JP2000194164A - Toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a toner having fog-free clear image characteristics and excellent in endurance stability by using carbon black having a specified ionization potential as a colorant and a bonding resin having a specified acid value. SOLUTION: The toner contains at least a bonding resin and a colorant. This colorant is carbon black having <=4.60 eV ionization potential and the acid value of the bonding resin is 5-30 mgKOH/g, preferably 10-20 mgKOH/g. When the ionization potential of the carbon black exceeds 4.60 eV, the electrical affinity for the bonding resin becomes small and the carbon black is not sufficiently dispersed in the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner used in an image forming method such as an electrophotographic method and a toner jet.

[0002]

2. Description of the Related Art In electrophotography, a latent image is formed by uniformly applying an electrostatic charge to a photoconductive layer by corona discharge and exposing the image to a light image corresponding to a document, thereby extinguishing the charge in an exposed portion. Perform 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, latent image processing, or overcoating.

The developing method includes, for example, a cascade developing method, a magnetic brush method, and a touch-down method. In addition, the developing method includes an AC component and a DC component between a developer carrier (developing sleeve) and a photoconductive layer. There is a so-called J / B development method disclosed in JP-A-62-63970 in which a bias electric field is applied to perform development.

The most commonly used method is a magnetic brush method. In this method, magnetic particles such as steel and ferrite are used 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 SW 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.

[0005] However, this method has extremely low development efficiency because the ratio of 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. Also, if a large amount of developer is used to increase the development efficiency, the size of the developing device becomes large,
This causes an increase in weight, which is unsuitable for reducing the size and weight of the copying machine.

Conventionally, carbon black is generally used as a colorant used in black toner for electrophotography. However, when a large amount of carbon black is used to compensate for low development efficiency, the conductive effect is increased. Along with this, the charging ability is reduced, and toner adhesion to non-image areas, so-called fogging and dispersibility is reduced, and a difference in the triboelectric charging amount is caused between low temperature, low humidity, and high temperature, high humidity environments.

In order to prevent such a problem, a method of using carbon black having a high coloring power to reduce the content in the toner and a method of oxidizing the surface of carbon black to increase the resistance of the carbon black are proposed. No.

As the surface oxidation treatment method, for example,
There is an oxidation treatment method using potassium permanganate as described in JP-A-31139. However, in this method, metal ions tend to remain as a counter ion of the carboxyl group on the carbon black surface, and the resistance of the carbon black decreases, and when used in a toner, it is not enough to improve the durability under high humidity. Effects cannot be obtained.

Further, Japanese Patent Application Laid-Open No. 3-200158 discloses a surface oxidation treatment method using ozone, the content of which is described in US Pat. The purpose is to improve the dispersibility of black, but it is not sufficient in terms of improving the durability characteristics of the toner under high humidity.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a toner which has clear image characteristics without fogging and has excellent durability stability.

Another object of the present invention is to provide a toner which has little environmental dependency of triboelectric charging.

[0012]

According to the present invention, there is provided a toner containing at least a binder resin and a colorant, wherein the colorant is carbon black having an ionization potential of 4.60 eV or less. Has an acid value of 5 to 3
0 mgKOH / g.

According to the present invention having the above-described structure, the dispersibility of the colorant is improved by combining it with a binder resin.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, the coloring power of carbon black increases as the particle size decreases, and especially increases dramatically below 50 nm. Therefore, if the particle size is reduced, the carbon black content can be suppressed to obtain a high image density, which causes fog due to low toner resistance and a difference in the amount of triboelectricity between environments. There is no.

However, it is generally known that the smaller the particle size of carbon black, the worse the dispersibility in the resin. If the dispersibility is poor, the carbon black aggregates, causing an increase in the conductivity and a concomitant decrease in the charge amount.

As a method of improving the dispersibility of carbon black, it has been found that the problem can be solved by focusing on the ionization potential of carbon black.

Further studies were conducted, and as a result of intensive studies, the ionization potential of the carbon black surface was 4.6 e.
V or less, and an acid value of 5 to 30 mg KO
It has been found that, when a toner is produced by combining a binder resin in the range of H / g, the dispersibility of carbon black in the binder resin is greatly improved.

"Ionization potential" in the present invention
The term “is defined as the ionization potential of the carbon black when the photoelectrons are measured while irradiating the carbon black with light and changing the wavelength (energy) thereof.

