JP3233660B2 - Manufacturing method of carrier for electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic carrier used for electrophotography, electrostatic printing, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a method of developing an electrostatic latent image using toner, a cascade developing method (US Pat.
8552) and a magnetic brush developing method (see U.S. Pat. No. 2,870,063). In each of these methods, a two-component dry developer is used. In this two-component dry developer, fine toner particles are held on the surface of a relatively large carrier particle by electric force generated by friction between the two particles. The attraction force in the latent image direction on the toner particles due to the electric field formed by the latent image overcomes the bonding force between the toner particles and the carrier particles, and the toner particles are attracted and adhered on the electrostatic latent image, and Are visualized. The developer is used repeatedly while replenishing the toner consumed by the development. In this case, the toner particles must have the correct chargeability and charge magnitude such that they are always preferentially attracted to the desired image area on the photoconductor. In addition, the carrier must always have the desired polarity for the toner particles and have been triboelectrically charged to a sufficient charge amount during long-term use.

[0003] However, the conventional developer suffers from mechanical collisions such as collisions between particles and between particles and a developing machine.
Alternatively, due to the heat generated by these, some of the toner particles have a property of physically attaching to the surface of the carrier particles to form a film. In such a state, a film of the toner material gradually accumulates on the surface of the carrier particles, and the frictional charge between the carrier particles and the toner particles is replaced by the frictional charge between the toners, so that the friction of the entire developer is The chargeability deteriorates, and a large amount of toner adheres to the background portion of the copy image, causing a so-called background stain phenomenon, resulting in a decrease in copy quality.

Further, when the formation of the toner film on the carrier surface increases, the entire developer must be replaced, which leads to an increase in cost. In order to prevent such spent, a method of coating the carrier surface with various resins has conventionally been proposed, but no satisfactory method has yet been obtained. For example, a carrier coated with a resin such as a styrene-methacrylate copolymer or a styrene polymer has excellent charging characteristics, but has a relatively high critical surface tension on the surface, and as a result of repeated copying, the surface becomes more spent. Since it occurs, the life of the developer is not so long.

Further, since the carrier coated with the ethylene tetrafluoride polymer has a low surface tension, it is difficult for the toner to be spent, but the ethylene tetrafluoride polymer is located at the most negative side in the triboelectric series. Therefore, the toner cannot be used when charging the toner to a negative polarity.

Further, a carrier coated with a coating layer containing a silicone resin has been proposed as having a low surface tension. For example, an unsaturated silicone resin, an organosilicone, a silanol, or the like mixed with a styrene-acryl resin to coat the carrier surface (US Pat. No. 35
No. 62533), a carrier whose surface is coated with a polyphenylene resin and an organosilicone terpolymer resin (U.S. Pat. No. 3,847,127); Coated carrier (U.S. Pat. No. 3,627,522); carrier coated with a coat layer containing a silicone resin and a nitrogen-containing resin having positive charge characteristics (Japanese Patent Laid-Open No. 55-127)
567); and a carrier whose surface is coated with a resin-modified silicone resin (JP-A-55-157751).

Although the use of a carrier coated with a silicone resin improves the spent resistance, the apparent specific resistance of the carrier is increased, so that the peripheral effect is likely to occur, and the reproducibility of a wide black region and a halftone region is deteriorated. There is. In addition, since the counter charge at the time of toner detachment becomes excessive, carrier adhesion to a non-image portion due to electrostatic development is likely to occur. In particular, this phenomenon occurs remarkably at a high bias.

Therefore, it has been proposed to mix a conductive substance such as carbon black into a coating layer made of a silicone resin. For example, JP-A-56-126
No. 843 discloses a carrier coated with a material containing carbon black and a resin as main components.
JP-A-182759 discloses a carrier coated with a silicone resin containing carbon black subjected to coupling treatment, and JP-A-62-45884 discloses a carrier in which porous carbon black is contained in a coating layer. Carriers are disclosed.

[0009]

As described above, when the carrier surface is coated with a silicone resin containing carbon black, the spent resistance is improved, and the resistance of the carrier can be easily adjusted. Antistatic particles such as silicone particles and carbon black float. These charge-inhibiting particles temporarily reduce the charging ability that the carrier can originally hold. If the chargeability of the carrier is apparently reduced, the phenomenon of increase in the chargeability of the carrier accompanying the consumption of the charge-inhibiting particles occurs relatively early after the development starts. As a result, the toner density in the developing section increases, and background stains occur on the image. In view of the above, there is a need to provide a silicone resin-coated carrier containing carbon black that has a small increase in the charging ability of the carrier and to propose a method for producing the same.

