JP2007058134A - Electrophotographic toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic toner superior in both of transferability and cleanability. <P>SOLUTION: The electrophotographic toner containing a binder resin, a colorant and an external additive and having average circularity of ≥0.920 to <0.950 contains silica of 12 to 20 mm in average grain size as the external additive, in which the content of the silica satisfies formula (I): 8/Dv<SB>50</SB>≤X≤30/Dv<SB>50</SB>(I) (where, X is the content (weight%) of the silica; Dv<SB>50</SB>is the volume mean grain size (μm) of the toner). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic toner used for developing a latent image formed in an electrophotographic method, an electrostatic recording method, an electrostatic printing method or the like.

In an electrophotographic system, a toner image developed on a photoconductor is transferred onto paper by electrostatic force or pressure. Therefore, transferability is one of important properties required for toner. Since a void phenomenon or the like in which a part of the image is not transferred becomes an image defect, a toner having a good transfer property is required to achieve high image quality. In view of this, a technique has been proposed in which the toner is made spherical, that is, the transferability is improved by setting the circularity to 0.95 or more (see Patent Document 1).
Japanese Patent Laid-Open No. 11-295931

However, toner with a high degree of circularity is in point contact between the photoconductor and the toner, so that the contact area is small and transferability is excellent. On the other hand, friction with the cleaning blade and the cleaning brush is small, and cleaning failure tends to occur.
On the other hand, when the profile is changed, the cleaning is good, but the transferability is poor.

  An object of the present invention is to provide an electrophotographic toner that is excellent in both transferability and cleaning property.

The present invention is an electrophotographic toner comprising a binder resin, a colorant and an external additive and having an average circularity of 0.920 or more and less than 0.950, wherein the external additive has an average particle size of 12 to 20 nm. Of silica, and the content of the silica is represented by the formula (I):
8 / Dv ₅₀ ≦ X ≦ 30 / Dv ₅₀ (I)
(Wherein X is the silica content (% by weight) and Dv ₅₀ is the volume-median particle size (μm) of the toner)
The present invention relates to an electrophotographic toner that satisfies the requirements.

  The toner for electrophotography of the present invention exhibits excellent effects in both transferability and cleaning properties.

  The electrophotographic toner of the present invention contains at least a binder resin, a colorant, and an external additive, has a specific average circularity, and has a specific particle size as an external additive. It has one feature in that it contains a specific amount.

  The average circularity of the toner of the present invention means the average circularity of toner particles contained in the toner.

  In this specification, the average circularity is the following formula:

Is the average value of the circularity calculated by the "circumference length of a circle having the same area as the projected image of the particle" and "perimeter length of the projected particle image" are flow type particle image analyzers (FPIA-1000, FPIA- 2000 or FPIA-3000; manufactured by Toago Medical Electronics Co., Ltd.). Moreover, since the value obtained by the above-described analyzer is a value obtained as an average value of several thousand and at least 3000, the reliability of the average circularity in the present invention is extremely high. In the present specification, the average circularity measuring device is not limited to the above-mentioned device, and any device can be used as long as the average circularity can be obtained based on the above equation based on the same principle. May be measured.

  The average circularity of the toner of the present invention is 0.920 or more and less than 0.950, preferably 0.925 to 0.945, more preferably 0.930 to 0.940. Since the average circularity is obtained from “the circumference of a circle having the same area as the projected image of the particle” and “the circumference of the projected image of the particle”, this value accurately represents the shape of the toner particle, that is, the uneven state of the particle surface. The closer it is to 1, the closer it is to an uneven circle. A toner having a high degree of circularity is excellent in transferability, but is easily deteriorated in cleaning properties. However, in the present invention, the average circularity is adjusted within the above range, and a specific amount of specific silica is included as an external additive, so that both transferability and cleaning properties are achieved. Although the detailed reason is unknown, it is presumed that silica having a specific particle size contained in a specific amount imparts appropriate non-aggregation property and charge amount to the toner, and the transfer force overcomes the adhesion force to the photoreceptor. The average circularity can be adjusted by pulverization conditions such as wind force, collision plate shape and the like.

  The average particle diameter of the silica is 12 to 20 nm, preferably 13 to 19 nm, more preferably 14 to 18 nm, from the viewpoint of imparting appropriate fluidity, non-aggregation and charging properties to the toner.

