JPH0332787B2 - - Google Patents

Description

[Brief Description of the Drawings] Figure 1 is a schematic cross-sectional view showing the appearance of spikes of developer on the developing sleeve when the developing device is stopped;
FIG. 2 is a schematic cross-sectional view showing the appearance of spikes of developer on the developing sleeve when the developing device is operating;
Fig. 3 is an enlarged sectional view of the developing layer in Fig. 2, Fig. 4 is a characteristic diagram showing changes in copy density depending on the contact between the latent image surface of the photoreceptor and the developing layer, and Fig. 5 is the spike height of the developing layer. Fig. 6 is a characteristic diagram showing changes in the regulating blade gap and the height of the developing layer due to changes in the rotation ratio and rotation direction of the developing sleeve and magnet roll as well as the material of the regulating blade. FIG. 7 is a characteristic diagram showing an example of a comparison of the amount of carrier adhesion in a copy image obtained by the conventional method and the method of the present invention.

1... Magnet roll, 2... Developing sleeve, 3
...Magnetic developer, 6...Regulation blade.

[Brief explanation of the drawing]

The present invention relates to a dry developing method applicable to electrophotographic copying machines and the like. Conventionally, as a method of developing an electrostatic latent image on the surface of a photoreceptor using a magnetic developer, for example, as described in Japanese Patent Application Laid-Open No. 17881/1981,
A fixed magnetic pole is arranged inside a rotatable non-magnetic developing sleeve, and the electrostatic potential formed on the photoreceptor is generated by a magnetic brush that is formed by rotating the developing sleeve and transporting the developer. A rotary sleeve type for developing an image is known. Alternatively, as described in Japanese Patent Application Laid-Open No. 52-67336, a developing sleeve made of a non-magnetic material is fixed and a magnet roll placed inside the developing sleeve is rotated to develop a latent image. The formula is also known. Furthermore, as described in JP-A-54-116233 and JP-A-54-119935, a developing method has recently been proposed in which the developing sleeve and magnet roll are rotated in the same direction. has been done. However, these three methods each have the following problems. For example, the sleeve rotation type or magnet rotation type has the disadvantage that it is difficult to obtain a uniform image. In addition, since the developer used in these devices is fine, the powder has poor fluidity and is sensitive to humidity, pressure, and foreign substances such as paper dust, making it difficult to convey the developer uniformly on the developing sleeve. This makes it difficult to obtain a uniform image. In addition, the above-mentioned sleeve rotation type and magnet roll rotation type have problems such as difficulty in increasing the development density, easy occurrence of edge effects, difficulty in removing fog, poor clarity, and inability to apply to high-speed development. ing. In this regard, the recently proposed method of rotating the developing sleeve and the magnet roll in the same direction can solve the above-mentioned problem. In other words, it can be said that the present invention has been significantly improved in terms of uniform developer transport and stable images. However, the drawback of the method of rotating the developing sleeve and magnet roll in the same direction is the gap between the developing sleeve and the regulating blade for regulating the height of the spikes of the developing layer formed on the surface of the developing sleeve (blade gap). However, the gap between the developing sleeve and the photoreceptor (developing gap) is very delicately balanced, and the blade gap itself is also very small. This is a very big practical problem. In other words, in order to achieve the accuracy of the blade gap and developing gap, it is necessary to not only improve the accuracy of the photoreceptor, developing sleeve, and doctor blade, but also the accuracy and installation accuracy of the various parts to which these parts are attached. be. Here, the concept of optimal values for the blade gap and development gap will be explained. FIG. 1 is a conceptual diagram showing a state in which magnetic developer 3 stands up when attached to a rotatable developing sleeve 2 containing a rotatable magnet roll 1. As shown in FIG. When the developing sleeve 2 and magnet roll 1 are stationary, as shown in FIG.
The developer above the magnetic poles forms a high spike as shown by a, and between the magnetic poles the developer forms a low spike as shown by b. Figure 2 is a conceptual diagram when the developing sleeve and magnet roll of the developing device shown in Figure 1 are rotated, and Figure 3 is an enlarged cross-sectional view of the developing layer in Figure 2 when observed with a microscope from the direction c. It is a diagram. As shown in Figure 3,
