JPH02296255A - Black toner for color image - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrophotographic toner, and more particularly to a color black toner useful for full-color copying.

[Prior Art] In electrophotography, a photoconductive layer is uniformly given an electrostatic charge by corona discharge, and a light image corresponding to the original is exposed to this, thereby eliminating the charge in the exposed area and forming a latent image. Let's do it. Development is carried out by depositing toner on the obtained electrostatic latent image. The toner is attracted to the electrostatic latent image depending on the amount of charge on the photoconductive layer, forming a toner image with shading. This toner image is transferred to the support surface and permanently fixed to the support surface using a suitable fixing means such as heat, pressure, solvent treatment, or overcoating.

Development methods include, for example, a cascade development method, a magnetic brush method, a touchdown method, etc. In addition, a bias electric field consisting of an AC component and a DC component is applied between the developer carrier (development sleeve) and the photoconductive layer. The so-called J method is disclosed in Japanese Patent Application Laid-Open No. 62-63970, which performs development.
/B development method etc.

The most commonly used method is the magnetic brush method. This method uses magnetic particles such as steel and ferrite as carriers. A developer consisting of toner and magnetic carrier is held by a magnet, and the magnetic field of the magnet arranges the developer in a brush shape. When this magnetic brush contacts the electrostatic latent image surface on the photoconductive layer, only toner is attracted from the brush to the electrostatic latent image to effect development.

However, this method has extremely low development efficiency because the proportion of consumable toner in the magnetic brush in the development section is small. For example, in some cases, only 1 to 5% toner is used in the total developer. Further, if a large amount of developer is used to increase the developing efficiency, the developing device becomes larger and weighs less, making it unsuitable for reducing the size and weight of a copying machine.

In addition, in terms of image quality, scratches caused by the magnetic brush appear on the developed image like sweeping marks, and the strong mixing of toner and carrier inside the developing device tends to cause electrostatic deterioration, causing non-image areas to deteriorate. There are problems such as so-called fogging, in which toner adheres to the surface.

Further, in the J/B development method, as shown in FIG. 1, a bias electric field consisting 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. In the developing region, 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, and the electric field of the alternating current component is 1000 to 300011z, and 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. , the developing sleeve 13
In this method, the toner on the photosensitive drum 1 and the toner adhering to the surface of the carrier are transferred onto the photosensitive drum 1 to develop a latent image.

In recent years, with the demand for color copying images, there has been a rapid shift from black-and-white copying machines to full-color copying machines, and with the release of two-color color copying machines and digital full-color copying machines, It is done in the market.

Color image formation by full-color electrophotography generally requires 3
All colors are reproduced using the primary colors of yellow, magenta, and cyan toner and four colors including black.

The general method is to first form an electrostatic latent image on a photoconductive layer by passing light from an original through a color-separating light transmitting filter whose color is complementary to the color of the toner. The toner is then held on the support through development and transfer steps. Next, the above-mentioned steps are repeated several times in sequence, and the toners are superimposed on the same support while registering, and a final full-color image is obtained by fixing only one time. The black toner used here has the effect of partially overlapping the upper or lower layer of a toner image composed of three primary colors, similar to the black ink used for printing, to tighten the copied image. It has important functions such as obtaining sharp images and improving the reproducibility of intermediate tones in gray areas.

The present applicant and others have proposed toners and developers that produce black color by combining three non-black chromatic colorants, but the black toners suffer from subtle color changes depending on the manufacturing lot of the colorants and coloring strength. Differences in the level of the black toner or in the kneading manufacturing process of the black toner may cause the bottom color of the black toner to vary significantly, and differences in the dispersibility of the colorant used during kneading may affect the charging characteristics, fluidity, and overall electrophotographic characteristics. However, there are problems in that the selection of the coloring agent and the manufacturing process require extreme care, such as having an adverse effect on the coloring agent.

Carbon black is a coloring agent commonly used as a black toner for electrophotography.

However, when selecting carbon black for full-color use, in addition to the selection criteria for conventional monochrome black-and-white copying machines, the reproducibility of intermediate tones as mentioned above, the undertone color of halftone areas, and the contrast of dark color areas during inking are important. Care must be taken for a wide range of performance reasons, such as high image density and fog removal on white paper.

