JP2798969B2 - Roller transfer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a roller transfer device in an electrostatic recording device such as an electrophotographic device.

(Prior Art) Conventionally, there are a system using a corona charger in a device for electrostatically transferring toner from a toner carrier to transfer paper, and a system using a conductive roller or a drum to externally apply a voltage. ing.

The transfer device using the corona charger is widely used in general monochrome copying machines because of the simple structure of the device.However, this device generates electric charges from the back of the transfer paper using the corona charger. Because the toner is transferred from the toner image carrier to the transfer paper by the electric field formed by the charge attached to the transfer paper, the charge is generated by the electrical resistance of the transfer paper even if the amount of charge generated by the corona charger is the same. The amount of adhesion varies and the strength of the electric field varies. In general, the electrical resistance of plain paper used as transfer paper greatly changes depending on the environmental humidity. Therefore, when performing color expression by superimposing color toners such as color recording, the color balance is lost and stable. Color recording cannot be performed. Also, in monochrome recording, there is a problem that the density between images often changes due to environmental humidity. Further, when the transfer paper comes into contact with and separates from the toner image carrier, gas discharge occurs due to the charge of the transfer paper, and the toner transferred to the transfer paper is scattered, resulting in a problem that the image is disturbed.

These are also problems in the case of monochrome recording, but in color recording in particular, the transfer efficiency of each color toner is stable even if the electrical resistance of the recording paper as the transfer paper changes due to environmental humidity, and the toner image of each color is stable. Since there is a strong demand for accurate overlapping without disturbing the image, a solution has been long-awaited.

Therefore, various proposals have conventionally been made to solve these problems. As one of them, corona discharge is performed from the back side of the insulating mesh attached to the hollow drum, that is, from the opposite side of the mesh in contact with the transfer paper, as disclosed in, for example, JP-A-56-164370. There is a method in which the transfer paper is charged to make it contact with the toner image carrier softly, and the insulating mesh has an appropriate time constant to leak the charge after the toner transfer, thereby preventing gas discharge.

However, even with such a method, the problem that the transfer efficiency changes due to the electrical resistance of the transfer paper that changes due to environmental humidity cannot be solved.

On the other hand, a system using a soft conductive rubber roller as a transfer roller has been proposed as disclosed in Japanese Patent Application Laid-Open No. 50-22640. FIG. 5 shows the configuration of an electrostatic recording apparatus using such a transfer roller. In the electrostatic recording apparatus shown in FIG. 5, a negative charge 103 is applied to an organic photoreceptor 101 as a toner carrier using a charger 102, and an optical signal such as a laser beam is applied to the organic photoreceptor 101 having the negative charge 103. Irradiate 104 to form an inverted electrostatic latent image. Then, the electrostatic latent image is developed by a developing device 106 having a negative toner biased 105 by a negative voltage of 600 V which is substantially equal to the surface potential on the organic photoreceptor 101, and a visible image 107 is developed.
Is formed on the organic photoreceptor 101.

On the other hand, a positive voltage 110 of about 800 V is applied to the transfer roller 108, and the transfer paper 109 is separated from the organic photoreceptor 101 and the transfer roller 108.
And the toner of the visible image 107 formed on the organic photoreceptor 101 is moved from the surface of the organic photoreceptor 101 to the transfer roller 108 side while passing while the two are pressed against each other. Thus, a toner image 111 is formed on the transfer paper 109.

Then, the toner 112 remaining on the organic photoconductor 101 is cleaned by a cleaner device 113, and the electrostatic charge on the organic photoconductor 101 is erased by an erasing lamp 114, so that the organic photoconductor 101 is prepared for the next transfer.

In this electrostatic transfer device, the toner of the unnecessary image portion on the organic photoconductor 101 that is larger than the paper width of the transfer paper 109 is directly transferred onto the transfer roller 108, and the transfer roller 108 is stained. Also, when a transfer error of the transfer paper 109 occurs, all the toner images on the organic photoconductor 101 adhere to the transfer roller. Further, even when the apparatus is operating normally, the transfer roller 108 may become dirty due to the adhesion of the floating toner.

Therefore, the toner stain on the transfer roller 108 is wiped off by a cleaning blade 115 provided around the transfer roller 108, and collected as waste toner 117 in the toner receiver 116.

