JPH086293A - Toner - Google Patents

Abstract

PURPOSE:To obtain a toner having high image quality and high coloring power and excellent in durability at high humidity by incorporating carbon black having a specified average particle diameter and a specified amt. of active hydrogen in the surface as a colorant in an electrophotographic toner contg. a bonding resin as well as the colorant. CONSTITUTION:This toner is an electrophotographic toner contg. a colorant and a bonding resin and the colorant is carbon black having <=50nm average particle diameter and 13X10<-4>mol/g active hydrogen in the surface. The coloring power of carbon black increases generally in accordance with the reduction of the particle diameter and becomes remarkably high especially in the case of <=50nm. The carbon black content of the toner can be therefore made low while attaining high image density and fog due to the reduction of the resistance of the toner and difference in the extent, of triboelectric charge during circulation are not produced. The dispersibility of the carbon black in the resin can be considerably improved.

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 electrophotography.

[0002]

2. Description of the Related Art In the electrophotographic method, a static charge is uniformly applied on a photoconductive layer by corona discharge, and a light image corresponding to a document is exposed to the static charge to eliminate the charge in the exposed portion to form a latent image. Do. Development is performed by attaching toner to the obtained electrostatic latent image. The toner is attracted to the electrostatic latent image according to the magnitude of the amount of charge on the photoconductive layer to form a toner image having a shade. This toner image is transferred to the support surface and permanently fixed on the support surface by using an appropriate fixing means such as heating, pressurizing, latent image treatment or overcoating treatment.

Further, as a developing method, there are, for example, a cascade developing method, a magnetic brush method, a touchdown method and the like, and in addition, an alternating current component and a direct current component are formed between the developer carrying member (developing sleeve) and the photoconductive layer. There is a so-called J / B developing method disclosed in JP-A-62-63970, in which a bias electric field is applied to perform development.

The most commonly used method is the magnetic brush method. In this method, magnetic particles such as steel and ferrite are used as a carrier. The developer composed of toner and magnetic carrier is held by a magnet, and the magnetic field of the magnet causes the developer to be arranged 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 for development.

However, in this method, the developing efficiency is extremely low because the ratio of the consumable toner in the magnetic brush in the developing section is small. For example, there are cases where only 1 to 5% of the toner in the total developer is used. Further, if a large amount of developer is used to improve the developing efficiency, the developing device becomes large and heavy, which is not suitable for making the copying machine compact and lightweight.

Conventionally, carbon black has been generally used as a coloring agent used in black toner for electrophotography, but when a large amount of carbon black is used to compensate for the low development efficiency, the toner to the non-image area is toner. Adhesion, so-called fog, deterioration of dispersibility, and difference in triboelectrification amount between environments under low temperature and low humidity and high temperature and high humidity.

In order to prevent such problems, a method of suppressing the content in the toner by using carbon black having a high coloring power and a method of increasing the resistance of the carbon black by subjecting the surface of the carbon black to an oxidation treatment. Can be mentioned.

As the surface oxidation treatment method, for example, Japanese Patent Publication No.
There is an oxidation treatment method using potassium permanganate as described in JP-A-31139. However, in this method, metal ions are likely to remain as counter ions of the carboxyl groups on the surface of carbon black, resulting in low resistance of carbon black, and when used in toner, it is sufficient to improve durability under high humidity. Can not be obtained.

Further, although Japanese Patent Laid-Open No. 3-200158 discloses a surface oxidation treatment method using ozone,
The content is intended to improve the dispersibility of carbon black due to the interaction between the carboxyl groups on the surface and the polyester as the binder resin for toner. Regarding the degree of oxidation, the amount of carboxyl groups on the carbon black surface is 0. Since it is not so high as less than 1 × 10 ⁻³ mol / g,
It is not sufficient in terms of improving the durability characteristics of the toner under high humidity.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a toner having less fog and high coloring power.

Another object of the present invention is to provide a toner having excellent durability characteristics even under high humidity.

[0012]

The present invention relates to an electrophotographic toner containing at least a colorant and a binder resin, which comprises (a) an average particle size of 50 nm or less and (b) a surface of the toner. The present invention relates to a toner containing carbon black having an active hydrogen amount of 3 × 10 ⁻⁴ mol / g or more.

The present invention will be described in detail below.

