JP2002278170A - Liquid developer, its producing method and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide liquid developer having the high transfer efficiency of a formed image and high resistance to repetitive use, its producing method and an image forming apparatus. SOLUTION: The liquid developer is obtained by dispersing toner particles having dyestuff particles distributed one-sidedly on the surfaces of resin particles insoluble in electrical insulating carrier liquid in the carrier liquid, and the mutual contact of the resin particles is restrained by the dyestuff particles. The dyestuff particles are distributed one-sidedly on the surfaces of the toner particles so as to cover the surfaces of the resin particles. The liquid developer is produced by kneading the dyestuff particles in resin particle dispersed liquid and making colorant particles press-contact with the surfaces of the resin particles. The latent image holding body of the image forming apparatus is pressed to a transfer body, so that the surface of the latent image holding body has a difference in traveling circumferential speed from the transfer body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid developer for electrostatic charge development for forming an electrophotographic image, a method for producing the same, and a transfer of a developed image from a photoreceptor to a transfer member when the liquid developer is used. The present invention relates to an image forming apparatus in which satisfactorily performed by heat and pressure.

[0002]

2. Description of the Related Art In electrophotography, in order to form a good image on a recording medium such as paper, it is necessary to efficiently transfer a toner image composed of developed dye dots on a photoconductor from a photoconductor to a transfer target such as a transfer roller. It needs to be well transcribed. This transfer method includes a method using an electric field and a method using heat or pressure.

[0003] In the method using an electric field, a transfer object is brought close to or in contact with the surface of a photoreceptor, and corona discharge is performed from the back surface of the transfer object so that the transfer object side has the opposite polarity to the charge of the toner. This method is widely used as a method of facilitating transfer by suctioning onto an object to be transferred. However, this method is susceptible to the electrical resistance of the transfer object and is sensitive to changes in temperature and humidity. Alternatively, there is a method in which a direct current bias is applied between the photoreceptor and the transfer-receiving member to transfer the image. However, in many cases, the image is disturbed and the transfer efficiency is reduced due to the injection of charge into the toner. These problems are essential drawbacks of the method using an electric field, and occur both in a dry system and a wet system.

[0004] On the other hand, the transfer method using heat and pressure is excellent in that transfer to a transfer object can be performed with high efficiency while maintaining high image quality without being affected by temperature or humidity. However, in order to realize this method, it is necessary that the surface of the photoreceptor has very high releasability. Therefore, it is necessary to devise a method of coating the surface of the photoreceptor with a thin film having high releasability.

In general, it is assumed that the liquid developer toner is self-fixed (fixed at room temperature without using a fixing device). For this purpose, a resin having a Tg temperature of room temperature or lower is used. However, since such resin particles have a strong adhesive force, when the transfer method using heat and pressure described above is adopted, if the peelability of the surface of the photosensitive member is slightly reduced by continuous use, the resin is adhered to the photosensitive member. In addition, transfer failure is likely to occur. Further, due to its softness, the photosensitive member easily deforms into a film shape when subjected to some force on the photosensitive member. The toner in the form of a film is liable to inhibit transfer from the photoreceptor, and particularly when the releasability of the photoreceptor surface locally decreases, the transfer inhibition spreads over a wide range.

On the other hand, as disclosed in JP-B-63-33141, there is an example in which a toner is produced using a resin having a Tg temperature of room temperature or higher. According to the publication, a colorant is mixed in a state in which the resin is dissolved in a solvent in which the resin is soluble (for example, a chlorine-based solvent), and then the mixture is dispersed as toner particles in a carrier solvent in which the resin is insoluble. Agents are being prepared. Such toner particles of the developer hardly cause adhesion to the photoreceptor and deformation into a film shape in a normal state as compared with toner particles made of a resin having a Tg temperature of room temperature or lower. However, when a transfer method using heat or pressure is adopted, the resin particles are plastically deformed and strongly adhered to each other due to being strongly pressed against the photoreceptor during transfer to the transfer-receiving member, thereby easily forming a film. Adhesion with the photoreceptor also increases. Therefore, the transfer efficiency is reduced.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and has a high resolution and a stable chargeability. In particular, a method of transferring a toner image to a transfer target by pressure or heat. The present invention provides a liquid developer for electrostatic charge development capable of maintaining the initial characteristics even when repeatedly used in the above, and a method for producing the same.

Further, the present invention provides an image forming apparatus suitable for forming an image using the above liquid developer.

[0009]

In order to solve the above-mentioned problems, a liquid developer for electrostatic charge development according to the present invention comprises toner particles having a resin and pigment particles distributed unevenly on the surface of the resin; The gist of the present invention is to provide an insulating carrier liquid.

