JPH0416861A - Toner for developing electrostatic latent image and production thereof - Google Patents

Abstract

PURPOSE:To obtain strong uniform additive coatings on toner particles by stirring a suspension contg. the toner particles and additive particles at a temp. above the glass transition point of resin forming the toner particles and melt- sticking the additive to the surfaces of the toner particles. CONSTITUTION:Toner particles and an additive such as a flowability rendering agent, an electrostatic charge controlling agent or a flocculation inhibitor are dispersed and suspended in a solvent such as water under proper conditions with a surfactant, etc. The resulting suspension is heated to a temp. above the glass transition point or softening point of resin forming the toner particles, moderate stirring is carried out and the surfaces of the toner particles are coated with the additive. The coated toner particles are dehydrated and dried. The surface of the toner can uniformly and strongly be coated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a toner used for developing an electrostatic latent image in electrophotography or electrostatic recording, and a method for producing the toner.

(Prior Art) Methods for developing electrostatic latent images include (a) a one-component development method in which a thin layer of toner is formed on a conductive layer and developed by bringing it close to or in contact with the electrostatic latent image; (b) ) A two-component development method in which the toner is triboelectrified to a predetermined polarity by mixing and stirring with carrier particles having a particle size larger than the toner and developed by bringing the toner close to or in contact with the electrostatic latent image; 2. Description of the Related Art A development method in which a latent image is immersed in an insulating liquid in which fine toner particles are dispersed is generally known.

Incidentally, in the cases (a) and (b) above, that is, the toner for dry development is generally manufactured as follows. The first method is a method called a kneading and pulverizing method or a dry kneading method. That is, a thermoplastic resin is used as a base material, and a coloring agent and, if necessary, a magnetic material powder, a frictional charge control agent, a mold release agent, etc. are added, heated, melted, and kneaded, then cooled, crushed, and classified. Toner particles with an average particle diameter of 20 μm are obtained, and in order to further improve fluidity and charging properties, so-called external additives or surface treatment agents such as hydrophobic silica particles and titanium oxide particles are added and mixed to coat the surface. In this method, the desired toner can be obtained.

The second method is the suspension polymerization method disclosed in, for example, Japanese Patent Publication No. 3B-10231 and Japanese Patent Publication No. 47-518305. In this suspension polymerization method, fine monomer particles having a polymerizable unsaturated group, a coloring agent, and if necessary magnetic material powder, a triboelectric charge control agent, a mold release agent, etc. are mixed into a solvent such as water with surface active properties. Disperse and stir using a
By performing polymerization and granulation under the action of a polymerization initiator at a temperature of approximately 90°C to 90°C, toner particles of a predetermined size are obtained, which are then washed and dried to form a powder. In order to improve fluidity and chargeability, a desired toner is obtained by mixing and adding hydrophobic silica particles, titanium oxide particles, etc. to coat the surface. Incidentally, if necessary, the particle size distribution is adjusted by classification either before adding the external additive or after coating with the external additive.

(Problems to be Solved by the Invention) However, the above-mentioned conventional electrostatic latent image developing toner and method for producing the same have the following problems. For example, suspension polymerization is seen as a promising toner production method in the future because it simplifies the process because it does not require kneading or pulverization, and it is suitable for efficiently obtaining smaller toner particles. However, the manufacturing process for this toner remains complicated in that it requires two steps: a wet process and a dry process, in which the toner particles are formed in a wet process and external additives are added after drying. .

In the toner manufacturing process using the above suspension polymerization method, although the purpose is different from coating the toner surface, silica powder is used as a dispersion aid at an early stage such as when dispersing polymerizable monomers. There are examples where it is added for the purpose of However, in this case, silica powder etc. are incorporated into the monomer oil droplets during the polymerization granulation stage, and almost no external additives are exposed on the surface of the final polymerized resin particles. not exist. As a result, although silica is contained inside the toner, the important surface of the toner is not coated with silica, and as described above, the actual situation is that an external additive must be added again after drying. In this case, it is possible to add a large amount of silica from the beginning so that enough silica remains in the final stage of polymerization, but do not add so much silica at the beginning that it remains until the end and covers the toner surface. If more is added, there is a problem in that the polymerization reaction and the formation of polymer particles (granulation) are significantly hindered.

In this way, in conventional toner manufacturing methods, external additives are simply mechanically mixed in a dry powder state.
The added external additives are only attached mainly due to electrostatic force. Therefore, during use (during development), there is a problem that the external additive easily separates from the toner particles and adheres to the carrier particles or the photoreceptor. In other words, the detached external additives are often the main cause of problems in cleaning the photoreceptor and short-term deterioration in developing performance.

