JPH06289660A - Carrier for electrostatic charge image developing - Google Patents

Abstract

PURPOSE:To improve electrification property and to decrease leak of charges under high temp. and high humidity conditions by incorporating a polymer obtd. by polynm. of cycloalkyl methacrylate monomers as the essential cmponent and specifying the amt. of residual surfactant in the polymer. CONSTITUTION:This electrostatic charge image developing carrier has a coating layer on the core and is used for a negative charge toner. Polymers in this carrier include a polymer obtd. by polynm. of cycloalkyl methacrylate monomers and contains 5-500ppm by weight of residual surfactant in the polymer. The polymer used is synthesized, preferably by emulsion polymn. and using a surfactant. By using an anion type surfactant, the use amt. for synthesis is small and a smaller particle size of the synthesized polymer is obtd. Thereby, an anion surfactant is more preferable than a cation or nonion surfactant, and especially, an alkylbenzene sulfonic acid compd. is preferable because it influences little on the electrification property.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for developing an electrostatic charge image used in electrophotography, electrostatic photography, electrostatic printing and the like.

[0002]

2. Description of the Related Art A two-component developer used in electrophotography or the like comprises a toner and a carrier, and the carrier is used for the purpose of imparting a triboelectric charge having a proper polarity and a proper amount to the toner. It is a thing.

As such a carrier, a resin-coated carrier in which a resin coating layer is provided on the surface of core material particles is used for various purposes such as improving the triboelectric charge imparting property.

As a method for coating the surface of the core material with these resins, there is a solvent coating method as described in JP-A-47-13954, but a dry coating method is more preferable.

This is because when the solvent coating method is used, the solvent remains in the coating layer and the presence of pores due to solvent evaporation causes
It is considered that the effects of the present invention may not be sufficiently exhibited. In addition, the durability is often slightly lower than that of the dry coating method, probably because of uneven coating.

Furthermore, the dry coating method is disclosed in
As described in 63-235959, a method has been proposed in which magnetic particles and resin polymer particles are mixed and an impact force is repeatedly applied thereto.

Styrene-based, silicon-based, acrylic acid-based polymers and the like are used as the negatively charged developing carrier. However, since the styrene-based carrier itself has a low positive charging property, it is not suitable for a negatively charged developer. Not suitable. On the other hand, the silicon-based material has a problem that it is difficult to produce fine particles.

Therefore, acrylic acid-based polymers are considered to be the most suitable, and among them, methacrylic acid ester-based polymers which can set a high glass transition point are preferred.

However, in the case of using a methacrylic acid ester type, especially polymethylmethacrylate which is a typical compound thereof, the carrier particles leak charge when the developer is left for a long time without copying under high temperature and high humidity. Easy, and as a result,
There are problems such as deterioration of image quality, fogging and toner scattering.

This problem becomes particularly noticeable when a fine particle toner having a volume average particle size of 9 μm or less or a fine particle carrier having a volume average particle size of 80 μm or less is used because the specific surface area becomes large.

From the viewpoint of hydrophobicity, Japanese Patent Application Laid-Open No. 59-104664
Although cycloalkylesters have been proposed as in JP-A No. 2004-242242, the fact is that sufficient performance has not been obtained due to solvent coating.

[0012]

DISCLOSURE OF THE INVENTION According to the present invention, the chargeability is good, the charge rises quickly, the charge leak is extremely small even under high temperature and humidity conditions, and the toner resin or the like hardly adheres to the carrier surface. , To make an electrostatic image developer composed of carrier particles having extremely high durability.

[0013]

The present invention provides a carrier for developing an electrostatic charge image having a coating layer on the surface of a core material, which is obtained by polymerizing a cycloalkyl methacrylate monomer at least in the amount of the polymer. It is achieved by being a carrier for negatively charged toner, which contains a coalesce and has a residual surfactant amount in the polymer of 5 to 500 PPM on a weight basis.

It is also described in JP-A-59-104664 that cycloalkyl esters are more hydrophobic than methyl esters.

On the other hand, although there are various methods for synthesizing a polymer, the emulsion polymerization method is preferable for producing a fine and uniform shape. However, a large amount of surfactant is often used during synthesis, and this surfactant tends to remain.

[0016] When the cycloalkyl ester was used, we thought that controlling the amount of the residual surfactant appropriately is the point of enhancing the charging performance as a carrier.

As a result of the examination, if the residual surfactant exceeds a certain value, the charge leakage upon standing is large, and if it is less than a certain value, the rise of charging is also adversely affected, and it does not have sufficient practical characteristics. I found a thing.