For example, JP-A-59-187353, JP-A-5910
Publication No. 2250 and Publication No. 53-33151 disclose the use of carbon with a specified range of particle size and oil absorption. The dispersibility of the film becomes poor (and the uneven distribution of carbon!) increases, resulting in an increase in fog. This becomes especially noticeable when the J/[1 development method is used.

However, as the carbon particle size decreases, the tinting power clearly increases and the maximum image density increases with decreasing particle size. This phenomenon is a positive trend for monochrome copying machines as it increases the ta of line images, but when considering full-color copying and trying to satisfy both line image density and halftone gradation, Ba,
The use of this small particle size carbon has to be prohibited. This is because the toner using this has a contrast potential (
V) This is because the slope of the curve obtained from the so-called V-D curve, which is a graph of image density (D) versus image density, becomes very steep, and there is almost no tonality in the middle tones. .

The oil absorption amount in carbon black indicates the length of the stracture of carbon particles, and is a measure of electrical resistance. For example, as the oil absorption becomes smaller, the dispersibility of carbon becomes easier and the electrical insulation properties of the toner increase. Although JP-A-57-181553 specifies only the oil absorption amount, if other characteristics such as electrostatic toner charging characteristics and environmental resistance characteristics are taken into consideration, carbon should be selected based on only these items. I can't.

JP-A No. 54-151648 describes adding 5 to 15 parts by weight of furnace type carbon, but according to studies by the present inventors, 5 parts by weight or more is added when using the J/B development method. Although high image density can be obtained by adding , it has been found that fogging is likely to occur under high temperature and high humidity conditions.

On the other hand, as mentioned above, in color electrophotography, in which multiple toner layers are superimposed on the same support and a copied image is obtained by a single fixing, the fixing characteristics are extremely important even for black toner. is an element. A color copy image in which four color toners are fixed needs to have appropriate gloss and gloss to suppress diffuse reflection caused 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 toners of other colors.

Normally, color toners use sharp-melt binder resins in consideration of gloss and color mixing properties. The same holds true for black toner, but in order to exhibit better offset resistance than other color toners using the same binder resin, it is necessary to select preferably the carbon black to be mixed and dispersed. In other words, as the particle size of carbon becomes finer,
Due to the filler effect, the hot melt viscosity of the black toner becomes high during fixing, and the offset resistance increases. On the other hand, when the particle size becomes larger, the dispersibility of carbon becomes easier, but the offset resistance due to the filler effect decreases.

[Problems to be Solved by the Invention] An object of the present invention is to provide a color black toner that has high image density in dark color areas when inked and has good gray gradation in halftone areas.

Another object of the present invention is to provide a color black toner with good anti-offset properties.

Another object is to provide a black color toner having sufficient triboelectric charging properties.

Another object is to provide a color black toner with high gloss that improves image quality.

Another object of the present invention is to provide a color black toner which has excellent durability even after repeated copying.

[Means and effects for solving the problems] The present invention is characterized by at least an electrophotographic toner comprising a colorant and a binder resin, in which the colorant has an average particle size of 50 to 50.
80mp, oil absorption 50-100cc/100g, pH
6,0 to 9.0, electrical resistance 0.5 to 10 Ω・Cnl, and the toner was heated at 90°C and 100°C.
The apparent viscosity of 104 to 106 poise and 5
Black for colors ranging from 10" to 5 x 105 poise].

The present invention will be explained in detail below.

The average particle size range of carbon black used in the present invention is 5
0 to 80 mp, preferably 55 to 75 mp.

If the amount is less than 50 mg, the dispersibility of carbon becomes extremely difficult.
lF.

Therefore, fogging is likely to occur due to poor dispersion.

It is possible to manufacture toner and improve carbon dispersion by using a sophisticated dispersion device or passing through a dispersion device multiple times, but these all increase the production cost by 1- and are not desirable. It's not a thing. At 80 mp or more, the coloring power is low (and even if the content is increased in the toner, no significant effect can 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 pl+, and volatile content.

Toners used in electrophotography must have a suitable balance between triboelectric charging properties and leakage properties.

In other words, if only the charging characteristics are excellent, a charge-up phenomenon is likely to occur (particularly in low temperature and low humidity environments, the electrostatic force due to excessive charges accumulated by repeated frictional charging causes the toner and carrier to adhere very strongly, causing l. This prevents the toner from flying to the photosensitive drum, causing a low image density.