Further, problems caused by the detachment of external additives also occur significantly in the -component development method. In other words, the toner on the developing roller loses external additives such as silica, which play a role in releasability and fluidity between the developing roller and the toner, resulting in a sudden decrease in development sensitivity and the removal of external additives. There is a problem in that the triboelectric charging properties are impaired due to the influence, resulting in poor images. Furthermore, as mentioned above, external additives basically have the disadvantage of being easily removed, so if the amount added is increased, they become even more likely to be removed and side effects become noticeable, so it is not possible to add the necessary and sufficient amount. However, it was difficult to completely coat the toner surface with external additives. Therefore, there remains the problem that there is a limit to its function as a release agent that prevents toners from agglomerating and solidifying when left to stand, as well as to its ability to improve storage stability and fluidity.

Furthermore, in order to improve the storage stability of toner, it is necessary to select a resin with a high glass transition point as the main component of the toner. There were completely contradictory requirements, and it was difficult to achieve a satisfactory level of coordination. Also,
These problems become more pronounced as the toner particle size becomes smaller, and solving these problems is essential for the practical use of small-particle toners with excellent image quality.

In order to solve the above problems, the present inventor researched various methods of adding external additives to toner, and found that it is possible to melt the external additives from the toner by fusing the external additives to the resin constituting the toner. We tried mixing toner dispersed by wind in hot air with an external additive and coating it with the external additive, but temperature control was difficult and the toner melted. In order to ensure that the external additives are well coated, the temperature may be too low and the toners may fuse together, the external additives may get inside the toner particles and no longer function, or the temperature may be too low and the toner particles do not fuse properly. However, it was difficult to achieve uniform and highly accurate temperature control, and the objective could not be achieved.

As described above, these problems have not yet been solved with conventional toners, and are common problems that must be solved in order to realize even more improved high-performance toners. Furthermore, it is difficult to produce toner with a particle size smaller than approximately 8 μm;
In particular, it is impossible to produce toner having a particle size of around 1 μm for use in liquid development using a pulverization method. Although this is possible by the suspension polymerization method, sufficient performance could not be obtained because it is difficult to add external additives to such fine powder by the above-mentioned means.

The present invention has been made to solve the above problems, and provides a toner for developing electrostatic latent images that has a stronger and more uniform external additive coating and has excellent durability, fixability, storage stability, and image quality. The object of the present invention is to provide a manufacturing method that can easily obtain this toner for developing electrostatic latent images.

[Structure of the Invention (Means for Solving the Problems)] The present invention involves granulating toner particles whose main component is a thermoplastic synthetic resin by a melt-kneading method, and mixing the toner particles and external additives with water. It is dispersed in a solvent such as sodium dodecylbenzenesulfonate, sodium tetradecyl sulfate, sodium octyl sulfate, sodium laurate, etc. under appropriate conditions such as using a surfactant such as sodium dodecylbenzenesulfonate, sodium tetradecyl sulfate, sodium octyl sulfate, sodium laurate, etc. This is based on the knowledge that a uniform and strong coating can be formed on the toner surface by heating and stirring appropriately.

In other words, in the above method, since the specific gravity of the toner and water are similar, the toner particles and the external additives to be coated can be maintained uniformly dispersed for a long time, and the temperature can be easily and uniformly controlled. Moreover, since the required coating can be performed with high precision, it has been discovered that the desired toner surface treatment is possible, and this has led to the present invention.

That is, the present invention involves dispersing and suspending toner particles having a desired particle size manufactured by a melt-kneading method in a solvent together with external additives for imparting fluidity, controlling charge, or preventing agglomeration. The surface of the toner particle body is coated with the external additive by raising the temperature of the suspension to a temperature equal to or higher than the glass transition point of the resin constituting the toner particle body, and then dehydrating and drying the suspension. A toner for developing electrostatic latent images and a method for producing the same.

(Function) The toner for developing an electrostatic latent image according to the present invention has a toner particle body mainly composed of a thermoplastic resin containing a colorant, and an external additive layer that coats the surface of the toner particle body. , and the external additive layer is integrated with the surface of the toner particle body in a thermally fused manner. That is, according to the present invention, a toner particle body mainly composed of a thermoplastic resin containing a colorant, etc., and a fluidizable material such as a metal oxide such as hydrophobic silica, titanium oxide, or alumina, or a fluororesin such as polyfluoroethylene, etc. Dispersing external additives for the purpose of improving cohesiveness or charging properties in a dispersion liquid such as water, heating and stirring the dispersion system at a temperature equal to or higher than the glass transition point of the thermoplastic resin, The main idea is that an external additive is fused to the surface of the toner particle body.