The average particle size of the carbon black used in the present invention is 50 nm or less. Generally, the coloring power of carbon black increases as the particle size decreases,
In particular, it dramatically increases at 50 nm or less.

Therefore, the carbon black content can be suppressed to a low level in order to obtain a high image density, and the fog due to the low resistance of the toner and the difference in the triboelectric charge amount between environments do not occur.

However, it is generally known that the smaller the particle size of carbon black, the worse the dispersibility in the resin. As a method for improving the dispersibility of such carbon black, for example, in JP-A-3-200158, a binder resin for toner is obtained by increasing the amount of carboxyl groups on the surface of carbon black by oxidizing the surface of carbon black. Although a method for improving the dispersibility in polyester has been described, the fact is still not sufficient.

As a result of diligent studies, the present inventors have found that the amount of active hydrogen on the surface of carbon black is 3 × 10 ⁻⁴ mol / g.
The above is selected, and the main component of the binder resin is O
It has been discovered that when a toner is produced in combination with a polyester resin having an H value of 5 or more, the dispersibility of carbon black in the resin is greatly improved.

This is because a bond similar to an ester bond is formed by the interaction between the carboxyl group on the surface of carbon black and the alcohol group in the resin, and the carbon black particles are covered with the resin so that the carbon black particles are bonded to each other. It is thought that this is because re-aggregation of is prevented.

Further, in the study by the present inventors, the above model is estimated from the fact that the higher the OH value of the polyester resin, the higher the coloring power as a toner.

Here, when the amount of active hydrogen on the surface of carbon black is x × 10 ⁻⁴ mol / g and the OH value of the polyester resin is y, the range is preferably 15 ≦ x × y ≦ 600. Good, and more preferably, a range of 20 ≦ x × y ≦ 500 is preferable.

In the range of x × y <15, sufficient dispersibility cannot be obtained because the interaction between the carboxyl groups on the carbon black surface and the alcohol groups in the polyester resin is small. Further, in the range of 600 <x × y, it is considered that carbon black has an action similar to that of the cross-linking agent because the interaction is too strong, and the fixability as a toner tends to be lowered. In the examination of the above, the image density has decreased.

Therefore, by adjusting the amount of active hydrogen on the surface of the carbon black and the OH number of the polyester resin within the above-mentioned range to improve the dispersibility of the carbon black particles, the coloring power as the toner becomes high, so the carbon In addition to being able to keep the amount of black added low, the oxidation state of the carbon black surface is high and the resistance is high enough. It was revealed that the durability characteristics below have a remarkable effect.

The amount of active hydrogen on the surface is 3 × 10 ^-4 mo.
It was also clarified that even with carbon black of less than 1 / g, the same effect can be obtained by increasing the amount of active hydrogen to 3 × 10 ⁻⁴ mol / g or more by the oxidation treatment.

As a method of oxidizing the carbon black surface, there is a method of using nitric acid, for example, but it is not so preferable from the viewpoint of the corrosiveness of the apparatus and the post-treatment. Further, in the oxidation treatment method using potassium permanganate as disclosed in the specification of JP-B-5-31139, K ⁺ ions are likely to remain on the surface of carbon black as described above, and the conductivity due to ion conduction is generated. When the toner is used as a colorant for toner, its durability under high humidity deteriorates.

Therefore, a method using ozone is preferable as the oxidation treatment method. However, as described above, in the oxidation treatment in which the amount of surface carboxyl groups is less than 0.1 × 10 ⁻³ mol / g as disclosed in JP-A-3-200158, alcohol of polyester resin which is a binder resin is used. In addition to insufficient formation of an ester bond with the group and high resistance, a toner having a high tinting strength and excellent durability under high humidity cannot be obtained.

In the toner of the present invention, the amount of carbon black added is 20 with respect to 100 parts by weight of the binder resin.
An appropriate amount is not more than 15 parts by weight, more preferably not more than 15 parts by weight. When the addition amount exceeds 20 parts by weight, the resistance as a toner is reduced, the charge amount is also reduced, and the durability under high humidity is reduced.

In the present invention, the amount of carboxyl group is Li
Carbon black as a sample is mixed in an AlH-ether solution, and the change in internal pressure of the reaction tank due to the generation of hydrogen gas is measured with a manometer and calculated from the following conversion formula.

