JP2697832B2 - Image density control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrophotographic toner, and more particularly to an image density control method using an electrophotographic toner suitable for controlling image density. The present invention can also be used as an infrared marker for determining the authenticity of printed matter such as securities.

2. Description of the Related Art In an electrophotographic apparatus or an electrostatic printing apparatus, an electrostatic latent image formed on a carrier by a predetermined method is supplied with charged colored particles called toner from a developing apparatus and is developed and copied. The toner in the developing device is usually agitated, and when the toner is mixed with the carrier particles, or when the toner is mixed with the carrier particles, a difference in the composition ratio (toner concentration) between the toner and the carrier particles causes a difference in the toner. The amount of frictional charge changes during continuous copying, and the amount of frictional charge of the toner is also affected by environmental temperature and humidity. If the charge amount of the toner deviates from the standard, the density of the copied image becomes lighter or darker. Therefore, it is necessary to make the image density constant, and as a method of controlling the image density, a method of photoelectrically detecting the developed image density on the latent image carrier and feeding back the detection result to a factor system for control is used. .

In this image density control method, there is an example in which light having a wavelength in a visible region is used as detection light of a density sensor to be used. In this case, photoreceptor light fatigue occurs and the photoreceptor irradiated with the detection light is used. Cannot obtain a desired potential, and a potential contrast with a non-irradiated portion occurs, resulting in an abnormal image such as a white streak in a black portion of an image and a black streak in a non-image portion.
Therefore, a method using detection light having a near-infrared wavelength is advantageous and generally used to prevent photo-fatigue of the photoconductor as described above. In an apparatus for detecting image density using near-infrared wavelength light as detection light, when a black toner image containing a black colorant such as carbon black is irradiated with near-infrared wavelength light, the toner emits the near-infrared wavelength light. Since it absorbs relatively well, its density can be accurately detected. However, as shown in FIG. 1, the conventional color toner does not absorb light in the near infrared region, so that it does not absorb the latent image carrier. The difference in reflectance was so small that the image density (toner attachment amount) could not be detected accurately. As a result, the image density could not be accurately controlled.

[Purpose] An object of the present invention is to provide a highly accurate image density control method that overcomes the conventional disadvantages.

[Constitution] The present inventor has conducted intensive studies to achieve the above object. As a result, the image density control method of the present invention forms an electrostatic latent image on a latent image carrier, and converts the electrostatic latent image to 400 to 700 nm. Has no substantial absorption in the visible light region, and is developed with an electrophotographic toner containing a substance having a clear spectral absorption peak in a wavelength region of 700 nm or more to obtain a reference density pattern. In an image density control method in which the density is photoelectrically detected and the image density is controlled in accordance with the detection result,
It has a wavelength region of 0 nm or more, that is, has a clear spectral absorption peak in near-infrared light, and is characterized in that the density of the reference density pattern is detected by near-infrared light.

 That is, the feature of the present invention has the following configuration.

(I) A compound having substantially no light absorption in the visible wavelength region of 400 nm to 700 nm and having a light absorption peak in a long wavelength region of 700 nm or more is added to the toner, and the toner itself has a wavelength of 700 to 1,000 nm.
To absorb light.

(Ii) Develop the reference electrostatic pattern with the above toner, 700n
The image density is detected with light having a wavelength of m or more, and a signal for controlling the image density is generated.

In the above (i), the compound contained in the toner must be 70
Although it may have only the physical property of having a light absorption peak in a long wavelength region of 0 nm or more, in the present invention, particularly when it is contained in a color toner for color copying, it has important and fine characteristics as a color toner. It is important to have a characteristic of having no absorption in the visible wavelength region of 400 to 700 nm so as not to change a certain color tone. As an example of a substance having such properties, a compound represented by the following structural formula can be given.

[Where X ⁺ represents a cation, and preferred cations include H ⁺ , NR ₄ ⁺ (R represents H or an alkyl group having 1 to 5 carbon atoms) and the like. These infrared-absorbing compounds are preferably contained in the toner in an amount of 0.
It is used in an amount of from 01 to 1% by weight.

The toner can be manufactured by a conventionally known method, and as a binder, a conventionally known styrene-acryl ester copolymer, polyester resin, epoxy resin, phenol resin, a modified product of these resins, or the like is used, and a desired color is imparted. Add known pigments, dyes, etc., which are colorants to be added, and further add a property modifier such as a polarity controlling agent, add a compound having the above properties, melt-knead, cool and pulverize to obtain a desired particle size. To obtain a toner. The toner thus produced preferably has a particle size of 5 to 25 μm.

