner 1 and the carrier in Example 1, a developer was prepared in the same manner as in Example 1, and a real-image test was performed. It was stable. However, scattering was large as a whole, fogging occurred, image density was uneven, and good gradation was not obtained. Further, fog and scattering significantly deteriorated under high temperature and high humidity. 90 ℃ of this toner, 1
The apparent viscosity at 00 ° C is 7.53 × 10 ⁶ poise and 6.3 ×
It was 10 ⁵ poise. Since the black toner had poor heat melting properties as a whole, low-temperature offset was liable to occur, the fixing cleaning web was often stained, and the image was poor in glossiness.

Comparative Example 2 In the toner composition of Example 1, the amount of carbon black contained in the toner was 1.5% by weight based on the weight of the toner.
Contain, average particle size 28mμ as carbon black,
Electric resistance 8.5Ωcm, lubrication amount 130cc / 100g-DBP and pH value 2.
A developer was prepared in the same manner as in Example 1 except that Sample No. 8 was used, and a real-image test was performed. As a result, no fogging or the like occurred in the non-image area.
83 (23 ° C., 60% RH), a low value was obtained.

[Effects of the Invention] As described above, according to the present invention, a high-quality clear color image can be obtained.

[Brief description of the drawings]

1 and 2 are views showing a J / B development method, and FIG. 3 is a view showing an apparatus for measuring the electric resistance of carbon black.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshinobu Baba 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-62-291667 (JP, A) JP-A-63 -128363 (JP, A) JP-A-1-100563 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/09

Claims (2)

(57) [Claims] 1. A color image forming black toner for forming a color image in combination with a color toner containing a chromatic colorant, wherein the black toner contains at least carbon black as a colorant and a binder resin. Contains, the carbon black has an average particle size of 50 to 80 mμ, an oil absorption of 50 to 90 cc / 100 g, pH
The black toner has an apparent viscosity at 90 ° C. in the range of 10 ⁴ to 10 ⁶ poise, and an apparent viscosity at 100 ° C. of 5 × 10 ³ to 10 × 10 ³ Ω · cm. A black toner for forming a color image, which is in a range of 5 × 10 ⁵ poise. 2. The black toner according to claim 1, wherein the black toner is selected from the group consisting of a magenta toner, a cyan toner, and a yellow toner.
The black toner for forming a color image according to claim 1, wherein the black toner is used for forming a color image in combination with at least one kind of color toner.