Although the theoretical support for improving the dispersibility by the ionization potential is not clear, it can be estimated as follows.

It is considered that the carbon black particles are covered with the resin by the electric affinity between the surface of the carbon black and the resin, thereby preventing re-aggregation of the carbon black particles. It was found that it was closely correlated with the ionization potential of the surface. As a result of repeated detailed studies, when the ionization potential on the surface of the carbon black was at the above value, the dispersibility was the best.

The reason that the ionization potential of carbon black is limited to 4.60 eV or less is that the ionization potential of carbon black exceeds 4.60 eV.
This is because the electric affinity with the binder resin is reduced, and the carbon black is not sufficiently dispersed in the resin.

On the other hand, the acid value of the binder resin is 5 to 30 mg KO.
H / g, preferably 10 to 20 mgKOH / g.

If the acid value of the resin is less than 5 mgKOH / g, the binder resin does not have sufficient acid groups for adsorbing carbon black, and carbon black aggregates are present and cannot be uniformly dispersed. As a result, the chargeability decreases due to the increase in conductivity.

When the amount exceeds 30 mg KOH / g,
A large amount of functional groups are present in the binder resin, and the moisture resistance is reduced.

The primary average particle size of the carbon black used in the present invention is preferably 50 nm or less, more preferably 40 nm or less.
nm or less.

If the thickness exceeds 50 nm, a large amount of carbon black must be added in order to weaken the coloring power and produce a satisfactory black color. Will occur.

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

In the toner of the present invention, the amount of carbon black added is 10 to 100 parts by weight of the binder resin.
The appropriate amount is not more than 6 parts by weight, more preferably not more than 6 parts by weight. If the addition amount exceeds 10 parts by weight, the resistance as a toner decreases, the charge amount also decreases, and the durability under high humidity decreases.

As a specific method for measuring the ionization potential of carbon black, a method under the following conditions can be used.

Ionization potential measurement device: Surface analysis device AC-1 (manufactured by Riken Keiki Co., Ltd.). This device counts photoelectrons excited by ultraviolet light in the atmosphere and analyzes the sample surface. Ambient temperature and relative humidity during measurement: 20 ° C, 60% Counting time: 10 seconds / 1 point Light intensity setting: 50 μW / cm ² Light intensity correction: Corrected with attached program with the above settings Energy scanning range : 3.4 to 6.2 eV Ultraviolet spot diameter: 1 mmSQ Unit photon: 1 × 10 ¹⁰ / cm ² · sec

The measurement sample is 1 mm deep and 7 mm in diameter.
Put the charge transport material powder in the aluminum pan of
The distance between the powder surface of the charge transport material and the ultraviolet irradiation position is 2 m
m. The calculation of the ionization potential is performed according to the attached work function calculation program, and the count value (C
The linear portion obtained from the square root of (PS) versus the ultraviolet excitation energy is extrapolated to a point that intersects the background, and that point is defined as the ionization potential.

FIG. 1 shows the CP measured by the above method.
3 is a graph showing an example of a curve showing the relationship between the square root of S and ultraviolet excitation energy (eV), and a method for obtaining an ionization potential from the curve. A shown in FIG. 1 is obtained as a substance-specific ionization potential.

The binder resin used in the toner of the present invention is not particularly limited as long as it satisfies the above-mentioned acid value.
Chlorostyrene copolymer, styrene-acrylate copolymer, styrene-methacrylic acid copolymer, rosin-modified maleic resin, epoxy resin, polyester resin, polyethylene resin, polypropylene resin, polyurethane resin and the like can be mentioned. These may be used alone or as a mixture.

As the colorant, at least carbon black is used, and the use of other colorants is not particularly limited.

As other coloring agents, any suitable pigments,
Or a dye can be used. Examples include coloring agents such as titanium oxide, zinc white, alumina white, phthalocyanine blue, peacock blue, permanent red, lake red, rhodamine dyes, anthraquinone dyes, monoazo and diazo pigments, and quinacridone dyes alone or as a mixture. Can be used together.

As the charge control agent that can be used in the present invention as required, any suitable charge control agent can be used. For example, a nigrosine dye or a quaternary ammonium salt is used for a positively charged toner, and a metal-containing monoazo dye is used for a negatively charged toner.