Hereinafter, an example of the image density control method of the present invention will be described with reference to the accompanying drawings.

FIG. 2 schematically shows an example of an apparatus for carrying out the toner density control method according to the present invention. The photosensitive drum 11 rotates at a constant speed in the clockwise direction, and its surface is first uniformly charged by the corona charger 12. A platen glass that moves to the left on the charged photoconductor surface
An original 14 placed on 13 is projected through a stationary exposure system 15. The charge on the photoreceptor 11 is selectively discharged in accordance with the brightness of the projected document image, and an electrostatic latent image corresponding to the document image is formed there. This electrostatic latent image is visualized by supplying toner from the developing device 16. Developing device
In a container 16, a two-component developer 18 comprising the toner and iron powder carrier is contained in a container 17, and this developer is pumped up by the rotation of a developing sleeve 19 containing a magnet therein, and the static electricity on the photoconductor is removed. The latent image is developed by contact with the latent image. A bias voltage Vs is applied to the developing sleeve 19 to prevent background contamination. Since the toner in the developer is consumed by the development, new toner 21 is supplied from the toner tank 20 by the pumping roller 22 as appropriate. The developed image on the photoconductor is then transferred to a transfer paper, and the residual toner on the photoconductor is cleaned.

Next, an example of the toner density control method of the present invention will be described.

a) First, a latent image for the reference density pattern is formed on the photosensitive drum. This is formed by providing a black reference pattern 23 having a reflection density of about 1.0 in a non-image area at the leading end of the platen glass 13 and projecting it on a photoconductor before projecting the document 14.

b) The reference pattern latent image thus formed is developed by the developing device 16 under a constant bias voltage Vs.
A reference density pattern 24 is obtained on the photoreceptor.

c) Before the reference density pattern 24 passes through the sensor unit including the light emitting element 25 and the light receiving element 26, the relative reflectance of the non-image portion of the photosensitive drum 11, that is, the surface portion of the background on which the toner is not attached, The measurement is performed by irradiating the surface of the photoconductor with the light emitting element 25 and receiving the reflected light by the light receiving element 26. The intensity of the light incident on the light receiving element 26 is converted into the magnitude of a voltage, which is amplified by an amplifier 27, converted into a digital signal by an A / D converter 28, and further input to a computer 29, where it is input. It is held. Let this value be Vo.

d) Next, the computer 29 detects that the central portion of the reference density pattern 24 on the photoreceptor has come to the sensor portion, and instructs to measure the relative reflectance. Similarly,
The relative reflectance at the center of the reference pattern 24 is measured, and the digital signal is held in the computer 29. This value is defined as Vp.

e) The computer 29 obtains Vp corrected by Vs, that is, Vps, from two variables of the developing bias voltage Vs and the reference pattern reflection density value Vp. This can be replaced with the developing ability value X of the developer (which is proportional to the toner density), and is obtained, for example, as X = Vp−kVo (k: constant). The smaller the value of X, the higher the developing ability.

f) The computer 29 further calculates X ÷ Vo = Y,
The value of Y is compared with a specific reference value S. S is ROM 30
Set to.

g) When Y> S, a signal for instructing toner replenishment is issued from the computer 29, whereby the driver 31
Is operated, the toner supply solenoid 32 is operated, the toner pumping roller 22 rotates, and the toner 21 in the toner tank 20 is supplied into the developing container 17.

h) If V ≦ S, a signal to stop toner supply is issued from the computer 29, and the toner pumping roller 22
Rotation stops.

In the present invention, since the reference density pattern 24 is formed on the non-image portion of the photoconductor, it is not transferred to the transfer paper, but must be removed from the photoconductor for the next measurement. This not only places an extra burden on the photoreceptor cleaning device, but also accelerates the deterioration of the toner. Therefore, the toner concentration is not measured each time a normal document is copied. It is preferable to perform it periodically, about once every 5 to 10 times. To do so, an erase lamp 33 for erasing the latent image for the reference pattern is arranged between the exposure position and the development position for the photoconductor, and this is normally turned on. When the density is measured, it may be turned off so that the latent image for the reference pattern does not disappear.