In the case of an electrostatic transfer apparatus using such a transfer roller, an electric field is applied between the transfer sheet and the toner image carrier using a foaming conductive rubber roller, so that the transfer sheet is not charged, and therefore, the environmental humidity , A stable transfer efficiency can be obtained. Further, since the electric resistance of the conductive roller continuously decreases as the conductive roller is compressed, the electric resistance of the conductive roller becomes the lowest at the contact point between the conductive roller and the toner image carrier, that is, at the toner transfer point. Transfer electric field becomes strong enough,
Before and after the contact between the two, the electric resistance is increased due to the increased electric resistance, the electric field is weakened, gas discharge between the conductive roller and the toner image carrier is prevented, and there is an advantage that the disturbance of the transferred image can be reduced.

(Problems to be Solved by the Invention) However, even a roller transfer device using such a foamable conductive rubber roller as a transfer roller has the following problems. One of the problems is that the shape of the foamable conductive rubber roller cannot be produced with high accuracy. In addition, in order to impart conductivity to the foamable rubber roller, conductive particles such as conductive carbon black are generally mixed into the rubber material. However, the elasticity of the roller changes depending on the mixing ratio, so that desired elasticity is obtained. There were also technical difficulties. In addition, there is a problem that a discharge is generated in bubbles inside the foamable conductive rubber roller, thereby shortening the life of the foamable conductive rubber roller and deteriorating the quality due to the discharge.

Further, when the contact pressure between the transfer roller and the toner carrier is large, there is a problem in that the toner is not transferred to the transfer paper at the center of the toner image, resulting in a "hollow-out" phenomenon, deteriorating the image quality. In addition, if the contact width between the toner image carrier and the transfer roller changes due to mechanical vibration or the like, there is a problem that the image density changes and the image quality deteriorates. The last problem is a phenomenon that occurs particularly remarkably in a humid atmosphere.

The present invention has been made in view of such a conventional problem. By using a transfer roller having a structure in which the influence of environmental humidity is small and a desired elasticity and resistance can be obtained independently, the surroundings can be improved. It is an object of the present invention to provide a roller transfer device that is not affected by environmental conditions, does not cause a hollow phenomenon, and has little fluctuation in image density during transfer.

[Means for Solving the Problems] The roller transfer device of the present invention covers a foamable elastic support pillar with a laminate of a flexible resistive layer and a flexible conductive layer,
A transfer roller is formed by penetrating a shaft at the center of the support column, and a rigid guide ring having a radius slightly smaller than the radius of the transfer roller is attached to the outer periphery of both ends of the transfer roller. The transfer roller is brought into close contact with the rigid guide rings on both ends thereof and rotated, so that the toner image is transferred onto the transfer paper by passing the transfer paper through the portion in close contact with the toner image carrier and the transfer roller.

(Operation) In the roller transfer device of the present invention, the transfer roller is formed by covering the laminate of the flexible resistive layer and the conductive layer with the foamable elastic support pillar, thereby carrying the transfer paper and the toner image. When the toner image carrier is brought into contact with the transfer roller, a rigid guide ring having a radius slightly smaller than the radius of the transfer roller comes into contact with the toner image carrier. The transfer roller can be transferred with a stable contact pressure without causing the transfer roller to be deformed larger than the radius and without causing a dropout phenomenon.

In addition, by covering the outer periphery of the foamable elastic support column with a resistance layer and a conductive layer, the influence of environmental humidity is reduced, and toner transfer with little image density fluctuation can be performed. Furthermore, since the portion to which the positive voltage is applied is not the foamable elastic support pillar but the conductive layer and the resistance layer coated on its outer periphery, it is possible to prevent the occurrence of discharge in bubbles and prolong the life. I can do it.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which 1 is a resistance layer, 2 is a conductive layer, 3 is an elastically deformable foamable elastic support column, and 4 is a metal shaft.

The resistance layer 1 is made of synthetic resin such as polyester, polyethylene, vinyl chloride, or rubber, or conductive carbon,
A conductive sheet in which conductive fine particles such as fine metal particles such as copper and nickel are dispersed, or a resistive sheet having excellent flexibility such as a conductive polymer resin can be used.

