JPH05188655A - Electrostatic latent image developing composition - Google Patents

Abstract

PURPOSE:To improve the dispersibility of toner particles, image density and transfer efficiency and to obtain a transfer image free from image flowing or painting out and excellent in resolution by forming a adsorbing layer of a high molecular surfactant on the surface of the toner to generate cohesion force among the toner particles on the surface of a photosensitive body. CONSTITUTION:The high molecular surfactant is adsorbed on the surface of the toner. The thickness of the adsorbing layer is controlled to be the same as or preferably slightly thinner than the thickness of the electrical double layer around the charged toner particles. And in the developing process, the toner particle migrates to the surface of the photosensitive body by the force receiving from electric field and is pressed on the surface of the photosensitive body by the sane force. As a result, the electrical double layer of the toner is physically compressed and finally the distance among the particles is compressed to a distance (the thickness of the surfactant) generating cross-link between the particles by the high molecular surfactant. In the toner particles are cross-linked and coupled and a developing image having excellent compression strength is formed on the surface of the photosensitive body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is characterized in that an image formed by the composition has excellent resolution and fixability, forms an image portion having a sufficient printing density, and has a high transfer efficiency. It relates to a liquid composition for developing an electrostatic latent image.

[0002]

2. Description of the Related Art Electrophotographic developers are classified into dry type and wet type. Wet type developers (hereinafter referred to as wet type toners) have the advantage of originally high resolution because they have a smaller particle size than dry type toners, but they are charged. Due to electrostatic repulsion between the toner particles, the development density of the latent image and the transfer efficiency to the supporting sheet such as paper are difficult to increase, and further, the image deletion and line thickening of the developed image area are likely to occur. is there. Further, the fixing after the developed image is transferred to the supporting sheet has a drawback that the adhesiveness is poor because the image area containing the carrier liquid is dried and fixed.

Japanese Unexamined Patent Application Publication No. Sho 5 (1994) whose inventor is Landa
No. 7-178252, JP-A-57-20049 and JP-A-58-48064 show electrostatic latent image developing compositions in which toner particles having a small specific charge are used to increase the developing density and transfer efficiency. ing. These series of patents do not teach the present invention. Japanese Patent Laid-Open No. 61-180248, which is also the inventor of Lander, shows toner particles and a method for producing the particles, in which a plurality of fibers are formed on the surface of the particles to increase the developing density and the resolution. .. This patent does not teach the present invention.

Japanese Patent Publication No. 2-4174 whose inventor is Yanagida et al.
No. 9 describes toner particles using a graft polymer composed of a vinyl polymer soluble in an aliphatic hydrocarbon solvent and a vinyl polymer insoluble in the solvent as a fixing agent.
The purpose of this fixing agent is to improve the dispersion stability by the soluble portion, while improving the transfer efficiency and the cleaning property of the toner particles onto the paper by the insoluble portion. However, nothing is said about the addition of flocculants or similar.

Japanese Patent Publication No. 3-503 in which Randa et al. Are the inventors
456 describes a liquid toner composition containing a silicone agent as a releasing agent for reducing the adhesion of toner particles to the surface of a photoreceptor and a thermoplastic polyamide resin as an increasing agent for causing an apparent increase in cohesiveness of toner particles. I am doing it. The idea that the additive can reduce the adhesive force between the toner particles and the photoreceptor surface and increase the cohesive force between the toner particles is the same as in the present invention. The feature is that it can reduce the adhesive force and increase the cohesive force. In addition, Randa et al. Do not describe the surfactant used in the present invention and do not teach the present invention.

[0006]

Toner particles in a wet toner are stable in a carrier liquid while a colorant and a fixing agent are bonded to each other to maintain a constant particle diameter (preferably 0.1 to 1 μm). Although it is necessary that they are dispersed, there is a problem that such fine particles generally tend to aggregate. However, when the charge amount of the toner particles is increased, electrostatic repulsion can improve the dispersion stability. Further, increasing the charge amount of the toner particles increases the electrophoretic velocity of the toner particles when developing the electrostatic latent image. Therefore, the developing process is accelerated and the density of the obtained developed image is increased. Furthermore, the force for moving the toner particles from the photoconductor toward the paper at the time of transfer to the paper becomes strong, and the transfer efficiency and speed are improved.