N = ΔP · V / RT (mol) ΔP: pressure change V: reaction tank volume R: 0.0821 T: absolute temperature Carboxyl group amount = n ÷ sample weight (g)

In the present invention, the average particle size is measured by directly measuring the carbon black particle size from a transmission electron micrograph of carbon black, and determining the average particle size from the distribution degree of 100 measured data.

The OH value of the polyester binder resin is
It is measured by the following method according to the method shown in JIS K007.

1 ml of 6 g sample in a 200 ml Erlenmeyer flask
Precisely weigh in g, add a mixed solution of acetic anhydride / pyridine = 1/4 with 5 ml hole pipette, and add pyridine 25
Add ml with a graduated cylinder. A condenser is attached to the Erlenmeyer flask mouth, and the reaction is performed in an oil bath at 100 ° C. for 90 minutes.

3 ml of distilled water was added from the upper part of the cooler, shaken well and left for 10 minutes. With the condenser attached, the Erlenmeyer flask is pulled up from the oil bath and allowed to cool. When the temperature reaches about 30 ° C., the condenser and the flask outlet are washed with a small amount of acetone (about 10 ml) from the condenser upper opening. THF50
ml is added by a graduated cylinder, and neutralization titration is carried out with an alcoholic solution of phenolphthalein as an indicator with a N / 2KOH-THF solution using a 50 ml (scale 0.1 ml) biuret. 25 ml of neutral alcohol just before the end point of neutralization
(Methanol / acetone = 1/1 volume ratio) is added and titration is carried out until the solution becomes slightly red. At the same time, perform a blank test.

Then, the OH value is calculated according to the following equation.

[0034]

[Equation 1]

As the polyester resin which is the binder resin for toner used in the present invention, the following formula

[0036]

Embedded image

(Wherein R is an ethylene or propylene group, x and y are each an integer of 1 or more, and x +
The average value of y is 2 to 10. ), A bisphenol derivative or a substituted compound represented by the formula (1) is used as a diol component, and a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (eg, fumaric acid, maleic acid, maleic anhydride, phthalate) Acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc.) are more preferable because they have a sharp melting property.

A charge control agent may be added to the toner according to the present invention in order to stabilize the charge characteristics. When the charge control agent is blended with the toner, it is preferable to add 0.1 to 10 parts by weight to 100 parts by weight of the binder resin.

If necessary, the toner of the present invention may be mixed with additives within a range not impairing the characteristics of the toner. Examples of such additives include Teflon, zinc stearate, and polyvinylidene fluoride. Such lubricants or fixing aids (for example, low molecular weight polyethylene, low molecular weight polypropylene, etc.) are available.

As the fluidity improver used in the present invention, any fluidity improver can be used as long as it can be added to the colorant-containing resin particles to increase the fluidity before and after the addition. For example, hydrophobic colloidal silica fine powder,
Examples thereof include colloidal silica fine powder, hydrophobic titanium oxide fine powder, titanium oxide fine powder, hydrophobic alumina fine powder, alumina fine powder, and mixed powder thereof.

In the production of the toner of the present invention, the constituent materials are well kneaded by a heat kneader such as a hot roll, a kneader or an extruder, and then mechanical pulverization or classification is used, or a binder resin solution is used. After dispersing a material such as a colorant, a method of obtaining by spray-drying, or after mixing a predetermined material with a monomer that should constitute the binder resin, and then polymerizing this emulsion suspension to give a toner Each method such as a method for producing a polymerized toner to be obtained can be applied.

The toner of the present invention can be used in either a one-component developer or a two-component developer. When used as a two-component developer, the carrier used is, for example, surface-oxidized or unoxidized iron. , Nickel, copper, zinc, cobalt, manganese, chromium, magnesium, rare earth metals and their alloys or oxides and ferrites, and particularly preferably 2 selected from these metals.
Ferrite containing more than one type of metal can be used. In addition, there is no particular limitation 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.

Examples of the substance adhered to the carrier surface are polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal complex of di-tert-butylsalicylic acid, styrene resin, acrylic resin. It is suitable to use, but not limited to, a system resin, polyamide, polyvinyl butyral, nigrosine, amino acrylate resin, basic dye and its lake, fine silica powder, fine alumina powder, etc., alone or in plural.

In general, the treatment amount of the above compounds is preferably 0.1 to 30% by weight based on the carrier.