The present invention is intended to solve the above-mentioned problems. (1) The first object of the present invention is to provide a silicone resin-coated carrier containing carbon black without impairing a strong preventive action against carrier adhesion. An object of the present invention is to provide an electrophotographic carrier having excellent spent resistance and having a small increase in carrier charging ability at the beginning of development. (2) Further, a second object of the present invention is to provide a carrier of the above (1), in which the processing capacity in a drying and curing step is improved. (3) A third object of the present invention is to provide the carrier of the above (1) by making the separation / removal step and the magnetic separation step the same, thereby reducing the number of steps. (4) A fourth object of the present invention is to improve the processing ability in the step of separating and removing the charge-inhibiting particles when providing the carrier of the above (1). (5) A fifth object of the present invention is to provide a carrier according to the above (1), wherein the carrier charging ability is further prevented from increasing.

[0011]

According to the present invention, an electrophotographic carrier, the surface of which is coated with a silicone resin containing carbon black, is dried and cured by a fluid dryer having no stirring blades inside. The carrier is mixed with particles having triboelectrification, and then the dynamic electrical resistance of the carrier obtained by separating and removing the silicone resin and carbon black suspended in an air classifier is 0.3 to 3.0 × 10 ^8.
An electrophotographic carrier characterized by having a smooth surface property of Ω and fluidity of 34 seconds / 50 g or less, and a method for producing the same.

Next, the present invention will be described in detail. First, the fluidized dryer used in the present invention is roughly classified into a batch type and a continuous type according to the processing method. Further, the drying method is classified into a band type dryer, a fluidized bed dryer, a rotary type dryer and a cylindrical type dryer. Any dryer may be used as long as it does not have a stirring blade, but it is most preferable to use a continuous dryer in consideration of the processing capacity.

The air classifier used in the present invention includes:
The classification method is roughly classified into a centrifugal classifier, an airflow classifier, a sieve classifier, and a magnetic classifier, and any air classifier may be used. However, it is most preferable to use a magnetic force type air classifier in that the magnetic separation step, which is the primary step, can be performed simultaneously and the step can be omitted.

As the frictionally chargeable particles used in the present invention, any particles may be used as long as they exhibit frictional chargeability when mixed with a carrier. For example, inorganic particles such as silica, hydrophobic silica, alumina, hydrophobic alumina, and silicon carbide, and resin particles such as polyester, polystyrene, and polyacrylate are exemplified.

However, the particle size is 0.05 to 0.15 with respect to the volume average particle size of the carrier.
Is most preferable. This is because if the particle diameter is extremely small, the electrostatic adhesion between the carrier and the triboelectrically-charged particles becomes strong, so that the separation and removal efficiency of the triboelectrically-chargeable particles is reduced as compared with the above range. On the other hand, if the particle diameter is extremely large, the electrostatic adhesion and contact probability between the triboelectrification particles and the charge inhibition particles decrease,
The efficiency of separation and removal of the charge-inhibiting particles is lower than that in the above range. Therefore, if the particle diameter of the triboelectrically-chargeable particles is too small or too large, the processing capacity in the separation and removal step will be reduced.

The composition of the triboelectrically chargeable particles used in the present invention is not particularly limited as long as it exhibits triboelectric chargeability as described above. Among them, the composition is the same as that of the toner in the developer. Some are most preferred. This is because, of course, its triboelectric chargeability and particle size are the most suitable, and its acquisition and quality control are very easy. Further, even if the triboelectrically-charged particles slightly remain on the carrier surface, side effects on the developer such as defective fixing do not occur.

The silicone resin used in the present invention may be any conventionally known silicone resin, and may be modified with a straight silicone resin consisting only of an organosiloxane bond, or with an alkyd, polyester, epoxy, urethane or the like. Silicone resin.