The above-mentioned uneven distribution of the dye particles can be detected as the presence of a surface layer having a thickness of 10 nm or more having a viscoelasticity higher than the viscoelasticity of the central portion of the toner in the toner particle image obtained by measuring the microviscoelasticity distribution. it can.

According to another aspect of the present invention, there is provided a liquid developer for electrostatic charge development, comprising: an electrically insulating carrier liquid; and toner particles dispersed in the carrier liquid. An agent, wherein the toner particles have resin particles insoluble in the carrier liquid, and pigment particles adhering to the surface of the resin particles so as to cover the surface of the resin particles, and the resin particles formed by the pigment particles The point is that the surface coverage is 3.5% or more.

The glass transition temperature of the resin particles may be 30 ° C. or higher.

Further, in the method for producing a liquid developer for electrostatic charge development according to the present invention, the resin liquid and the pigment which are insoluble in the carrier liquid are independently added to the electrically insulating carrier liquid. At a temperature equal to or lower than the glass transition temperature of the resin.

Further, the image forming apparatus of the present invention comprises: a latent image carrier on which a developed image is developed on the surface from an electrostatic latent image by the liquid developer; and a recording medium for transferring the developed image from the latent image carrier to the recording medium. And a transfer member for transferring the latent image to the transfer member.
The invention is characterized in that the latent image holding member is pressed at a pressure of cm ^{2 to} 50 kg / cm ^{2 and} the surface speed ratio of the latent image holding member to the transfer member is 0.8 to 0.99 or 1.01 to 1.20.

According to the above configuration, the pigment particles function as spacers on the surface of the photoreceptor, so that excessive adhesion of the toner particles can be suppressed even if the resin is plastically deformed by applying pressure.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid developer is obtained by dispersing and carrying toner particles containing a colorant and a binder resin as main components in a liquid dispersion medium. A conventional toner is a colorant, that is, a pigment particle and a binder resin. And a uniform mixture of the above. Therefore, the resin is exposed on the surface of the toner particles. Resins are easily adhered to each other by contact, so that even when the Tg temperature is equal to or higher than room temperature, toner particles whose surfaces are made of resin undergo plastic deformation and adhesion by a slight load or heating to form a film. . Tg dissolved in solvent
The same applies to JP-B-63-33141, in which a toner is prepared from a mixture of a resin and a dye having a temperature of room temperature or higher.
The resin is exposed to the surface of the toner particles and has a property of easily forming a film.

The present invention improves the structure of the toner particles of the liquid developer, and biases the distribution of the pigment particles toward the surface of the toner particles so that the resin particles are not adhered to each other even if the toner particles are pressed against each other. And has a structure in which the surface of the resin particles is substantially covered with dye particles.
Since it is essential to prevent the adhesion between the toner particles, it is not always necessary that the surface of the resin particles be completely covered with the pigment particles. Even if the resin is exposed between the pigment particles, the pigment particles act as a spacer and the contact between the resin particles is prevented. Therefore, it is sufficient that the pigment particles on the surface of the resin particles can suppress the contact between the resin particles between the toner particles.

In the production of the liquid developer as described above, for example, in a state where the resin particles for toner and the pigment particles are dispersed in a liquid dispersion medium, the pigment particles are kneaded while maintaining the temperature at or below the Tg temperature of the resin. This is achieved by pressure bonding to the surface of the resin particles. This includes a mode in which the pigment particles are added to the resin dispersion and kneading, and a mode in which the resin particles or the resin dispersion are gradually added to the dispersion of the pigment particles and kneaded.
At this stage, if the temperature exceeds the Tg temperature of the resin, the pigment particles are likely to be buried in the resin, so that the temperature is preferably equal to or lower than the Tg temperature. However, raising the temperature to around the Tg temperature only at the initial stage of kneading so that only the resin surface layer is softened is effective in increasing the coating efficiency of the pigment particles. The dispersion medium for dispersing the resin particles is not particularly limited as long as the resin and the pigment particles are not dissolved, but the pigment particles are dispersed in an electrically insulating liquid medium that is a toner carrier liquid of a liquid developer. It is preferable to knead with a liquid developer because it is not necessary to replace the liquid medium during the step of preparing the liquid developer. The volume of the dispersion medium is about 2 to 25 L / kg with respect to the weight of the solid content (dye particles and resin particles) in consideration of the suppression of heat generation during the operation and the efficiency of kneading (in general, the solid content content relative to the total weight). (5 to 49% by weight). The particle size of the resin particles affects the size of the toner particles and the resolution of the image. The primary particle size of the pigment to be used is smaller than or equal to the particle size of the resin particles, preferably about 1/250 to 1/10 (0.4% to 10%) of the resin particle size. Is preferred. Using a grinder or the like used in a general kneading operation, 30
By performing kneading for at least about one minute, preferably for at least 120 minutes, the pigment particles are pressed or partially embedded in the surface layer of the resin, and the resin surface is roughly covered with the pigment particles. When a liquid developer is prepared using generally available resins and dyes according to the method described above, the toner particles have a structure as shown in, for example, SEM photographs in FIGS. Is schematically shown in FIG. 5A. The pigment particles C are pressed against the surface of the resin particles R,
Depending on the pressure during kneading, it is partially embedded in the resin particles.

