JPH10268581A - Electrophotographic liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrophotographic liquid developer excellent in stability with time with which a high system rate is obtd., by incorporating an oil-soluble ionic surfactant as a charge controlling agent and incorporating a specified polyester resin as a binder resin into color fine particles. SOLUTION: This electrophotographic liquid developer is produced by dispersing color fine particles in an electrically insulating liquid medium, into which an oil-soluble ionic surfactant is incorporated as a charge controlling agent. The color fine particles contain a polyester resin having the acid value between >=40 mgKOH/g and <=100 mgKOH/g as a binder resin. The acid value is measured under conditions according to JIS K5400. Since a polyester resin having a rather high acid value as >=40 mgKOH/g and <=100 mgKOH/g is used as the binder resin for the toner in a preferable state of the electrophotographic liquid developer, large charges of the toner particles can be obtd. and the developing rate can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic liquid developer used for developing an electrostatic latent image in an image forming apparatus such as an electrophotographic copying machine or a printer.

[0002]

2. Description of the Related Art Generally, in electrophotographic image formation, an electrostatic latent image is formed on an electrostatic latent image carrier such as a photoreceptor by exposing the image according to a document image. The electrostatic latent image is developed into a visible toner image, and the toner image is transferred and fixed on a recording material to obtain a target image.

[0003] The developing method is divided into a dry developing method and a wet developing method. In the dry development method, colored fine particles (toner) or a toner to which a carrier having magnetism or the like is added is used as a developer. The dry toner generally comprises a pigment and a binder resin as main components, and a charge control agent, a conductivity control agent, a plasticizer, a release agent and the like are added internally or externally as needed. The magnetic toner further contains a magnetic powder such as Fe ₃ O ₄ . In the dry development method, the toner is usually contacted with a specific surface of the developing device, contacted with each other, or in the case of a two-component developer containing a carrier, contact charging due to contact with a carrier or the like, electrostatic induction by an electric field, charge injection, Charged by ion adsorption or the like due to ionization discharge of air, transported by electrostatic force, mechanical force, magnetic force, etc. to an electrostatic latent image portion on an electrostatic latent image carrier such as a photoconductor, and subjected to development with electrostatic force .

The dry toner used in dry development cannot be made very fine because it may escape into the surrounding atmosphere and float in the air. Those having a size of about 10 μm are used.
Since the dry toner has such a relatively large toner particle size, the resolution in development is not so high. On the other hand, in the wet developing method, an electric insulating dispersion medium (carrier liquid) is currently used and mainly used as a developer.
Colored fine particles (toner) containing pigment and binder resin as main components are dispersed therein. The charge of the toner is
When a charge control agent is added to the charge by the binder resin itself or to the colored fine particles or the carrier liquid, it is thought to be due to ion adsorption of the charge control agent, and the charged toner is subjected to development by the principle of electrophoresis. .

[0005] Since toner used in wet development does not escape into the atmosphere, it can be made finer, and those having an average particle size in the submicron range are also practical.
Thus, there is an advantage that an image with high resolution and excellent gradation is obtained. In the liquid developer used in the wet development method, the binder resin is a toner image transferability,
It is an important factor affecting the fixability, color, chargeability and dispersibility of toner particles, and the like. The chargeability and dispersibility of the toner in the liquid developer affect the developability and the transferability when performing electrostatic transfer.

For example, according to Japanese Patent Publication No. 52-3306, a semi-soluble graft copolymer prepared by copolymerizing a soluble monomer and an insoluble monomer in a hydrocarbon organic solvent used as a carrier liquid. A liquid developer has been disclosed in which a toner coated with a pigment by a binder resin composed of a dispersion is dispersed to improve transferability and fixability of a toner image, dispersibility and chargeability of toner particles, and the like.

However, when the fixing property, the chargeability, the dispersibility, and the like are controlled together with the binder resin alone, it is difficult to individually control each property to an optimum state. Further, when image formation is repeated for a long time while replenishing the concentrated toner replenishing liquid, each characteristic cannot be maintained individually by this replenishment, so that various characteristics of the developer can be maintained at the same level as the initial state. Have difficulty.

For this reason, it is preferable to control the transferability, the fixability and the chargeability and dispersibility of the toner particles by using different substances. Specifically, transferability, fixability, etc. are stabilized by using a resin insoluble in a hydrocarbon-based organic solvent used as a carrier liquid as a binder resin, and the toner particles are formed by adding a charge control agent separately. What is necessary is just to control chargeability and dispersibility. For example, U.S. Pat. No. 5,407,771 discloses a liquid developer using a thermoplastic resin, for example, an ethylene-vinyl acetate copolymer, as a binder resin insoluble in a hydrocarbon organic solvent.

However, the binder resin is required to have a light-transmitting property when an image is fixed. In particular, when a color image is obtained by superimposing a plurality of color developers, if the resin has poor translucency, the image becomes dark and it becomes difficult to obtain a desired color. The ethylene-vinyl acetate copolymer and the like disclosed in the above-mentioned U.S. Pat. No. 5,407,771 have poor light transmittance of a resin in a toner image after being fixed to a recording material, and it is difficult to obtain an appropriate color value at the time of forming a color image. .

