JPH01185657A - Developer for electrophotography - Google Patents

Abstract

PURPOSE:To obtain a developer which decreases sleeve ghosts and is less fluctuated in image density by externally adding dry type silica of the same polarity to a dry type one-component toner and mixing and dispersing the mixture, then externally adding wet type silica to the mixture. CONSTITUTION:The dry type negative silica is externally added to the toner prepd. by incorporating magnetite into a styrene/acrylic copolymer and incorporating a metal-contg. complex as a charge generating layer into said copolymer and the mixture is mixed and dispersed by a Henschel mixer. Further, the wet type weakly negative silica is externally added to this toner and the toner is mixed and dispersed by the Henschel mixer to form the developer. The sleeve ghosts are greatly decreased and the development at the less fluctuating image density is executed if the developer formed in such a manner is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a developer used in copying machines LBP, LED printers, etc. that obtain printed images using an electrophotographic method.

[Prior Art] Conventionally, in order to control the amount of charge (hereinafter referred to as tripo) of a dry single-component magnetic toner, dry-process silica (based on a gas phase process) or wet-process silica (based on a neutralization reaction of water glass) has been used. It is widely known that external attachments (objects) are added.

For example, by externally adding dry negative polarity silica to a negative polarity toner containing magnetite in a styrene-acrylic copolymer, the fluidity as a developer increases and the amount of tripo also generally increases.

It is widely known that when known jumping development is performed using this developer, images with higher image density and less roughness can be obtained than with a developer to which silica is not externally added.

[Problems to be Solved by the Invention] However, when dry silica is externally added to negative polarity toner as a developer, which exhibits even stronger negative polarity than the toner in terms of charge series, the amount of tripo contained in the dry silica increases with the toner. It is several tens of times larger than the previous model, so in low humidity environments, etc.
It is easy to hold more tripo than necessary, and a strong positive sleeve ghost occurs.

According to the experiments and considerations of the present inventors, this ghost formation is deeply related to the fine powder layer (particle size of 5 to 6 μm or less) formed on the sleeve. In other words, there is a clear difference in the particle size distribution of the toner bottom layer of the developing sleeve between the toner consumption area and the toner non-consumption area, and a fine powder layer is formed in the toner bottom layer of the non-toner consumption area. Due to its physical properties, fine powder has a larger amount of triboelectric charge per mass than particles of larger size, and is strongly electrostatically restrained against the sleeve by mirroring force. Therefore, the toner on the part where the fine powder layer is formed cannot be sufficiently triboelectrically charged with the (metallic) developing sleeve, reducing the developing ability and causing sleeve ghosts to appear on the image.

The sleeve ghost described above is a phenomenon that occurs because the formation of a fine powder layer and the charging of the toner largely depend on frictional charging with the sleeve. Therefore, the present inventors have confirmed that, for example, by externally adding wet-process silica exhibiting weakly negative polarity characteristics to a negative polarity toner, fogging can be reduced and ghosting can be improved. However, wet-process silica generally has a larger particle size (10 to 100 times) than dry-process silica, and is thought to have a surface energy close to that of toner, so it does not have good fluidity as a developer and also reduces toner lipo. This time, on the contrary, there was a problem in that negative ghosting occurred due to insufficient supply of new developer to the developer consuming portion and insufficient tripod.

[Means and effects for solving the problems] The present invention externally adds dry homopolar silica to dry component toner in order to ensure fluidity as a developer, increase toner lipo and maintain density. Thereafter, a developer is provided in which wet-process silica, which has a polarity opposite to that of the toner in terms of charging series, is externally added in order to apply triplicate to the toner from a source other than frictional charging with the metal sleeve. When this developer is used, it has become possible to perform electrophotographic development in which sleeve ghosts are greatly reduced compared to conventional methods and there is less variation in image quality.

[Example] Example 1 A toner was prepared by making a styrene-acrylic copolymer containing 60 parts by weight of magnetite and 2 parts by weight of a metal-containing complex as a charge control agent.
100 layers of HMDS (hexamethylene disilazane) for 0.2 vapor phase silica? Added 0.3 parts by weight of 10 parts by weight and heat-treated)
This was mixed and dispersed using a Henschel mixer. Furthermore, 0% of wet weakly negative polarity silica (for example, Nippon Silica E-150X treated to make it hydrophobic) was added to this toner.
．． 4 parts by weight were added externally, and this was mixed and dispersed with toner using a Henschel mixer to obtain a developer.

FIG. 1 is a cross-sectional view of a developing device that actually produced an image using this developer. In FIG. 1, l is a toner hopper;
2 is a developer, 3 is a magnet, 4 is a non-magnetic metal (aluminum) sleeve (diameter r), 5-a is a magnetic blade, and 6 is an image carrier (photosensitive drum).

The gear tooth width between the magnetic blade 5-a and the aluminum sleeve 4 is 250H, and the magnetic force of N1, which is the cut pole, is 75H.
0. Gauss. As the aluminum sleeve rotates, the blade portion is uniformly coated with developer. The developer on the sleeve is at the development pole S) (820g
auss). At this time, a developing bias in which a DC voltage of -450 V is superimposed on an AC voltage with a frequency of 1800 Hz and a peak-to-beak of IEtooV is applied to the sleeve.

All images output by jumping development using such a developer have ghosting compared to images obtained by externally adding dry negative silica and images obtained by externally adding wet weakly negative polarity silica. Improved images are now available.

Example 2 Next, in place of dry negative silica, aminosilane (amino group-containing silane coupling agent was added to dry positive silica (vapor phase silica) at a ratio of 10 parts by weight per 10012 of aminosilane (silane coupling agent containing an amino group) to the above-mentioned prototype toner, and the mixture was heat-treated. things) to 0.
3 parts by weight were added externally, and this was mixed and dispersed with the toner in the same manner as in Example 1. Further, in the same manner as in Example 1, 0.5 parts by weight of wet weakly negative polar silica was mixed and dispersed in this toner to prepare a developer.

This developer improves sleeve ghosting more than the developer of Example 1, but the solid density decreases due to the small amount of toner lipo (reflection density is 0.9 at room temperature and humidity). For this reason, the inventors conducted an experiment using a developing device as shown in FIG. 2 instead of the developing device shown in FIG. This developing device coats the aluminum sleeve uniformly with an elastic blade (urethane rubber, etc.) against the sleeve as shown in 5-b.
This was done by pressing. By doing this, the toner lipo was raised and the reflection density was increased by about 0.3 compared to the case where a metal magnetic blade was used, and a solid density of about 1.2 to 1.3 could be obtained. As shown in Fig. 3, the elastic blade can be brought into contact with the sleeve in such a way that the tip of the elastic blade faces in the opposite direction to the rotational direction of the sleeve, or in the forward direction. Almost the same results were obtained.

[Effects of the Invention] As described above, by using the developer of the present invention, sleeve ghosts can be greatly reduced, and adverse effects such as density unevenness can also be reduced.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views of a developing device that performs development using the developer of the present invention. l...Developer hopper 2...Developer 3...Developing magnet 4...Metal sleeve 5-a...Metal magnetic blades 5-b, 5-c...Elastic blade

Claims (1)

[Claims] (1) An electrophotographic developer characterized in that dry-processed silica is first externally added to a dry-processed one-component magnetic toner, mixed and dispersed, and then wet-processed silica is further externally added, mixed and dispersed. .