JPH01114878A - Developing method - Google Patents

Abstract

PURPOSE:To eliminate the sleeve ghost by using a one-component developer obtained by adding externally a substance whose polarity is opposite to that of a toner, or a substance whose polarity is the same as that of the toner and whose electrification characteristic is lower than or equal to the toner, to the toner, and mixing and dispersing them. CONSTITUTION:A toner in a toner hopper 1 has triboelectricity by friction against a non-magnetic developing sleeve 4 and friction of each toner, and also, the friction becomes strong by an elastic blade 5 which is pressed against the sleeve 4, the triboelectricity is raised and coating is executed. A developer on the sleeve 4 is developed against an electrostatic latent image which is formed on a photosensitive body 6. In this case, a one-component developer obtained by adding externally a substance which is electrified to the polarity opposite to that of the toner, or a substance which is electrified to the same polarity as that of the toner, but whose electrification characteristic is lower than or equal to the toner, to the toner is used. In such a way, the sleeve part ghost is prevented, and also, the image density can be held satisfactorily.

Description

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

[Conventional technology]

Conventionally, substances for controlling the amount of charge (hereinafter referred to as tripo) of dry-component magnetic toner, such as vapor-phase silica (hereinafter referred to as dry silica) and wet-process silica (hereinafter referred to as wet silica), have been added to toner. It is widely known that it is attached.

For example, for a negative polarity toner containing 60 parts by weight of magnetite in styrene acrylic, dry negative silica (200 rrl of vapor phase silica), which exhibits strong negative characteristics, is
By externally adding DS (10 parts by weight per 100 durability and heat treated), the triboelectricity of the developer is generally increased. When this developer is used to develop a thin layer on a sleeve, such as by known jumping development as shown in Figure 2, the image density is higher and roughness occurs compared to a developer without external addition of silica. It is widely known that it is possible to obtain images with fewer images.

[Problems to be Solved by the Invention] However, in the case of a developer to which negative silica, which is strong against negative toner, is externally added, sleeve ghosts, which are traces of printed patterns, occur on the developing sleeve, and these ghosts also appear on printed images. In particular, when an elastic blade is used, the ghost becomes even stronger (appears). The sleeve ghost that occurs when using a developer in which negative silica is externally added to negative toner becomes a positive ghost, as shown in FIG.

In other words, because the non-printing area (white background) continues, even if printing is performed, only light development is performed (a), and because printing continues, dark development is performed (b).
There will be uneven density between different parts.

According to the experiments and considerations of the present inventors, the mechanism of this ghost formation is that the fine powder (particle size 5
It is deeply involved in the layer (~6 μm or less). 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. Since fine powder has a large surface area per volume, it has a large amount of triboelectric charge per mass compared to particles with a large particle size, and is strongly electrostatically attracted to the sleeve by its own reflection force. Therefore, the toner on the portion where the fine powder layer is formed cannot be sufficiently triboelectrically charged with the developing sleeve, resulting in a decrease in developing ability and appearing as a sleeve ghost on the image. The above-mentioned sleeve ghost is a phenomenon that occurs because, in addition to the formation of a fine powder layer, the charging of the toner largely depends on frictional charging with the developing sleeve.

Therefore, in order to remove sleeve ghosts, it was necessary to reduce the amount of frictional electrification of the toner (and thereby reduce the mirroring force with the sleeve). When developing with a developer using a magnetic plate as shown in the figure, there was a problem that the density decreased and in extreme cases, the image did not come out.(In Figure 2, 1 is the developer housing, 2 is a one-component developer made of toner mixed with an external additive for charge control; 3 is a magnet placed in a non-magnetic sleeve 4; 4 is a magnet that supports and conveys the one-component developer; It rotates in the direction of the arrow with a non-magnetic sleeve that serves as a developer carrier made of stainless steel or the like that provides an electric charge. 5' is provided with a small gap between it and the sleeve 4, and a thin developer layer is placed on the sleeve. The formed magnetic blade faces one pole of the magnet. Reference numeral 6 denotes a carrier for an electrostatic latent image developed by the developer, such as an electrophotographic photoreceptor, which is opposed to the sleeve 4 and rotates in the direction of the arrow.) [Means for Solving the Problems] According to the present invention, toner is charged with a substance that is charged to the opposite polarity to the toner, or a substance that is charged to the same polarity as the toner but has lower charging characteristics than the toner, or , by using a one-component developer to which an equivalent substance is externally added, that is, by frictional charging between the external additive and the toner, triboelectricity is imparted to the toner, and furthermore, by using an elastic body to carry the developer. After applying it to the body and adjusting the layer thickness, it is transported to the development area.
By performing development, sleeve ghosts are eliminated (and the density is sufficiently high).

