JPS6295547A - Two-component developer for positive electrostatic charge - Google Patents

Abstract

PURPOSE:To maintain specified quantity of electrostatic charge and to continuously obtain an image having high quality by constituting a coating layer of a styrene acrylic resin at 0.1-5wt% of a ferrite carrier and colloidal silica at 0.1-2wt% of the styrene acrylic resin. CONSTITUTION:The coating layer of a two-component developer for positive electrostatic charge consisting of a positive charge toner prepd. by using 1 or >=2 kinds among styrene acrylic resin, epoxy resin and polyester resin as an essential binder and dispersing a charge applying material therein and the ferrite carrier having the coating layer is constituted of the styrene acrylic resin at 0.1-5wt% of the ferrite carrier and the colloidal silica at 0.1-2wt% of the styrene acrylic resin. The change rate DELTAQ of the quantity of the electrostatic charge decreases gradually with an increase in the quantity of Si to form a valley approximate at about 1% and thereafter said rate increases gradually with an increase in the quantity of Si. On the other hand, said rate changes with the quantity of SA as well and shows a tendency to increase thereafter with about 1.0% of the quantity of SA as a boundary. The stability of the quantity of the charge is thereby made remarkably high.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a two-component developer for developing an electrostatic image on a photoreceptor by electrophotography used in copying machines, printers, etc. In particular, the present invention relates to a positively charging two-component developer for developing electrostatic images with a long life and less reduction in charge amount.

[Conventional technology]

Conventional electrophotography involves forming an electrical latent image on a photoreceptor using a photoconductive substance through exposure, and then developing it with toner charged with static electricity through frictional charging, and transferring it to transfer material such as paper. After the toner is transferred, it is fixed by heat or pressure to obtain a visible image. The most commonly known method for triboelectrically charging a toner is to charge the toner by stirring the toner together with magnetic powder called a carrier.

And by the combination of the above carrier and toner.

Various different polarities and amounts of charge can be applied to the toner.

[Problem that the invention seeks to solve]

However, in conventional developers, when copying and printing are continued continuously, the developer consisting of toner and carrier deteriorates.

In other words, it is mainly a change in the absolute value of the amount of charge on the toner.

Also, variations occur in the amount of charge of each toner. For example, when the absolute value of the amount of charge increases.

Since the charge of the electrostatic latent image on the photoreceptor is constant, the total charge of the toner that develops the latent image is also constant, so a small amount of toner fills up the latent image, and the density of the resulting visible image is descend. Furthermore, if there is variation in the amount of charge of each toner, toner particles with a small amount of charge will scatter to areas other than the electrostatic latent image on the photoconductor, and the resulting visible image will have a lot of so-called fog. Become something. Furthermore, when the toner loses its chargeability, the toner also flies around the developing machine and contaminates the inside of the machine. As described above, when conventional developers are used, it is not possible to maintain a constant charge amount and continuously obtain high-quality images during continuous copying and printing. Yet again. Under the environmental conditions of high temperature, low humidity, and high temperature cylinder H, the change in the amount of charge of the developer becomes even greater, making it extremely difficult to continuously maintain a high quality level of copied images.

In order to solve the above problems,
A carrier surface coated with a styrene acrylic resin as described in Japanese Patent No. 54 has been proposed. However, although the environmental resistance of developers using such carriers is slightly improved, there are still problems such as a decrease in image density due to variation and instability in the amount of charge, and toner scattering, and it is not satisfactory. It has not reached the developer.

The present invention solves the above-mentioned problems with conventional developers, and uses two components for positive charging that can maintain a constant amount of charge even during continuous copying and printing, and can continuously obtain high-quality images. The purpose is to provide a developer.

[Means for solving problems]

In order to achieve the above object, the present invention employs the following technical means. That is, a positively charging toner comprising a positively charging toner in which one or more of styrene acrylic resin, epoxy resin, and polyester resin is used as a main binder and a charge imparting agent dispersed therein, and a ferrite carrier having a coating layer. In the two-component developer, the coating layer is composed of a styrene acrylic resin of 0.1 to 5% by weight of the ferrite carrier and a styrene acrylic resin of 0.1 to 5% of the ferrite carrier.
It is composed of 1 to 2% by weight of colloidal silica.