Therefore, in addition to stably maintaining a desirable amount of charge,
Charge leakage characteristics in toner are important. The electrical resistance of the carbon black contained in the toner is a factor that affects the charge leakage characteristics of the toner. If the electrical resistance is too low, only the charge leakage characteristics will be exhibited and only a low charge amount can be obtained, resulting in high temperature and high temperature. Inadequately charged toner that is not controlled to be charged under humid conditions can cause fogging and image loss.

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

It has appropriate gloss and color mixing properties to improve the quality of color copied images, and is in the top layer of the toner layer as a black 1 to toner for inking, and in order to maintain offset resistance against the fixing roll, 90% The apparent viscosity at ℃ and 100℃ is 104 to 106 poise and 5X10" to 5X1, respectively.
05 poise is required. 90℃ and 100℃
It is important that the viscosity at °C is within this range, and neither color mixing properties nor anti-offset properties can be satisfied if the viscosity is above or below this range.

Also, the oil absorption amount is 50 to 100 cc/100 g, preferably 50 to 90 cc/100 g, and the pll is 6.0 to 9.
0, preferably in the range of 6.5 to 9.0.

In the present invention, the following can be used as the binder resin for toner. 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-acrylic acid ester copolymer Polymers (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-phenyl acrylate copolymer) polymers, etc.)
, styrene-methacrylate copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-phenyl methacrylate copolymer, etc.),
Styrene resins such as styrene-α-methyl chloroacrylate copolymer, styrene-acrylonitrile-acrylic acid ester copolymer (styrene or a homopolymer or copolymer containing a styrene substitute), vinyl chloride resin, styrene- Vinyl acetate copolymer, rosin-modified maleic acid resin, phenol resin, epoxy resin, polyester resin, low molecular weight polyethylene, low molecular weight polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene There are resins, polyvinyl butyral resins, etc. Particularly preferred resins for carrying out the present invention include styrene-acrylic acid ester resins and polyester resins.

In particular, the following formula (wherein R is ethylene or propylene group, x, y
are each an integer of 1 or more, and the average value of X+y is 2 to 10. ) as a diol component, and a carboxylic acid component consisting of a divalent or higher carboxylic acid, its acid anhydride, or its lower alkyl ester, such as fumaric acid, maleic acid, maleic anhydride, phthalate. A polyester resin obtained by cocondensation polymerization with at least an acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc. is particularly preferable because it has sharp melting characteristics.

As the carrier used in the present invention, known materials can be used as long as they do not interfere with the gist of the present invention, such as surface oxidized or unoxidized iron, dimethyl, copper, zinc,
These include metals such as cobalt, manganese, chromium, and rare earths, their alloys or oxides, and ferrites. Particularly preferred are ferrites containing two or more metals selected from the metals zinc, copper, nickel, and cobalt. Can be used. Furthermore, there are no special restrictions on the manufacturing capacity method.

It is also possible to coat the surface of the carrier with a resin or the like. As a method for this, any conventionally known method can be applied, such as a method in which a coating material such as a resin is dissolved or suspended in a solvent and applied and adhered to the carrier, or a method in which a powder is simply mixed.

Substances that adhere to the carrier surface vary depending on the toner material, but include, for example, polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, and g-tert-
It is appropriate to use metal complexes of butylsalicylic acid, styrene resins, acrylic resins, polyacids, polyvinyl butyral, nigrosine, aminoacrylate resins, basic dyes and their lakes, fine silica powder, fine alumina powder, etc., singly or in combination. However, it is not necessarily limited to this.

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

In the present invention, as a particularly preferred embodiment, Cu-Z
It is a ternary n-Fa ferrite, and its surface is coated with a combination of resins such as fluororesin and styrene resin, such as polyvinylidene fluoride and styrene-methyl methacrylate resin; polytetrafluoroethylene and styrene-based resin.
Methyl methacrylate resin, fluorine-based copolymer and styrene-based copolymer; etc. 90:10 to 20:130
．． Preferably 70. : A mixture with a ratio of 30 to 30,001 to 5% by weight, preferably 0.1
Examples include those that are coated ferrite carriers with a weight of 1 to 1. As the fluorine-based copolymer, vinylidene fluoride-tetrafluoroethylene copolymer (
Examples of styrene-based copolymers include styrene-2-ethylhexyl acrylate (20:80-80:20), and styrene-2-ethylhexyl acrylate (20:80-80:20).
-ethylhexyl-methyl methacrylate (20-60:
5-30:10-50) is exemplified.