When a two-component developer is prepared, the mixing ratio is 2.5 to 15 as the toner concentration in the developer.
Good results are usually obtained with weight percentages, preferably from 3.0 to 13%. If the toner concentration is less than 2.5% by weight, the image density is low and it becomes unpractical, and if it exceeds 15% by weight, fog and scattering in the machine are increased, and the useful life of the developer is easily shortened.

[0047]

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

(Resin Production Examples A to C) Polyester resin A having an OH value of 35 mgKOH / g was synthesized by polycondensing terephthalic acid, propoxylated bisphenol and ethoxylated bisphenol.

Further, the reaction conditions were adjusted to synthesize a polyester resin B having an OH value of 10 and a polyester resin C having an OH value of 3.

Toner Production Example 1 100 parts by weight of polyester resin A 4 parts by weight of 3,5-di-tert-butylsalicylic acid Chromium complex compound 3 parts by weight of carbon black A

A black powder having a weight average particle diameter of 8 μm having the above structure is designated as a toner classified product A.

The production method is as follows. Pre-mixing each of the above-mentioned formulation amounts with a Henschel mixer, melt-kneading, cooling, and roughly pulverizing to about 1 to 2 mm using a hammer mill,
Then, it was pulverized to a particle size of 40 μm or less by an air jet pulverizer. Further, the obtained finely pulverized product was classified, and 2 to 20 μm was selected to obtain Toner 1.

Physical properties of carbon black A and carbon blacks B to G used in the following production examples are shown in Table 1.

Toner Production Examples 2 and 3 Toners 2 and 3 were obtained in the same manner as Toner Production Example 1 except that polyester resins B and C were used as the binder resin.

Toner Production Examples 4 to 6 Toners 4 to 6 were obtained in the same manner as in Toner Production Example 1 using polyester resin A as the binder resin and carbon blacks B to D as the carbon black.

Toner Production Examples 7 to 9 Toners 7 to 9 were obtained in the same manner as in Toner Production Example 1 using polyester resins A to C as binder resins and carbon black E as carbon black.

Toner Production Examples 10 to 12 Toners 10 to 12 were obtained in the same manner as in Toner Production Example 1 using polyester resin A as the binder resin and carbon blacks F and G as the carbon black.

Toners 1 to 12 obtained as described above
The prescription of is summarized in Table 2.

[0059]

[Table 1]

[0060]

[Table 2]

Example 1 100 parts by weight of Toner 1 was mixed with 1.0 part by weight of titanium oxide fine powder as a fluidity improver by a Henschel mixer, and Cu-Z was used as a coating material of silicone resin.
A developer was prepared by mixing with an n-Fe ferrite carrier (average particle size 50 μm) in a weight ratio of 10:90.

A commercially available electrophotographic copying machine (CL
C500 remodeling machine made by Canon), 30 ℃, 80%
After continuous copying under RH environment, 10,000 from the beginning
A stable high image density of Macbeth reflection density of 1.55 to 1.57 was obtained throughout the sheet, and a clear image without fog and scattering was obtained.

Example 2 The same durability evaluation as in Example 1 was carried out except that Toner 2 was used, and the image density was stable from 1.52 to 1.58 from the initial stage to after 10,000 sheets, and a clear image was obtained. was gotten. Almost no stain due to toner scattering inside the copying machine was observed.

Example 3 The same durability evaluation as in Example 1 was carried out except that Toner 4 was used, and the image density was stable at 1.61 to 1.64 from the initial stage to after 10,000 sheets, and a clear image was obtained. was gotten.

Durability was evaluated in the same manner as in Example 1 except that the toners 7 and 8 in Examples 4 and 5 were used. In all cases, the image density remained stable from the initial stage to after 10,000 sheets, and a clear image with less fog was obtained. An image was obtained.

Comparative Example 1 The same durability evaluation as in Example 1 was carried out except that Toner 3 was used. As a result, the image density remained low from the initial stage to 10,000 sheets. This is probably because the polyester resin, which is a binder resin, has a low OH value, 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 carried out except that Toner 5 was used. As a result, the charge amount was low from the initial stage and the fog was poor.
An image with low image density was obtained. After 10,000 sheets, the charge amount was further reduced and the fog was worsened. Also, dirt inside the aircraft was noticeable. This is probably because the amount of surface carboxyl groups on the carbon black is small and thus the dispersion in the binder resin is poor, and the resistance of the carbon black is also low, resulting in insufficient durability under high humidity.

