JPH01101572A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To stably obtain a clear printing quality free from fogging by arranging a toner recovering device between a developing part and a transfer part and removing a part of developed toner. CONSTITUTION:The toner recovering device for removing a part of developed toner is arranged between the developing part and the transfer part. When the developed toner is reached to the toner recovering part, toner having unsuitable charge out of toner stuck to the surface of a carrier is electrostatically transferred to the surface of a toner transfer roll 13, and then the developed toner is reached to the transfer part, transferred to a transfer sheet and then fixed to obtain a hard copy. Since toner having unsuitable charge out of the developed toner is electrostatically removed prior to transfer, a clear image free from dust around character parts or fogging can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrophotographic method, in particular, developing an electrostatic latent image by a magnetic brush method, then transferring it to a transfer member such as plain paper, and then fixing it. Regarding the electrophotographic process of obtaining copies.

[Prior Art] An electrophotographic method involves forming an electrostatic latent image on the photoconductive surface of a photoreceptor, developing this electrostatic latent image to obtain a toner image, and directly fixing this toner image or forming a toner image. is transferred onto a transfer member and then fixed to obtain a copy. When developing electrostatic latent images, a magnetic brush development method is usually used. The developer used in the magnetic brush development method is a two-component developer which is a mixed powder of a conventional non-magnetic toner and a carrier such as iron powder or ferrite. In the magnetic brush development method using this two-component developer, carrier and toner are mixed at a predetermined ratio, both are triboelectrically charged, the toner is charged to a predetermined magnetic property, and only the toner is transferred onto the electrostatic latent image carrier surface. It is something that is attached.

In addition, one-component magnetic toner containing magnetic powder and resin as main components is also used in similar processes.

In order to make these toners adhere to the electrostatic latent image carrier surface and obtain a good image, the key is how faithfully the toners are made to adhere to this latent image.

In other words, in a regular development process such as in a copier, it is necessary to apply toner only to the latent image area, and in a reversal development process such as a printer, it is necessary to apply toner only to the non-latent image area, but in reality, it is necessary to apply toner to areas other than these areas. Since the toner also adheres to the paper, it causes deterioration in print quality such as deterioration of sharpness and background fog in actual copies.

These are greatly affected by development conditions, developer material, and environmental conditions, and lead to the lifespan of the developer, and are the items that machine manufacturers have the most difficulty with.

[Object of the Invention] An object of the present invention is to provide an electrophotographic process that eliminates the above-mentioned drawbacks of the prior art, and in particular can stably obtain clear print quality without background fog.

[Means for Solving the Problems] The present invention forms an electrostatic latent image on the surface of a material layer, develops a charged portion or an uncharged portion of the electrostatic latent image with a toner that is a colored resin fine powder, and In an electrophotographic process in which the developed toner is then transferred to a transfer member and then fixed, a toner collection device is provided between the development section and the transfer section for removing a part of the developed toner. It is an electrophotographic process.

In order to obtain copies with excellent print coverage, it is necessary to faithfully adhere toner to the electrostatic latent image area during regular development and to the non-electrostatic latent image area during reversal development.

To achieve this, in the case of a two-component developer consisting of carrier and toner, it is necessary to balance the electrostatic attraction force of the toner to the (non-)electrostatic latent image area and the electrostatic attraction force between the toner and the carrier. If this collapses, toner may adhere to the peripheral areas of characters and background areas, and these toners may be simultaneously transferred to the transfer member during transfer, resulting in image defects, or conversely, sufficient toner may not be developed, resulting in insufficient image density. It happens.

The former is usually the problem, and in order to minimize toner adhesion that causes these image defects, development conditions such as latent image potential, developer transport speed, and gap between the latent image area and toner transport area are adjusted. In addition to optimization, materials are also selected from the developer site to optimize toner particle size, charge amount, etc.

However, these conditions are not always constant and change over time, and also vary greatly depending on the environmental conditions (
It is possible to attach and develop toner only on the non-electrostatic latent image area.
It becomes very difficult.

The cause of this is particularly related to a change in the amount of electric charge (charge amount) possessed by the toner. That is, toner is an aggregate of fine particles, and when paying attention to the individual particles, they include particles ranging from small to large charges. -Generally, when the toner has a small electric charge, the electrostatic attraction force of the carrier is weak, and the toner is attracted by a slight electrostatic latent image attraction force, which causes the toner to adhere to the background area or around the literary area. Become. Therefore, the development balance is selected so that these problematic adhesion phenomena do not occur even with the least charged toner, but usually cannot be made completely zero.