The resistance value of the resistance layer 1 is desirably a unit having a cross-sectional resistance per unit area of 5 × 10 ⁷ to 10 ⁹ Ω · cm ² , particularly 1 × 10 ⁸ to
The range of 3 × 10 ⁸ Ω / cm ² is preferable.
However, in order to maintain appropriate flexibility, the thickness is desirably in the range of 0.02 to 2 mm. As a result, the volume resistance of the resistance layer 1 is in the range of 2.5 × 10 ^{8 to} 5 × 10 ¹¹ Ω · cm, preferably in the range of 5 × 10 ⁸ to 1 × 10 ¹⁰ Ω · cm. The volume resistance of the resistive layer 1 is controlled by changing the mixing ratio of the conductive fine particles into the resin or the rubber or by changing the amount of the ion donor mixed into the polymer resin such as the fluororesin. It can be done by doing.

It is desired that the volume resistance value of the resistance layer 1 does not change or the change is small with respect to changes in environmental conditions such as external pressure and temperature and humidity. However, the resin sheet structure has an air chamber inside. Since there is no foamed structure, the resistance value is stable with respect to the temperature as compared with the foamed structure.

With such a characteristic, even if transfer paper of different thickness such as paper, postcard, postcard, etc. enters between the toner carrier and the transfer roller in the pressed state, or the electric toner is applied regardless of the temperature and humidity. Transfer conditions can be kept the same.

Further, it is desirable that the surface of the resistance layer 1 is smooth. If unnecessary toner accumulates on the surface of the resistance layer 1, the back surface of the transfer paper will be removed. It will be easier.

For the conductive layer 2, a conductive resin in which conductive fine particles such as conductive carbon are dispersed in polyester or the like, a thin sheet of metal, a conductive adhesive, or the like can be used.
The volume resistance value of the thin electric layer 2 must be lower than that of the resistance layer 1, and is desirably 1 × 10 ⁶ Ω · cm or less. Further, electrical connection between the conductive layer 2 and the resistance layer 1 must be ensured. Further, the thickness of the conductive layer 2 is preferably as thin as possible so as not to impair the flexibility of the elastic support 3. For this reason, the sum of the thickness of the low resistance layer 1 and the conductive layer 2 is set to 10 times the thickness of the elastic support column 3. The function of the elastic support pillar 3 can be maintained by setting it to 1 / l or less.

As the elastically deformable foamable elastic support pillar 3, a compressively deformable elastic material such as foamed rubber sponge, foamed polyethylene, or foamed urethane can be used. Since the transfer roller 5 is used by repeatedly pressing a part of the toner image bearing member against the toner image carrier, it is necessary that the elastic supporting column 3 be deformed flexibly when pressed and restored to its original shape when pressed and released. And it is necessary to operate stably against this repetition, for which anti-grip,
A material excellent in plastic deformation resistance is desirable.

The foamed structure of the foamable elastic support column 3 may be either a continuous foamed structure or a closed foamed structure. However, the continuous foamed structure is preferable because the shape is stable regardless of the ambient temperature. Can be used for Further, the flexibility of the elastic support column 3 can be obtained as desired by changing the constituent material, the foam structure, the degree of foaming, and the like. A hardness equal to or less than the sponge rubber hardness 30 of the closed cell structure is preferable. Used for

In addition, the thickness of the elastic support column 3 needs to be 2 mm or more because the flexible structure does not function if it is too thin.

Further, as shown in FIG. 1, a conductive treatment is performed from the end of the elastic support column 3 so that a part of the conductive elastic portion 6 is formed.
With such a structure, the conductive layer 2 and the shaft 4 can be electrically connected to the conductive elastic portion 6. Can be applied. In addition, as a structure for applying a voltage to the resistance layer 1, a part of the conductive layer 2 may be exposed and power may be supplied therefrom.

Next, a method of manufacturing the transfer roller 5 shown in FIG. 1 will be described. Urethane foam having a rubber hardness of 20 is formed around the 8 mmφ SUS shaft 4 by casting to a thickness of 10 mm to form a foamable elastic support column 3. Then, conductive treatment is performed on both ends of the elastic support column 3 to form a conductive sponge layer 7 having a volume resistance of 1 × 10 ⁴ Ω · cm and a width of about 5 mm on both ends of the elastic support column 3.

Further, conductive carbon is dispersed in the polyester resin on the outer periphery of the elastic support column 3 to have a volume resistance of 1 × 10 ⁴ Ω · cm.
The conductive layer 2 is adjusted to have a volume resistivity of 2.5 × 10 ¹⁰
Each of the resistance values 1 adjusted to Ω · cm is formed by injection into a thickness of 0.1 mm.

Finally, guide rings 7 made of an incompressible insulator such as Delrin having a radius smaller than the radius of the transfer roller 5 by about 300 μm are fitted into both ends of the transfer roller 5.

