JPH03102035A - Paper sheet feeder - Google Patents

Abstract

PURPOSE:To prevent a sheet from being electrostatically charged without using a discharge brush when separating the sheet from other sheets stacked by specifying the volumetric resistance of a separating member for separating the one sheet from other sheets. CONSTITUTION:An idler roller 9 as a separating member is made of a material of a volumetric resistance of 10<10>OMEGA.cm or less, preferably below 10<7>OMEGA.cm or less. As a result, the paper sheet surface potential at the contacting portion of the idler roller 9 is not high, and black lines and white lines are not produced under low humidity environment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to paper feeding devices for printers, copying machines, and the like.

[Conventional technology]

FIG. 6 shows a conventionally used paper feeding device for printers, copying machines, etc.

Referring to the figure, 1 is a paper cassette, and sheets of paper 2 are stacked therein. The paper 2 is pushed up by a middle plate 3 with a spring 4 attached, and the uppermost paper 2a is set to abut against the separation claw 5. Next, to describe the operation during paper feeding, the paper feeding roller 6 rotates in the direction of the arrow in the figure, contacts the uppermost paper 2a, and the paper 2a is transported to the transport roller 7; Paper is transported. When the paper 2a is transported to the transport roller 7, the paper feed roller 6 is placed in a non-pressurized state with the paper 2a, so as shown in the figure, the paper feed roller 6 has a half-moon-shaped cross section. Generally, urethane rubber, chloroprene rubber, etc. with a hardness of 15 to 30 degrees and excellent abrasion resistance are used.

In this method, the corners of both ends of the paper are held by the separation claws, so when the paper feed roller 6 rotates, the topmost paper 2
Only a is separated and conveyed.

However, this method has the following drawbacks. That is, when putting the paper 2 into the paper cassette 1, the separating claw becomes an obstacle and makes it difficult to put the paper 2 into the paper cassette 1. Further, when the topmost paper comes off the separation claw 5 during paper feeding, the corners of the paper bounce and generate noise. This is particularly noticeable when using stiff cardboard. Furthermore, since the separation claw 5 alone is relied upon to prevent double feeding of paper, if a plurality of sheets of paper pass through the separation claw, double feeding will occur.

In order to solve this problem, Figures 7 (a), (b) and 8
Figure (a). There is a method shown in (b).

Figure 7(a). (b) shows a paper feeding device that has improved the above-mentioned problem. The paper feed roller 6 has a feeding surface 6b that contacts the paper and applies feeding force, and a non-feeding surface 6C that has a smaller diameter than the feeding surface 6b and does not contact the paper, and when not in operation, the non-feeding surface 6C The machine is configured so that the machine waits facing the paper.

The idler roller 9 is rotatably supported by a drive shaft 6a to which a paper feed roller 6 is fixed. The radius of the idler roller 9 is smaller than the radius of the feeding surface 6b of the paper feeding roller 6, and larger than the radius of the non-feeding surface 6C. Therefore, the idler roller 9 contacts the paper or the separation pad 8 only when the non-feeding surface 6c faces the paper.

The method is similar to that described above in that the paper 2 is transported by the paper feed roller 6 to the transport roller 7, but the separation pad 8 and the idler roller 9 prevent electric transport. To be more specific, the topmost paper 2a is fed and conveyed by the frictional force with the paper feed roller 6. The fed paper rubs against the separation pad 8, but the friction force with the separation pad 8 is stronger than the paper feed roller 6.
Since the frictional force between the paper 2a and the paper 2a is greater, the paper 2a passes through the separation pad 8.

However, in very rare cases, double feeding may occur when the paper is conveyed by the paper feed roller 6. In this case, the top paper 2a is subjected to frictional force with the paper feed roller 6 and frictional force with the paper 2a,
Since the frictional force with the paper feed roller 6 is greater, the second sheet of paper 2b is transported to the transport roller 7, but the frictional force between the paper 2a and the separation pad 8 acts, and the frictional force with the separation pad 8 acts on the second sheet 2b. Because it is large, it is not conveyed beyond separation pad 8.