The coverage of the resin particles with the pigment particles is as follows:
It can be approximately converted as follows. That is, assuming that the resin particles and the pigment particles are spherical as shown in FIG. 5B, the projected area of the pigment particles B onto the resin particles A is approximately the radius a of the resin particles A and the radius b of the pigment particles B. a, it is possible to the projected area = π (ab / (a + b)) 2, coverage of the resin particles a by a single pigment particles B, π (ab / (a + b)) 2 / 4πa 2 = b ^2/4 (a +
b) It becomes ² . Therefore, the specific gravity n _a of the resin particles A, the specific gravity n _b of pigment particles B, and, from the weight ratio K for the resin particles A of deposited color particles B, in terms of coverage of the resin particles A surface θ by the color particles B Then, it is possible to ^{_{θ = Kn a a 3 / [}} 4n b b (a + b) 2]. Based on this conversion value, when the coverage ratio θ of the liquid developer is about 3.5% or more, the effect of preventing contact between resins is remarkably exhibited, and the object of the present invention is substantially achieved. . The actual coverage of the particles may be different from the above depending on the method of producing the particles and the particle crushing during kneading, etc., but can be used as a guide, and the production conditions of the developer may be adjusted as appropriate while confirming with SEM photographs and the like. I just need.

As a method for visualizing information on the inside and the surface of the toner particles having the pigment particles adhered to the resin particle surface,
There is a method of embedding the toner particles in an epoxy resin or the like to prepare a section sample using a microtome, and then observing the section sample with a SEM or a TEM. Alternatively, if the particles to be observed are very small (1 μm or less), the AFM (Atomic Force Mi
There is also a method of performing microviscoelastic distribution measurement using a croscope. This is because the cantilever is 1 to 10k by the piezoelectric element.
Hz, and the deformation vibration of the sample due to this is detected,
A method of displaying the difference in viscoelasticity with light and dark contrast,
A slight difference in viscoelasticity can be distinguished and visualized. In the measurement of toner particles, since the pigment particles having higher hardness than the resin have high viscoelasticity, if the distribution density of the pigment particles is different between the inside and the surface of the toner particles, the difference can be observed by the difference in viscoelasticity. it can. Therefore, it is effective as a method for observing the particle structure. In the image obtained by measuring the microviscoelastic distribution of the toner particles prepared according to the above-described manufacturing method,
Since the distribution of the pigment particles is biased toward the surface of the toner particles, it is observed that a high viscoelastic layer having higher viscoelasticity than the inside of the particles exists on the surface of the toner particles (see FIG. 8 described later).
Suitable toner particles generally have a thickness of the highly elastic layer in the image of about 10 nm or more, preferably 10 nm to 1 μm,
By such toner particles, a fine electrophotographic image can be stably formed.

To the dispersion of toner particles having pigment particles adhered to the surface of resin particles, an auxiliary agent such as a charge control agent or wax is added as necessary, and the amount of the liquid medium is adjusted so as to have an appropriate dispersion concentration. By doing so, a liquid developer is obtained. Although the liquid developer of the present invention can be obtained using a resin having a Tg temperature of room temperature or lower, the resin having a Tg temperature of room temperature or higher is selected because the toner particles are easily deformed and the control of the manufacturing process is strict. Is preferred.

The components of the liquid developer outlined above will be specifically described below.