FIG. 2 shows a main part of a roller transfer device using the transfer roller 5 thus obtained. In the roller transfer device shown in FIG. 2, the toner image 9 on the toner carrier 8 is moved to the section B in accordance with the rotation of the toner image carrier 8 in the direction of the arrow.
-C is transferred to the toner transfer section. Then, in the toner transfer section, the toner image 9 is pressed against the plain paper 10 as the transfer paper.

During this time, a high-voltage transfer voltage having a polarity opposite to the electrostatic charge (here, negative polarity) of the toner image supplied from the high-voltage generation power supply 11 acts on the toner image 9, and the toner image 9 is electrostatically charged on the plain paper 10.
To form an image 12 on plain paper 10.

The high-voltage transfer voltage at this time is a voltage of about 2 KV in the case of a normal phenomenon in which toner having a polarity opposite to the electrostatic charge on the toner image carrier 8 is formed on the electrostatic charge on the toner image carrier 8. In the case of reversal development in which toner having the same polarity as that of the electrostatic charge on the toner image carrier 8 is formed on the portion of the toner image carrier 8 where the electrostatic charge has been erased, a transfer voltage of about 1 KV is required. is required.

In the toner transfer section in the section B-C, the toner image carrier 8 and the plain paper 10 are separated by the elastic deformation of the elastic support column 3 of the transfer roller 5 and the guide ring 7 having a radius slightly smaller than the radius of the transfer roller 5. Adhere at a certain nip width. In this section, the transfer pressure can be kept substantially constant by the flexible structure of the elastic support column 3. In addition, since the resistance layer 1 has no pressure resistance in the volume resistance value, uniform transfer conditions can be obtained in the entire nip width region.

In general, in roller transfer, if the transfer pressure is too high, the toner in the center of the toner image will not be transferred to the transfer paper, causing a hollow phenomenon.For example, in character recording, only white characters, that is, only character-shaped frames may be recorded. Occur. FIG. 3 shows the relationship between the transfer pressure when the roller transfer device shown in FIG. 2 is used and the rate of occurrence of hollowing. Here, a square isolated toner image is used as the rate of occurrence of hollowing. The ratio of the white background portion in the transferred image obtained by transfer to the entire image is shown.

In FIG. 3, a transfer image having no practical problem was obtained if the appearance ratio of hollow portions was 10% or less. On the other hand, if the transfer pressure was too low, the nip width became narrower.
The transfer density decreases. In the transfer apparatus according to the embodiment of the present invention, a transfer pressure in a range of about 300 g / cm ² or less is suitable, and a transfer pressure of about 200 g / cm ² or less is suitable. Therefore, the rubber hardness of the elastic layer 1 of the transfer roller 5 is 30
A degree or less is appropriate. The amount of deformation of the transfer roller at this time is 300 μm or less in the radial direction, preferably 150 μm or less, and the nip width is 3 mm or less, preferably 2 mm or less. It should be noted that there is no change in the density of the transferred image within the range of fluctuation of the nip width transfer time.

Further, FIG. 4 shows a transfer efficiency of 90% with respect to the amount of deformation in the radial direction of the transfer roller using the environmental humidity at this time as a parameter.
The range of the optimum transfer roller resistance value that gives the above is indicated by the shaded portion, and the amount of radial deformation of the transfer roller is a value obtained by subtracting the guide ring radius from the sum of the transfer roller radius and the transfer paper thickness. And the transfer roller resistance value is a resistance value per unit area of the resistance layer 1.

Here, the transfer efficiency of the toner is a percentage of the amount of the transferred toner to the sum of the amount of the toner transferred to the transfer paper (referred to as the transferred toner amount) and the amount of the toner remaining on the toner image carrier. .

The resistive resin sheet forming the resistive layer 1 can be designed with emphasis on only electrical characteristics. If the resistance value of the resistance layer 1 is too low, a discharge occurs between the resistance layer 1 and the toner image carrier when a transfer voltage is applied, or a reverse polarity toner is generated by charge injection, so that transfer efficiency is significantly reduced. On the other hand, if the resistance value is too high, the transfer voltage distributed to the toner layer decreases, and the transfer efficiency decreases. Therefore, as shown in FIG. 4, in the roller transfer device of this embodiment, the resistance in the cross-sectional direction per unit area of the resistance layer 1 of the transfer roller is desirably in the range of 5 × 10 ⁷ to 10 ⁹ Ω · cm ^2. In particular, a range of 1 × 10 ^{8 to} 3 × 10 ⁸ Ω · cm ² can be suitably used.