With the paper 2a on the top surface being conveyed to the conveyance roller 7,
The paper feed roller 6 has a half-moon shape so as to be in a non-pressurized state. At this time, the idler roller 9, which has a slightly smaller diameter than the paper feed roller 6, becomes pressurized.

The uppermost paper 2a is continuously transported by the transport roller 7, but the second sheet 2b is pressed by the idler roller 9, which exerts a frictional force with the separation pad 8 to prevent double feeding.

Figure 8(a), Cb) shows a further improved paper feeding device.

Figure 7(a). In the method shown in (b), double feeding is prevented by using a separation pad 8, but in this example, a retard roller 1 that rotates in the opposite direction to the paper conveyance direction is used.
Using 0 prevents double feeding.

To explain in detail, the top paper 2a is fed by the paper feed roller 6.
The paper is fed by At this time, the frictional force between the paper 2a being fed and the paper feed roller 6 is
As a result, the paper 2a is transported to the transport roller 7.

Furthermore, similarly to the method described above, when feeding paper by the paper feed roller 6, there are cases where the topmost paper 2a and the second paper 2a are fed, but in this case, Although the paper 2a is subjected to the frictional force between the paper feed roller 6 and the paper 2b, the frictional force between the paper feed roller 6 and the paper 2b is greater, so that the paper 2a is transported to the transport roller 7. On the other hand, the paper 2b is subjected to a frictional force with the paper 2a and a frictional force with the retard roller IO, but since the frictional force with the retard roller 10 is large, the paper 2b stops at the position of the retard roller 10 and is not conveyed any further. In this way, double feeding is prevented, but in this paper feeding device,
Since the retard roller 10 that rotates in the opposite direction to the paper feeding direction is used, as shown in FIG. 9(a). Double feeding can be prevented even more reliably than the method using the separation pad 8 shown in (b).

[Problem that the invention is trying to solve] However,
In the above conventional example, when paper is fed, the friction between the paper feed roller, idler roller, separation pad, and retard roller causes the paper to become strongly charged, especially in a low humidity environment, resulting in the following problems. occurs.

FIG. 9 shows, as an example, an electrophotographic printer using the paper feeding device shown in FIG. 7.

To explain along the figure, the photosensitive drum 11 rotating in the direction of the arrow in the figure is uniformly charged to -700V by the charger l2. Next, image exposure is performed using light 13 from a light emitting element such as a laser or LED to form a latent image.

This latent image is reversely developed using a developing device RL14 containing negative toner to form a toner visible image.

This toner visible image is applied onto the paper fed from the paper feeding device described in FIG. 9, and a positive voltage is applied to the transfer charger 15.
The toner image is transferred and fixed by a fixing device l7.

In such an electrophotographic printer, especially in a low humidity environment, when feeding paper, the paper feed roller 6 and idler roller 9
, the separation pad 8 and the paper 2 are strongly charged by friction.

When the paper 2 is triboelectrically charged, when the paper is positively charged, the negative toner forming a visible toner image on the photosensitive drum 11 during transfer is attracted to the strongly positively charged portion of the paper. In particular, the idler roller 9 and separation pad 8 are subject to appropriate pressure to prevent double feeding of paper and are constantly in contact with the paper, so the above-mentioned phenomenon is likely to occur. When printed, the portion of the paper that comes into contact with the idler roller 9 appears as a black line B, as shown in FIG.

This is because originally, the toner visible image is transferred to the paper by the transfer electric field formed by the transfer charger 15 only in the part A in FIG. This is a phenomenon in which the toner of the toner visible image on the photosensitive drum 11 is transferred by the electric field generated by the charging of the paper itself before the part A that is drawn, and appears as a black streak B.

When the surface potential of the paper was measured with a surface potential meter made by Monroe Co., Ltd. after it was fed in a state where such black streaks B were generated, it was found that the contact area of the idler roller 9 where the black streaks occurred was +3KV or more (the measuring device over range), other parts are +50
It was 0V.

Furthermore, when an acrylic material that negatively charges paper was used for the idler roller 9, white streaks as shown in FIG. 1l occurred on the entire halftone printed image. This is because, contrary to the black streak phenomenon mentioned above, the part of the paper that comes into contact with the idler roller 9 is strongly negatively charged, so the negative toner on the photosensitive drum 1 is repelled and the transfer is not successful. Due to not being done. When the surface potential of the paper was measured in this state, the contact portion of the idler roller 9 showed a potential of -3 KV or less, and the other portions showed a potential of +500 V.