Furthermore, environmental conditions 1.・Toner charge amount is greatly affected by humidity in particular. In other words, in high humidity, toner charge decreases, and in some cases, toner with opposite polarity is generated.
Significantly reduces print quality.

Also, the so-called spent phenomenon, in which toner adheres to the carrier surface, causes similar problems. The main purpose of the carrier is to transport the toner stably and to give it an appropriate charge. This amount of charge is determined by the triboelectric series (performance) between the carrier and the toner, and the greater the difference, the greater the amount of charge on the toner. Therefore, when toner adheres to the surface of the carrier, it mixes and rubs together the toners, which naturally reduces the amount of charge the toner has, causing the same phenomenon as mentioned above to occur, which reduces print quality. lower.

On the other hand, a similar problem occurs with single-component toners that do not use carriers. In recent years, there has been an increase in the number of charged type component toners in which charge control is added to the toner and the toner is previously charged to a positive or negative polarity. The members that give charge to the toner are, instead of the carrier, the toner particles, a doctor blade member, a developing unit part such as a developing sleeve, and frictional charges are generated by contact and rubbing with these members.

In order to obtain clear images without background fog, it is necessary to have a stable toner charge, but as with two-component toners, toners with weak chargeability or with opposite polarity may be generated depending on environmental conditions.

As mentioned above, for both two-component toner and one-component toner, it is necessary to attach the toner only to a predetermined portion of the electrostatic latent image during development, but it is impossible to completely create these development conditions. .

During transfer, this developed toner is transferred almost unchanged to a transfer medium such as plain paper, resulting in background fog and poor resolution.

These electrostatic latent images in the image area and non-image area are made to adhere only to predetermined locations by balancing the charge of the toner, but in reality, the amount of charge on each toner particle is not constant; This includes things that are weak, strong, or have opposite charges.

In regular development, it is necessary to attach toner only to the electrostatic latent image portion, and if the latent image polarity is positive, negatively charged toner contributes to development. Although the potential of the latent image in the non-image area is almost zero, a bias voltage is usually applied to the developer conveying member so that the electrostatic attraction force with the toner is at its lowest.
If the toner contains positively charged toner, the toner will adhere to areas where the latent image potential is close to zero, causing background fog. Furthermore, even if the toner has a negative charge, if the value is too large, the toner will adhere to areas where the latent image potential is close to zero.

Furthermore, even if the latent image potential polarity is positive, negative polarity may appear in a part of the periphery of the pattern.

Weakly charged or reversely (positively) charged toner is less likely to adhere to such areas, resulting in a decrease in sharpness.

Therefore, the toners that cause these image defects are charged toners that are deviated from the appropriate charge amount, that is, toners with too large charges, those with too small charges, and those charged with opposite polarity.

For this reason, attempts have been made to develop a toner with a toner charge amount distribution as sharp as possible, but it is currently extremely difficult.

Therefore, the present invention electrostatically removes only the toner with unsuitable charges that was developed in a place other than the target area during development, and transfers only the appropriate toner onto the transfer paper, resulting in a good image with no background fog. It is used to obtain images.

This can be achieved by, for example, bringing an electrostatic transfer roller to which a bias voltage is applied into contact with or close to the latent image carrier between the developing section and the transfer section, and rotating the latent image carrier at approximately the same speed. This is accomplished by removing only the appropriate toner.

[Example] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing an example of a printing device for carrying out the present invention.

This apparatus is equipped with an electrostatic latent image carrier (hereinafter simply referred to as carrier) l, which is, for example, a conductive substrate on which a photoconductive layer is formed. A charger for uniformly charging the surface of the carrier 1 and a charger for irradiating a light image onto the surface of the carrier 1 to form an electrostatic latent image are disposed around the carrier 1 in the direction of rotation shown by the arrow. (none of which are shown), a developing device 2 for visualizing the electrostatic latent image, a toner collecting device 12, a transfer device 17 for transferring the developed toner onto plain paper, etc. is located.