In addition, an external additive such as silica fine powder or alumina can be added to the toner particles in order to improve the fluidity and aggregation resistance of the toner.

The method for producing the toner is not particularly limited. For example, a binder resin, a charge control agent and a colorant are sufficiently mixed by a mixer such as a Henschel mixer, and then melt-kneaded by a twin screw extruder or the like. After cooling, pulverizing and classifying, adding an external additive, and mixing with a mixer or the like.

The toner of the present invention can be used for either a one-component developer or a two-component developer. When the toner is used as a two-component developer, the carrier to be used is, for example, surface oxidized or unoxidized. Iron oxide, nickel, copper,
There are metals such as zinc, cobalt, manganese, chromium, magnesium, rare earths, alloys thereof, oxides and ferrites, and particularly preferably ferrites containing two or more metals selected from these metals can be used. . In addition, there is no particular limitation on the manufacturing method.

It is also possible to cover 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.

Examples of the substance fixed to the carrier surface include polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal complex of di-tert-butylsalicylic acid, styrene resin, and acrylic resin. It is appropriate to use one or more of a series resin, polyamide polyvinyl butyral, nigrosine, aminoacrylate resin, basic dyes and lakes thereof, silica fine powder, alumina fine powder, etc., but it is not necessarily limited thereto.

The treatment amount of the above compound is generally desirably 0.1 to 30% by weight based on the total amount of the carrier.

When a two-component developer is prepared, the mixing ratio is 2.5 to 1 as a toner concentration in the developer.
Good results are usually obtained with 5% 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 the toner. 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.

[0044]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

(Resin Production Examples A to D) Polyester resin A having an acid value of 10 mgKOH / g was synthesized by condensation polymerization of terephthalic acid, propoxylated bisphenol and ethoxylated bisphenol.

The reaction conditions were adjusted and the acid value was adjusted to 30 mgK.
OH / g polyester resin B and acid value 3 mg KOH /
g of polyester resin C and a polyester resin D having an acid value of 50 mgKOH / g were synthesized.

Measurement of acid value of binder resin: A sample is precisely weighed, dissolved in a mixed solvent and water is added. The solution is subjected to potentiometric titration with 0.1 N-NaOH using a glass electrode to determine an acid value (according to JIS K1557-1970).

[Toner Production Example 1] 100 parts by weight of polyester resin A 4 parts by weight of aluminum complex compound of 3,5-di-tert-butylsalicylic acid 3 parts by weight of carbon black A 3 parts by weight The above-mentioned formulation amounts were premixed with a Henschel mixer. Doing, melt kneading, cooling and using a hammer mill about 1 ~
It was roughly pulverized to about 2 mm, and then finely pulverized to a particle size of 40 μm or less by a pulverizer using an air jet method. Furthermore, the obtained finely pulverized material is classified, and 2 to 20 μm is selected.
Toner 1 having a weight average particle size of 8 μm was obtained.

Table 1 shows the physical properties of the carbon black A and the carbon blacks BG used in the following production examples.

[Toner Production Examples 2 to 4] Toners 2, 3 and 4 were obtained in the same manner as in Toner Production Example 1 except that polyester resins B, C and D were used as binder resins.

[Toner Production Examples 5 to 8] As the binder resin,
Toners 5 to 8 were obtained in the same manner as in Toner Production Example 1 using polyester resin A and carbon blacks B to E as carbon black.

Table 2 summarizes the formulations of the toners 1 to 8 obtained as described above.

<Example 1> To 100 parts by weight of toner 1, 1.0 part by weight of alumina fine particles as a fluidity improver was mixed by a Henschel mixer, and then Mn-Mg-Fe containing silicone resin as a coating material was used. A ferrite carrier (average particle size: 45 μm) was mixed with the toner so as to have a toner concentration of 8% to obtain a developer.

The above developer was used in a commercially available electrophotographic copying machine (CL
C700, manufactured by Canon Inc.) at high temperature and high humidity (30 ° C.,
Continuous copying was performed using an original image having an image area ratio of 25% under an environment of 80% RH.

Table 3 shows the obtained results.

As can be seen from the table, 100
A stable high image density of Macbeth density of 1.56 to 1.58 was obtained through 00 sheets, and a clear image without fog or scattering was obtained.