As the resin used in the present invention, any known resin can be used as long as it is insoluble in the electrically insulating carrier liquid as a dispersion medium. If necessary, plural kinds of resins may be mixed and used. You may. Further, if necessary, other resins may be used together in an addition amount within a range not to impair the technical effects of the present invention. A resin having a Tg temperature of room temperature or higher is desirable, and among commercially available non-aqueous solvent-dispersed resins, any resin which is insoluble in a solvent to be used and has a Tg temperature of room temperature or higher can be suitably used. Specifically, an acrylic resin, a polyester resin, an olefin resin, and the like can be given.
As long as the conditions of the present invention are satisfied, a resin manufactured using a novel structure or a synthetic method may be used. For example, JP-A-55-71713, JP-A-55-90521, and the like disclose a graft polymer of a polymer soluble in an aliphatic hydrocarbon and a polymer insoluble in the solvent as a non-aqueous dispersion resin. Although a liquid developer to be used has been proposed, from such special resins, those which are substantially insoluble in the electrically insulating carrier liquid when the Tg temperature of the whole resin is equal to or higher than room temperature may be used.

As the electrically insulating carrier liquid used in the present invention, for example, an organic solvent having a high electric resistance of 10 ⁹ Ω · cm or more and a low dielectric constant of 3 or less can be used. For example, hexane, pentane , Octane, nonane,
In addition to decane, undecane, and dodecane, the boiling point is in the range of 68 to 250 ° C., such as organic solvents sold under the trade names such as Isopar H, G, K, L, and M from Exxon Chemical Co., Ltd. Various kinds of aliphatic hydrocarbon solvents can be used. These may be used alone or in combination of two or more.

Insoluble pigments and / or dyes are used as the colorant in the present invention. These are not particularly limited, and various conventionally known dyes or pigments can be used. Specific examples thereof include, for example, carbon black: C.I. I. Pigment Yellow 1, 3, and 7
Acetoacetic acid arylamide-based monoazo yellow pigments such as 4, 4, 97, and 98; and imidazolone-based monoazo yellow pigments, such as 181; I. Pigment Yellow 12, 13
Azoacetoacetyl arylamide-based disazo yellow pigments such as those described in Examples 14 and 17: C.I. I. Solvent Yellow 19, 7
7, ibid. 79, C.I. I. Yellow dyes such as Disperse Yellow 164: C.I. I. Pigment Red 48, 4
Red or red pigments such as 9: 1, 53: 1, 57, 57: 1, 81, 122, 5, and 146, etc .:
C. I. Red dyes such as Solvent Red 49, 52, 58 and 8: C.I. I. Pigment Blue 15:
Blue dyes and pigments of copper phthalocyanine and its derivatives such as 3,15: 4, etc .: C.I. I. Pigment Green 7, 36
Green pigments such as (phthalocyanine green) can be used. These dyes / pigments may be used alone or in combination of two or more.

The toner of the liquid developer of the present invention can contain a charge control agent as required, and any of those usually used in a liquid developer for electrostatic charge development can be used. . Examples include cobalt naphthenate, copper naphthenate, copper oleate, cobalt oleate, zirconium octylate, cobalt octylate, sodium dodecylbenzenesulfonate, calcium dodecylbenzenesulfonate, soybean lecithin, aluminum octoate, and the like.

Auxiliary agents such as waxes may be blended, and any of those usually used in liquid developers for electrostatic charge development can be used. For example, paraffin wax, polyethylene wax, polypropylene wax, ethylene copolymer, propylene copolymer and the like can be mentioned.

Auxiliary agents such as the above-described charge control agents and waxes can be used by blending them in the binder resin before the dye is attached.

The liquid developer prepared in accordance with the above has toner particles as shown in FIGS. 1 to 4 and 7 to 8 shown in Examples described later, and is transferred from the photoreceptor to the transfer target by using heat and pressure. It is preferably used in a general electrophotographic image forming apparatus for transferring the image to a recording medium, but is more effective when applied to the image forming apparatus of FIG. 6 described below.

The image forming apparatus shown in FIG. 5 includes a charging charger 1, a latent image carrier 10 comprising an amorphous silicon photoreceptor 13 having a peelable surface layer 12, a laser optical device 2, a developing unit 30, a squeeze roller 4, a solvent removal. It has a unit 5, an intermediate transfer medium 50, and a backup roller 8. The developing unit 30 includes a developing roller 32 disposed at a predetermined gap from the latent image holder 10, and the laser optical device 2 applies the latent image holder (photoconductor) 10 uniformly charged by the charging charger 1 to the developing unit 32. The latent image formed by the exposure becomes a visible image in which the toner is aggregated by the liquid developer supplied by the developing roller 32.
Excess developer and carrier liquid are scraped off by the squeeze roller 4, and portions other than the toner image portion are almost completely dried by the solvent removing unit 5. The toner image on the latent image carrier 10 is transferred to the intermediate transfer medium 5 by heat and pressure.
After being transferred onto the recording medium 9, it is pressed and transferred onto the recording medium 9 by the backup roller 8. The surface of the latent image holding member 10 is cleaned by the cleaning roller 6.