[Example 1] Styrene acrylic contained 60 parts by weight of magnetite, 2 parts by weight of a metal-containing complex as a charge control agent, and was crushed and classified to produce a dry one-component negative polarity magnetic toner.

Thereafter, negative polarity silica having lower charging characteristics or equivalent to that of the toner was externally added, mixed and dispersed.

In this example, 0.5 parts by weight of wet negative silica which had been hydrophobized with a silane coupling agent was added externally, and this was mixed and dispersed using a Henschel mixer to form a developer.

In the case of the developer used in this example, the charge amount of the toner was approximately -15 μc/g by the two-component mesh method, that is, the method of mixing with carrier (iron powder), blowing it off, and measuring the charge amount with a coulomb meter. The amount of charge of the wet negative silica was about -12 μc/g. In addition, when the amount of charge of the dry negative silica described in the conventional example was measured using a two-component mesh method, it was found to be a large value of -100 μc/g.

Further, the appropriate amount of silica to be added is in the range of 0.1 to 1.0 parts by weight, and when it exceeds 1.0, the concentration decreases significantly.

Using this developer, an elastic blade 5 as shown in FIG.
An image was formed using a developing device that coated the sleeve 3 with the developer 2. In the figure, each member except member 5 is the second
Although it is similar to the figure, 1 is a toner hopper, 2 is the developer, 3 is a magnet, and 4 is a non-magnetic metal sleeve (AI!
, SUS, etc.), 5 is an elastic blade (made of urethane rubber and has a thickness of 1.0 mm), and 6 is a photosensitive drum. The toner has triboelectricity due to the friction with the sleeve 4 and the toner particles colliding with each other. Further, due to the elastic blade 5 which is in pressure contact with the sleeve 4, the above-mentioned friction is increased, and the tribo is increased and coating is performed. The developer on the sleeve develops the electrostatic latent image formed on the photoreceptor 6 in the vicinity of the development pole Sl (800 Gauss), which is the closest area.

At this time, the distance between the drum and sleeve is about 300 μm,
The sleeve has a frequency of 1800Hz as a developing bias.
A peak-to-peak voltage of 1600V (7) A DC voltage of -450V (+100V variable) superimposed on an AC voltage is applied.

In this experiment, we used a laser beam printer with a reversal development method that adheres toner to the bright area potential, and the dark area potential and bright area potential of the electrostatic latent image were -700V and -700V, respectively.
-100V. At this time, the reflection density of the solid black image with respect to the development contrast was approximately 1.35.

On the other hand, the reflection density when an image is produced by the conventional developing device shown in FIG. was only 0.9. As can be seen from this, the density is low in the magnetic blade application developer, but if the developer is applied using an elastic blade, the triboelectricity increases and a sufficiently high density can be obtained.

Next, Table 1 shows the degree of sleeve ghosting.

ΔD in Table 1 is the black area (
This is the density difference between the part (b) and the ghost part (part (a)). That is, as can be seen from ΔD'' D (b) D (a), the sleeve ghost was also 0.05D, which was quite good (improved to the extent that it could not be distinguished from the image).

For comparison, images were produced using a developer in which 0.5 parts by weight of dry negative silica, which exhibits the strong characteristics described in the conventional example, was externally added to a commonly used dry type one-component negative polarity magnetic toner. If you also show the image, you can obtain an image with a sufficiently high density (
Reflection density = 1.3 to 1.4), and the sleeve ghost shown in Table 1 is quite bad (ΔD = 0.3 for magnetic blades; ΔD = 0.35 for elastic blades) and is noticeable on the image, resulting in a good quality image. was not obtained.

Table 1 [Example 2] For the toner of Example 1, a silane coupling agent having an amino group was added to the positive polar silica, in this example, vapor phase silica, and dry positive polar silica was heat-treated. 0.3 parts by weight of was added externally and mixed and dispersed for seven minutes to prepare a developer.