Therefore, if any of the above requirements is not taken into consideration, stable chargeability can be obtained for a long period of time in any use environment, and good image quality cannot be obtained.

It has also been clarified that this effect becomes remarkable especially when it is used for a fine particle toner or a fine particle carrier. In the case of toner, the term “fine particles” as used herein means a volume average particle size of
The particle size is preferably 9 μm, and the carrier preferably has a volume average particle size of 20 to 80 μm, particularly about 40 to 70 μm.

The content of the cycloalkyl methacrylate monomer component is preferably at least 30% by weight, more preferably at least 50% by weight, based on the total polymer for carrier coating. Further, characteristically, those having a cyclohexyl group having 6 carbon atoms are most desirable.

[0021]

The method for synthesizing the polymer used in the present invention is preferably the emulsion polymerization method as described above, but a surfactant is often used. As the surfactant, an anion-based compound can be used in a small amount at the time of synthesis and a smaller synthetic polymer particle size can be obtained. Therefore, it is more preferable than the cationic or nonionic type. Among them, alkylbenzene sulfonic acid compounds are particularly preferable because they have little influence on the charging property.

Further, in terms of the charged amount of the surfactant at the time of synthesis, the concentration in the aqueous solution is preferably in the range of 0.05 to 5.0% by weight from the viewpoint of easy formation of particles and removal of the surfactant after the synthesis. It is preferably 0.1 to 3.0% by weight.

In this case, the primary particle diameter of the resulting polymer fine particles is preferably about 30 to 500 nm.

In this case, if it is too small, it tends to aggregate,
Therefore, there may be a problem in film formation. If it is large, heat and pressure will be insufficient, resulting in a porous film. As a result, moisture is likely to be adsorbed, and a desirable result cannot be obtained.

It has been found that after the carrier is prepared, the glass transition point of the polymer is relatively high, and the adhesion of the toner resin to the carrier surface decreases when the temperature is around 80 to 105 ° C.
Further, the coating property is good even when the core material is coated with the polymer, and there is an advantage in producing the carrier.

The weight average molecular weight of the polymer used is 10
About 000 to 500000 is preferable from the viewpoint of film strength and coatability.

[0027]

【Example】

<Preparation of sample> 1) Synthesis of polymer (1) Cyclohexyl methacrylate: styrene = 90: 10
(Monomer Weight Ratio) (2) An emulsion polymerization method was carried out by using sodium benzenesulfonate having an alkyl group having 17 carbon atoms as a surfactant to a concentration of 0.3% by weight in an aqueous medium.

(3) After polymerization, the product was washed with water using an ultrafiltration device and dried with a spray dryer. The washing conditions were controlled to prepare different ones having different surfactant contents.

The other methods and conditions used in public use were used.

2) Characteristics of polymer Average particle diameter 175 nm Amount of residual surfactant 3,6,24,15
0,480,700PPM glass transition temperature 93 ° C weight average molecular weight 110000 In the same manner, a polymer having different monomer weight ratios and a polymer in which cyclohexyl methacrylate was changed to methyl methacrylate were prepared.

The measuring methods and the like used for investigating the characteristics are as follows.

A) Residual Surfactant Amount The resin fine particles were accurately weighed, dissolved in methyl ethyl ketone, methanol was added to this solution to precipitate the resin component, and the filtered filtrate was concentrated to obtain a test liquid. Quantitation was performed using high performance liquid chromatography under the following measurement conditions.

Column GS-310 7.6 mm ID × 500 mm Column temperature 30 ° C. Mobile phase Methanol / 0.2 M NaCl aqueous solution = 8
5/15 pH = 2.5 (prepared with concentrated phosphoric acid) Flow rate 1 ml / min Detector UV240nm Sample amount 20 μl Quantification was performed by peak area.

C) Glass transition point Differential scanning calorimeter DSC-20 type (Seiko Denshi Kogyo)
Measured by. Temperature rising rate is 10 ° C / min d) Weight average molecular weight Gel permeation chromatography method (GP
Determined by C).

3) Production of carrier Using a conventional mixing and stirring device, magnetic particles and polymer resin are mixed and stirred (blade peripheral speed: 4 m / sec, 15 minutes), and subsequently, the glass transition point of the polymer resin. Stirring was performed at a temperature of + 5 ° C (blade peripheral speed 8 m / sec, 30 minutes) to immobilize and obtain a coating carrier.

The quantitative ratio is as follows.

Core material magnetic particles (spherical ferrite particles having an average particle size of 60 μm) 100 parts by weight Polymer resin fine particles 2 parts by weight Table 1 shows the characteristics of the obtained sample.