On the other hand, an adverse effect is also caused by increasing the charge amount. That is, the electrostatic repulsion between the toner particles inevitably reduces the cohesive force between the particles, so that the developed image on the photoconductor becomes loose, and image deletion and crushing are likely to occur. The present invention provides a wet toner capable of improving the dispersion stability of toner particles, the developing density and the transfer efficiency described above, and obtaining a transferred image with good resolution without image flow or crushing.

[0008]

The present invention relates to toner particles having a sufficient amount of charge and at the same time having a surface adsorbed with a polymeric surfactant. In the developer in which the toner particles are dispersed, the toner particles exhibit good dispersion stability due to electrostatic repulsion, and further, during the development, a rapid electrophoretic effect makes it possible to speed up the development process and improve the development density. To do.

On the other hand, in the developed image on the surface of the photoreceptor, the action of the polymer adsorption layer on the surface of the toner particles causes a cohesive force between the particles so that the particles are connected to each other. In this way an image with clear edges and high resolution is obtained. Further, since the developed image has a good compression strength, it is possible to prevent the image from being crushed and the line being thickened even when the image is transferred from the surface of the photoconductor to the paper.

To control the thickness of the developed image, that is, the development density, the potential of the photoconductor is changed, the development time is changed, the potential of the developing roller is changed, the particle concentration in the toner liquid is changed, and the toner is changed. Electrical properties of particles (conductivity,
Charge characteristics), particle size changes, or chemical (composition etc.) or physical (shape etc.) characteristics of the particle surface may be changed, and the present invention is one of these methods. Of course, it can be used in combination with more than one. The surfactant used in the present invention may be of one type, but it goes without saying that two or more types can be used in combination as required.

[0011]

Function: The polymer surfactant is adsorbed on the surface of the toner particles as shown in FIG. 1 to form an adsorption layer (loop layer). The mechanism of action of the polymeric surfactant is interparticle cross-linking formation (bridging), and the tip of the polymer adsorption layer adsorbed on the surface of the particle is adsorbed on the surface of the adjacent particle to form a polymer bridge between two particles. , Which connects the particles. The connection of the toner particles by the cross-linking of the surfactant is one of the features of the present invention, which is not present in the conventional toner-related technology regardless of whether it is wet or dry.

A polymer surfactant is adsorbed on the surface of the toner particles as shown in FIG. The thickness of the adsorption layer is controlled to be equal to the thickness of the electric double layer around the charged toner particles, and preferably to be a little thinner. Since the particle concentration in the toner liquid is at most about 10 wt% or less, the toner particles can be stably dispersed in this liquid by electrostatic repulsion while maintaining a sufficient interparticle distance (Fig. 2 (a)). ) And FIG. 3).

In the developing process, the toner particles migrate toward the surface of the photoconductor by the force received from the electric field, and are pressed against the surface of the photoconductor by the same force. As a result, the electric double layer of the toner particles is physically compressed, and finally the inter-particle distance is compressed to a distance (= thickness of the active agent adsorption layer) where cross-linking occurs between the particles by the polymer activator (FIG. ). Here, the toner particles are connected to each other by cross-linking, and a developed image having good compression strength is formed on the surface of the photoconductor (FIG. 2).
-(B)). It is one of the features of the present invention that the effect of compression of the electric double layer by the physical external force and the effect of aggregation by the polymer cross-linking are used in combination.

FIG. 4 shows the case where the electric double layer is too thick with respect to the polymer adsorption layer, and the electrostatic repulsion is too strong to form crosslinks. On the contrary, FIG. 5 shows the case where the adsorption layer is significantly thicker, and repulsion occurs due to steric hindrance due to the overlapping of the adsorption layers before the formation of crosslinks. Therefore, there is an optimum range for the thickness of the polymer adsorption layer in relation to the thickness of the electric double layer. Thus, not only the addition amount of the polymer coagulant but also the thickness of the adsorption layer is controlled That is one of the features of the present invention.