The case where a negative toner is used has been described above, but when a positive toner is used, white streaks occur if the paper is strongly positively charged, and black streaks occur if the paper is strongly negatively charged. In any case, when the absolute value of the surface potential of the paper exceeded 3 KV, black or white streaks appeared on the print. Similarly, the separation pad and paper feed roller have an absolute potential of 3K at the part where they contact the paper.
If it is more than V, black or white streaks will occur.

Conventionally, in order to solve this problem, there is a method of discharging the paper by installing a static eliminating brush made of conductive fibers made of stainless steel, carbon, etc. before the transfer process, but this method requires a new static eliminating brush to be installed. Is it necessary to use conductive fibers after using it for a long time? This has the disadvantage that it comes off and is conveyed adhering to the paper, causing leakage in the transfer charger 15.

[Means for solving problems]

An object of the present invention is to prevent the sheets from being charged when separating stacked sheets into one sheet and other sheets without using a static eliminating brush.

The configuration of the present invention for achieving the above object is such that the volume resistance of the separation member that comes into contact with the stacked sheets and separates the stacked sheets into one sheet and other sheets is 101.
This paper feeding device is characterized by having a resistance of 6Ω·cm or less.

〔Example〕

FIG. 1 shows an embodiment to which the present invention is applied. The paper feeding operation and image forming process are the same as those in the conventional example shown in FIG. 7, so their explanation will be omitted.

The feature of this embodiment is that the idler roller 9 serves as a separating member.
The reason is that a member having a volume resistivity of l■I@Ω●cm or less is used. When using negative toner, if the paper rubs against the paper feed roller, idler roller, separation pad, etc. and becomes positively charged,
As mentioned above, black streaks occur on prints, but we believe that this problem can be solved by reducing the volume resistance of each member to 10.
It has been found that the problem can be solved by reducing the resistance to 10Ω·cm or less.

Table 1 shows the surface potentials of paper and the idler roller 9 when the idler roller 9 was made of various materials.

Table 1 As is clear from Table 1, when acrylic is used for the idler roller 9, the surface potential of the paper at the idler roller contact portion is -3k. Potential higher than V, acrylic roller +3
The potential was higher than kV, and white streaks appeared on the print. On the other hand, when PTFE (polytetrafluoroethylene) is used for the idler roller 9, the surface potential of the paper at the roller contact area is +3 kV or more, and the PTFE roller is -3 kV.
The potential was higher than kV, and black streaks appeared on the print. On the other hand, when aluminum or brass is used for the idler roller 9, the potential of the paper at the idler roller contact area is -
The idler roller exhibited a potential of 500 kV and Ov, and neither white nor black streaks were generated on the print.

This is because when aluminum, brass, and paper are triboelectrically charged, the paper becomes negatively charged, but since the electric resistance of the rollers is low, the generated charge escapes through the rollers, which acts as a neutralizing effect, and the surface potential of the paper is -3kV. It is thought that the electric potential will not be higher than that, and white sushi will not occur. Therefore, we used polyacetal with carbon dispersed as the idler roller 9.
A similar experiment was conducted by changing the volume resistivity by changing the amount of carbon.

The experimental results are shown in Table 2.

Table 2 Boriacetal in which no carbon is dispersed has a volume resistivity of 10' Ω・cm, and the surface potential of the paper at the contact part of the idler roller with the paper is +3 kV or more, and the surface potential of the roller was -3 kV or more, and black streaks appeared on the print.

Next, when carbon is dispersed in 5 parts by weight, the volume resistance is 10'! Ω・cm, the surface potential of the paper at the contact part of the idler roller is +3kV or more, and the surface potential of the roller is -2k
It showed a potential of V, and black streaks were generated.

This means that the idler roller volume resistance is 1016Ω・cm,
This is thought to be because the static elimination effect does not occur at 10th Ω·cm.