In the above image forming apparatus, the latent image holding member 1
0 about 15～20Kg / pressure cm ² is applied to the intermediate transfer medium 50, the pressure also about 7.5～10Kg / cm ² between the intermediate transfer medium 50 and the backup roller 8 is subjected I have. Further, the rotation speed is set so that the surface speed of the latent image holding member 10 is about 2-3% faster than the surface speed of the intermediate transfer medium 50. No special speed difference is set between the intermediate transfer medium 50 and the backup roller 8, and the intermediate transfer medium 50 is driven relative to the intermediate transfer medium 50. Shear stress acts on the toner image due to such peripheral speed difference and pressure, and transfer efficiency is improved. When an apparatus having such a configuration is used, it is necessary that the toner particles have resistance to pressure, and it is necessary to prevent the toner particles from being formed into a film more than necessary when pressure is applied. According to the present invention, by forming the toner particles of the liquid developer from a hard resin and pigment particles covering the same, the toner image can maintain a small adhesive force (adhesive force) with the photoreceptor, and the toner image can be higher. Image formation can be performed with transfer efficiency.

As one embodiment of the present invention, image formation and transfer are performed, for example, as follows.

With the charging charger 1, the potential on the latent image holding member 10 is +
It is uniformly charged to a surface potential of 750 V, and is exposed by the laser optical device 2 corresponding to 600 dpi, and the potential of the exposed portion becomes +100 V. The developing unit 30 is such that the developing roller 32 made of stainless steel is
The latent image holding member rotates at a peripheral speed of 220 mm / sec, and the development is performed such that the peripheral surface of the developing roller 32 and the peripheral surface of the latent image holding member 10 run in the same direction. The roller 32 rotates at a triple speed in a direction opposite to that of the latent image holding member, whereby the developer 31 is supplied. The developing solution has a positive polarity, and the developing roller to which a potential of +600 V is applied serves as a counter electrode, and the toner selectively migrates only to the exposed portion to form an image. Further, a squeeze roller 4 made of stainless steel and disposed with a gap of 50 μm from the surface of the latent image holding member 10 rotates in the same rotation direction as the latent image holding member 10 and runs at a peripheral speed of 220 mm / sec. As the peripheral surface of the squeeze roller 4 travels at a speed three times as fast as the peripheral surface of the latent image holding member 10, excess solvent is removed. Further, the portions other than the toner image portion are almost completely dried by the solvent removing unit 5, and the toner image portion is
It contains about 20% by weight of solvent. The solvent removing unit 5 is usually provided with a porous urethane roller for absorbing the solvent or an air blower for spray drying, and both may be used. The intermediate transfer medium 50 is heated to 80 ° C. by a heating source 53 provided on a base shaft 51, and the toner image on the latent image holding member 10 has a thickness of 200 μm covering the surface of the intermediate transfer medium 50 by heat and pressure.
m is transferred onto the silicone rubber layer 52. The intermediate transfer medium 50 runs at a peripheral speed of 213.4 mm / sec. Furthermore,
The toner image is transferred to the recording medium 9 by the stainless steel backup roller 8 heated to 80 ° C. by the heating source. The backup roller 8 runs at the same speed as the intermediate transfer medium 50.

In the above configuration, the image is formed using a single color toner. However, it is needless to say that a full color image may be formed. In this case, for each color, the image forming operation by the charging charger 1, the developing unit 30, and the squeeze roller 4 may be performed to repeat the image forming operation by the number of colors. Alternatively, the developing units may be arranged on the same latent image holding member and a full-color image may be formed by one rotation.

Further, the intermediate transfer medium 50 may be constituted by a belt-shaped sheet. In this case, the latent image carrier 1
Two rollers that support the inner surface of the sheet are provided at the positions where the rollers 0 and the backup roller 8 are in contact.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

[0037]

EXAMPLES Example 1 16 parts by weight of a polyester resin having a specific gravity of 1.1 (trade name: NE-384, manufactured by Kao Corporation) and a solvent (trade name: Isopar L, manufactured by Exxon Chemical Co., Ltd.) 18
0 parts by weight was put into a sand grinder and mixed and stirred at a speed of 1500 revolutions per minute for 2 hours while cooling the vessel with water to obtain a resin dispersion having a solid content of 8.16% by weight. Care was taken to keep the temperature below the Tg temperature of the resin during mixing so that the resin did not plasticize. The average particle size of the resin dispersed at this time was about 5 μm. 4 parts by weight of phthalocyanine blue (trade name: KET BLUE111, manufactured by DIC) having an average primary particle size of 50 nm and a specific gravity of 2.0 were further added to this solution, and mixed under stirring under the same conditions for 2 hours. Thus, a colored resin dispersion having a solid content of 10% by weight was obtained.