Evaluation of fog: REFLE manufactured by Tokyo Denshoku Co., Ltd.
It was measured using a COMETER MODEL TC-6DS and calculated by the following equation. The smaller the value, the less fog.

Fog (reflectance) (%) = Reflectance of standard paper (%) − Reflectance of non-image portion of sample (%)

Measurement of toner charge amount: In the measuring apparatus shown in FIG. 2, a metal measuring container 12 having a conductive screen 13 of 500 mesh (which can be appropriately changed to a size not allowing the passage of carrier particles) at the bottom is placed on a sleeve. And the metal lid 14 is closed. At this time, the weight of the entire measurement container 12 is weighed and set as W1 (g). Next, in the suction device 11 (at least a portion in contact with the measurement container 12 is at least an insulator), the pressure is suctioned from the suction port 17 and the air volume control valve 16 is adjusted to adjust the pressure of the vacuum gauge 15 to 250 mmAq. In this state, suction is sufficiently performed (about 2 minutes) to remove toner by suction. The potential of the electrometer 19 at this time is set to V (volt). Here, 18 is a capacitor whose capacity is C (μ
F). Further, the weight of the whole measurement container after suction is weighed to be W2 (g). The triboelectric charge (μC / g) of the toner is calculated as in the following equation.

The triboelectric charge (μC / g) = C × V / (W1−W2)

Evaluation of dirt in the machine: The evaluation criteria are as follows. ○ Good ○ △ No practical problem △ Practical problem

Example 2 The same durability evaluation as in Example 1 was performed except that toner 2 was used.
Until after 000 sheets, the image density was stable at 1.54 to 1.58, and a clear image was obtained. Almost no dirt due to toner scattering inside the copier was seen.

Example 3 The same durability evaluation as in Example 1 was performed except that toner 5 was used.
The image density was stable at 1.51 to 1.59 after 000 sheets, and a clear image was obtained.

Example 4 The same durability evaluation as in Example 1 was performed except that toner 6 was used. In each case, the image density was stable from the initial stage to after 10,000 sheets, and a clear image with less fog was obtained. Obtained.

<Comparative Example 1> Durability was evaluated in the same manner as in Example 1 except that toner 3 was used.
After 000 sheets, the image density was relatively low. This is probably because the acid value of the polyester resin as the binder resin is low, so that the interaction with the carbon black surface is insufficient and the dispersibility of the carbon black is not good.

<Comparative Example 2> The same durability evaluation as in Example 1 was performed except that toner 4 was used. As a result, an image having a low charge amount, poor fog suppression, and a low image density was obtained from the beginning. After 10,000 sheets, the charge amount further decreased and fog suppression also worsened. In addition, dirt on the aircraft was noticeable.

<Comparative Example 3> Durability was evaluated in the same manner as in Example 1 except that toner 7 was used.
After 000 sheets, fog was noticeable and the charge amount was reduced. Dirt inside the aircraft was also noticeable. This is because the ionization potential of the used carbon black surface is large,
This is probably because the electric affinity with the resin is weak and the dispersibility of carbon is not good.

<Reference Example> A durability evaluation was performed in the same manner as in Example 1 except that the toner 8 was used.
The image density was slightly lower until after 00 sheets. It is considered that the toner coloring power was slightly reduced due to the large particle size of the carbon black. However, there was no problem with the fog and the durability of the charge amount.

[0069]

[Table 1]

[0070]

[Table 2]

[0071]

[Table 3]

[0072]

According to the present invention, there is provided a toner comprising a carbon black having an ionization potential of 4.6 eV or less as a coloring agent and a binder resin having an acid value of 5 to 30 mgKOH / g or less. By manufacturing
It is possible to provide a toner which has clear image characteristics with little fog, has excellent durability stability, and has little environmental dependency of triboelectric charging.

[Brief description of the drawings]

FIG. 1 is a diagram showing basic characteristics of an ionization potential.

FIG. 2 is a schematic explanatory view of a measuring device of a toner charge amount.

Claims (2)

[Claims] 1. A toner containing at least a binder resin and a colorant, wherein the colorant is carbon black having an ionization potential of 4.60 eV or less, and the acid value of the binder resin is 5 to 30 mgKOH / g. 2. The toner according to claim 1, further comprising carbon black having a primary average particle size of 50 nm or less.