When preparing a two-component developer by mixing with color toner,
The mixing ratio is 2.5 to 2.5 as the toner concentration in the developer.
Good results are usually obtained at 15% by weight, preferably from 3.0 to 13% by weight. If the toner concentration is less than 2.5% by weight, the image density will be low (it is likely to become unpractical, and 15% by weight)
The above increases fogging and the number of cartridges in the machine, and tends to shorten the useful life of the developer.

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

Oil absorption was measured using an absolute meter, according to ASTM.

Measure according to D-24.

Moreover, the pH value is measured according to the following method.

Weigh 1~log of carbon black into a beaker and give 10mj per 1g of sample. Add water at the same rate and boil for 15 minutes. A few drops of ethyl alcohol may be added to wet the sample. After boiling, cool to the chamber and remove the supernatant liquid by decanting or centrifugation, leaving a slurry. Place the electrode of a glass electrode pH meter into this slurry and adjust the pH.
Measure. In this case, the measured value may change depending on the position of the electrode, so move the beaker to change the position of the electrode, be careful to make sufficient contact between the electrode surface and the mud surface, and then Read the value when the value becomes constant.

The electrical resistance of carbon black is measured with an ohmmeter using a device as shown in FIG.

In this device, carbon 17 to be measured is filled in the center of a cylindrical glass container, and conductive plungers 16.1B', preferably metal plungers, are placed above and below the carbon 17 to be measured.
Lead wires from the upper and lower plungers are connected to an ohmmeter 15.

At this time, a load 18 of 51 (g) is applied to the upper blower.

In addition, the apparent viscosity can be measured using a flow tester CFT-50.
This is carried out using Type 0 (manufactured by Shimadzu Corporation). The sample weighs approximately 1.0 to 1.5 g of a 60-mesh pass product. This is pressurized for 1 minute using a molding machine under a load of 1001+g/cm2.

A flow tester measurement is performed at a temperature of about 20 to 30°C and a humidity of 30 to 70% R11 to obtain a temperature-apparent viscosity curve.

From the obtained smooth curve, determine the apparent viscosity at 90°C and 100°C, and use this as the apparent viscosity for the temperature of the sample.

R to TE TEMP I
i, O07M (℃ l min) SET TEMP
70. ODEG (℃)MAX TE
MP 200. ODEGINTERVAL
3. ODEGPREIIIEAT
300. OSEC (seconds) LOAD
20. OKGF (kg) DIE (DIA)
1.0 MM (IIlm)DIE
(LENG) 1.0 MMPLIIN
GER1, OCu2 (cm2) [Example] The present invention will be explained in detail with reference to Examples below.

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

The manufacturing method is to sufficiently premix the above prescribed amounts using a Henschel mixer, melt-knead them at least twice using a three-roll mill, and after cooling, coarsely pulverize them using a hammer mill to about 1 to 2 mm. It was pulverized to a particle size of 40 pm or less using an air jet type pulverizer. Furthermore, the obtained finely pulverized product was classified and a particle size distribution of 2 to 20 pm was selected so as to have the particle size distribution of the present invention.

The carbon black in the above has an average particle size of 60m.
p, electrical resistance 1.02Ω'cm, oil absorption 65cc/1
00g and a pH value of 8.0.

Further, to the toner according to the present invention, 0.7 parts by weight of fine silica powder treated with Hekitomedildisilazane was added as a fluidity improver per 100 parts by weight of the classified product.

On the other hand, as a carrier, resin-coated Cu-Zn-F
e-type Ferrai I particles were used.

5 parts by weight of toner obtained with the above configuration and 95 parts by weight of carrier
parts by weight to prepare a developer having a total weight of 100 parts. Using this developer, a commercially available color electrophotographic copying machine (color laser copier, manufactured by Canon) having the configuration shown in Fig. 2 is used to create an original manuscript.
When copying was carried out using a copying machine containing text and photographs, a clear copy image with high image density, no image density unevenness, no fogging, and excellent halftone reproducibility was obtained. Furthermore, in order to check the durability of the above developer, repeat 1.
After conducting a copying test of 10,000 copies (normal temperature and humidity 23℃, 6
0%R11), and after 10,000 copies, a clear image without fogging was obtained, similar to the initial image. On the other hand, under a high temperature and high humidity atmosphere (
30℃, 80% old I) and low temperature and low humidity atmosphere (20℃1)
Even with 10% old 1), a good visible image without image density unevenness or fog was obtained.