The example of the image density detection and control system has been described above, but the present invention is not limited to this. In order to control the image density, it is general to control the toner density in the developer. In addition, the developing bias is controlled to control the potential (charge amount) of the electrostatic image by known means. You may.

Next, the present invention will be described more specifically with reference to the following examples, but it is needless to say that the present invention is not limited to these examples.

Example Polyester resin RN-110 (manufactured by Kao Corporation) 100 parts by weight Lionol Blue KL (copper phthalocyanine) (manufactured by Toyo Ink Co., Ltd.) 5 parts by weight Zinc ditertiary butylsalicylate 2 parts by weight bis (dithiobenzyl) nickel 0.05 parts by weight of ammonium complex salt (MIR-102 manufactured by Nippon Carlit Co., Ltd.) is melt-kneaded by a hot roll mill, cooled, pulverized to an average particle size of 7 μm by a jet mill, and classified by an air classifier to an average particle size of about 10 μm. The toner was used. This toner is converted to a ferrite carrier having a silicon resin coating layer with a particle size of 100 μm.
The mixture was mixed at a weight ratio of 3: 100 to obtain a two-component developer. The charge amount of the toner in this developer was -18 μc / g. An electrostatic latent image on an organic photoreceptor (OPC) having a constant potential was developed with this developer, and a toner was developed. FIG. 3 shows the spectral reflectance of the toner on the photosensitive member at that time. The amount of toner adhered to the photoreceptor is expressed as an output voltage of a photodiode obtained by irradiating an LED with a main wavelength of 950 nm and a half-value width of 30 nm, and the results are shown in FIG. Using the above developer with Ricoh copier FT
FIG. 5 shows the result of image density transition when the image data is stored in the 5510 and is continuously copied. (This copier has a main emission wavelength of 950 nm and a half width of 30 nm
Irradiates the photoreceptor with an LED, detects the image density with a photodiode, generates a toner replenishment signal, changes the toner density in the developer, and controls the image density).

Comparative Example 100 parts by weight of polyester resin RN-110 5 parts by weight of Lionol Blue KL 2 parts by weight of zinc ditertiary butylsalicylate 2 parts by weight A comparative toner was prepared in the same procedure as described above. The charge amount of the toner was -19 μc / g.
Hereinafter, the same experiment as in the above example was repeated using this comparative toner, and the obtained results are shown in FIGS.

From the results shown in FIG. 3, it can be seen that the reflectance of the toner of this example in the vicinity of the spectral wavelength region of 870 nm is significantly lower than that of the toner of the comparative example. As can be seen from the results in FIG. 4, the toner of the present embodiment has much sharper sensitivity of the output voltage of the light receiving element corresponding to the amount of adhered toner than the toner of the comparative example, and the detection accuracy is improved. . Further, from the results shown in FIG. 5, it can be seen that the toner of the present embodiment has a stable control of the image density even when the number of copies is increased as compared with the toner of the comparative example, and the control is stable.

[Effects] As described above, according to the present invention, the relationship between the image density and the output voltage of the light receiving element approaches the black toner, and a stable output can be obtained. As a result, the image density detection in the copying machine can be achieved. The ability was improved, and a stable copy image density was obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the spectral reflectance of each color toner on the organic photoreceptor. FIG. 2 is a schematic explanatory view of an apparatus for implementing the toner density control method of the present invention. FIG. 3 is a graph showing the spectral reflectance of the toner of this embodiment and the toner of the comparative example. FIG. 4 is a graph showing the relationship between the toner adhesion amount on the photosensitive member and the output voltage of the light receiving element. FIG. 5 is a graph showing the relationship between the copy image density and the number of copies. 11 photoconductor, 12 corona charger 14 original, 18 developer 19 developing sleeve 21 toner 22 pumping roller 23 standard pattern 24 standard density pattern 25 Light-emitting element 26 Light-receiving element 33 Standard pattern erase lamp

Claims (1)

(57) [Claims] An electrostatic latent image is formed on a latent image carrier, and said electrostatic latent image has no substantial absorption in a visible light region of 400 to 700 nm and is clearly defined in a wavelength region of 700 nm or more. Image density control for developing a reference density pattern by developing with an electrophotographic toner containing a substance having a spectral absorption peak, photoelectrically detecting the density of the reference density pattern, and controlling the image density according to the detection result An image density control method, wherein the density of the reference density pattern is detected by near-infrared light.