Comparative Example 3 The same durability evaluation as in Example 1 was carried out except that Toner 6 was used. As a result, fog was noticeable from the beginning to 10,000 sheets, and the charge amount also decreased. The dirt inside the aircraft was also noticeable.

Like the toner 5, it is considered that the carbon black used had an insufficient amount of surface carboxyl groups, resulting in insufficient dispersibility and resistance, and insufficient durability under high humidity.

Comparative Example 4 When the same durability evaluation as in Example 1 was carried out except that Toner 9 was used, the image density remained slightly lower from the initial stage to 10,000 sheets.

It is considered that the dispersibility of carbon black is insufficient because the OH value of the binder resin is low.

Comparative Example 5 The same durability evaluation as in Example 1 was carried out except that Toner 10 was used, and as a result, fog and charge amount were stable from the initial stage to after 10,000 sheets, and no stain inside the machine was observed. Only low image densities were obtained. x × y
As can be seen from the high value of = 669, the interaction between the carbon black and the polyester resin is so strong that the toner solidifies as a toner, and the fixability is thought to have deteriorated.

Comparative Example 6 The same durability evaluation as in Example 1 was carried out except that Toner 11 was used. As a result, the charge amount was low from the initial stage and the fog was conspicuous, and after 10,000 sheets, the charge amount was further lowered and the fog was worse. have done. Also, dirt inside the aircraft was noticeable.

It is considered that this is because when the carbon black was oxidized, potassium permanganate was used, so that potassium ions remained on the surface of the carbon black and the resistance of the carbon black became low.

Comparative Example 7 When the same durability evaluation as in Example 1 was carried out except that Toner 12 was used, the image density changed slightly from the initial stage to 10,000 sheets. It is considered that the toner coloring power was slightly reduced due to the large particle size of carbon black. However, there was no problem with the fog and the durability of the charge amount.

The above results are summarized in Table 3.

[0077]

[Table 3]

1) Evaluation of fog: REF manufactured by Tokyo Denshoku Co., Ltd.
It measured using LECTOMER MODEL TC-6DS and calculated from the following formula. The smaller the number, the less fog.

Fog (reflectance) (%) = reflectance (%) of standard paper−reflectance (%) of non-image area of sample 2) Toner charge amount: Measured by the apparatus shown in FIG.

A conductive screen 13 having a bottom of 500 mesh (the size can be appropriately changed so that carrier particles do not pass through)
The developer sampled from above the sleeve is put into a metallic measuring container 12 having a metal, and the metallic lid 14 is closed. At this time, the weight of the entire measuring container 12 is weighed and set as W ₁ (g). Next, in the suction device 11 (at least the portion in contact with the measurement container 12 is an insulator), suction is performed from the suction port 17 to adjust the air volume control valve 16 to adjust the pressure of the vacuum gauge 15 to 250 mmAq. In this state, suction is sufficiently performed (for about 2 minutes) to remove the toner by suction. The potential of the electrometer 19 at this time is V (volt). Here, 18 is a condenser, and the capacity is C (μ
F). The weight of the entire measuring container after suction is weighed and is W ₂ (g). This triboelectric charge amount T (μC / g) is calculated by the following formula.

[0081]

[Equation 2]

3) Evaluation of dirt inside the machine: Evaluation criteria are as follows.

○ ・ ・ ・ Good ○ △ ・ ・ ・ ・ No practical problem △ ・ ・ ・ Practical problem

[0084]

[0085]

According to the present invention, a toner is manufactured by combining carbon black having a specific particle size and a specific amount of surface carboxyl groups with a polyester resin having a specific OH value in a specific range. As a result, it is possible to obtain a toner having high image quality, high coloring power, and excellent durability under high humidity.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a toner charge amount measuring device.

Claims (2)

[Claims] 1. An electrophotographic toner containing at least a coloring agent and a binder resin, wherein the coloring agent has (a) an average particle diameter of 50 nm or less, and (b) an active hydrogen amount on the surface of 3 × 10 ⁻⁴ mol. / G or more of carbon black is contained in the toner. 2. The toner according to claim 1, wherein the main component of the binder resin is a polyester resin having an OH value of 5 or more.