In order to impart stable transferability, fixability and excellent light transmittance to a liquid developer, among thermoplastic resins, a saturated polyester widely known as a binder resin for a color toner in dry development is used. It is desirable to use a resin as a binder resin. Polyester resin not only can change physical properties such as thermal properties over a wide range, but also has excellent translucency when obtaining color images, so beautiful colors can be obtained, and it has excellent spreadability and viscoelasticity, so it is fixed. The later resin film is tough and has good adhesion to a recording material such as paper. A liquid developer using such a polyester resin as a binder resin is disclosed in, for example, JP-A-7-9.
No. 2,742, JP-A-8-220813 and the like.

[0011]

On the other hand, since a high-definition image can be obtained, the wet developing method has been increasingly used in a full-color high-speed printer or the like as an alternative to a light printer, and has been used at a higher speed. There is a new demand for being able to form images. In this regard, for example, Japanese Patent Application Laid-Open No.
In the case of using a liquid developer using the polyester resin disclosed in Japanese Patent Publication No. 2 as a binder resin for the toner, the maximum system speed is as high as about 400 mm / sec, which cannot be achieved. This is mainly because the acid value of the binder resin is too low, so that the charge amount of the toner particles is small and the developing speed is low.

On the other hand, if the acid value of the binder resin is increased, the liquid developer becomes unstable, making it difficult to stably form an image over a long period of time. Accordingly, the present invention provides a liquid developer for electrophotography using a polyester resin as a binder resin for a toner, which provides a high system speed and excellent stability over time. Make it an issue.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an electrophotographic liquid developer in which colored fine particles are dispersed in an electrically insulating medium liquid. Agent as a charge control agent, and the colored fine particles have an acid value of 40 mgKOH / g or more and 100 mgKOH / g or more.
A liquid developer for electrophotography, comprising: a polyester resin of not more than g as a binder resin.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid developer for electrophotography according to a preferred embodiment of the present invention has an acid value of at least 40 m.
The toner contains a toner containing a polyester resin of gKOH / g or more and 100 mgKOH / g or less as a binder resin, and a carrier liquid containing an oil-soluble ionic surfactant as a charge control agent.

The acid value is measured under the conditions of JIS K5400. According to the liquid developer for electrophotography of the preferred embodiment of the present invention, the acid value of the toner binder resin is 40 mgKOH / g or more and 100 mg or more.
Since the polyester resin having a relatively high acid value of KOH / g or less is used, the charge amount of the toner particles is large and the developing speed can be increased, and the maximum is 800 mm / sec.
System speeds as high as c are obtained. Acid value is 40mg
If it is lower than KOH / g, it is difficult to improve the system speed, and if the acid value is higher than 100 mgKOH / g, it becomes difficult to produce a polyester resin while maintaining a predetermined molecular weight. Also, when the acid value of the binder resin is high, various properties of the liquid developer tend to be unstable, but by using an oil-soluble ionic surfactant as a charge control agent, It can be stable.

In the liquid developer for electrophotography according to a preferred embodiment of the present invention, the transferability and the fixability are controlled by a binder resin, and the chargeability and the dispersibility are controlled by a charge control agent. Therefore, it is easy to individually control each characteristic to an optimum state. In addition, since a polyester resin having good translucency is used as the binder resin, it is easy to obtain an appropriate color even when a color image is formed.

The liquid developer according to a preferred embodiment of the present invention can be manufactured, for example, as follows. First, a binder resin and a colorant are kneaded using a kneader such as a three-roll mill, and the colorant is dispersed in the resin. The coloring agent is not limited thereto, but the following pigments and the like can be used. A typical example of the black colorant is carbon black. In particular, acidic carbon is a coloring agent having strong polarities such as COOH, OH, and CＯO on the surface thereof, and is therefore particularly effective when the toner is negatively charged.

Examples of colorants for colors other than black include:
Yellow pigment, magenta pigment and cyan pigment can be exemplified. Color image formation is performed by subtractive color mixing based on these pigment colors. Examples of the yellow pigment include Color Index (CI) Pigment Yellow.
Examples thereof include disazo yellow pigments represented by w12, 13, 14, 17, 55, 81, 83 and the like. Examples of the magenta pigment include C.I. I. Pigment Red4
8, 57 (Carmin 6B), 5, 23, 60, 114,
146, 186, etc., azo lake magenta pigments, insoluble azo magenta pigments, thioindigo magenta pigments,
C. I. And quinacridone-based magenta pigments such as CI Pigment Red 122 and 209. Examples of the cyan pigment include C.I. I. Pigment Blue 1
Examples thereof include copper phthalocyanine blue-based cyan pigments such as 5: 1 and 15: 3.

The amount of the colorant added to the binder resin is preferably about 5 to 20 parts by weight based on 100 parts by weight of the resin. Note that the resin itself may be colored. The polyester resin here is a thermoplastic resin, and is obtained by polycondensation of a polyhydric alcohol and a polybasic acid (polycarboxylic acid).