When the developing sleeve 2 and magnet roll 1 rotate, they are made up of two layers: a developing layer 4 with a high developer density on the side near the developing sleeve 2 and a developing layer 5 with a low density on the side close to the surface of the developing layer. There is. Note that d ₃ and d ₄ in FIG. 3 are the heights of the developing layers 4 and 5 from the developing sleeve, respectively. The curve in FIG. 4 shows the change in copy density when the gap between the surface of the photoreceptor and the developing sleeve (developing gap) is changed. d ₃ and d ₄ on the horizontal axis in FIG. 4 are lengths corresponding to d ₃ and d ₄ in FIG. 3. That is, when the development gap reaches the height of the spikes _d3 , the developer and the electrostatic latent image begin to come into contact with each other, and development begins. The development gap is d ₄ .
Between d _{and 3} , the smaller the gap, the higher the density of the copy. The maximum density can be obtained when the development gap is around _d4 , but if it becomes too small, the density will decrease. This is because if the photoreceptor penetrates into the developing layer 4, which has a high density, the developer transported by the developing device will not be able to pass through the developing gap, resulting in the formation of a developing puddle or worse. In this case, excessive pressure is applied to the developer between the development gaps, making it impossible to perform normal development. That is, in this type of development method, the optimum values of the blade gap and the development gap are destined to be limited to a very narrow range on the _d4 side. Next, considering the relationship between the regulating blade gap and the height of the spikes of the developing layer, this depends on the material of the regulating blade, the rotation of the developing sleeve and magnet roll, and the rotation direction of the developing sleeve and magnet roll. dependent. In practice, a characteristic required of the regulation blade gap is that the blade gap can be set large for a constant developing gap. If the blade gap is small, developer clogging is likely to occur between the regulating blade and the developing sleeve, which poses a serious problem in practice. The present invention further improves the drawbacks of the above-mentioned developing method in which the developing sleeve and the magnet roll are rotated in the same direction. When developing an electrostatic latent image formed on a photoreceptor such as a photoreceptor drum by a magnetic brush formed by the developer, which is attached to the surface of a non-magnetic developing sleeve by magnetic force. , the direction of rotation of the magnet roll and the direction of rotation of the developing sleeve are made different, and the gap between the developing sleeve and the regulating blade that regulates the height of the developing layer on the developing sleeve is set as d ₁ , and the developing sleeve and the photosensitive The gist of this is to set d ₁ ≧ d ₂ when the gap with the body is d ₂ . The present invention has the following advantages as compared to conventional methods, particularly a developing method in which a developing sleeve and a magnet roll are rotated in the same direction. That is, the first feature of the present invention is that compared to the conventional method,
The balance range between the regulating blade gap and the developing gap is wide. As mentioned above, the optimum image is obtained when the latent image on the photosensitive drum is positioned within a very limited range near the boundary between the developing layers 4 and 5 in FIG. The curves in FIG. 4 and the curves already described show a comparison between the conventional method and the present invention. As is clear from FIG. 4, in the conventional method, the range of the developing gap is limited to d ₄ or slightly smaller as shown by l ₁ in FIG. 4, but compared to that in the present invention. Fourth
Since the density is high in the range from d ₃ to _{d 4} on the horizontal axis in the figure, the setting range of the development gap becomes wide as shown by l ₂ in FIG. 4. This reason is based on the difference in developer transport speed between the conventional method and the method of the present invention. The conveying speed of the developer due to the rotation of the developing sleeve and the magnet roll can be approximately determined by the following equation. The conveyance speed by the developing sleeve, Vs, is: Vs=πD/πD−hP・NsπD/60…(1) The conveyance speed, Vm by the magnet roll, is: Vm=hP/πD−hP・Nm・πD/60…( 2) Here, D: Outer diameter of the developing sleeve [cm] h: Height of developer spikes [cm] P: Number of magnetic poles of the magnet roll Ns, Nm: Number of rotations of the sleeve and magnet roll [rpm] Since Vs and Vm are in opposite directions, the conveyance speed of the developer in the conventional method is Vtotal=Vs−Vm (3). In the method of the present invention, Vs and Vm are in the same direction, so Vtotal=Vs+Vm (4). As an example, D=3cm, h=0.05cm, P=8,
Calculating with Ns=100rpm, Nm=1000rpm,
In the conventional method, the conveying speed is 15.7 cm/sec, whereas in the present invention, the conveying speed is 38.9 cm/sec. Also, as an example, D=3cm, h=0.05cm, P=8,
When Ns = 50 rpm and Nm = 1000 rpm, the conventional method has a speed of 2.1 cm/sec, while the present invention has a speed of 25.3 cm/sec.
cm/sec, and it can be seen that in any case, the developer transport speed according to the present invention is very advantageous compared to the conventional method. A second feature of the present invention is that it is possible to increase the processing speed of photoreceptors compared to conventional methods. Generally, in the magnetic brush development method, the faster the developer transport speed, the higher the image density. 1st