Further, the coverage of the toner with silica varies depending on the particle size of the toner. From this viewpoint, the content of silica is represented by the formula (I):
8 / Dv ₅₀ ≦ X ≦ 30 / Dv ₅₀ (I)
(Wherein X is the silica content (% by weight) and Dv ₅₀ is the volume-median particle size (μm) of the toner)
Satisfied. In the formula (I), X is preferably 8.5 / Dv ₅₀ or more, more preferably 9 / Dv ₅₀ or more. X is preferably 28 / Dv ₅₀ or less, more preferably 26 / Dv ₅₀ or less.

The fine powder of silica (SiO ₂ ) may be either a dry method or a wet method. In addition to anhydrous silica, it may contain aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, zinc silicate, etc., but preferably contains SiO _{2 in an amount} of 85% by weight or more.

  The silica is preferably hydrophobic silica that has been hydrophobized. Examples of the hydrophobizing agent include silane coupling agents such as hexamethyldisilazane (HMDS) and dimethyldichlorosilane (DMDS), and silicone oils such as dimethyl silicone oil and amino-modified silicone oil. Among these, A silicone oil having a suitable balance between fluidity and chargeability is preferred.

The treatment method using the hydrophobizing agent is not particularly limited as long as the hydrophobizing agent is adsorbed on the silica surface. For example, a solution obtained by diluting the hydrophobizing agent with a solvent while stirring the silica in a mixing tank. A method of spraying and heating and drying in a tank for a certain time while stirring is mentioned. The treatment amount with the hydrophobizing agent is preferably 1 to 7 mg / m ² per surface area of the external additive.

  Further, in the present invention, external additions of silica, titania, alumina, zinc oxide, magnesium oxide, cerium oxide, iron oxide, copper oxide, tin oxide, etc. other than the above silica, as long as the effects of the present invention are not impaired. An agent may be used in combination.

  Examples of the binder resin in the present invention include polyester resins, vinyl resins such as styrene-acrylic resins, epoxy resins, polycarbonates, polyurethanes, hybrid resins having two or more resin components, and the like. Among them, polyester is preferable from the viewpoint of durability and fixability. The polyester content is preferably 50 to 100% by weight in the binder resin, more preferably 70 to 100% by weight, and still more preferably 100% by weight.

  The raw material monomer of the polyester is not particularly limited, and a known alcohol component and a known carboxylic acid component such as carboxylic acid, carboxylic acid anhydride, or carboxylic acid ester are used.

  Alcohol components include alkylenes of bisphenol A such as polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane (Carbon number 2 to 3) Oxide (average added mole number 1 to 16) adduct, ethylene glycol, propylene glycol, glycerin, pentaerythritol, trimethylolpropane, hydrogenated bisphenol A, sorbitol, or alkylene thereof (carbon number 2 -4) Oxide (average added mole number 1-16) adduct and the like.

  The carboxylic acid component includes dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, fumaric acid, maleic acid, adipic acid and succinic acid, alkyl groups having 1 to 20 carbon atoms such as dodecenyl succinic acid and octenyl succinic acid, or carbon. Trivalent or higher polyvalent carboxylic acids such as succinic acid, trimellitic acid and pyromellitic acid substituted with alkenyl groups having 2 to 20 carbon atoms, anhydrides of these acids and alkyls of these acids (1 to 3 carbon atoms) ) Esters and the like.

  The polyester can be produced, for example, by subjecting an alcohol component and a carboxylic acid component to condensation polymerization at a temperature of 180 to 250 ° C. in an inert gas atmosphere, if necessary, using an esterification catalyst.

  From the viewpoint of durability and fixability, the softening point of the polyester is preferably 80 to 165 ° C, the glass transition point is preferably 50 to 85 ° C, and the acid value is preferably 0.5 to 60 mgKOH / g. The desired softening point and acid value can be obtained by adjusting the condensation polymerization temperature, reaction time, and the like.