Examples of the polyhydric alcohol include, but are not limited to, propylene glycol such as ethylene glycol, diethylene glycol, triethylene glycol, and 1,2-propylene glycol; butane such as dipropylene glycol and 1,4-butanediol. Diols, neopentyl glycols, alkylene glycols (aliphatic glycols) such as hexanediols such as 1,6-hexanediol, and adducts of these alkylene oxides;
Bisphenols such as bisphenol A and hydrogenated bisphenol; phenolic glycols of these alkylene oxide adducts; alicyclic and aromatic diols such as monocyclic or polycyclic diols; triols such as glycerin and trimethylolpropane; Can be These can be used alone or in combination of two or more.

In particular, neopentyl glycol, an alkylene oxide 2 to 3 mol adduct of bisphenol A,
The polyester resin, which is a product, is suitable for a binder resin for a toner of a liquid developer in terms of solubility and stability, and is also preferable because of its low cost. Examples of the alkylene oxide include ethylene oxide and propylene oxide.

As the polybasic acid (polycarboxylic acid),
Although not limited thereto, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, phthalic acid and its modified acids (for example,
Saturated or unsaturated dibasic acids such as hexahydrophthalic anhydride), isophthalic acid and terephthalic acid, and trifunctional or higher saturated polybasic acids such as trimellitic acid, trimesic acid, pyromellitic acid and methylnadic acid; And their acid anhydrides and lower alkyl esters. These can be used alone or in combination of two or more.

In particular, isophthalic acid and terephthalic acid are preferable in terms of solubility and stability of the resulting polyester resin as a binder resin for a toner of a liquid developer, and are also preferable because they are inexpensive. As a method of polycondensation,
Generally known polycondensation methods can be used. Although it differs depending on the type of the raw material monomer, it may be generally performed by the following method.

As the polycondensation method, generally known polycondensation methods can be used. Although it depends on the type of the raw material monomer, it is generally carried out at a temperature of about 150 ° C. to 300 ° C. In addition, the reaction can be performed under any conditions, such as using an inert gas as the atmosphere gas, using various solvents, and setting the pressure in the reaction vessel to normal pressure or reduced pressure.
An esterification catalyst may be used to promote the reaction. As the esterification catalyst, metal organic compounds such as tetrabutyl zirconate, zirconium naphthenate, tetrabutyl titanate, tetraoctyl titanate, and 3/1 stannous oxalate / sodium acetate can be used.
Those that do not color the product ester are preferred. Further, an alkyl phosphate, an allyl phosphate, or the like may be used as a catalyst or a hue adjuster.

In order to control the molecular weight of the polyester resin as the product, the polymerization temperature, the reaction system pressure, the reaction time and the like may be adjusted. Further, the acid value can be controlled by the molar ratio of the carboxylic acid and alcohol to be reacted, the molecular weight of the polymer, and the like. In addition to the polyester resin, a styrene-acryl copolymer resin, a styrene-acryl-modified polyester resin, a polyolefin copolymer (especially an ethylene-based copolymer), an epoxy resin, a rosin-modified phenol resin, if necessary, may be used as the binder resin. , A resin such as rosin-modified maleic resin and paraffin wax may be mixed in an appropriate amount within a range of 30% by weight or less based on the total weight.

Next, a colored kneaded product comprising the binder resin thus obtained and a coloring agent added as necessary is roughly pulverized using a cutter mill, a jet mill, or the like. Further, a wet grinding treatment is performed in a small amount of a carrier liquid in which a charge control agent described later is dissolved, and the volume average particle diameter of the toner is 0.1 to
Finely pulverized to a thickness of about 10 μm, preferably about 0.5 to 5 μm to obtain a concentrated liquid developer. The concentrated liquid developer thus obtained is optionally charged control agent,
Dilution and dispersion treatment may be performed with a carrier liquid containing an additive such as a dispersant (dispersion stabilizer) until the concentration becomes appropriate.

The volume average particle diameter of the toner particles is 0.1
If the diameter is smaller than μm, the zeta potential is reduced, so that the force received from the electric field during development is reduced, and the development speed is reduced. In addition, a high electric field is required when performing electrostatic transfer, making transfer difficult. Further, the volume average particle size of the toner particles is 1
If it becomes larger than 0 μm, it becomes difficult to obtain high resolution.

The carrier liquid has a resistance value (about 10 ¹¹ to 10 ¹⁶ Ω · cm) that does not disturb the electrostatic latent image. At the time of development, it may be in a liquid state when the temperature is raised to a temperature higher than the softening point of the resin to be dispersed, and the state at normal temperature is not limited. Further, the boiling point is preferably such that it is easy to dry after fixing. Further, a solvent having no odor or toxicity and having a relatively high flash point is preferable.

For example, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes and the like can be used. Particularly, a normal paraffin solvent and an isoparaffin solvent are preferable from the viewpoints of odor, harmlessness, and cost. Specifically, Isopar G, Isopar H, Isopar L, Isopar K (all manufactured by Exxon Chemical Co., Ltd.), Shellsol 71 (manufactured by Shell Petrochemical Co., Ltd.), IP Solvent 1620, IP Solvent 202
8 (all manufactured by Idemitsu Petrochemical Co., Ltd.) and the like. At room temperature, solid waxes, paraffins and the like can also be used. When these waxes and paraffins which are solid at ordinary temperature are used, they may be heated back to liquid before use as a liquid developer.