Since the above external additive is fused to the surface of the toner particle body, the toner for developing electrostatic latent images according to the present invention maintains excellent durability, fixability, storage stability, and image quality.・Exercise. Further, since the production is carried out by a dispersion method in liquid, the required temperature can be easily controlled and the desired toner can be obtained with good reproducibility.

(Example) Examples of the present invention will be described below.

Example 1 FIG. 1 is a flowchart showing an example of the manufacturing process of a toner for developing electrostatic latent images according to the present invention. First, styrene-acrylic acid ester copolymer resin (Mitsubishi Rayon, glass transition point Toner particle bodies without any external additives and having an average volume particle diameter of 11.8 .mu.m were first produced by a known melt-mixing milling method using carbon black powder as a colorant (65 DEG C.) and carbon black powder as a colorant.

100 parts of the toner particle body produced above was mixed with 5000 parts of water.
1 part and 0.1 part of sodium dodecylbenzenesulfonate as a dispersion stabilizer to prepare toner particle dispersion A.

On the other hand, external additive B was prepared by pre-wetting 5 parts of hydrophobic silica (R972) with a particle size of 15 to 20 mμ (millimicrons) and 70 parts of methanol using a high-speed stirrer (nanomizer).
is added to the toner particle main body dispersion A, and 2-b a processing tank C equipped with a propeller type stirrer (homogenizer).
4 while stirring to the extent of causing relatively strong turbulence.
This was maintained for a certain period of time to thermally fuse hydrophobic silica fine particles to the surface of the toner particle main body, thereby covering the surface with an external additive layer.

Next, the dispersion containing the toner particles coated with the external additive layer is sent to a cleaning means to remove water from the dispersion, washed with distilled water, and dried at 45° C. in a drying means E.
After drying under reduced pressure for 10 hours, surface treatment (external additive coating)
dried toner particles were obtained. Further, the toner particles were passed through a classifier F to remove coarse particles. This classification step is unnecessary unless coarse particles are generated, and is not an essential step in the present invention.

Next, the particle size of the toner obtained above was measured using a Coulter counter, and the 50% average particle size was 125 μm. Ferrite carrier for electrophotography (PSL102013. manufactured by Kanto Denka) 40g per 1kg of this toner
A two-component developer was prepared by mixing the two components, and when the charge amount was measured using a commercially available blow-off charge amount n1 constant machine, it was found to be -3.
It was 4 μc/g (microcoulombs/gram). Furthermore, even after the toner was placed in a polyethylene container and left in a water tank at 50° C. for 20 hours for a toner storage test, no aggregation or solidification was observed. Although quantitative evaluation of fluidity was omitted, a sensory comparison test with existing toners by shaking a transparent container revealed that the toner easily had higher fluidity.

Copied images were taken using a commercially available electrophotographic copying machine (BD5110 manufactured by Toshiba) using the toner (developer) prepared above. Initial characteristics equivalent to or better than those of the regular developer were obtained.

Furthermore, in order to test the durability of this developer, a large amount of toner was made under the above conditions and 50,000 copies were made, but almost no filming of toner components on the photoreceptor was observed. There was also much less change in image quality compared to the regular developer, and it was confirmed that printing durability was improved. When this toner was observed under an electron microscope, it was found to have a nearly perfect spherical shape due to thermal melting, and its surface was extremely uniformly and densely coated with hydrophobic silica. Moreover, almost no change in this appearance was observed even after the life test.

The reason for this is that the resin particles are placed at a temperature higher than their softening temperature or glass transition point and come into contact with the silica particles in a viscous state, so they are coated with strong force to completely adhere or fuse. It is judged that it is for the sake of safety. Moreover, the coated external additive is not completely buried inside the toner, but is attached to the surface in an exposed state.
This is the most significant feature of the toner according to the present invention. In addition, the above-mentioned characteristics are considered to be the cause of the high fluidity, preservability (blocking resistance), and high durability that could not be achieved by conventional addition methods.

Furthermore, the reason why almost no silica is observed to be attached to the carrier is that even if there is silica that is attached or floating, it is removed by cleaning after the coating treatment. In the end, it is determined that the fact that it does not exist also contributes.