The amount of charge on this silica was +100 μC using the two-component mesh method.
/g. The appropriate amount to add is in the range of 0.1-1.0 parts by weight, but if it is too large, fogging may occur or the density may decrease. Since this developer externally contains silica having a polarity opposite to that of the toner, the proportion of triboelectric charges in the toner due to direct charging with silica increases. Therefore, compared to the developer of Example 1, the sleeve ghost is even better and reaches a level that cannot be seen in the image. As shown in Table 1, the magnetic blade has a value of ΔD.

However, since the total tribo amount of the toner is reduced, the image density is reduced. This developer has a reflection density of 20 in a magnetic blade application developer. 8, the concentration is too low to be of practical use.

However, in the case of applying with an elastic blade using the apparatus shown in FIG. 1, an image density of 1.2 was obtained with a development contrast of 350V and a reflection density of 1.2.

Therefore, if the developer is applied with an elastic blade, there will be almost no sleeve ghost (ΔD
=0.02), an image with satisfactory density was obtained.

In addition, in a developing device in which a magnetic blade was applied with a developer externally added with reverse polarity silica, fog and black spots occurred on the white background, but these fogs were reduced by using an elastic blade.

Table 2 (Example 1) (Example 2) C: Reverse polarity silica externally added developer The effects of the present invention will be explained using Table 2. A developer that has the same polarity as a conventional toner and has stronger charging characteristics than the toner causes strong ghosting (Developer A).

An embodiment of the present invention is a developer to which silica is externally added, which has the same polarity as the toner and has the same or lower chargeability than the toner.
Developer B in Table 2) was used with a magnetic blade due to its low density and could not be put to practical use, but it was developed using a development method in which the sleeve was coated with the developer using an elastic blade made of urethane rubber, phosphor bronze, etc. However, the concentration has reached a point where it can be put to practical use.

In addition, in another example, a developer externally added with silica having a polarity opposite to that of the toner (Developer C in Table 2) was developed using a development method in which the sleeve was coated with an elastic blade.
Not only was it possible to increase the density, but also the fog was reduced to a level that does not pose a practical problem.

In the embodiments of the present invention, the charge amount of negative toner is controlled as an example, but the charge amount of positive toner may also be controlled.

In addition, in the embodiment, an example will be explained in which the elastic blade is brought into contact with the sleeve in the rotational direction of the sleeve, but in the next example, the elastic blade is brought into contact with the sleeve in the opposite direction, that is, in the direction opposite to the rotational direction of the sleeve. I don't mind.

In addition, the blade is also made of silicone rubber.

Rubber elastic bodies such as NBR, metal elastic bodies such as stainless steel,
Synthetic resin elastomers such as polyethylene terephthalate can also be used.

Note that in this specification, when the elastic blade is in contact with the sleeve, it means that when there is no developer, the blade is in direct contact with the sleeve, and when there is developer, it presses a thin layer of developer onto the sleeve. Needless to say, it is elastically urged toward the sleeve.

〔effect〕

According to the present invention, sleeve ghosts are prevented and image density is maintained at a good level.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an elastic blade coating developer used in an embodiment of the present invention. FIG. 2 is a diagram showing a conventional magnetic blade coating developer. FIG. 3 is a diagram for explaining an image of a sleeve ghost. 1 is a toner hopper 2 is a developer 3 is a magnet 4 is a non-magnetic developing sleeve 5 is an elastic blade 6 is a photosensitive drum.

Claims (2)

[Claims] (1) A one-component developer in which a second substance with the opposite polarity to the toner or a third substance with the same polarity as the toner and lower or equivalent charging characteristics than the toner is externally added, mixed and dispersed. A developing method comprising: forming a thin layer on a developing sleeve using an elastic member that contacts a developer carrying member with elastic force, and then conveying it to a developing area to visualize an electrostatic latent image. (2) The one-component developer is a dry one-component negative polarity magnetic toner to which positive polarity silica or silica with negative polarity and charging characteristics lower than or equivalent to that of the toner is externally added, mixed and dispersed. The developing method according to claim 1, characterized in that a negative polarity magnetic developer is used.