The charge control agent is substantially solvated or dissolved in the carrier liquid, and is added to the carrier liquid for the purpose of affecting the chargeability of the toner particles. Further, it may be added to the toner particles as needed. Representative examples of the oil-based ionic surfactant used as the charge control agent include a surfactant containing, as a main component, an alkylallyl sulfonate having an alkyl group having 20 or more carbon atoms. Specifically, alkylbenzene sulfonates having an alkyl group having 20 or more carbon atoms (calcium salts, barium salts, etc.), petroleum sulfonates (barium salts, calcium salts, magnesium salts, etc.), basic petroleum sulfonates ( Barium salt, calcium salt, magnesium salt, etc.).

Of these, petroleum sulfonates (barium salts and calcium salts) and basic petroleum sulfonates (barium salts and calcium salts) are particularly effective. Examples of the charge control agent as described above include Sulhole Ca-45N, Sulhole Ca-45, Sulhole 1040, Moresco Amber SC-45N, Moresco Amber SC-45, Sulhole Ba-30N, Moresco Amber SB-50N
(All of these are manufactured by Matsumura Oil Research Institute Co., Ltd.), Basic Barium Petronate (Basic Barium P
(Etronate), Neutral Barium Petronate (Neutral Barium Petronate)
e) Basic calcium petronate (Basic
Calcium Petronate, neutral calcium petronate (Neutral Calc)
ium Petronate, Basic Magnesium P
etronate) (Witco Chemi
cal Co. And the like are specific examples of products.

The charge control agents can be used alone or in combination of two or more. Further, the charge control agent varies depending on the type and the like, but is added to the carrier liquid in an amount of 0.1 to 1.0.
It is preferable to add about 01 to 5% by weight. It is preferable to add about 0.1 to 50% by weight of the toner. A dispersant (dispersion stabilizer) may be used to stabilize the dispersion of the toner particles in the liquid developer. As the dispersant (dispersion stabilizer), a polymer or the like which is adsorbed on the toner particles and which has an affinity for the carrier liquid and which is soluble, semi-soluble or swells in the carrier liquid can be used.

The polymer having solubility, semi-solubility or swelling in the carrier liquid includes, but is not limited to, polyolefin-based petroleum resin, linseed oil, polyalkyl methacrylate and the like. In order to increase the viscosity, a copolymer of a monomer having a polar group such as methacrylic acid, acrylic acid, or alkylaminoethyl methacrylate can also be used. In this case, the solubility in the carrier liquid, the affinity to the toner particles, and the adsorptivity can be controlled by the amount of the polar group to be copolymerized. Affinity and adsorptivity increase.

The dispersing agent is preferably added in an amount of about 0.01 to 20% by weight based on the carrier liquid from the viewpoint of improving the dispersibility and preventing the viscosity of the carrier liquid from increasing by the addition thereof. More preferably, it is about 0.1 to 10% by weight. Ratio of the total weight of solid components such as toner, charge control agent and dispersant to the total weight of liquid developer (solid content ratio)
Is preferably about 1 to 90% by weight. In order to reduce the total amount of the liquid developer used for development and facilitate handling, the solid content ratio is more preferably 2 to 50% by weight.

The concentration of the toner with respect to the carrier liquid is preferably from 0.5 to 50% by weight, more preferably from 2 to 10% by weight, in view of the developing speed, image fog and the like. This density is the density at the time of development, and is not limited to the time of storage, replenishment, transportation and the like.

[0036]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. In the following examples, “parts” means “parts by weight” unless otherwise specified, “Tg” means “glass transition temperature”, and “Mw” means “weight average”. "Mn" means "number average molecular weight".

In the following examples, the acid value is determined according to JIS
It was measured under the conditions of the K5400 method. Tg was measured using a differential scanning calorimeter DSC-20 (manufactured by Seiko Instruments Inc.) under the conditions of a sample amount of 35 mg and a heating rate of 10 ° C./min. Mw and Mn were respectively calculated from the results of gel permeation chromatography. Gel permeation chromatography was performed using a high-performance liquid chromatograph pump TRI ROTAR-V (manufactured by JASCO Corporation), an ultraviolet spectrometer UVIDEC-100-V (manufactured by JASCO Corporation), and a 50 cm-long column Shode.
x GPC A-803 (manufactured by Showa Denko KK), and the molecular weight of the test sample was calculated as polystyrene standard Mw and Mn from the results of the chromatography by using polystyrene as a standard substance. The test sample used was one in which 0.05 g of a binder resin was dissolved in 20 ml of tetrahydrofuran (THF). Production of Polyester Resin Polyester Resin 1 In a round-bottom flask equipped with a reflux condenser, a water / alcohol separator, a nitrogen gas inlet tube, a thermometer and a stirrer, 1700 propylene oxide adduct of bisphenol A was added.
Parts (polyhydric alcohol) and 890 parts of isophthalic acid (polybasic acid), introduce nitrogen gas with stirring, and add
Dehydration polycondensation or dealcohol polycondensation was performed at a temperature of 00 to 240 ° C. When the acid value of the produced polyester resin or the viscosity of the reaction solution reached a predetermined value, the temperature of the reaction system was lowered to 100 ° C. or less, and the polycondensation was stopped. Thus, a thermoplastic polyester resin 1 was obtained.