If the amount of roller deformation is too large, the contact time between the toner image carrier and the transfer paper and the transfer roller, that is, the nip width of the transfer roller that determines the transfer time increases. FIG. 4 shows the roller resistance value and the allowable roller deformation required for the transfer of the toner image carrier at a speed of 100 mm / sec and the transfer efficiency of 90%. The allowable deformation is 300 μm or less in the radial direction, preferably 1
It shows that a range of 50 μm or less is suitable. Therefore, as a guide ring, the transfer roller radius of 30
In order to make it slightly smaller within a range not exceeding 0 μm, it is preferable to set it to about 150 μm.

Generally, as the speed of the toner image carrier increases, the transfer time corresponding to the same nip width decreases, but the deformation amount
Even at a nip width equivalent to 300 μm, there is no change in the density of the transferred image. When the speed of the toner image carrier decreases, the transfer time increases, and the image density fluctuates.
This effect is small at a nip width corresponding to 0 μm. Therefore, from this point as well, it can be said that the roller deformation amount is a desirable value in the above range.

Since the guide ring is formed of a hard insulator, it is desirable that the guide ring be in contact with the periphery of the toner image carrier, which is not the image forming area, so as not to damage the toner image carrier. If the contact friction with the toner image carrier is increased by coating
The rotation of the transfer roller can be made easier.

As described above, the conductive layer and the resistance layer are coated on the outer periphery of the foamable elastic support pillar as the transfer roller, and the transfer roller is not more than 300 μm by the guide ring, preferably 150 μm.
Since the deformation is regulated so as not to exceed μm, even if the environmental humidity is 90% or more, a toner transfer efficiency of 90% or more can be obtained.

[Effects of the Invention] As described above, according to the present invention, since the transfer roller is configured by covering the flexible resistive layer and the flexible conductive layer with the foamable elastic support pillar, a high voltage can be applied. Unlike the conventional case, there is no bubble chamber in the conductive portion to be applied, and there is no deterioration due to air discharge, and stable transfer performance can be maintained for a long period of time. In addition, since the amount of deformation of the transfer roller is regulated by the rigid guide ring, a good transfer image can be obtained without causing the contact portion of the transfer roller with the toner image carrier to be widened and the hollowing-out phenomenon not to occur. be able to.

[Brief description of the drawings]

FIG. 1 is a sectional view of a transfer roller according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing a contact transfer portion between a toner image carrier and a transfer roller of a roller transfer device using the above-described transfer roller. FIG. 3 is a graph showing the relationship between the transfer pressure and the transfer characteristics in the above embodiment. FIG. 4 is a graph showing the range of the optimum roller resistance value with respect to the amount of deformation of the transfer roller in the radial direction in the above embodiment. FIG. 5 is a diagram illustrating the principle of a general roller transfer device. DESCRIPTION OF SYMBOLS 1 ... Resistive layer 2 ... Conductive layer 3 ... Foaming elastic support pillar 4 ... Shaft 5 ... Transfer roller 6 ... Conductive rubber layer, 7 ... Guide ring 8 ... Toner image carrier , 10 ... Transfer paper

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-125778 (JP, A) JP-A-64-6988 (JP, A) JP-A-2-176778 (JP, A) JP-A-1- 117149 (JP, A) JP-A-1-211779 (JP, A) JP-A-48-51640 (JP, A) JP-A-1-316774 (JP, A) JP-A-2-24686 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/16

Claims (2)

(57) [Claims] 1. A transfer roller is formed by covering a foamable elastic support column with a laminate of a flexible resistance layer and a flexible conductive layer, and penetrating a shaft through the center of the support column. A rigid guide ring having a radius slightly smaller than the radius of the transfer roller is attached to the outer periphery of both ends of the transfer roller, and the transfer roller is brought into close contact with the toner image carrier together with the guide rings at both ends thereof, and is rotated. A roller transfer device for transferring a toner image onto a transfer sheet through a transfer sheet through a portion in close contact with a transfer roller. 2. A resistance value in a cross-sectional direction per unit area of the flexible resistive layer on a surface of the transfer roller, wherein the radius of the guide ring does not exceed 300 μm. ^2. The roller transfer device according to claim 1, wherein the pressure is set to 5 × 10 ⁷ to 10 ⁹ Ω · cm ² .