As explained in the feature section, the developer transport speed of the present invention is faster than that of the conventional method.
It is clear that this is a developing method that can be applied at high speed. The third feature of the present invention is that when the developing gap is constant, the gap of the regulating blade for regulating the spike height of the developing layer can be made larger than in any conventional method. be. When the development gap is kept constant, it is necessary to adjust the regulating blade to optimize the contact between the development layer and the photoreceptor. If you want clear development that is faithful to the original without edge effects, the development gap must be 0.5 mm or less. In the conventional method, the development gap is 0.4 to 0.5.
mm, the blade gap must be set between 0.20 and 0.25 mm. In the initial state when the developer is fresh, it is possible to obtain a good image with the above setting conditions, but after making many copies, paper dust, foreign matter, and blocking substances in the developer may be mixed into the developer. Therefore, with a blade gap of 0.20 to 0.25 mm, there was a problem in that the developer could become clogged due to coarse foreign matter mixed in between the blade and the sleeve. First, the relationship between the regulation blade gap and the height of the spikes of the developing layer will be explained. FIG. 5 is a schematic diagram of the apparatus used in the experiment. In the figure, when a developer is placed on the surface of the developing sleeve 2, and the rotational speed and direction of the developing sleeve 2 and the magnet roll 1, and the blade gap _d1 between the regulating blade 6 and the developing sleeve 2 are changed, the developing position is changed. The height of the spikes of the high-density development layer 4 and the low-density development layer 5 formed on point e was measured. In this case, the spike height of the developed layer was measured using a graduated microscope 8 under illumination from a lamp 7 shown in FIG. The measurement results are shown in FIG. In FIG. 6, the horizontal axis represents the ratio of the rotational speeds of the magnet roll and the developing sleeve, and the vertical axis represents the height of the spikes of the developing layers 4 and 5 with reference to the blade gap _d1 . As is clear from FIG. 6, the spike height is determined by the rotation ratio of the magnet roll and the developing sleeve. The solid line in FIG. 6 is the measurement result when a blade made of non-magnetic material is used, and the dotted line is the measurement result when a blade made of ferromagnetic material is used. Here, the spike height of the developing layer 4 in the conventional method is defined as a line.
With A ₁ and A ₂ , the height of the spikes of the developing layer 5 is also set as a line.
It is represented by B ₁ and B ₂ . On the other hand, the height of the spikes of the developing layer 4 in the present invention is represented by lines C ₁ and C ₂ , and the height of the spikes of the development layer 5 is represented by lines D ₁ and D ₂ . As is clear from FIG. 6, the change in the spike height depending on the rotation ratio shows completely different changes depending on the mutual rotation direction of the magnet roll and the developing sleeve. In the conventional example, the height of the spike is larger than the blade gap, and as the rotation ratio increases, the height of the spike becomes even larger. In contrast, in the method of the present invention, the spike height shows a decrease as the rotation ratio increases. From this, as explained in Fig. 4, when the blade gap is set to d ₁ , the 6th
The appropriate gap can be inferred from the line showing the change in the developing layer 4 in the figure. This is because a suitable gap exists near the boundary between the developing layers 4 and 5. If we were to specifically express this relationship numerically, the rotation ratio of the magnet roll and developing sleeve would be:
20, the appropriate development gap when the blade gap d ₁ = 0.5 mm is, as shown in Fig. 6, for the non-magnetic blade according to the conventional method, the f point ~ 1.0 mm, and for the magnetic blade, the g point ~ 0.7 mm. According to the present invention, in the case of a non-magnetic blade, the h point is ~0.5 mm, and in the case of a magnetic blade, the i point is 0.3 mm. That is, from the opposite perspective, it can be seen that when the developing gap is constant, this developing method can maximize the gap of the regulating blade compared to any conventional method. Especially JP-A-53