The obtained polyester resin 1 had Mw = 50.
50, Mn = 2550, Tg = 54.9 ° C., acid value = 4
It was 5.2 mgKOH / g. Polyester Resin 2 In the production of the polyester resin 1, bisphenol A propylene oxide adduct was added at 1450 as a raw material.
A thermoplastic polyester resin 2 was obtained in the same manner as in the production of the polyester resin 1 except that 10 parts of isophthalic acid and 1090 parts of isophthalic acid were used.

The obtained polyester resin 2 had Mw = 39.
00, Mn = 1950, Tg = 45.1 ° C., acid value 75.
It was 0 mgKOH / g. Polyester resin 3 In the production of polyester resin 1, bisphenol A propylene oxide adduct was used as a raw material at 1650.
A thermoplastic polyester resin 3 was obtained in the same manner as in the production of the polyester resin 1 except that parts and 800 parts of isophthalic acid were used. The obtained polyester resin 3 has Mw = 4
500, Mn = 2700, Tg = 40.3 ° C., acid value 3
It was 4.9 mgKOH / g. Production of Liquid Developer Liquid Developer 1 (Example 1) (Wet pulverization method) A mixture of 60 parts by weight of the polyester resin 1 and 40 parts by weight of carbon black Mogal L (manufactured by Cabot Corporation) was mixed with three bottles. 4 at 180 ° C using a kneader with roll
The mixture was kneaded for a long time to obtain a high-concentration pigment mixture. This high-concentration pigment kneaded material was diluted with the polyester resin 1 using a kneader to finally obtain a colored resin kneaded material having a carbon black concentration of 15% by weight. After sufficiently cooling the colored resin kneaded material, coarsely pulverized using a cutter mill, and further finely pulverized using a jet mill (manufactured by Nippon Pneumatic Industries, Ltd.) to obtain colored toner coarse particles having an average particle size of about 10 μm. I got 30 g of the colored toner coarse particles and 0.5% by weight of barium petroleum sulfonic acid sulfol Ba-30N
IP Solvent 1620 (manufactured by Matsumura Oil Research Institute Co., Ltd.)
(Idemitsu Petrochemical Co., Ltd.) 70 g of the solution was mixed, and a sand grinder (IGARASHI KIKAI SEI) was mixed.
ZO CO. , Ltd. 1) glass beads (150 cc) having a diameter of 1 mm as media, and wet grinding by treating at a cooling water temperature of 20 ° C. and a disk rotation speed of 2000 rpm for 15 hours in a １ ／ gallon vessel equipped with a water jacket. . Thus, a concentrated liquid developer having a volume average toner particle diameter of 1.45 μm was obtained.

Further, in 100 parts of the concentrated liquid developer,
900 parts of a 0.5% by weight sulfol Ba-30N IP solvent 1620 solution was added to dilute the dispersion, and a dispersion treatment device was used.
T. K. Auto homomixer M type (Special Kika Kogyo Co., Ltd.)
The liquid developer 1 was obtained by subjecting to a dispersion treatment at 10,000 rpm for 5 minutes using the following method. Liquid Developer 2 (Example 2) (Wet Grinding Method) In the production of the liquid developer 1, the polyester resin 1
Was replaced by a polyester resin 2. The volume average particle size of the obtained toner particles was 1.46 μm. Otherwise, a liquid developer 2 was obtained in the same manner as in the production of the liquid developer 1. Liquid developer 3 (Example 3) (Emulsion dispersion granulation method) 100 parts of the polyester resin 1 was completely dissolved in methylene chloride so as to be 20% by weight, and carbon black Mogar L was used as a colorant. 15 parts (manufactured by Cabot Corporation) were dispersed using a disperser Eiger Motor Mill (manufactured by Eiger Japan) to obtain a colored resin solution.

This colored resin solution was dispersed in an aqueous solution containing 1% by weight of methylcellulose Metroose 65SH-50 (manufactured by Shin-Etsu Chemical Co., Ltd.) and 1% by weight of sodium lauryl sulfate, and a dispersion processor ROBOMICS (manufactured by Tokushu Kika Kogyo Co., Ltd.) was used. The mixture was emulsified and dispersed at 10,000 rpm for 20 minutes to obtain an oil-in-water (O / W) emulsion. This emulsification and dispersion was performed at room temperature. Next, this dispersion processor was replaced with four stirring blades, and methylene chloride was distilled off while stirring at 40 to 45 ° C. for 3 hours to obtain an aqueous suspension of resin fine particles for toner having a volume average particle size of 1.82 μm. A liquid (suspension) was obtained.

The resulting aqueous suspension of the resin particles was centrifuged at 10,000 rpm for 5 minutes using a centrifuge to remove solids. The obtained solid content was placed in a beaker, and about 5 times by weight of distilled water was added thereto, pre-washed with an ultrasonic disperser for 10 minutes, and the solid content was taken out again using a centrifuge. The solid content after washing was spread on filter paper, and water was evaporated and dried at room temperature to obtain resin particles.

20 parts by weight of the resin particles were placed in a beaker, and a 20% by weight of a barium petroleum sulfonic acid salt 20% IP solvent 162 containing throughhole Ba-30N was used as a washing liquid.
0 solution was added and the mixture was stirred with a stirrer at 25 ° C. at 200 rpm for 48 hours. The mixture slurry was centrifuged at 10,000 rpm for 5 minutes using a centrifugal separator to remove solids. The obtained solid content was spread on filter paper and dried at room temperature to such an extent that the surface was lightly wet to obtain washed resin particles.