To 100 parts by weight of this colored resin dispersion, 2 parts by weight of zirconium naphthenate (non-volatile content: 49 wt%, manufactured by Dainippon Ink and Chemicals, Inc.) was added, and the solid content was about 10 wt%.
% Liquid developer concentrate. Further, this concentrated liquid was diluted 10-fold with a solvent (Isoper L, manufactured by Exxon Chemical Co., Ltd.) to obtain a final liquid developer (cyan). When this developer was measured with a zeta potential measuring device (ESA-9800, manufactured by Meitec Applied Science), +85 m was measured.
V zeta potential and a particle size measuring device (LA-92
0, manufactured by Horiba, Ltd.) was about 5 μm.

FIGS. 1 and 2 show the SEM images of the toner particles after drying the liquid developer thus obtained at room temperature. FIG. 1 is a photograph of one toner particle at a magnification of 15000 times. Particle size is large and 10μ
m, and the shape is irregular. FIG. 2 shows a further enlarged view of this surface at a magnification of 60,000. The slightly bright particles (200 to 2) on the surface of FIG.
0 nm) is a pigment. Thus, it can be seen that the pigment particles exist on the surface of the resin particles and cover the resin. As described above, if the mixing and stirring temperature during the preparation of toner particles is maintained at a temperature at which the resin does not plasticize (Tg temperature or lower),
The pigment particles are pressed onto the surface without being embedded in the resin. The calculated coverage of the toner particles is 337% when the resin particle diameter is 5 μm and the pigment diameter is 50 nm.
Actually, it seems that the pigment is partially aggregated and the coverage is considerably small.

Next, a test was performed using this developer by an image forming apparatus as shown in FIG.

First, the surface of the latent image holding member 11 was uniformly charged to a surface potential of +750 V by the charging charger 1 and exposed by the laser optical device 2 (corresponding to 600 dpi). The potential of the exposed portion was + 100V. The developing roller 32 was set so as to keep a gap of 100 μm from the surface of the latent image holding member, and the peripheral speed of the latent image holding member was set to 220 mm / sec. The developing roller 32 was rotated so that the peripheral surface traveled at the triple speed in the same direction as the peripheral surface of the latent image holding member. The developing solution had a positive polarity, and the developing roller to which a potential of +600 V was applied served as a counter electrode, and the toner selectively migrated only to the exposed portion, thereby forming a toner image. Further, 5
Excess solvent was removed by rotating the peripheral surface of the SUS squeeze roller 4 arranged with a gap of 0 μm so as to run at 3 times speed in the opposite direction to the peripheral surface of the latent image holding member. . Thereafter, the solvent removing unit 5 having a porous urethane roller dried the peripheral surface of the latent image holding member except the image area almost completely. Image part is 20wt
% Of the intermediate transfer medium 5 containing about
On the surface of the intermediate transfer medium 50, a silicone rubber layer 52 having a thickness of 200 μm was transferred by heat and pressure.
Further, the final image was transferred onto a recording paper passing between the backup roller 8 heated to 80 ° C. and the intermediate transfer medium 50.

When an image having a printing rate of 10% was continuously output on 10000 sheets of A4 size recording paper in accordance with the above-described operation, no problem such as transfer omission on the latent image holding member occurred, and the image was changed from the beginning to the beginning. A very high image quality could be obtained.
Also, no solvent transfer to the recording paper was observed.

Example 2 16 parts by weight of a styrene acrylic resin having a specific gravity of 1.1 (trade name: CPR-100, manufactured by Mitsui Toatsu Chemicals) and a solvent (trade name: Isopar L, manufactured by Exxon Chemical) 180 The parts by weight were mixed and stirred in the same manner as in Example 1 to obtain a resin dispersion having a solid content of 8.16% by weight.
At this time, the average particle size of the dispersed resin was about 1.5 μm. To this solution, 4 parts by weight of phthalocyanine blue (trade name: KRO, manufactured by Sanyo Dyeing Co., Ltd.) having an average primary particle size of 50 nm and a specific gravity of 2.0 were added, and mixed under stirring under the same conditions for 2 hours. Thus, a colored dispersion having a solid content of 10% by weight was obtained.