[0018]

Embedded image

In the above formula, R ₁ is a hydrogen atom, having 1 to 1 carbon atoms.
4 alkyl groups or phenyl groups, R ₂ and R ₃ represent a hydrogen group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 1 carbon atoms, a phenyl group, a phenoxy group, an alkenyl group having 2 to 4 carbon atoms Or an alkenyloxy group having 2 to 4 carbon atoms, a hydroxy group, a carboxyl group, an ethylene oxide group, a glycidyl group, or a group represented by the following formulas.

[0020]

Embedded image (In the above formula, R ₄ and R ₅ are a hydroxy group, a carboxyl group, an alkyl group having 1 to 4 carbon atoms, and 1 to 4 carbon atoms.
, An alkenyl group having 2 to 4 carbon atoms, an alkenyloxy group having 2 to 4 carbon atoms, a phenyl group, a phenoxy group, k, l, m, n, o, and p are integers of 1 or more. )

Each of the above substituents is, in addition to unsubstituted ones, for example, an amino group, a hydroxy group, a carboxyl group, a mercapto group, an alkyl group, a phenyl group, an ethylene oxide group,
It may have a substituent such as a glycidyl group or a halogen atom. For example, as a commercially available straight silicone resin, KR271, KR255, KR manufactured by Shin-Etsu Chemical Co., Ltd.
152, Toray silicone SR2400, SR24
05 and the like. The modified silicone resins are KR206 (alkyd-modified), KR5208 (acryl-modified), ES1001N (epoxy-modified), KR30 manufactured by Shin-Etsu Chemical Co., Ltd.
5 (urethane modified), SR211 made of Toray silicone
5 (epoxy modification), SR2110 (alkyd modification)
and so on.

When the carrier core material is coated with only the silicone resin, the electrical resistance of the silicone resin itself is high.
When used as a developer, solid part halftone reproducibility is poor,
Carrier adhesion also tends to occur. However, when carbon is dispersed and mixed in the silicone resin, the resistance of the silicone resin layer covering the carrier core material is reduced, and when used as a developer, solid halftone reproducibility is significantly improved, and the margin for carrier adhesion is also improved. Significantly improved.

In the present invention, the carrier core particles coated with the silicone resin have an average particle size of 10 to 1000.
μm, preferably 30-500 μm sand, cobalt,
Conventionally used materials such as nonmetals such as iron, copper, nickel, zinc, aluminum, brass, and glass, metals, and metal alloys are widely used. As a method for forming the silicone resin layer, the coating composition may be applied to the surface of the core particles by a conventionally known means such as a spraying method. In the present invention,
If the thickness of the coating layer is too small or too large, inconvenience is likely to occur, and the thickness is preferably 0.1 to 20 μm.

The carbon black used in the present invention is 1 to
All carbon blacks having an average particle diameter of 500 μm, such as furnace black, acetylene black, and channel black, can be used.

As the toner constituting the developer together with the carrier of the present invention, a toner in which an appropriate pigment or dye is contained in a resin is used. Examples of the pigment or dye include carbon black and nigrosine dye (C.I.
I. No. 50415B), aniline blue (CI.
No. 50405), chalcone blue, chrome yellow (CI No. 14090), ultramarine blue (CI No. 77103), methylene blue chlorite (CI No. 52015), phthalocyanine blue (C.I. No. 74160), Dupont Oil Red (CI No. 26105), Quinoline Yellow (CI No. 47005), Malachite Green Oxalate (CI No. 42000), Lamp Black ( CI No. 77266), Rose Bengal (CI No. 45435), Zapongphas Black New (CI No. 12195 Solvent)
Dye) and mixtures thereof.

Further, as the resin used for the toner,
A styrene resin is mainly used, and the styrene resin includes a homopolymer of styrene and a copolymer of styrene and another vinyl monomer. Other vinyl monomers include ethylenically unsaturated monoolefins such as ethylene, propylene and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide and vinyl fluoride; vinyl esters such as vinyl acetate; methyl acrylate Acrylates such as ethyl acrylate and phenyl acrylate; vinyl ethers such as vinyl methyl ether and vinyl ethyl ether; vinyl ketones such as vinyl methyl ketone and vinyl hexyl ketone; N-vinyl pyrrole;
One or more of N-vinyl compounds such as N-vinylpyrrolidone; acrylonitrile; methacrylonitrile; acrylamide; and methacrylamide are used.