[0038]

[Table 1]

4) Toner tested in combination: 100 parts by weight of cross-linked polyester, 8 parts by weight of carbon black, and 3 parts by weight of low molecular weight polyolefin were sequentially charged into the following equipment.

Mixing: Henschel mixer Kneading: Biaxial kneading extruder Coarse crushing: Cutter mill Crushing: Jet type crusher Classifier: Air classifier As a result, colored fine particles having a volume average particle diameter of 8.0 μm were obtained.

100 parts by weight of the colored fine particles and hydrophobic silica
0.6 part by weight was mixed with a Henschel mixer to obtain a toner.

5) Sample developer A carrier 1800 g and a toner 75 g were mixed and prepared.

<Performance Test Results> As shown in the following table (Table 2), the carrier of the present invention showed good results in both charging speed and charge leak amount.

However, when the residual amount of the surfactant is lower than that of the present invention, the rising speed of charging is slow. Therefore, when it is used for development in an actual copying machine, so-called fogging in the morning and toner scattering occur, which causes a problem.

On the other hand, when the residual amount of the surfactant in the carrier resin is too large, the charging rises quickly, but
A large amount of charge leakage causes deterioration of image quality.

Further, as shown in other comparative examples, the same results were obtained with a polymer composition in which the amount ratio of cycloalkyl methacrylate was lower than the range of the invention and a composition in which methyl methacrylate was changed to methyl methacrylate. . Moreover, the same tendency was shown even if the manufacturing method was changed.

[0047]

[Table 2]

The method of measuring the characteristics was as follows.

<Measurement of Charge Rate> 0.8 g of toner and 19.8 g of carrier are put in a 20 cc glass sample tube and left for 2 hours in an environment of 10 ° C. and 20% without a lid. Then 200
Shaking was continued under the condition of stroke, and the developer was sampled every 10 seconds. The charge amount was measured by a usual blow-off method.

The shaking time was plotted on the horizontal axis and the charge amount was plotted on the vertical axis, and the time required for the charge amount to reach 20 μC / g was read. It was determined that the shorter the time, the faster the charging rate.

<Charge Leakage Experiment> 0.8 g of toner and 19.8 g of carrier are put in a 20 cc glass sample tube and left for 2 hours in an environment of 40 ° C. and 90% without a lid. Then 20
Shake for 5 minutes under the condition of 0 stroke, and set the charge amount Q1 (μC / g) at that time. The sample tube is left open for 48 hours under the condition of 40 ° C. and 90% with the lid open, and the charge amount after that is set to Q2 (μC / g).

The amount of charge leakage was judged by Q1-Q2.

[0053]

According to the present invention, it is possible to manufacture a carrier for developing an electrostatic charge image, which has a high charging rate at a low temperature and a low humidity and at a high temperature and a high humidity, and has a very small charge leak amount.

Therefore, it is possible to obtain a durable carrier which does not deteriorate in image characteristics even when the external environment is greatly changed and is left unused without stirring for a long time.

Claims (7)

[Claims] 1. A carrier for developing an electrostatic charge image, comprising a polymer coating layer on the surface of a core material, wherein the polymer contains a polymer obtained by polymerizing at least a cycloalkyl methacrylate monomer as a main component. And the amount of residual surfactant in the polymer is 5 to 500 PPM on a weight basis, a carrier for negatively charged toner. 2. A carrier for developing an electrostatic image having a coating layer of a polymer on the surface of a core material, wherein the polymer contains as a main component a polymer obtained by polymerizing at least a cycloalkyl methacrylate monomer. A carrier for negatively charged toner, characterized in that the coating layer is applied by dry coating. 3. The carrier for developing an electrostatic charge image according to claim 2, wherein the coating method is to mix and stir the magnetic particles and the resin particles and repeatedly apply an impact force thereto. 4. An electrostatic charge image developing carrier having a polymer coating layer on the surface of a core material, wherein a polymer obtained by polymerizing at least a cycloalkyl methacrylate monomer is used as a main component. A carrier for electrostatic image development, which comprises an emulsion polymerization method for polymer synthesis. 5. A carrier for developing an electrostatic image having a coating layer of a polymer on the surface of a core material, wherein a polymer obtained by polymerizing at least a cycloalkyl methacrylate monomer is used as a main component. A method for producing a carrier for developing an electrostatic charge image, characterized by using an emulsion polymerization method for synthesizing a polymer. 6. Emulsion polymerization uses a surfactant, and the residual amount of the surfactant in the polymer is 5 to 500 PPM. Career. 7. A carrier for developing an electrostatic charge image, which is manufactured by the method according to claim 6, and is manufactured by mixing magnetic particles and resin particles and applying an impact force to the particles when dry coating.