To 100 parts by weight of the colored resin dispersion, 2 parts by weight of zirconium naphthenate (non-volatile content: 49 wt%, manufactured by Dainippon Ink and Chemicals, Inc.) was added to obtain a liquid developer concentrate having a solid content of about 10 wt%. Was. The calculated coverage of the toner particles is 97% when the resin particle diameter is 1.5 μm and the pigment diameter is 50 nm.

Further, this concentrated solution was diluted 10-fold with a solvent (trade name: Isopar L, manufactured by Exxon Chemical Co., Ltd.) to obtain a final liquid developer (cyan). When this liquid developer was measured with a zeta potential measuring device (ESA-9800, manufactured by Meitec Applied Science), it had a zeta potential of +68 mV, and had a volume average measured by a particle size measuring device (LA-920, manufactured by HORIBA, Ltd.). Particle size is about 1.5μ
m.

FIGS. 3 and 4 show SEM images of the thus obtained liquid developer after drying at room temperature. FIG. 3 is a photograph of one toner particle at a magnification of 15000 times. Many of the particles have a submicron size, but some particles are also agglomerated. The surface of one of these particles was further enlarged to 600
FIG. 4 is an image observed at a magnification of 00 times. The pigment (200 to 20 nm) that looks bright on the particle surface in FIG. 4 is a pigment. Thus, it can be seen that the pigment exists on the surface of the resin particles and covers the resin.

In the same manner as in Embodiment 1 using the above-described liquid developer, an A4-size recording paper 1000
When an image with a printing rate of 10% was continuously output on zero sheet, high image quality could be obtained as in the initial state without any problem such as transfer omission on the latent image holding member. Also, no solvent transfer to paper was observed.

Example 3 The same styrene as in Example 2
To 10 parts by weight of the acrylic resin, 0.2 parts by weight of zirconium naphthenate as in Examples 1 and 2 was added, and 90 parts by weight of a solvent (Isoper L) was further added, and the mixture was charged into a sand grinder. 20 minutes per minute
Mix and stir for 5 hours at a speed of 00 rotations,
A resin dispersion of wt% was obtained. At this time, the average particle size of the dispersion resin was 0.4 μm. 0.4 parts by weight of the same phthalocyanine pigment as in Example 2 was further added to this solution,
Subsequently, the mixture was mixed and stirred for 2 hours to obtain a colored resin dispersion having a solid content of about 10% by weight.

To 100 parts by weight of this colored resin dispersion, 2 parts by weight of zirconium naphthenate was added, and a solid content of about 1 part was added.
A liquid developer concentrate of 0% by weight was obtained.

The calculated coverage of the toner particles is 3.5 when the resin particles are 0.4 μm and the pigment particle diameter is 50 nm.
%.

Further, this concentrated liquid was diluted 10 times with a solvent (trade name: Isopar L, manufactured by Exxon Chemical Co., Ltd.) to obtain a final liquid developer (cyan). When this liquid developer was measured by a zeta potential measuring device (ESA-9800, manufactured by Meitec Applied Science), it had a zeta potential of +50 mV, and had a volume average measured by a particle size measuring device (LA-920, manufactured by HORIBA, Ltd.). Particle size is about 0.4μ
m.

Example 4 Styrene-acrylic resin fine particles having a specific gravity of 1.1 and an average particle diameter of 0.4 μm (trade name:
2 parts by weight of the same phthalocyanine pigment as in Example 2 were added to 8 parts by weight of MP-5000 (manufactured by Soken Chemical Co., Ltd.), and a solvent (trade name: Isopar L, manufactured by Exxon Chemical Co., Ltd.)
90 parts by weight were added to a sand grinder and mixed and stirred at a speed of 2000 revolutions per minute for 2 hours while cooling the vessel with water to obtain a colored resin dispersion having a solid content of 10% by weight.

2 parts by weight of zirconium naphthenate was added to 100 parts by weight of this colored resin dispersion, and a solid content of about 1 part was added.
A liquid developer concentrate of 0% by weight was obtained. 0.4 resin particle size
Assuming that the particle size is 50 μm and the pigment particle size is 50 nm, the calculated coverage of the toner particles is 3.5%.

Further, this concentrated solution was diluted 10 times with a solvent (trade name: Isopar L, manufactured by Exxon Chemical Co., Ltd.) to obtain a final liquid developer (cyan). When this liquid developer was measured with a zeta potential measuring device (ESA-9800, manufactured by Meitec Applied Science), it had a zeta potential of +24 mV, and had a volume average measured by a particle size measuring device (LA-920, manufactured by HORIBA, Ltd.). Particle size is about 0.6μ
m.