Next, 0.5 parts with respect to 3 parts of the cleaning resin particles
Wt% Sulfol Ba-30N IP Solvent 16
The liquid developer 3 was obtained by mixing 100 parts of the 20 solution and dispersing the mixture for 5 minutes using an ultrasonic disperser. The volume average particle size of the toner particles was 1.76 μm. Liquid Developer 4 (Example 4) (Wet Grinding Method) In the production of the liquid developer 1, the IP solvent 1 mixed with the colored toner coarse particles during the production of the concentrated liquid developer
Instead of adding 0.5% by weight of barium petroleum sulfonate sulfol Ba-30N as a charge control agent to 620, barium alkylbenzene sulfonate Moresco Amber SB-50N (manufactured by Matsumura Petroleum Institute Co., Ltd.)
Was added in an amount of 5.0% by weight. Further, no charge control agent was added to the IP solvent 1620 for diluting the concentrated liquid developer. The volume average particle size of the obtained toner particles was 1.25 μm. Otherwise, a liquid developer 4 was obtained in the same manner as in the production of the liquid developer 1. Liquid Developer 5 (Example 5) (Wet Pulverization Method) In the production of the liquid developer 1, the IP solvent 1 mixed with the colored toner coarse particles during the production of the concentrated liquid developer
No charge control agent was added to 620. Also, instead of adding 0.5% by weight of petroleum barium sulfonate sulfol Ba-30N to IP solvent 1620 for diluting a concentrated liquid developer, basic petroleum calcium sulfonate sulfol 1040 (Matsumura Oil Co., Ltd.) 0.5% by weight was added. The volume average particle diameter of the obtained toner particles was 2.56 μm. Otherwise, a liquid developer 5 was obtained in the same manner as in the production of the liquid developer 1. Liquid Developer 6 (Example 6) (Wet Grinding Method) In the production of the liquid developer 1, as a charge control agent,
Barium Petroleum Sulfonate Basic Bari Petroleum Sulfonate Instead of Sulfol Ba-30N Basic Bari
um Petronate (manufactured by Witco Chemical Co.) was used. The volume average particle diameter of the obtained toner particles is 1.41 μm.
Met. Otherwise, in the same manner as in Example 1, a liquid developer 6 was obtained. Liquid Developer 7 (Comparative Example 1) (Wet Grinding Method) In the production of the liquid developer 1, the polyester resin 1
Was replaced by a polyester resin 3. The volume average particle size of the obtained toner particles was 1.44 μm. Otherwise, a liquid developer 7 was obtained in the same manner as in the production of the liquid developer 1. Liquid Developer 8 (Comparative Example 2) (Wet Grinding Method) In the production of the liquid developer 1, the IP solvent 16
20. Barium petroleum sulfonate as a charge control agent
Instead of adding 0.5% by weight of Sulhole Ba-30N, 1.0% by weight of lecithin (soy lecithin manufactured by Wako Pure Chemical Industries, Ltd.) was added. The volume average particle size of the obtained toner particles was 1.49 μm. Otherwise, a liquid developer 8 was obtained in the same manner as in the production of the liquid developer 1. Liquid Developer 9 (Comparative Example 3) (Wet Grinding Method) In the production of the liquid developer 1, the polyester resin 1
Was replaced by a polyester resin 2. Further, instead of adding 0.5% by weight of barium petroleum sulfonate sulfol Ba-30N as a charge control agent to IP solvent 1620, 1.0% by weight of lecithin (soy lecithin) was added. The volume average particle size of the obtained toner particles was 1.49 μm. Others are the liquid developer 1
Liquid developer 9 was obtained in the same manner as in the production of. Liquid Developer 10 (Comparative Example 4) (Wet Grinding Method) In the production of the liquid developer 1, the IP solvent 16
20. Barium petroleum sulfonate as a charge control agent
Instead of adding 0.5% by weight of sulfol Ba-30N, 1.0% by weight of N-vinyl-2-pyrrolidone / lauryl methacrylate copolymer (compounding ratio 5:95) A was added.
Was added. The volume average particle size of the obtained toner particles was 1.42 μm. Otherwise, a liquid developer 10 was obtained in the same manner as in the production of the liquid developer 1. Liquid Developer 11 (Comparative Example 5) (Wet Grinding Method) In the production of the liquid developer 1, the polyester resin 1
Was replaced by a polyester resin 2. Further, instead of adding 0.5% by weight of barium petroleum sulfonate sulfol Ba-30N as a charge control agent to the IP solvent 1620, an N-vinyl-2-pyrrolidone / lauryl methacrylate copolymer (compound ratio 5 : 95) A was added in an amount of 1.0% by weight. The volume average particle size of the obtained toner particles was 1.44 μm. Otherwise, a liquid developer 11 was obtained in the same manner as in the production of the liquid developer 1.