Incidentally, in this Example 1, the developing method is 5.
A seven-shot development method was used. At this time, the amount of developer (+-ner concentration 5%) applied to the developing sleeve was 34.5 m.
g/cm", and development was carried out by applying a frequency of 2KIIz and a peak to peak voltage of 1.81 (V).
The apparent viscosity at 0°C is 1.2Xlo' poise and
It was 2.3 x 10' poise.

Example 2 Carbon black used as a colorant has an average particle size of 6
8nBt, electrical resistance 2.04Ω・cm, oil absorption 76c
c/100 g and a pH value of 6.0, and the carrier particles to be stirred and mixed with the toner containing the carbon black are styrene-methyl methacrylate-acrylic acid 2-egyl-acrylic acid-coated carrier particles. Cu-Z
n-Fe-based Feli I-particles were used.

A developer was prepared according to Example 1 using the toner and carrier obtained with the above configuration, and the same evaluation was performed one after another. Fog was found!・High-density, clear visible images were obtained that did not cause any distortion.

The apparent viscosity of this toner at 90°C and 100°C was 4.8 x 105 poise and 3.2 x 104 poise.

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

(Margin below) At this time, the developer concentrations of yellow, magenta, cyan, and black toner of Example 1 were 5% and 5%, respectively.
%, 6%, and 5%.

It is shown in FIGS. 1 and 2. A full color copying test was conducted using a color electrophotographic device having a PC photosensitive drum.

Development and transfer of each color toner is magenta toner.

Development and transfer was performed in the order of cyan toner, yellow toner, and black toner so that the black toner was on the top layer.

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

Using this method and using an original with an image area of about 20% in full color mode, a full color image that faithfully reproduces the original color chart with little edge effect even after printing 300,000 sheets was obtained. Further, even during continuous copying, images without blurring or loss of density were obtained, and transport within the copying machine and developer measurement detection were also good and stable. Also, no off-setting of the fixing roller occurred, and there was almost no staining 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 in the 1-toner configuration, the binder resin was styrene-butylene acrylate-medyl methacrylate copolymer and carbon black. Carbon black has an average particle size of 15mp, electrical resistance of 13.5Ω・cm, and oil absorption of 125cc/100.
g-DBP and 911 value of 2.5 were 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 photocopying test was conducted. However, there was a lot of scattering overall (fogging and uneven image density, and good gradation could not be obtained.Furthermore, fogging and scattering worsened significantly under high temperature and high humidity conditions. The temperature of this toner at 90°C
.

The apparent viscosity at 100°C is 7.53X 104
Poise was 6.3 XIO3 poise. Since the black toner had poor thermal meltability overall, low-temperature offset was likely to occur, there was a lot of staining on the fixing cleaning web, and the image was poor in gloss.

Comparative Example 2 In the toner composition of Example 1, the amount of carbon black included in the toner was 1.5% by weight based on the toner weight.
Contains carbon black with an average particle size of 28mp
, electrical resistance 8.5Ω・cm, oil absorption 130cc/10
The same procedure was used except that 0 g-DBP and a 911 value of 2.8 were used, and Example 1 was prepared using ε (a developer was prepared for the first time, and a real photo test was conducted. No fogging occurred in the non-image area. However, the maximum image density was 0.83 (23℃,
Only a low value of 60% (1111) was obtained.

[Effect of the Invention 1 As described above, according to the present invention, high-quality and clear copied images can be obtained.

[Brief explanation of drawings]

1 and 2 are diagrams showing the amount of J/B development, and FIG. 3 is a diagram showing an apparatus for measuring the electrical resistance of carbon black.

Claims (1)

[Claims] (1) An electrophotographic toner comprising at least a colorant and a binder resin, the colorant having an average particle size of 50 to 8
0mμ, oil absorption 50-100cc/100g, pH 6.
Using carbon black with an electric resistance of 0 to 9.0 and an electrical resistance of 0.5 to 10 Ωcm, the apparent viscosity of the toner at 90°C and 100°C is 10^4 to 10^6 poise and 5 × 10^, respectively.
A black toner for color use that is characterized by being in the range of 3 to 5 x 10^5 poise.