FIG. 7 shows an SEM image of the thus obtained liquid developer after drying at room temperature. FIG. 7 is a photograph of one toner particle at a magnification of 100,000 times. It can be seen that the toner particle diameter is about 0.5 to 0.6 μm and has an irregular shape. Further, a section sample was prepared by embedding the toner particles in an epoxy resin, and the image of FIG. 8 was obtained by measuring the microviscoelastic distribution of the cross section of the toner particles.

In FIG. 8, a layered portion which looks bright in an almost elliptical ring shape is observed, and its thickness is about 20 nm. This layered part is a part having higher viscoelasticity than other parts,
This shows a portion where many high-hardness pigment particles are present. As described above, due to the presence of the high viscoelastic layer on the particle surface in the toner particle image obtained by the microviscoelastic distribution measurement, the high-hardness dye whose distribution is biased or embedded in the low-hardness resin particle surface and is biased toward the toner particle surface Particles can be identified.

[0057]

According to the present invention, the resolution is high, the chargeability is stable, the transfer efficiency of the toner image when transferring by pressure or heat is maintained well even in repeated use, and the initial characteristics are improved. A liquid developer for electrostatic charge development that can be maintained is provided.

[Brief description of the drawings]

FIG. 1 is an SEM photograph (magnification: 15000) showing an example of toner particles of a liquid developer according to the present invention.

FIG. 2 is an SEM photograph (magnification: 60000) of toner particles of the liquid developer of FIG.

FIG. 3 is an SEM photograph (15,000 times) showing another example of the toner particles of the liquid developer according to the present invention.

FIG. 4 is a SEM photograph (magnification: 60,000) of toner particles of the liquid developer of FIG. 3;

FIG. 5 is a schematic diagram for explaining the structure of the liquid developer according to the present invention.

FIG. 6 is a schematic configuration diagram of an image forming apparatus that forms an image using a liquid developer according to the present invention.

FIG. 7 is an SEM photograph (magnification: 100,000) showing another example of the toner particles of the liquid developer according to the present invention.

FIG. 8 is an image obtained by measuring microviscoelastic distribution of toner particles of the liquid developer of FIG. 7;

[Explanation of symbols]

R and A resin particles, C and B dye particles, 1 charger, 2 laser optical device, 4 squeeze roller, 5 solvent removal unit, 6 cleaning roller, 8 backup roller, 9 transfer medium, 1
Reference Signs List 0 latent image holder, 12 peelable surface layer, 13 amorphous silicon photoreceptor, 30 developer, 31 developer, 32 developer roller, 50 intermediate transfer medium, 51
Main shaft, 52 Silicone rubber layer, 53 Heat source

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Aoki Ooka 1 Koga Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa F-term in Toshiba R & D Center (reference) 2H069 AA03 CA01 DA00 DA02 2H074 AA03 BB02 BB43 BB60

Claims (6)

[Claims] 1. A liquid developer, comprising: toner particles having a resin and pigment particles distributed unevenly on the surface of the resin; and an electrically insulating carrier liquid. 2. The uneven distribution of the pigment particles is detected as the presence of a surface layer having a thickness of 10 nm or more having a viscoelasticity higher than the viscoelasticity of the central portion of the toner in the toner particle image obtained by the micro viscoelasticity distribution measurement. The liquid developer according to claim 1, wherein 3. An electrostatic charge developing liquid developer comprising an electrically insulating carrier liquid and toner particles dispersed in the carrier liquid, wherein the toner particles comprise resin particles insoluble in the carrier liquid; And a pigment particle attached to the surface of the resin particle so as to cover the surface of the resin particle, wherein a surface coverage of the resin particle by the pigment particle is 3.5% or more. . 4. The resin particles have a glass transition temperature of 30 ° C.
The liquid developer according to claim 1, wherein: 5. After independently adding a resin particle and a pigment which are insoluble in the carrier liquid to the electrically insulating carrier liquid,
A method for producing a liquid developer, wherein the carrier liquid is stirred at a temperature equal to or lower than the glass transition temperature of the resin. 6. A latent image carrier on which a developed image is developed from an electrostatic latent image on the surface by the liquid developer according to claim 1, and the developed image is recorded from the latent image carrier. An image forming apparatus having a transfer member for transferring to a medium, wherein the latent image holding member is 0.5 kg / cm with respect to the transfer member.
Is pressed at a pressure of ^{2 ~50kg} / cm ^2, the image formation surface velocity ratio for said transfer member of the latent image holding member is characterized in that it is a from 0.8 to 0.99 or 1.01 to 1.20 apparatus.