If the styrene acrylic resin used in the present invention is less than 0.1% by weight of the ferrite carrier, it is inconvenient because the charge amount will change greatly at the beginning of copying, and if it exceeds 5% by weight, it will be charged during continuous copying or printing. A decrease in the amount of toner is observed, causing toner scattering and contaminating the inside of the 7 mechanical device. Therefore, the ferrite carrier's 0.
It was limited to 1 to 5% by weight. In addition, colloidal silica is effective in reducing deterioration of the coating layer due to friction and extending the continuous copying life, but if it is less than 0.1% by weight of the styrene-acrylic resin, it cannot be expected to have an effect of improving fluidity. This is disadvantageous because it reduces the density of one image. What if it exceeds 2% by weight? The A-activity becomes excessive, and the effect of maintaining a good charge amount cannot be expected. Therefore, it was limited to 0.1 to 2% of the styrene acrylic resin.

[Example 1] The raw materials for the positively chargeable toner are shown below.

Styrene acrylic resin (Fujikura Kasei HTRO2) 85
Parts by weight Polypropylene (Sanyo Kasei 660 P) 2 Parts by weight Nigrosine dye (Orient Bontron Arashi 3) 3 Parts by weight Carbon blank (Mitsubishi Kasei #44) 10 parts by weight The above raw materials were kneaded for 30 minutes in a kneader with a heated roller, After pulverization, jet mill fine pulverization is performed.

The toner was classified to 5 to 15 μm to obtain a positively chargeable toner.

Next, the ferrite carrier (KBNloo) was put into a fluidized bed granulation coating device, and the styrene acrylic resin and colloidal silica (Nippon Aerosil R972) dissolved in a solvent were added.
Spray the mixture with about 10cn! A coated carrier was prepared by ejecting at a flow rate of /min and drying at 150° C. for 30 minutes.

Various coated carriers were prepared by changing the amounts of styrene acrylic resin and colloidal silica that form the coating layer,
It was mixed with the positively chargeable toner to form a developer, and continuous copying was performed. The table below shows the results, and Figure 1 shows the colloidal silica content (wt%) for styrene acrylic resin.
) and the amount of change in charge amount.

ΔQ=IQ, -QG IQo = initial charge amount (μC/g) Ql; charge amount after copying 20,000 sheets (μC/g) SAi
Ratio of styrene acrylic resin to ferrite carrier Si amount Ratio of colloidal silica to styrene acrylic resin Below margin Below margin As is clear from the table and figure, the charge amount change ΔQ is:
It gradually decreases as the amount of Si increases, forms a valley around approximately 1%, and then gradually increases as the amount of Si increases. On the other hand, ΔQ is SA
It also changes depending on the amount of SA, and as the amount of SA increases from 0.05%, it gradually decreases, and there is a tendency for it to increase after SAi reaches approximately 1.0%. It is empirically known that the allowable limit for the amount of change in charge amount ΔQ is 10 μC/g.

The optimum ranges for the amount of Si and the amount of SA can be determined to be 0.1 to 2% and 0.1 to 5%, respectively.

[Example 2] A ferrite carrier (KBNloo) was placed in a fluidized bed granulation coating device, a styrene acrylic resin was dissolved in a solvent, and a coated carrier was prepared in the same manner as in Example 1 by spraying. By mixing and stirring this coated carrier and colloidal silica in a Henschel mixer at a temperature near the softening point of the styrene acrylic resin, a carrier in which colloidal silica was fused to the styrene acrylic resin coating layer was prepared. . As in Example 1, the amounts of styrene acrylic resin and colloidal silica were varied and mixed with the positively chargeable toner to form a developer, and continuous copying was performed. The results were substantially the same as in Example 1 above.

〔Effect of the invention〕

Since the positively charging two-component developer of the present invention has the structure described above in 9 or above, it is possible to greatly improve the stability of the charge amount during continuous copying (printing), which has been insufficient in the past. can. It also has excellent environmental stability, as there is little change in toner charge amount.

Copies with uniform image density and high quality can be obtained.

Furthermore, even under harsh environmental conditions, it has a long life effect that could not be expected with conventional developers.

[Brief explanation of drawings]

The figure is a diagram showing the relationship between the colloidal silica content and the amount of change in charge amount, showing an example of the present invention.

Claims (3)

[Claims] (1) Positively charged toner consisting of a positively charged toner containing one or more of styrene acrylic resin, epoxy resin, and polyester resin as the main binder and in which a charge imparting agent is dispersed, and a ferrite carrier having a coating layer. A two-component developer for use, characterized in that the coating layer is composed of 0.1 to 5% by weight of a styrene acrylic resin based on a ferrite carrier, and 0.1 to 2% by weight of colloidal silica based on a styrene acrylic resin. A two-component developer for positive charging. (2) A two-component developer for positive charging according to claim 1, wherein colloidal silica is dispersed in a styrene-acrylic resin. (3) A two-component developer for positive charging according to claim 1, wherein fine particles of colloidal silica are fused to a styrene-acrylic resin.