  As the colorant, dyes and pigments used as toner colorants can be used. Carbon black, phthalocyanine blue, permanent brown FG, brilliant first scarlet, pigment green B, rhodamine-B base, solvent red 49, Solvent Red 146, Solvent Blue 35, Quinacridone, Carmine 6B, Disazo Yellow, etc., and these can be used alone or in admixture of two or more. Either toner or full color toner may be used. The content of the colorant is preferably 1 to 40 parts by weight and more preferably 3 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  In the present invention, in addition to the binder resin and the colorant, a charge control agent, a release agent, a fluidity improver, a conductivity modifier, an extender pigment, a reinforcing filler such as a fibrous substance, an antioxidant, You may use suitably additives, such as anti-aging agent and a cleaning property improving agent, as a raw material.

  As the charge control agent, any one of negative chargeability and positive chargeability can be used. Examples of the negatively chargeable charge control agent include metal-containing azo dyes, copper phthalocyanine dyes, metal compounds of salicylic acid alkyl derivatives, benzylic acid metal compounds, and nitroimidazole derivatives. Examples of the positively chargeable charge control agent include nigrosine dyes, triphenylmethane dyes, quaternary ammonium salt compounds, polyamine resins, and imidazole derivatives. In the present invention, from the viewpoint of preventing overcharging of the toner, the formula (II):

(Wherein M is boron or aluminum, m is an integer of 2 or more, and n is an integer of 1 or more)
The metal compound of the benzylic acid derivative represented by these is preferable. Such a metal compound may be either a metal salt or a metal complex.

  Examples of commercially available metal compounds of benzylic acid derivatives include “LR-147” (M: boron, manufactured by Nippon Carlit), “LR-297” (M: aluminum, manufactured by Nippon Carlit).

  The content of the metal compound of the benzylic acid derivative is preferably 0.1 to 2 parts by weight, more preferably 0.2 to 1 part by weight, and more preferably 0.3 to 0.8 parts by weight with respect to 100 parts by weight of the binder resin, from the viewpoint of charge rise. Is more preferable.

  Examples of mold release agents include polypropylene wax, polyethylene wax, synthetic wax such as Fischer Tropu, coal wax such as montan wax, petroleum wax such as paraffin wax, and wax such as alcohol wax. Or a mixture of two or more thereof. The content of the release agent is preferably 1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  The toner of the present invention is obtained through a step of surface-treating an untreated toner containing a binder resin and a colorant and, if necessary, various additives with an external additive. The untreated toner is preferably a pulverized toner. For example, a binder resin, a colorant, and the like are mixed with a mixer such as a Henschel mixer or a ball mill, and then melted and kneaded with a hermetic kneader or a single or twin screw extruder. After cooling, coarsely pulverized using a hammer mill or the like, further pulverized by a fine pulverizer or mechanical pulverizer using a jet stream, and predetermined by a classifier using a swirling airflow or a classifier using the Coanda effect It is obtained by classifying to a particle size of

  The surface treatment process of the untreated toner with the external additive is preferably a dry mixing method in which the external additive and the untreated toner are mixed using a high-speed stirrer such as a Henschel mixer or a super mixer, a V-type blender or the like. The external additives may be mixed in advance and added to a high-speed stirrer or a V-type blender, or may be added separately.

The volume median particle size (Dv ₅₀ ) of the present invention is preferably 3 to 7 μm, more preferably 3.5 to 6.5 μm, from the viewpoint of ease of handling as a powder. Further, the number median particle diameter (Dp ₅₀ ) of the toner is preferably 2.5 to 6.5 μm, more preferably 3.0 to 6.0 μm. In the present specification, the volume-median particle size (Dv ₅₀ ) means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle size. The number median particle size (Dp ₅₀ ) means a particle size at which the cumulative number frequency is 50% as calculated from the smaller particle size.

Further, from the viewpoint of uniformity of cohesive force between toners, the content of particles having a particle size of (1.4 × Dv ₅₀ ) μm or more is preferably 5% by volume or less, more preferably 4.8% by volume or less in the toner. More preferably, it is 4% by volume or less. On the other hand, the content of particles having a particle size of (0.6 × Dp ₅₀ ) μm or less in the toner is preferably 4% by number or less, more preferably 3% by number or less, and further preferably 2.5% by number or less in the toner. .

  The toner of the present invention can be used as a one-component developing toner as it is or as a two-component developer by mixing with a carrier. However, since the toner of the present invention is excellent in chargeability, it can be developed with a regulating blade or the like. The effect of the present invention is more remarkably exhibited by using the toner as one-component developing toner that charges the toner by passing through the gap with the roller.