Next, a material in which carbon is dispersed by weight in 1O has a volume resistivity of 1010 Ω・Cm, a surface potential of the paper in contact with the roller is +1 kV, and a surface potential of the roller exhibits a potential of -1 kV, which is slightly Although black streaks occurred, they were at a level that did not pose a problem in practical use.

Next, a material in which 15 parts by weight of carbon is dispersed has a volume resistivity of 10'Ω・am, a surface potential of the paper in contact with the idler roller is +700V, and a surface potential of the idler roller is -200V. , no black streaks occurred.

When 20 parts by weight of carbon is dispersed, the volume resistance is 1.
0'Ω・cm, 25 parts dispersed has a volume resistance of 1
In both cases, the surface potential of the paper in contact with the rollers was +500 V, the surface potential of the idler roller was Ov, and no black streaks were generated.

FIG. 2 is a graph showing the relationship between the volume resistance of the idler roller and the paper surface potential of the idler roller contact portion.

As you can see from the graph, the volume resistance is 10111Ω・
If it exceeds cm, the static elimination effect decreases and the surface potential of the paper increases rapidly, resulting in black streaks.

From the above, the volume resistance of idler roller 9 is 10I.
By setting the value to 0Ω・cm or less, preferably 10′Ω●Cm or less, the surface potential of the paper at the contact part of the idler roller 9 does not become high potential, and a low-humidity environment can be achieved without the need for special components such as static elimination brushes. It is now possible to prevent black and white streaks at the bottom.

Further, in this embodiment, the idler roller 9 is grounded, but in this case, the paper absorbs moisture in a high temperature environment, the resistance decreases, and the transfer current from the transfer charger 15 flows from the idler roller 9 to the ground through the paper. In some cases, a necessary transfer electric field is not generated and a so-called transfer failure occurs in which the toner image on the photosensitive drum l is not transferred.

In order to prevent this, it is recommended to insert a resistor of several + MΩ to several hundred MΩ in series between the idler roller 9 and the ground. Further, the bearing of the shaft supporting the idler roller may be constructed of a high-resistance molded member or the like, and the bearing may be grounded through this bearing.

[Other Examples]

FIG. 3 shows another embodiment of the invention. The paper feeding operation and the image forming process are the same as in the conventional example, so their explanation will be omitted. As mentioned above, by setting the volume resistance of the idler roller 9 to 10 IoΩ・cm or less, it is possible to prevent black streaks and white streaks on the print at the idler roller contact area. By setting the volume resistance of the separation pad 8 and the paper feed roller 6 as members to less than 10 Ω·cm, it is possible to prevent black streaks and white streaks on the print at the contact portion of the separation pad 8 and the paper feed roller 6. be. To explain in detail, the separation butt 8 is usually made by dispersing cork in urethane rubber with excellent abrasion resistance to achieve the desired friction coefficient, but by dispersing carbon and changing the amount, the volume can be adjusted. I changed the resistance value. The paper feed roller 6 has a hardness of 1
5 to 30 urethane rubber, chloroprene rubber, etc. are used, and carbon is similarly dispersed therein, and the volume resistivity is changed by changing the amount. Table 3 shows the surface potential of the paper at the contact area of the separation pad 8, the surface potential of the separation pad 8, and the appearance of the print when the separation pad 8 with different volume resistance is used as described above. Table 4 shows the results of similar experiments conducted on paper feed rollers.

Separation pad 8 and paper feed roller 6 are both idler roller 9
As in the case of , its volume resistance is 10'! In the case of Ω·cm or more, the surface potential of the paper at the contact portion of the separation pad 8 and paper feed roller 6 was +3 kV or more, and black streaks were generated. The separation pad 8 with a volume resistivity of 10111 Ω・cm and the paper feed roller 6 exhibited a surface potential of +1 kV on the surface of the paper at the contact portion of the above-mentioned members, and as in the case of the idler roller 9, some black streaks occurred, but it was not suitable for practical use. It was at a level with no problems. Also, the volume resistance is 10'Ω●cm, 10'Ω●Cm and 10''Ω◆
cm, the paper surface potential is +700V or +5
It showed a potential of 00V, and no black streaks were generated.