As resins other than styrene resins, polyethylene resins, polypropylene resins, vinyl ester resins, rosin-modified phenol-formalin resins, epoxy resins, and mixtures thereof are used. As the toner to be used together with the carrier of the present invention, a toner obtained by a conventionally known method is used. Specifically, a resin component and a colorant such as carbon black necessary for forming a visible image are mixed well. After kneading with a hot roll mill, the mixture is cooled, solidified, pulverized and classified.

[0027]

Next, the present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to these specific structures. The amounts (parts) of each component described in Examples and Comparative Examples are all parts by weight.

Example 1 [Composition of coating layer forming liquid] Carbon black (FW2 Degussa) 10 parts Silicone resin (SR2400 manufactured by Toray Dow Corning) 100 parts Toluene 100 parts The above mixture was dispersed with a homomixer for 20 minutes, and coated. A layer forming liquid was prepared. This coating layer forming liquid was applied to the surface of 1000 parts of spherical ferrite having a particle diameter of 100 μm using a fluidized bed type coating apparatus, and then dried by a batch type vibration fluidized bed dryer to obtain a silicone resin-coated carrier. Polyester particles having a volume average particle diameter of about 30 μm (particle diameter ratio 0.3) are mixed with the mixture so that the particle concentration becomes 1.0 wt%, and then a sieve air classifier having a 250 mesh wire mesh is used. This mixture was separated into a carrier and polyester particles to which the charge-inhibiting particles were attached. This carrier is referred to as a carrier a1.

Comparative Example 1 A carrier was obtained in the same manner as in Example 1 except that the composition ratio of carbon black used in Example 1 was changed to 5 parts. This carrier is designated as a2.

Comparative Example 2 A carrier was obtained in the same manner as in Example 1 except that the composition ratio of carbon black used in Example 1 was changed to 20 parts. This carrier is designated as a3.

Comparative Example 3 A carrier was obtained in the same manner as in Example 1 except that the steps of mixing and separating and removing the polyester particles were omitted. This carrier is a4
And

Comparative Example 4 A carrier was obtained in the same manner as in Example 1 except that the batch type vibrating fluidized bed drier used in Example 1 was changed to a shelf type drier. This carrier is designated as a5.

Comparative Example 5 A carrier was obtained in the same manner as in Example 1 except that the batch type vibrating fluidized bed dryer used in Example 1 was changed to a fluidized bed dryer with stirring blades. This carrier is designated as a6.

[Toner Production Example] Toner composition 80 parts polyester resin 20 parts Styrene-acrylate copolymer 20 parts Carbon black 10 parts Nigrosine dye 2 parts The above toner raw materials are mixed, kneaded by a hot roll mill, cooled and solidified, and further crushed and classified. As a result, a toner having an average particle diameter of 10 μm was obtained.

[Composition of developer] Coated carriers a1, a
2, a3, a4, a5, a6, and 100 parts of each ratio, 3 parts of the above toner were mixed, and developer A1, A2, A
3, A4, A5 and A6 were prepared.

[Measurement of Dynamic Electric Resistance] Coated carrier a1
While stirring ~ a6 with a conduction sleeve incorporating a magnet,
DC voltage was applied to the doctor blade installed on the sleeve. The value of the current flowing from the sleeve to the ground was measured and substituted into the following equation to determine the dynamic electric resistance.

[Fluidity] The coated carriers a1 to a6 were
The fluidity was measured by a method according to S-Z2502.

[Evaluation of Carrier Attachment] Images were formed on the developers A1 to A6 using FT-4820 manufactured by our company, and the presence or absence of carrier adhesion at the image area and the non-image area was evaluated.

[Spent resistance] Coated carriers a1 to a6
100 parts of each and 3 parts of the toner were placed in a 100 ml stainless steel pot, and continuously stirred for 24 hours to evaluate spent resistance. The spent amount is obtained by blowing off the developer (mixture of toner and carrier) after stirring for 24 hours and then measuring the weight (w ₁ ). Next, the fused material is dissolved in toluene and weighed (w ₂ ). The spent amount was determined by the following equation. ◎: 0 to 0.01 ：: 0.01 to 0.
02 Δ: 0.02 to 0.05 ×: 0.05 <

[Evaluation of Increase in Carrier Charging Ability] Developer A1
For A6, 5000 images were output with an FT-4820 manufactured by our company. The charging ability of the carrier at the initial stage and at the time of 5,000 sheets were measured, and the difference was evaluated. ：: 0 to 2 ：: 2 to 5 Δ: 5 to 7 ×: 7 <

[Carrier Surface Properties and Carrier Cracking] Evaluation was made with a scanning electron microscope (SEM) photograph.