[0015]

【Example】

Example 1 Carbon black (Mitsubishi Kasei Diamond Black # 30) 10 g Binder resin (Sanyo Kasei San Elis 725) 100 g (solid content 50 g) Polycarboxylic acid type polymer surfactant (Kao Homogenol L-95) 3 g Dispersion medium (Exxon Isopar) G) 77 g of cobalt naphthenate (DIC) 10 g was dispersed in a ball mill for 10 hours to obtain a concentrated toner having a solid content of 30 wt%, and 100 g thereof was dispersed in 900 g of Isopar G to prepare a liquid developer for electrostatic photography having a solid concentration of 3 wt%. did.

Next, this developer was put in a commercially available wet electrophotographic copying machine and copied on a commercially available coated paper, and an image having an image density of 1.80 and a transfer rate of 92% and excellent in resolution was obtained. A Macbeth densitometer was used to measure the concentration (the same applies hereinafter). The transfer rate was calculated by the following formula (the same applies hereinafter).

[0017]

[Equation 1]

Example 2 Carbon black (Mitsubishi Kasei MA100) 10 g Binder resin (Mitsubishi Rayon FR-101) 100 g (solid content 40 g) Polyoxyethylene alkyl ether (Daiichi Kogyo Seiyaku Neugen ET65) 2 g Dispersion medium (Exxon Isopar G) 73 g of zircon naphthenate (DIC) 15 g was treated in the same manner as in Example 1 to prepare an electrostatographic developer (solid content concentration 3 wt%). Using this developer, copying was performed in the same manner as in Example 1, and an image having an image density of 1.90 and a transfer rate of 90% and excellent resolution was obtained. Example 3 Magenta pigment (Chromofine Red 6820 manufactured by Dainichiseika) 15 g Binder resin (Sanyo Kasei Sunex 725) 100 g (solid content 50 g) Polyoxyethylene sorbitan fatty acid ester (Kao Leodol TWO106) 4 g Dispersion medium (Exxon Isopa-G) 91 g of cobalt naphthenate (DIC) 10 g was treated in the same manner as in Example 1 to prepare an electrostatographic developer (solid content concentration 3 wt%). Using this developer, copying was performed in the same manner as in Example 1, and an image having an image density of 1.55 and an excellent transfer rate of 88% was obtained.

[0019]

According to the present invention, by forming the adsorption layer of the high molecular surfactant on the surface of the toner particles, the condensing force between the toner particles is generated on the surface of the photoreceptor, so that the charge amount of the toner particles is increased. The advantage of doing so is to improve the dispersion stability, to improve the development density, to shorten the development time, to improve the transfer efficiency to paper, etc., and at the same time prevent the harmful effects that occur at the same time, that is, the crushing of the image during transfer, etc. It has an effect that a dense transferred image can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram of a polymer adsorption layer on the surface of toner particles.

FIG. 2 is a diagram of interactions between toner particles provided in the present invention.

FIG. 3 is a diagram of the effect of interparticle distance on the crosslink formation of toner particles provided by the present invention.

FIG. 4 is a diagram when the polymer adsorption layer is significantly thinner than the electric double layer.

FIG. 5 is a diagram when the polymer adsorption layer is significantly thicker than the electric double layer.

Claims (7)

[Claims] 1. A composition for developing an electrostatic latent image, comprising toner particles containing a pigment and a resin as a main component dispersed in a carrier liquid having a high insulating property and a low dielectric constant, wherein a polymer interface is formed on the toner particle surface. A composition for developing an electrostatic latent image, wherein a cohesive force is generated between toner particles on the surface of a photoreceptor by forming an adsorption layer of an activator. 2. The electrostatic latent image developing composition according to claim 1, wherein a polycarboxylic acid type polymer surfactant is used as the polymer surfactant. 3. The electrostatic latent image developing composition according to claim 2, wherein the polymeric surfactant is present in an amount of up to 25 wt% based on the weight of the toner particles. 4. The electrostatic latent image developing composition according to claim 1, wherein polyoxyethylene alkyl ether is used as the polymer surfactant. 5. The electrostatic latent image developing composition according to claim 4, wherein the surfactant is present in an amount of up to 20 wt% based on the weight of the toner particles. 6. The electrostatic latent image developing composition according to claim 1, wherein polyoxyethylene sorbitan fatty acid ester or polyoxyethylene sorbitol fatty acid ester is used as the polymer surfactant. 7. The electrostatic latent image developing composition according to claim 6, wherein the surfactant is present in an amount of up to 30 wt% based on the weight of the toner particles.