The N-vinyl-2-pyrrolidone / lauryl methacrylate copolymer (composition ratio 5:95) A used in the production of the liquid developers 10 and 11 was produced as follows. 95 g of lauryl methacrylate monomer was dissolved in 200 g of IP Solvent 1620 (manufactured by Idemitsu Petrochemical Co., Ltd.), and argon gas was blown into this solution for 10 minutes to replace the entire reaction system with argon gas. Next, 1 mol% of benzoyl peroxide (BPO) was added as a polymerization initiator to lauryl methacrylate monomer, and polymerization was carried out at 80 ° C. for 4 hours.
Next, after the reaction system was cooled to 30 ° C., N-vinyl-2 was added.
5 g of a pyrrolidone monomer was added, and 1 mol% of azobisisobutyronitrile (AIBN) was added to the N-vinyl-2-pyrrolidone monomer, and the mixture was kept at 90 ° C. for 4 hours to complete the polymerization. The N- thus obtained
The vinyl-2-pyrrolidone / lauryl methacrylate copolymer solution was designated as copolymer A.

Next, with respect to the liquid developers 1 to 11,
As parameters indicating the stability over time, changes in image density and edge effect before and after image formation was performed 100,000 times using the image forming experimental apparatus of FIG. 1 were evaluated. The image forming experiment apparatus shown in FIG. 1 is of an electrophotographic type having a built-in liquid developing device, has a photosensitive drum 1, and has a charger 2 surrounding the photosensitive drum 1, an image sent from a host computer (not shown) or the like. An image exposure device 3, a liquid developing device 4, a squeeze roller device 51, a squeeze charger 52, a transfer roller 6, a cleaner 7, and an eraser lamp 8 for sequentially generating a laser beam based on data are arranged in this order. Further, in the vicinity of the transfer roller 6, a paper feeding device 9, a fixing device 10 including a thermal fixing roller pair for fixing a toner image formed on the paper, and a discharge device on which the paper discharged from the inside of the printer is placed. A paper tray 11 is provided. The paper discharge tray 11 is provided with a paper discharge roller 111. The paper feeding device 9 includes a paper storage cassette 91 in which recording paper is stored, a paper feeding roller 92 for feeding out the paper in the cassette 91, and a timing roller 93.

The liquid developing device 4 is opposed to the photosensitive drum 1 at a small interval and has a lower portion immersed in the liquid developer, and a developing roller 41 which holds the liquid developer around the developing roller 41. A developer holding tank 42, a developer storage tank 43 for storing a liquid developer to be supplied to the developer holding tank 42, a developer supply device 44 for pumping the developer in the developer storage tank 43 to the developer holding tank 42, A developer recovery device 45 for returning the excess developer in the developer holding tank 42 to the developer storage tank 43;
And The developer in the developer storage tank 43 is supplied with a concentrated toner replenishing liquid at an appropriate time by a concentrated toner replenishing device (not shown), and is maintained at a substantially constant toner concentration. The developing gap between the developing roller 41 and the photosensitive drum 1 can be arbitrarily set within a range of 0 to 2 mm.

In forming an image, the photosensitive drum 1 is rotated at a speed of 80 cm / sec in the direction of arrow a in the figure, and its surface is uniformly charged by the charging charger 2 so as to have a surface potential of about -500 V. Be charged. Then, a laser beam is irradiated from the image exposure device 3 toward the photosensitive drum 1 based on image information, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. The exposed area of the surface of the photosensitive drum 1 is about 30% of the total surface area of the photosensitive member 1. As a result, the surface potential of the exposed portion of the photosensitive drum 1 becomes about -30 V
Attenuate.

The electrostatic latent image formed on the photosensitive drum 1 is
The liquid developing device 4 visualizes the image using a liquid developer. The developing roller 41 is rotated at a speed of 120 cm / sec in a direction indicated by an arrow b in the figure opposite to the rotation direction of the photosensitive drum 1, and a developing gap between the photosensitive drum 1 and the developing roller 41 is 100 μm. It is said. Further, a bias voltage of about -400 V is applied to the developing roller 41 to promote the adhesion of the developer to the exposed portion and to suppress the adhesion of the developer to the unexposed portion.

Thereafter, the liquid developer excessively adhering to the photosensitive drum 1 is squeezed out by a squeeze roller device 51 and a squeeze charger 52 which are rotated in the same direction as the photosensitive drum 1, and a slight amount of the liquid developer is left on the surface of the photosensitive drum 1. A toner image containing a liquid is formed on the toner image. Then, the toner image is rotated as it is to a transfer position facing the transfer roller 6,
Here, the paper comes in contact with the paper conveyed from the paper feeding device 9 and is transferred to the paper by electrostatic transfer. The transfer roller 6 includes
A transfer voltage of +1000 V is applied.

After the transfer paper is separated from the photosensitive drum 1, the paper is conveyed to a fixing device 10 having a pair of heat fixing rollers heated to 150 ° C., where the fixing is performed by heat and pressure to form one image. When the formation is completed, the sheet is discharged to the sheet discharge tray 11 by the sheet discharge roller 111. Thereafter, the liquid developer remaining on the surface of the photosensitive drum 1 is removed by the cleaner 7, and the remaining charge on the photosensitive drum 1 is erased by the eraser lamp 8 to prepare for the next image formation.