Table 1 shows the evaluation results of Example 1 and Comparative Examples 1 to 5.
It was shown to.

[0043]

[Table 1] <Explanation of symbols> ◎: extremely good ○: good △: bad ×: extremely bad

Example 2 A carrier was obtained in the same manner as in Example 1 except that the batch-type vibrating fluidized-bed dryer used in Example 1 was changed to a continuous-type dryer. This carrier was equivalent in quality to the carrier obtained in Example 1, but the processing ability in the drying and curing step was significantly improved.

Example 3 A carrier was obtained in the same manner as in Example 2 except that the sieve type air classifier having a wire mesh used in Example 2 was changed to a magnetic type air classifier. This carrier was equivalent in quality to the carrier obtained in Example 2, but the magnetic separation step could be omitted, so that the step could be omitted.

Example 4 A carrier was obtained in the same manner as in Example 3 except that the particle size ratio of the polyester particles used in Example 3 was changed to 0.1. This carrier was equivalent in quality to the carrier obtained in Example 3, but the processing capacity in the separation and removal step was significantly improved.

Example 5 The particle size ratio of the polyester particles used in Example 1 was 0.03.
A carrier was obtained in the same manner as in Example 1 except that the carrier was changed. This carrier was equivalent to Example 1 in terms of quality and production capacity of the air classifier.

Example 6 A carrier was obtained in the same manner as in Example 4 except that the polyester particles used in Example 4 were changed to a toner having a particle size ratio of 0.1. In this carrier, the increase in the charging ability of the carrier was further suppressed as compared with Example 4. Other quality aspects were the same as in Example 4. Example 1
Table 2 shows the evaluation results of Nos. To 6.

[0049]

[Table 2] <Explanation of symbols> ◎: extremely good ○: good △: bad ×: extremely bad

[0050]

As is apparent from the above description, according to the present invention, excellent anti-spent properties can be obtained without impairing any strong protective action against the adhesion of a carrier coated with a silicone resin containing carbon black, and at the beginning of development. It is possible to provide an electrophotographic carrier with little increase in the charging ability of the carrier.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasushi Nakamura 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (72) Inventor Satoshi Miyamoto 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (56) References JP-A-61-206443 (JP, A) JP-A-61-252560 (JP, A) JP-A-62-54278 (JP, A) JP-A-3-73965 ( JP, A) JP-A-60-87351 (JP, A) JP-A-3-132767 (JP, A) JP-A-2-93547 (JP, A) JP-A-55-75172 (JP, A) JP JP-A-60-196588 (JP, A) JP-A-56-133577 (JP, A) JP-A-62-174774 (JP, A) JP-A-60-51558 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G03G 9/113

Claims (5)

(57) [Claims] 1. A carrier for electrophotography, the surface of which is coated with a silicone resin containing carbon black, is dried and cured by a fluidized dryer having no stirring blades inside, and
This carrier is mixed with triboelectric particles,
After that, the dynamic electric resistance of the carrier from which the silicone resin or carbon black suspended in the air classifier was separated and removed was 0.3 to 3.0 × 10 ⁸ Ω, and the fluidity was 34 seconds / 5.
A method for producing an electrophotographic carrier having a smooth surface property of 0 g or less . 2. A fluid dryer is a dryer capable of continuous processing.
2. The carrier for electrophotography according to claim 1, wherein:
A. 3. The air classifier further separates using a magnetic force.
2. The electrophotographic key according to claim 1, wherein the key is removed.
Carrier manufacturing method. 4. Volume of triboelectrically-chargeable particles and carrier particles
The average particle size ratio is 0.05 to 0.1 with respect to the carrier particles.
5. The electrophotographic key according to claim 1, wherein
Carrier manufacturing method. 5. The method according to claim 1, wherein the triboelectrically chargeable particles are a toner and a carrier.
The same composition as the toner in the dry two-component developer
5. The method for producing an electrophotographic carrier according to claim 4, wherein
Construction method.