The developing device 2 includes a developer tank 3 and a magnet roll 4 provided therein. Magnet roll 4 is
For example, it includes a non-magnetic sleeve 5 for conveying a developer 11 made of toner and carrier to a development area, and a permanent magnet 6 having a plurality of magnetic poles. 6 is fixed. The thickness of the developer 11 on the non-magnetic sleeve 5 is regulated by the doctor member 7. Inside the developer tank 3, there is further a toner tank 8 having a toner replenishment roller 9 at the bottom, and the developer scraped off from the non-magnetic sleeve 5 after development and the replenishment roller 9.
An agitator 10 is provided for mixing the toner with the toner falling from the toner.

The toner recovery device 12 includes a toner transfer roller 13 that is close to or in contact with the carrier 1 and rotates at approximately the same speed as the carrier 1.
a bias voltage source 14 for applying a bias voltage to the toner transfer roller 13; and a bias voltage source 14 for applying a bias voltage to the toner transfer roller 13.
The toner removing scraper 15 is provided in contact with the toner collecting container 16.

The operation of the above device is as follows.

When the electrostatic latent image (not shown) formed on the carrier 1 reaches the development area, the surface of the carrier 1 is rubbed by the magnetic brush formed on the non-magnetic sleeve 5, and the electrostatic latent image is is developed. Next, when the developed toner reaches the toner collection section,
Among the toners adhering to the surface of the carrier, toners with inappropriate charges are electrostatically transferred to the surface of the toner transfer roller 13. Thereafter, the developed toner reaches a transfer section, is transferred onto a transfer sheet, and is then fixed to obtain a hard copy.

In this way, in the present invention, toner having an inappropriate charge among the developed toner is electrostatically removed before transfer, so a clear image without dust or background fog around the literature section can be obtained. .

[Specific example] Commercially available electrophotographic copying machine (Konishi Rokuo-B 1X3000
) was slightly modified, and the developing section and transfer section had a diameter of 20 mm.
A conductive rubber roller was set at a position almost in contact with the photoreceptor drum. Further, a stainless steel scraper was installed on the rubber roller to remove the toner transferred from the photoreceptor.

The surface potential of the photoreceptor was set to 750 V, and the developer was a mixture of ferrite carrier (KBN100 manufactured by Hitachi Metals) and a prototype toner (styrene-acrylic copolymer type negatively charged type) so that the toner concentration was 4.5% by weight. Printing was performed using almost the original settings.

In this case, even when the transfer roller according to the present invention was not installed, a very good image with an image density of 1.35 was initially obtained, but when the image was observed in detail with a microscope, it was found that the image density was 1.35.
am”, 3゛0 to 50 layers of toner with white background (background fogging toner) were observed, and there was also l O around the text area.
Adhesion of toner was observed over a width of about OPM.

Therefore, next, a conductive rubber roller was installed, a DC voltage of minus 509 V was applied to the shaft portion, and the rubber roller was rotated at the same speed as the copying process speed.

A similar image evaluation showed that the image density was 1.33, the number of background fogging toner per 1-2 was less than 5, and the scattered toner width around the literature section was about 20 to 30 microns, which was a very clear image. was gotten.

[Effects of the Invention] As described above, according to the present invention, the toner developed in areas other than the predetermined areas on the electrostatic latent image, which conventionally caused image defects, is electrostatically removed before transfer. , a good image can be obtained by selectively removing them.

Further, in the present invention, a conductive rubber roller is used as the toner removal roller, but it is clear that a dielectric roller having a similar function can also provide the same effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an example of a printing device for carrying out the present invention. 1: Electrostatic latent image carrier, 2 Developing device, 3: Developer tank, 4
: Magnet roll, 11: Developer (toner), 13:
toner transfer roller, 15: toner removal scraper,
7: Transfer device.

Claims (3)

[Claims] (1) An electrostatic latent image was formed on the surface of the material layer, charged or non-charged areas of the electrostatic latent image were developed with toner, which is a colored resin fine powder, and then the developed toner was transferred to a transfer member. An electrophotographic method in which a toner is then fixed, the method comprising: providing a toner collection device between a developing section and a transfer section to remove a portion of the developed toner. (2) The electrophotographic method according to claim 1, wherein the toner recovery device includes an electrostatic transfer roller to which a bias voltage is applied and which moves at substantially the same speed as the surface of the material layer. (3) The electrophotographic method according to claim 2, wherein the electrostatic transfer roller mainly removes toner that is undesirable in the image from among the developed toner.