The evaluation of the image density and the stability of the edge effect using the apparatus of FIG. 1 was performed as follows. On the photosensitive drum 1 of the apparatus of FIG. 1, the length in the longitudinal direction (the length in the direction of the rotation center line) is 20 cm, and the length in the circumferential direction is 5 cm.
Was formed, and the electrostatic latent image was visualized to obtain a 20 cm × 5 cm band image. This process was repeated 100,000 times so that the toner concentration in the developer storage tank 43 and the developer holding tank 42 was kept almost constant. 5 cm from both ends of each band-shaped image obtained
The reflection densities at three points at the inner position and the central position are measured using a densitometer PDM5 (manufactured by SAKURA), and the average value is obtained. The average reflection density is compared before and after 100,000 times of image formation. The stability of the image density and the stability of the liquid developer were evaluated. In addition, average reflection density of 2 or more is good, and 1.8 or more and less than 2 is somewhat good.
Less than 8 was determined to be defective.

The ratio of the higher one of the reflection densities at positions 5 cm inside from both ends of each of the obtained strip images and the reflection density at the center position (edge ratio = reflection density at the end portion / reflection density at the center portion). (Reflection density) was determined, and the edge ratio was compared before and after image formation 100,000 times to evaluate the stability of the edge effect and, consequently, the stability of the liquid developer. In addition, the edge ratio less than 1.2 is good, and 1.2 or more and less than 1.5 is slightly good.
1.5 or more was determined to be defective.

The edge effect is as follows. That is, in the developing section between the electrostatic latent image carrier and the developing roller, the toner particles electrophoresed by the action of the formed electric field and reached the electrostatic latent image on the electrostatic latent image carrier, The electrostatic latent image is visualized. The electric field acting at this time is shown in FIG.
As shown in (1), the intensity is different between the central portion of the electrostatic latent image and the end portion of the electrostatic latent image, and a stronger electric field acts on the end portion of the electrostatic latent image. Therefore, development proceeds at the end of the electrostatic latent image faster than at the center, and the development is completed faster at the end of the electrostatic latent image than at the center. For this reason, if the electrostatic latent image on the electrostatic latent image carrier passes through the developing unit before the development of the central portion of the electrostatic latent image is not sufficiently performed, the toner image finally obtained becomes electrostatic latent image. At a position corresponding to the image end, the image density is high, and at a position corresponding to the center of the electrostatic latent image, the image density is low, that is, an image having an edge effect is obtained. That is, the presence or absence of the edge effect indicates the developing speed of the central portion of the electrostatic latent image, that is, the electrophoretic speed of the toner particles.

The results are shown in Table 1 below.

[0056]

[Table 1]

According to this, Examples 1 to 6 of the present invention in which a polyester resin having an acid value of from 40 mgKOH / g to 100 mgKOH / g was used as a binder resin and an oil-soluble ionic surfactant was used as a charge control agent. In the liquid developer, the image density and the edge effect are both 10
It can be seen that the image is good and stable before and after image formation on every sheet.

On the other hand, the acid value of the binder resin is 34.
Comparative Example 1 using 9 mg KOH / g polyester resin
With the liquid developer, the edge ratio was good at the beginning of image formation, but became poor after 100,000 sheets of image formation, indicating that it was unstable. The liquid developers of Comparative Examples 2 and 3 using the amphoteric surfactant lecithin as a charge control agent,
And a nonionic N-vinyl-2 as a charge control agent.
In the liquid developers of Comparative Examples 4 and 5 using the pyrrolidone / lauryl methacrylate copolymer A, both the image density and the edge ratio were good or slightly good at the beginning of image formation, but image formation on 100,000 sheets It turns out to be defective later and it is found to be unstable.

[0059]

According to the present invention, there is provided a liquid developer for electrophotography using a polyester resin as a binder resin for a toner, which is capable of obtaining a high system speed and having excellent stability over time. Can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an example of an image forming experiment apparatus.

FIG. 2 is a diagram illustrating an edge effect of development using a liquid developer.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoreceptor drum 2 charging charger 3 laser beam image exposure device 4 liquid developing device 41 developing roller 42 developer holding tank 43 developer storage tank 44 developer supplying device 45 developer collecting device 51 squeeze roller 52 squeeze charger 6 transfer roller Reference Signs List 7 cleaner 8 eraser lamp 9 paper feeder 91 paper storage cassette 92 paper feed roller 93 timing roller 10 fixing device 11 paper output tray 111 paper output roller

Claims (3)

[Claims] 1. An electrophotographic liquid developer in which colored fine particles are dispersed in an electrically insulating medium liquid, wherein the liquid fine particle contains an oil-soluble ionic surfactant as a charge control agent, and the colored fine particles have an acid value. 40mgKOH / g or more and 100mgKOH
A liquid developer for electrophotography, comprising a polyester resin of not more than / g as a binder resin. 2. The liquid developer for electrophotography according to claim 1, wherein the oil-soluble ionic surfactant contains an alkylallyl sulfonate having an alkyl group having 20 or more carbon atoms as a main component. 3. The oil-soluble ionic surfactant is at least one selected from the group consisting of alkylbenzene sulfonates having 20 or more alkyl groups, petroleum sulfonates, and basic petroleum sulfonates. The liquid developer for electrophotography according to claim 1, which is a substance of the following.