Comparative Example In the case of Example 1, a toner obtained by adding 1% of hydrophobic silica to the toner weight by the conventional dry external additive addition method without performing the addition treatment of external additives in the liquid. When observed under an electron microscope, it was found that the silica powder was localized and covered the entire surface of the particles, and the shape of the toner was also irregular. Further, in a storage test under the same conditions as in Example 1, there were parts of the toner that were not crushed unless strongly vibrated.

On the other hand, although detailed manufacturing conditions are omitted, in the case of other toners with a glass transition point of 70 degrees Celsius manufactured by the kneading and pulverization method that can withstand the toner storage test mentioned above, sufficient fixing strength is obtained even when the fixing temperature is raised to 200 degrees Celsius. I couldn't get it.

Example 2 In the case of Example 1, as an external additive, a particle size of 0.5 to
A toner was produced under the same conditions except that 6 parts of 2 μm fluororesin fine powder (trade name Kynar) and 0.2 parts of surfactant were dispersed. The charge amount of this toner is -40μC
When a copying test was carried out using the same copying machine as in Example 1, a good image was obtained, and both the storage stability and fluidity were good.

Example 3 A toner was produced under the same conditions as in Example 1 except that the amount of external additives was 10 parts and methanol was 90 parts. Almost the same results as in Example 1 were obtained with this toner. This means that even if an excessive amount of external additive is dispersed, the surface of the resin particles will soften and the new external additive will stick only to the uncovered areas, so the excess external additive will not be incorporated. It is presumed that there is some leeway in the appropriate amount of external additive dispersion.

From the study of the above Examples and Comparative Examples, it has been found that the toner particle body having the desired particle size and thermal properties obtained by the melt-kneading method has a temperature higher than the glass transition point of the resin that constitutes the main component of the toner particle body. A good coating process with the external additive can be achieved in a solvent such as water, which is set at a temperature ranging from the softening temperature of the toner resin to the temperature at which the resin exhibits melt viscosity or thermal fluidity. In addition, when using a component such as wax that melts at a relatively low temperature, it is not preferable to use a component that melts at a relatively low temperature because elution tends to occur at too high a temperature.

On the other hand, through a series of studies, we found that there was a relatively large amount of leeway in the heating temperature and time; for example, even if the attached external additive were buried inside the toner, the toner surface would regain its viscosity. This is thought to be because new external additives adhere to the surface, and the external additives that are not completely buried are always buried in a semi-exposed state on the surface.

It should be noted that the developing method used for the toner of the present invention is not limited to the method exemplified above, and it goes without saying that it can perform its functions in any conventionally known developing method. be.

[Effects of the Invention] As described above, according to the toner for developing electrostatic latent images and the method for producing the same according to the present invention, after the shape and thermal conditions of the toner particle body are established after kneading and pulverization, Because the required surface coating treatment has been carried out, external additives can be coated with high strength under relatively leeway conditions, and it is a high-quality product that has a long life and good fluidity and storage stability (agglomeration resistance). It is now possible to provide a functional dry developing toner.

Further, even if a resin having a low fixing temperature is used, in the case of the present invention, the storage stability is improved and fixing performance is easily achieved, and the fixing temperature can be kept low.

In other words, there is an advantage that the temperature rise and power consumption of the developing device can be suppressed. It should be noted that the toner according to the present invention is not limited to any developing method, and it can be understood that the toner exhibits its function in common in all conventionally known developing methods from the essence of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an example of the manufacturing process of a toner for developing an electrostatic latent image according to the present invention. A: Toner particle main dispersion B: Wetted external additive C: External additive coating "processing tank D: Cleaning means E" ...Drying means F...Classifier Applicant: Toshiba Corporation

Claims (2)

[Claims] (1) Comprising a toner particle body for developing an electrostatic latent image, the main component of which is a resin granulated by a melt-kneading method, and an external additive formed and adhered to the surface of the toner particle body, The agent is characterized in that the toner particle body and a dispersed suspension of external additive particles are fused and formed by stirring at a temperature higher than the glass transition point of the resin that constitutes the main component of the toner particle body. Toner for developing electrostatic latent images. (2) a step of heating, kneading, and pulverizing a mixture containing at least a thermoplastic resin component and a colorant to granulate a toner particle body for electrostatic latent image development; and the granulated toner particle body and an external additive. A step of adding the particles to a dispersion medium to form a dispersion suspension, and heating the dispersion suspension to a temperature higher than the glass transition point of the resin that constitutes the main component of the toner particle body and a stirring process to form an external layer on the surface of the toner particle body. A process of fusing and forming an additive layer, and washing and washing the toner particles with the external additive layer fusing and forming on the surface.
1. A method for producing a toner for developing an electrostatic latent image, comprising the step of performing a drying treatment.