[Softening point]
Using a flow tester (Shimadzu Corp., CFT-500D), a 1 g sample was heated at a heating rate of 6 ° C / min, and a 1.96 MPa load was applied by a plunger, and extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. . The amount of plunger drop of the flow tester is plotted against the temperature, and the temperature at which half of the sample flows out is taken as the softening point.

[Glass transition point]
Using a differential scanning calorimeter (DSC210, manufactured by Seiko Denshi Kogyo Co., Ltd.), the sample was heated to 100 ° C at a temperature increase rate of 10 ° C / min and allowed to cool to -10 ° C at a temperature decrease rate of 100 ° C / min for 3 minutes. Thereafter, the temperature is raised to 25 ° C. at a temperature rising rate of 60 ° C./min, held for 2 minutes, and measurement is started at a temperature rising rate of 10 ° C./min. The glass transition point is defined as the temperature at the intersection of the base line extension below the glass transition point and the tangent that indicates the maximum slope from the peak rising portion to the peak apex.

[Acid value]
Measured by the method of JIS K0070.

[Average silica particle size]
Obtained from the following formula.
Average particle diameter (μm) = 6 / (ρ × specific surface area (m ² / g))
In the formula, ρ is the specific gravity of silica (2.2), and the specific surface area is the BET specific surface area determined by the nitrogen adsorption method of the raw material before the hydrophobization treatment.
The above formula is assumed to be a sphere having a particle diameter R, and
Specific surface area = S x (1 / m)
m (weight of particle) = 4/3 x π x (R / 2) ³ x specific gravity
S (surface area) = 4π (R / 2) ²
Is an expression obtained from

[Particle size distribution of toner]
Using a Coulter counter “Coulter Multisizer II” (manufactured by Coulter, Inc.), the particle size distribution of the toner is determined according to the following method.

(1) Preparation of dispersion: Add 10 mg of measurement sample to 5 ml of dispersion (Emulgen 109P (Kao Corporation, polyoxyethylene lauryl ether, HLB: 13.6) 5% by weight aqueous solution), and use ultrasonic disperser for 1 minute Then, 25 ml of an electrolytic solution (Isoton II (manufactured by Beckman Coulter)) is added, and further dispersed for 1 minute with an ultrasonic disperser to obtain a dispersion.
(2) Measuring device: Coulter Multisizer II (Beckman Coulter, Inc.)
Aperture diameter: 100 μm
Measurement particle size range: 2-60μm
Analysis software: Coulter Multisizer AccuComp version 1.19 (Beckman Coulter)
(3) Measurement conditions: 100 ml of electrolyte solution and dispersion are added to a beaker, and the particle size of 30,000 particles is measured at a concentration capable of measuring the particle size of 30,000 particles in 20 seconds.
(4) From the measured values, the volume median particle size (Dv ₅₀ , μm), the number median particle size (Dp ₅₀ , μm), and the content of particles having a particle size of (1.4 × Dv ₅₀ ) μm or more (volume%) ) And the content (number%) of particles having a particle size of (0.6 × Dp ₅₀ ) μm or less.

Resin production example 1
568 g of polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, 792 g of polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, 640 g of terephthalic acid and 10 g of tin octylate Was reacted with stirring at 210 ° C. under a nitrogen stream. The obtained resin is referred to as Resin A. Resin A had a softening point of 110 ° C., a glass transition point of 68 ° C., and an acid value of 3 mgKOH / g.

Examples 1-4 and Comparative Examples 1, 3-5
Resin A 100 parts by weight, release agent “Carnauba Wax C1” (manufactured by Kato Yoko Co., Ltd.) 4.5 parts by weight, colorant “ECB-301” (manufactured by Dainichi Seika Kogyo Co., Ltd.) 4.5 parts by weight and the charge control shown in Table 1 The agent was mixed with a Henschel mixer, and the resulting mixture was kneaded with a continuous two-open roll type kneader “NIDEX” (manufactured by Mitsui Mining Co., Ltd.).