Table 3, Table 4, and FIG. 4 show still another example, in which a method using the retard roller 10 shown in FIG. 8 as a paper feeding device is used. As explained in the conventional example, in this method, the retard roller 10 rotates in the direction of the arrow in the figure to prevent electrical transmission, but the retard roller IO rotates in the opposite direction to the traveling direction of the fed paper. Therefore, it is strongly charged by abrasion with the paper, and the surface potential of the paper at the contact portion of the retard roller 10 tends to become high potential, which tends to cause black streaks and white streaks on the print.

The retard roller 10 is made of urethane rubber, chloroprene rubber, or the like having a hardness of 15 to 30 degrees, similar to that of the paper feed roller 6.

In this configuration, the volume resistance of the retard roller 10 is set to 1
By setting the resistance to 018 Ω◆am or less, preferably 10' Ω◆cm or less, it is possible to prevent black streaks or white streaks. Although carbon is used to change the volume resistivity of the resin/rubber, it goes without saying that the present invention is not limited to this. For example, metal powder, zinc oxide, etc. may be used to reduce the volume resistivity to 10I0Ω or less.

FIG. 5 is a diagram schematically showing the main parts of the inkjet printer. An inkjet printer uses a piezoelectric element to change the volume of ink supplied from an ink reservoir 111 or a heater to cause the ink to bump, and a driving member 112 that utilizes the resulting volume change causes the ink to be ejected from a nozzle 113 onto a recording paper 115. It is an excellent non-impact printer that prints with high quality, low noise, and can easily print in color.

The ink droplets 114 ejected from the nozzle 113 are slightly charged, so when the recording paper 115 is fed,
When the aforementioned paper feed roller, idler roller, separation pad, etc. are frictionally charged and the potential becomes high, the ink droplets 114 ejected from the nozzle 113 do not fly to the correct position, and the recording paper 1
When the printer is bent by a potential of 15 and a halftone is printed on the entire surface, black streaks and white streaks occur, similar to printers using electrophotography. This problem can also be solved by applying the present invention. In other words, by using a paper feed member with a volume resistance of 10l0Ω・cm or less, the recording paper 115 is not exposed to a high potential, and therefore the nozzle 1
The ink droplets 114 ejected from the ink droplets 13 adhere to predetermined positions, and the problem of black and white streaks can be solved.

As explained above, in paper feeding devices used in printers, copying machines, etc., special members are newly provided by reducing the volume resistance of the members that come into contact with paper to 10'6 Ωcm or less when feeding paper. This makes it possible to prevent black or white streaks during halftone printing in a low-humidity environment.

The present invention can also be applied to a paper feeder having a separation claw as shown in FIG.

〔Effect of the invention〕

In the present invention, it is possible to prevent the sheets from being charged when separating stacked sheets into one sheet and other sheets without using a static eliminating brush.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention. Figure 2 shows experimental data showing the characteristics of the present invention. 3 and 4 show another embodiment of the present invention. Figure 5 is a schematic representation of the main parts of an inkjet printer. Figure 6(a), Figure 6(b), Figure 7(a), Figure 7(
b), FIG. 8(a), FIG. 8(b), and FIG. 9 are conventional examples. FIGS. 10 and 11 schematically represent the phenomenon to which the present invention is concerned. 1... Paper cassette 2... Paper 3... Middle plate 4... Spring 5... Separation claw 6... Paper feed roller 7... Conveyance roller 8... Separation pad 9...・Idler roller 10
... Retard roller 11 ... Photosensitive drum l
2... Charger 13... Image exposure 14...
Developing device l5...Transfer charger 16...Cleaner l7...Fixing device

Claims (4)

[Claims] (1) A paper feeding device characterized in that a separation member that contacts sheets and separates one sheet from another has a volume resistance of 10^1^8 Ω·cm or less. (2) The separation member has a rotating body that sends out one sheet from the stacked sheets by frictional force.
Paper feeding device as described in section. (3) The paper feeding device according to claim 1, wherein the separation member applies frictional force to sheets other than the one sheet to be separated. (4) The paper feeding device according to claim 1, further comprising an image forming means for forming a surface image using droplets formed on one separated sheet using thermal energy.