If used in combination with the ferromagnetic regulation blade described in Japanese Patent No. 125844, even more remarkable effects can be obtained. A fourth feature of the present invention is that the developed copy image is very good. One of the reasons for this is that, as mentioned above, in the present invention, the developer transport speed is high and sufficient development is performed, and the developer transport direction is only one direction, so the regulating blade stabilizes the developer. The reason for this is that the thickness of the developing layer at the developing point is always constant. On the other hand, in the conventional method, the developer transport speed is slow and the developer is transported in both directions, so it can be made constant using only the regulating blade. The thickness of the developed layer at the development point is unstable. The advantages of this method compared to the conventional method in terms of image quality are less fog, a smaller gamma value, better halftone reproducibility, better edge sharpness on the four sides of the solid image, and less carrier adhesion. There are few things. Carrier adhesion is a development in which carrier adheres to a portion of the electrostatic latent image on the photoreceptor where the potential contrast is strong at the boundary between the image portion and the non-image portion, and the quality of the copied image is significantly impaired. In the case of ordinary two-component developer carriers, the particles are large and, like iron powder, they have a high density and are easily magnetized.
There was almost no problem except when the toner density was extremely low. However, in 1973,
33152, JP-A-53-33633, JP-A-57-10150
In systems using carriers with small particle diameters, such as those described in the publications of the above issues, in conventional development methods, images were often damaged by carrier adhesion, but the present invention This problem has now been completely resolved. For example, FIG. 7 shows an example of a comparison of the amount of carrier adhesion in copy images obtained by the conventional method and the method of the present invention. The vertical axis represents the number of carrier particles deposited in a given image, and the horizontal axis represents the DC development bias value. As shown in FIG. 7, the carrier adhesion amount largely depends on the developing bias. At low bias carrier adhesion is not a problem. However, it is difficult to remove fog at a low bias due to the residual potential of the photoreceptor. Since this fog is caused by the optical characteristics of the photoreceptor, the fog cannot be completely removed even if the exposure amount is large. In order to completely remove fog, it is necessary to apply a developing bias of at least 100 to 150 V. Curve E in FIG. 7 is the amount of carrier deposited in the image obtained by the conventional method, and curve F is the amount of carrier deposited in the image obtained by the method of the present invention. In the conventional method, a bias of 80 V is the limit, and fog is sensitive to variations in the residual potential of the photosensitive drum and optical fatigue of the photosensitive drum, making it difficult to obtain stable images without fog. In addition, in the conventional method, it was necessary to set a higher exposure to remove fog, which had the disadvantage that fine lines tended to jump out, but in the method of the present invention, the curve F in Fig. 7
As shown in Figure 2, it is possible to apply a bias of 170 to 180 V, and it has become possible to stably obtain images with good clarity of fine lines and no fog. A fifth feature of the present invention is that there is little scattering of developer from the developing device. In the conventional method, the flow of the two developer layers trying to move in opposite directions on the sleeve caused a lot of developer scattering from the developing device, but in the present invention, the developer is transported only in one direction. Therefore, there is less developer scattering from the developing device. As is clear from the above description, the present invention has many excellent features, and can bring about great effects especially when applied to an electrostatic transfer type electrophotographic copying machine. It is conceivable that rotating the magnet roll and the developing sleeve in opposite directions would generate resistance and generate heat due to eddy currents in the developing sleeve, which cannot be ignored. However, after conducting experiments, we were able to confirm that there were no problems during long-term copying experiments. On the other hand, if the developing sleeve and magnet roll were rotated in the same direction, it could be considered unnatural to have the developer flow on the developing sleeve in the forward or reverse direction. . In the present invention, it goes without saying that good development can be carried out whether the developer is transported in the forward direction or the photoreceptor is rotated in the opposite direction.

Claims (1)

[Scope of Claims] 1. A developer having a magnetic component is attached by magnetic force to the surface of a rotatable non-magnetic developing sleeve containing a rotatable magnet roll,
When developing the electrostatic latent image formed on the photoreceptor by the magnetic brush formed by the developer, the direction of rotation of the magnet roll and the direction of rotation of the developing sleeve are made different; The gap between the developing sleeve and a regulating blade made of a magnetic material provided near the developing sleeve to regulate the height of the spikes of the developing layer on the developing sleeve is _d1 , and the gap between the developing sleeve and the photoreceptor is d. ₂ , d ₁
≧ _d2 , and the rotation ratio of the magnet roll and the developing sleeve is set so that the height of spikes of the developing layer having a large developer density is approximately _d2 . Method. 2. The developing method according to claim 1, wherein a developer comprising a carrier and a toner is used as the developer having a magnetic component.