  The continuous two-open roll type kneader used has a roll outer diameter of 0.14 m and an effective roll length of 0.8 m, and the operating condition is that the rotation speed of the high rotation side roll (front roll) is 75. The number of rotations per minute, the number of rotations of the low rotation side roll (rear roll) was 50 rotations / minute, and the roll gap was 0.1 mm. The heating and cooling medium temperature in the roll is 150 ° C on the raw material input side of the high-rotation roll, 130 ° C on the kneaded material discharge side, 35 ° C on the raw material input side of the low-rotation roll, and the kneaded material discharge side. The temperature of was set to 30 ° C. The feed rate of the raw material mixture was 10 kg / hour.

  Next, the obtained kneaded product was cooled in air, and then coarsely pulverized with a Rotoplex (manufactured by Hosokawa Micron) to obtain a coarsely pulverized product having an average particle diameter of 500 μm.

  The obtained coarsely pulverized product was finely pulverized and subjected to upper limit classification (crude powder removal) with a counter jet mill “400AFG” (manufactured by Hosokawa Micron). At this time, the desired average circularity (0.920 or more and less than 0.950) was adjusted by pulverizing at a pulverization pressure of 0.7 to 1.0 MPa.

  Further, the lower limit classification (removal of fine powder) was performed with a classifier “TTSP” (manufactured by Hosokawa Micron Corporation) to obtain an untreated toner.

  To 100 parts by weight of the obtained untreated toner, external additives shown in Table 1 were mixed with a Henschel mixer to obtain a toner. At that time, in order to enhance the adhesion of silica onto the toner surface, the mixing conditions were adjusted so that the value of [Froude number (Fr) × time (s)] was 94500. The fluid number (Fr) is

Is a value obtained by Table 1 shows the particle size distribution and average circularity of the obtained toner.

Comparative Example 2
A toner was obtained in the same manner as in Example 1 except that a mechanical pulverizer “Turbo Mill RSS Type” (manufactured by Turbo Kogyo Co., Ltd.) was used instead of the counter jet mill.

Test Example 1 [Transfer efficiency]
A solid image was printed by mounting toner on a color printer "MICROLINE 5400" (Oki Data). At this time, the amount of toner on the photoconductor for the solid image is adjusted to 0.40 to 0.50 mg / cm ² , the machine is stopped during the printing of the solid image, and the mending tape is applied to the photoconductor after passing through the transfer portion. Then, the toner that was not transferred and remained on the photoconductor was transferred to a mending tape, and the mending tape was peeled off from the photoconductor. The hues of the peeled and unused mending tapes were measured with X-Rite, and the transfer efficiency was evaluated based on the color difference ΔE. The transfer efficiency is good when the density ΔE is 4.0 or less. The results are shown in Table 1.

Test Example 2 [Cleanability]
After Test Example 1, 1000 solid images were further printed, and the charging roller was visually observed for toner contamination to evaluate the cleaning property. The results are shown in Table 1.

  From the above results, it can be seen that the toners of the examples are superior in both transferability and cleaning properties as compared with the comparative example.

  The toner for electrophotography of the present invention is suitably used for developing a latent image formed in electrophotography, electrostatic recording method, electrostatic printing method and the like.

Claims (4)

An electrophotographic toner comprising a binder resin, a colorant and an external additive, having an average circularity of 0.920 or more and less than 0.950, and containing silica having an average particle diameter of 12 to 20 nm as the external additive And the silica content is represented by formula (I):
8 / Dv ₅₀ ≦ X ≦ 30 / Dv ₅₀ (I)
(Wherein X is the silica content (% by weight) and Dv ₅₀ is the volume-median particle size (μm) of the toner)
Satisfying toner for electrophotography.   2. The electrophotographic toner according to claim 1, wherein the silica having an average particle diameter of 12 to 20 nm is hydrophobic silica hydrophobized with silicone oil. The volume median particle size (Dv ₅₀ ) of the toner is 3 to 7 μm, the content of particles of (1.4 × Dv ₅₀ ) μm or more in the volume particle size distribution is 5% by volume or less, and (0.6 × The toner for electrophotography according to claim 1 or 2, wherein the content of particles having a number-median particle size of 袖 m or less is 4% by number or less. Furthermore, as a charge control agent, the formula (II):

(In the formula, M is boron or aluminum, m is an integer of 2 or more, and n is an integer of 1 or more)
The toner for electrophotography according to claim 1, comprising a metal compound of a benzylic acid derivative represented by the formula: