JP2001125458A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppers the emission of an abnormal sound due to the chattering of a cleaning blade caused when a photosensitive drum decreases in rotating speed at the time of the feeding of OHT paper. SOLUTION: The emission of the abnormal sound due to the chattering of the cleaning blade 5 caused when the photosensitive drum 1 decreases in rotating speed at the time of the feeding of paper such as OHT by performing development on the photosensitive drum 1 by a developing device 3 so that toner is interposed at a primary transfer part where the photosensitive drum 1 and an intermediate transfer belt 4 abut against each other when the photosensitive drum 1, the intermediate transfer belt 4, and the fixing roller 14a and pressure roller 14b of a fixing device 14 are made lower in rotating speed than usual if a transfer material P is, for example, OHT before a toner image transferred primarily to the intermediate transfer belt 4 beings to be transferred secondarily to the transfer material P by a secondary transfer roller 11, can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which forms an image by an electrophotographic method.

[0002]

2. Description of the Related Art In a full-color image forming apparatus using an intermediate transfer member, a toner image of a first color (for example, yellow) is first formed on an electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. Then, the toner image is primarily transferred onto an intermediate transfer body (an intermediate transfer belt or an intermediate transfer drum) at a primary transfer position. Then, this primary transfer is sequentially performed for the other three colors, that is, magenta, cyan, and black, and the four color toner images are superimposed on the intermediate transfer member. Then, this 4
The secondary transfer member (for example, 2
The next transfer roller) collectively transfers 2 sheets to a transfer material such as paper.
By performing the next transfer, a full-color image can be obtained.

In the above-described image formation, O
OHT (Ov) as a transparent film-like transfer material used for HP (Ovre Head Projector)
When forming an image on a rehead transparency, it is necessary that the toner is sufficiently melted so as to be smoothly distributed on the OHT. If the toner is not sufficiently smooth, light will be scattered when projected by the projector, and clear color reproduction will not be possible.

Therefore, when the OHT is passed, the rotation speed of the fixing roller and the pressure roller of the fixing device is reduced, and sufficient heat is applied to the toner and the OHT so that the toner is sufficiently melted on the OHT. A method may be adopted.

Also, when a transfer material having a large heat capacity such as gloss film, gloss paper, or thick paper is passed, control is performed to reduce the rotational speed of the fixing roller and the pressure roller in order to sufficiently secure the fixing property. Sometimes.

In recent years, with the downsizing of image forming apparatuses such as copying machines and laser printers, in image forming apparatuses using the above-mentioned intermediate transfer member, secondary transfer in which the intermediate transfer member is secondarily transferred to a transfer material is used. It has become impossible to secure a sufficient space between the position and the fixing device located downstream of the position.
For this reason, the distance between the secondary transfer position and the fixing device may be shorter than the length of the transfer material on which an image is formed. In this case, there is a state where the fixing operation is performed at the leading end portion of the transfer material and the secondary transfer is performed at the trailing end portion of the transfer material.

For this reason, when the transfer material is controlled to slow down the rotation speed of the fixing roller and the pressure roller when fixing the above-described OHP or other special paper (gloss film, gloss paper, thick paper, etc.), It is necessary to reduce the speed of the next transfer. That is, the moving speed (rotation speed) of the intermediate transfer member and the rotation speed of the secondary transfer roller as the secondary transfer member are also reduced at the same rate. Image blur occurs during transfer.

Therefore, this deceleration must be performed before the secondary transfer. In addition, in order to prevent the throughput from lowering as much as possible, the above-described deceleration is usually performed after the completion of the primary transfer and before the secondary transfer.

[0009] Regarding the rotation speeds of the photosensitive drum and the intermediate transfer member, if there is any slight rotation variation or error, accurate color superposition on the intermediate transfer member cannot be performed.

In order to avoid this, the photosensitive drum and the intermediate transfer member are generally rotated by the same drive motor. Therefore, in this case, if the moving speed (rotation speed) of the intermediate transfer member is reduced, the rotation speed of the photosensitive drum is correspondingly reduced accordingly.

A cleaning blade made of an elastic material is brought into contact with the photosensitive drum in a counter direction with respect to the rotation direction of the photosensitive drum for the purpose of removing transfer residual toner remaining after the transfer of the toner image. When the photosensitive drum is rotating in a steady state, the stress applied to the cleaning blade is also in a steady state, so that the cleaning blade maintains a constant contact state with the photosensitive drum.

[0012]

However, when the rotation speed of the photosensitive drum is rapidly reduced, the stress applied to the cleaning blade also changes, and fine vibration (hereinafter referred to as chatter) occurs in the cleaning blade. The chattering cleaning blade eventually settles in a contact state suitable for the rotation speed of the photosensitive drum, and this chatter is reduced.However, due to the characteristics of the elastic member forming the cleaning blade, the chatter is considerably reduced. Takes time.

When the cleaning blade starts to vibrate, abnormal noise is generated at the vibration cycle. This abnormal noise continues to occur until the chatter of the cleaning blade stops and the steady state is reached.

As described above, in the related art, as described above, the noise is generated due to the chatter of the cleaning blade accompanying the reduction in the rotation speed of the photosensitive drum, and the user is discomforted.

In the image forming apparatus using the above-mentioned intermediate transfer member, a toner image is transferred from the photosensitive drum to the intermediate transfer member by applying a bias to the intermediate transfer member. In some cases, sufficient transferability cannot be ensured.

For this reason, conventionally, an operation of mechanically scraping the toner image on the photosensitive drum by increasing the rotation speed of the intermediate transfer member by about 0.5 to 2% than the rotation speed of the photosensitive drum is added. Thereby, transferability can be improved. In this case, a force from the intermediate transfer member is further applied to the photosensitive drum, and the stress applied to the cleaning blade when the rotation speed is reduced is further complicated. As a result, the occurrence of chatter of the cleaning blade is promoted and the amplitude of chatter is increased.

Accordingly, the present invention provides an image forming apparatus capable of suppressing the generation of abnormal noise caused by chattering of a cleaning blade which occurs when the rotation speed of a photosensitive drum is reduced by the passage of a transfer material such as an OHT. The purpose is to do.

[0018]

In order to achieve the above object, the present invention provides a rotatable image carrier for carrying an electrostatic latent image, and a surface of the image carrier which is developed by developing the electrostatic latent image. Developing means for forming a toner image on the image carrier; and a rotatable intermediate transfer body which abuts on the image carrier at a primary transfer portion and temporarily transfers and carries the toner image formed on the image carrier. A secondary transfer member for secondary-transferring the toner image primary-transferred to the intermediate transfer member onto a transfer material, and a rotation direction downstream of the image carrier with respect to the primary transfer portion on the image carrier. The tip abuts on the side,
The intermediate transfer, comprising: a plate-shaped cleaning member for removing transfer residual toner remaining on the image carrier; and a fixing unit having a pair of rotatable fixing rotators abutting on each other at a fixing unit. The toner image primarily transferred to the body is
Before the secondary transfer to the transfer material is started by the next transfer member, the rotational speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators is set at a fixed rate according to the type of the transfer material. In the image forming apparatus, the toner image primarily transferred to the intermediate transfer body is subjected to secondary transfer to the transfer material by the secondary transfer member according to the type of the transfer material. When changing the rotation speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators from a normal rotation speed, the image carrier, the intermediate transfer member, and the pair of fixing rotators are changed. At the timing when the rotation speed of each body changes, development on the image carrier is performed by the developing means such that toner is interposed in the primary transfer portion where the image carrier and the intermediate transfer body are in contact. It is characterized by performing.

When the transfer material is not a normal transfer material but a specific transfer material, secondary transfer of the toner image primarily transferred to the intermediate transfer member to the transfer material is started by the secondary transfer member. Before, the rotation speed of each of the image carrier, the intermediate transfer body, and the pair of fixing rotators is reduced at a substantially constant rate from a normal rotation speed at a fixed rate, and the transfer material is other than the specific transfer material. In this case, the rotation speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators is not changed from the normal rotation speed.

Further, the specific transfer material is a transparent film used for an overhead projector.

Further, the specific transfer material is a gloss film.

Further, the specific transfer material is gloss paper.

Further, the specific transfer material is a cardboard.

Further, the secondary transfer member abuts on the intermediate transfer member at the secondary transfer portion, and has a surface which rotates at a substantially constant speed in a forward direction with respect to a rotation direction of the intermediate transfer member to have elasticity. A secondary transfer roller having a toner image primary-transferred onto the intermediate transfer member onto a transfer material by the secondary transfer roller.
Before starting the next transfer, depending on the type of the transfer material, when changing the rotation speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators from a normal rotation speed, The rotation speed of the secondary transfer roller is changed accordingly.

Further, the rotation speed of the intermediate transfer member is slightly higher than the rotation speed of the image carrier.

Further, when the rotation speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators changes from the normal rotation speed, the image carrier and the intermediate transfer member are separated from each other. The toner interposed in the abutting primary transfer portion is interposed over the entire developable longitudinal region of the image carrier.

Further, a bias having a polarity opposite to the charging polarity of the toner is applied to the intermediate transfer body to transfer the toner on the image carrier to the intermediate transfer body.

Further, when the rotation speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators changes from the normal rotation speed, the image carrier and the intermediate transfer member are separated from each other. While the toner is interposed in the contacting primary transfer section, a bias having the same polarity as the charging polarity of the toner is applied to the intermediate transfer body.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus according to the present embodiment is a laser beam printer using an electrophotographic intermediate transfer body (intermediate transfer belt).

The image forming apparatus includes a photosensitive drum 1 as an image carrier, and a charging roller 2, a developing device 3, an intermediate transfer belt 4 as an intermediate transfer member, a cleaning blade around the photosensitive drum 1. An exposure device (laser scanner device) 6 is provided above the photosensitive drum 1 between the charging roller 2 and the developing device 3.

In the present embodiment, as shown in FIG. 2, a photosensitive layer (charge generation layer 1b and charge transport layer 1c) is applied to the outer peripheral surface of a conductive drum substrate 1a made of aluminum or the like. It is rotationally driven at a predetermined process speed (peripheral speed) in the direction of the arrow (counterclockwise) by a driving device (not shown).

The photosensitive layer (the charge generation layer 1b and the charge transport layer 1c) is usually an insulator, and has a characteristic that it becomes a conductor when irradiated with light of a specific wavelength. This is because the light irradiation generates hole-electron pairs in the charge generation layer 1b, and these serve as carriers of the charge flow. The charge generation layer 1b is a phthalocyanine compound having a thickness of about 0.2 μm, and the charge transport layer 1c is
It is composed of polycarbonate in which a certain amount of hydrazone compound is dispersed.

In some cases, another material may be dispersed in the charge transport layer 1c. One example is Teflon (trade name). Teflon is dispersed for the purpose of reducing the frictional force against the cleaning blade 5 described later, and its particle size is about 0.3 μm, and the dispersion amount is preferably 20% or less. If the amount of dispersion is too large, Teflon becomes an obstacle, the laser light emitted from the exposure device 6 is scattered, and a sharp electrostatic latent image may be alienated.

A charging roller 2 serving as a charging means contacts the photosensitive drum 1 with a predetermined pressure contact force, and makes the surface of the photosensitive drum 1 uniform to a predetermined polarity and potential by a charging bias applied from a charging bias power supply (not shown). Charge. The charging roller 2 is formed by covering an elastic rubber layer on a metal cored bar, and is rotated by the rotation driving of the photosensitive drum 1.

When a DC bias equal to or more than a threshold is applied to the core of the charging roller 2 from a charging bias power supply (not shown),
Discharge occurs near the nip between the charging roller 2 and the photosensitive drum 1. As a result, the photosensitive drum 1 is charged to the same polarity as the bias applied to the charging roller 2. When a bias is applied from a charging bias power supply (not shown) to the metal core of the charging roller 2 and an AC bias whose amplitude is equal to or greater than a discharge starting voltage is applied, the surface of the photosensitive drum 1 is substantially uniformly applied to the DC. It can be charged to component values.

An exposure device (laser scanner device) 6 outputs a laser beam modulated according to a time-series electric digital pixel signal of image information input from a controller (not shown) from a laser diode 6a, 6b, the surface of the photosensitive drum 1 is subjected to image exposure L,
An electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 1 charged by the charging roller 2.

The developing device 3 includes four developing devices, that is, developing devices 3a and 3b of a one-component developing system which respectively store yellow, cyan, magenta and black toners.
3c, 3d, and these developing units 3a, 3b,
3c and 3d are mounted on a rotatable rotating body 3A.
The developing device 3 is configured such that a developing device of a color used for developing the electrostatic latent image formed on the photosensitive drum 1 is provided on the surface of the photosensitive drum 1 by rotating the rotating body 3 </ b> A in the direction of the arrow (counterclockwise). It is arranged at a developing position opposite to the developing unit, and develops (visualizes) a toner image by attaching toner to the electrostatic latent image.

As shown in FIG. 3, each developing device (developing device 3a in the figure) includes a rotatable developing sleeve 20 composed of a metal roller that carries toner on its surface. Further, in order to increase the toner carrying force on the developing sleeve 20, the surface thereof may be coated with a material which increases the mirroring force.
The developing sleeve 20 is arranged so as to keep a constant small gap (about 0.3 mm) with respect to the photosensitive drum 1 and is rotated at a peripheral speed of about 150% in the forward direction with respect to the rotation direction of the photosensitive drum 1. .

A developing bias (appropriate bias between the charged potential on the photosensitive drum 1 and the surface potential of the laser beam irradiation surface on the photosensitive drum 1) is applied to the developing sleeve 20 from a developing bias power supply (not shown). As a result, the photosensitive drum 1
An electric field is generated between the photosensitive drum 1 and the developing sleeve 20, and only the toner on the developing sleeve 20 corresponding to the surface potential portion of the laser beam irradiation surface on the photosensitive drum 1 electrostatically jumps onto the photosensitive drum 1, and the development is stopped. finish.

In this development, extra toner may adhere to the charged potential portion on the photosensitive drum 1 in some cases. Therefore, by simultaneously applying the AC bias to the developing bias, the toner is transferred to the photosensitive drum 1 and the developing sleeve 20.
Therefore, development can be performed better than when only the DC component is applied. Therefore, usually D
A developing bias in which AC is superimposed on C is applied.

A toner regulating blade 21 abuts on the upstream side of the developing position of the developing sleeve 20 close to the photosensitive drum 1. The toner regulating blade 21 abuts on the developing sleeve 20 in the counter direction with a force of about 20 g of linear pressure,
The control is performed such that the amount of toner to be coated with a thin image on the developing sleeve 20 is always constant. The toner regulating blade 21 also has a role of negatively charging the toner when the toner passes. The intermediate transfer belt 4 includes a tension roller 8, a driving roller 9, a secondary transfer facing roller 10
It is an endless belt stretched therebetween, and is rotated in the direction of the arrow by the driving of the driving roller 9. Intermediate transfer belt 4
The photosensitive drum 1 is pressed by the primary transfer roller 7.
, A primary transfer nip portion N1 is formed.

The intermediate transfer belt 4 has a thickness of 100 to
200 μm, P with a volume resistivity of about 10 ¹¹ to 10 ¹⁶ Ωcm
A resin film such as VdF (polyvinylidene fluoride), polyamide, polyimide, PET (polyethylene terephthalate) or polycarbonate, or a resin layer having a good releasability provided on a rubber base layer having a thickness of about 0.5 to 2 mm. Can be used. Asker C is used as the primary transfer roller 7.
A low-resistance roller having a hardness of 30 to 60 ° and a volume resistivity of about 10 ⁵ Ωcm or less can be used. The primary transfer roller 7 is connected to a primary transfer bias power supply (not shown).

The secondary transfer opposing roller 10 is in contact with the secondary transfer roller 11 via the intermediate transfer belt 4 to form a secondary transfer nip N2. The secondary transfer roller 11 is freely movable toward and away from the intermediate transfer belt 4 (secondary transfer opposing roller 10). A belt cleaning roller 12 is provided on the outer peripheral surface side of the intermediate transfer belt 4 so as to face the secondary transfer opposing roller 10, and the belt cleaning roller 12 comes into contact with and separates from the intermediate transfer belt 4. It is free. The belt cleaning roller 12 is formed by covering a metal core with a medium-resistance elastic rubber layer.
Practically, it is preferable to use a layer provided with several layers for preventing damage to the intermediate transfer belt 4 such as inflow of overcurrent and sticking to the intermediate transfer belt 4. Further, a fixing device 14 is provided via a transport belt 13 on the downstream side of the secondary transfer nip N2 in the transport direction of the transfer material P.

The fixing device 14 has a fixing roller 14a and a pressure roller 14b, and the fixing roller 14a and the pressure roller 14b are respectively driven to rotate at a constant speed in a forward direction. The fixing roller 14a and the pressure roller 14b are formed of a metal core of a hollow cylindrical body and a silicon rubber having a thickness of about 2 mm covering the outside thereof. On the outside of the silicone rubber,
In some cases, a layer for improving the releasability is coated.
The elastic rubbers of the fixing roller 14a and the pressure roller 14b form layers so that their heat capacities are substantially equal.

A spring (not shown) is in contact with the lower part of the core of the pressure roller 14b, and a constant pressure is applied toward the center of the fixing roller 14a. Thereby, a fixing nip portion N3 is formed between the fixing roller 14a and the pressure roller 14b. Further, a halogen heater (not shown) is disposed in a hollow portion inside the fixing roller 14a and the pressure roller 14b, and when the halogen heater is energized, the surface temperature of the fixing roller 14a and the pressure roller 14b increases. Let it. A thermistor (not shown) is disposed in contact with the fixing roller 14a and the pressure roller 14b, and the fixing roller 14 is provided based on temperature information detected by the thermistor.
a and the surface temperature of the pressure roller 14b become constant,
ON / OFF control of the halogen heater. In this embodiment, the temperature of both the fixing roller 14a and the pressure roller 14b is 165 ° C. during standby, and 170 ° C. during image formation (fixing operation).

The cleaning blade 5 as a cleaning member scrapes off the primary transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer (the cleaning blade 5).
Will be described later).

In the present embodiment, as the size of the image forming apparatus is reduced, the next transfer nip portion N2 and the fixing device 14 are removed.
Between the fixing roller 14a and the fixing nip portion N3 of the pressure roller 14b, the length of the transfer material P (for example, the length of B5 size)
The above space cannot be secured.

Next, the image forming operation of the image forming apparatus will be described.

The photosensitive drum 1 is driven to rotate at a normal process speed (120 mm / sec in this embodiment) in the direction of the arrow (counterclockwise) by a driving device (not shown). The surface is uniformly charged (-600 V in this embodiment).

Then, the uniformly charged surface of the photosensitive drum 1 is exposed from an exposure device (laser scanner device) 6 to a reflection mirror 6.
An electrostatic latent image of each color corresponding to the image information is formed on the photosensitive drum 1 by the image exposure L by the laser light modulated according to the input image signal, which is output through the line b.

Then, the developing devices 3a, 3b, 3c, and 3d respectively containing the yellow, cyan, magenta, and black toners mounted on the rotating body 3A of the developing device 3.
Of the first color (the yellow developing device 3 in the figure)
a) is moved to a developing position facing the photosensitive drum 1 by the rotation of the rotating body 3A, and a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 1 is applied to the developing roller 20 of the developing device 3a. Then, the yellow toner is adhered to the electrostatic latent image on the photosensitive drum 1 and developed (visible image) as a yellow toner image.

This yellow toner image is supplied from a primary transfer bias power supply (not shown) to a primary transfer nip N1.
The primary transfer roller 7 to which the secondary transfer bias (the polarity opposite to the toner (positive polarity)) is applied is applied onto the intermediate transfer belt 4 by the primary transfer roller 7.
Next is transferred. At this time, the secondary transfer roller 11 is separated from the intermediate transfer belt 4 (secondary transfer opposing roller 10) at the secondary transfer nip portion N2.

It has been described that the primary transfer is performed by applying an appropriate positive bias to the primary transfer roller 7.
This alone may not transfer all the toner. In order to avoid such transfer failure, the moving speed of the intermediate transfer belt 4 is set to be 0.5 to less than the rotation speed of the photosensitive drum 1.
An operation of mechanically scraping the toner on the photosensitive drum 1 by increasing the speed by about 2% may be added. In the present embodiment, the moving speed of the intermediate transfer belt 4 is set to 121 mm / sec.
c, the photosensitive drum 1 is moved about 1% faster than the rotation speed.

As will be described in detail later, the toner of four colors is carried on the intermediate transfer belt 4 in a superposed manner. It is important to improve the positional accuracy of the color superimposition of the four colors in improving the color reproducibility of the color image forming apparatus. One cause of a decrease in the color overlay position accuracy is a variation or an error in the relationship between the rotation speed of the photosensitive drum 1 and the moving speed of the intermediate transfer belt 4. In order to avoid this, in the present embodiment, the rotation of the photosensitive drum 1 and the movement of the intermediate transfer belt 4 (the rotation of the drive roller 9) are performed by the same drive motor (not shown). Therefore, in this case, when the moving speed of the intermediate transfer belt 4 is reduced, the rotation speed of the photosensitive drum 1 is automatically reduced in the same manner.

The primary transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer is removed by the cleaning blade 5 and collected in the waste toner container 15.

As shown in FIG. 4, the cleaning blade 5 used in this embodiment has a polyurethane rubber 5a having a Wallace hardness of 69 degrees and is held at the tip of the metal plate 5b with a constant bite amount. Further, in order to secure the strength of the cleaning blade 5, a bent portion is provided on the metal plate 5b.

As shown in FIG. 5, the cleaning blade 5 is fixed so as to always satisfy a predetermined set angle φ and a penetration amount δ with respect to the photosensitive drum 1. The above set angle φ
Is the tangential line of the photosensitive drum 1 at the intersection between the photosensitive drum 1 and the leading end surface of the polyurethane rubber 5a, assuming that the leading end of the cleaning blade 5 has entered the photosensitive drum 1 without deformation. The angle formed by the bottom surface and the amount of intrusion δ are the distance between the intersection of the end face of the polyurethane rubber 5a and the photosensitive drum 1 and the edge of the polyurethane rubber 5a on the side where the polyurethane rubber 5a enters the photosensitive drum 1.

In this case, the cleaning blade 5 actually has a constant contact pressure with the photosensitive drum 1, a constant nip length of the contact portion with the photosensitive drum 1, and the front end surface of the polyurethane rubber 5 a and the photosensitive drum 1. The contact portion is stabilized while maintaining a certain angle with respect to the tangential direction of the contact portion.

Incidentally, the optimum values of the set angle φ and the penetration amount δ of the cleaning blade 5 with respect to the photosensitive drum 1 differ depending on the toner used. In the present embodiment, a toner having a shape factor SF1 of 100 to 120, which is a numerical value indicating the ratio of the roundness of the shape of the spherical substance, is used.

As shown in FIG. 6, the shape factor SF1 is
The square of the maximum length MXLNG of an elliptical figure formed by projecting a spherical substance on a two-dimensional plane is divided by the figure area to obtain 100π
/ 4. That is, the shape factor SF1 is represented by the following equation.

SF1 = ((MXLNG) ² / AREA)
× (100π / 4) In the present embodiment, the set angle φ of the cleaning blade 5 with respect to the photosensitive drum 1 is 27 degrees, and the penetration amount δ is 1.30 m.
m.

As shown in FIG. 4, the thickness of the polyurethane rubber 5a can be changed by changing the thickness of the end portion and the holding portion of the metal plate 5b so that the shock can be absorbed at the portion where the thickness changes. The vibration of the photosensitive drum 1 can follow.

When the primary transfer of the first color yellow toner image is completed as described above, the rotating body 3A rotates and the next developing device moves to the developing position facing the photosensitive drum 1, and
The formation, development, and primary transfer operations of the electrostatic latent image are sequentially performed for each of the colors magenta, cyan, and black in the same manner as in the case of yellow, and the four color toner images are sequentially superimposed on the intermediate transfer belt 4 to form a full-color image. Is formed.

When the leading end of the full-color toner image formed on the intermediate transfer belt 4 reaches the secondary transfer nip N2 between the secondary transfer roller 11 and the secondary transfer opposing roller 10, the timing is adjusted. The transfer material P such as paper in the cassette 16 is
Sheets are fed one by one and conveyed to a secondary transfer nip N2 via a registration roller (not shown) or the like.

Then, at the secondary transfer nip portion N2, the secondary transfer opposing roller 10
Is used as a counter electrode, and a secondary transfer roller 11 to which a secondary transfer bias is applied from a secondary transfer bias power supply (not shown) is swung so as to contact the secondary transfer counter roller 10 via the intermediate transfer belt 4. . Then, the secondary transfer nip N2
A full-color toner carried on the intermediate transfer belt 4 on the surface of the transfer material P by applying a bias of the opposite polarity (positive polarity) to the toner by the secondary transfer roller 11 to the back surface of the transfer material P conveyed to The images are transferred collectively (secondary transfer).

The transfer material P after the secondary transfer is transferred to the transport belt 13.
Is transported between the fixing roller 14a and the pressure roller 14b of the fixing device 14 through the fixing roller 14 and is heated and pressurized. After the full-color toner image is thermally fixed on the surface of the transfer material P,
8 to the outside.

The secondary transfer residual toner remaining on the surface of the intermediate transfer belt 4 after the secondary transfer is removed by the belt cleaning roller 12. The removal of the secondary transfer residual toner by the belt cleaning roller 12 is performed as follows.

That is, simultaneously with the start of the secondary transfer, the intermediate transfer belt cleaning roller 12 is brought into contact with the intermediate transfer belt 4, and a positive DC bias equal to or higher than the discharge start threshold is applied to
The next transfer residual toner is positively charged. The positively charged secondary transfer residual toner is applied to the photosensitive drum 1 surface potential and the positive DC voltage applied to the primary transfer roller 7 at the contact portion (primary transfer nip portion N1) between the photosensitive drum 1 and the intermediate transfer belt 4. The light is collected on the photosensitive drum 1 by the electric field generated by the bias.

In the image forming apparatus of the present embodiment, as described above, along with the miniaturization of the apparatus, the length of the transfer material P (for example, B5 size) is placed between the secondary transfer nip N2 and the fixing nip N3. Length) or more. Therefore, there is a state where the fixing operation is performed at the leading end portion of the transfer material P and the secondary transfer is performed at the trailing end portion of the transfer material P.

Therefore, the fixing operation and the transfer operation can be performed smoothly without interfering with each other.
It is necessary that the rotation speed of the pressure roller 4a and the pressure roller 14b is about 121 mm / sec, which is substantially equal to the rotation speed of the secondary transfer roller 11 and the moving speed of the intermediate transfer belt 4.

However, as described in the above section, when the rotation speed of the fixing roller 14a and the pressure roller 14b is as high as about 121 mm / sec, the amount of heat applied to the toner is reduced. Material P is OHT
If the thickness is too thick, the toner cannot be sufficiently melted so as to be smoothly distributed on the OHT. If the rotation speed of the fixing roller 14a and the pressure roller 14b is reduced to about 1/3 of this in order to give a large amount of heat to the toner, the toner melts until sufficient color reproduction is possible even when projected by OHP. I understood that.

For this reason, in the present embodiment, when the OHT is passed, after the color superposition (primary transfer) of the four colors on the intermediate transfer belt 4 is completed, the fixing roller 14a and the pressure roller 14b are moved before the secondary transfer is started. Control is performed to reduce the rotation speed from about 121 mm / sec to about 40.33 mm / sec (this control will be described with reference to a flowchart described later).

Also, in this case, the above-mentioned [prior art]
As described above, the moving speed of the intermediate transfer belt 4 and the rotating speed of the secondary transfer roller 11 are similarly set to 40.33 mm / sec.
c). If the speed is reduced during the execution of the secondary transfer, a deceleration shock causes image blurring at the time of the secondary transfer. Therefore, the deceleration is performed before the secondary transfer. Further, in order to prevent the throughput from lowering as much as possible, deceleration is performed at a timing after the completion of the primary transfer and before the secondary transfer.

As described above, in this embodiment, the driving speed of the intermediate transfer belt 4 is reduced to 1/3 since the same drive motor (not shown) is used to drive the photosensitive drum 1 and the intermediate transfer belt 4. Deceleration means that the rotation speed (process speed) of the photosensitive drum 1 is also automatically reduced by 1 /.
The speed is reduced to 40 mm / sec. When the photosensitive drum 1 is rotating at 120 mm / sec, the cleaning blade 5 is subjected to
A certain contact pressure against the photosensitive drum 1, a certain nip length of a contact portion with the photosensitive drum 1, and a polyurethane rubber 5 a
The angle between the front end surface of the photosensitive drum 1 and the tangential direction of the contact portion of the photosensitive drum 1 was kept constant and stable.

However, when the rotation speed of the photosensitive drum 1 is rapidly reduced, the stress applied to the cleaning blade 5 also changes. Further, in the present embodiment, the photosensitive drum 1
A slight peripheral speed difference is provided between the photosensitive drum 1 and the intermediate transfer belt 4 during deceleration.
The force received from changes. At this time, the cleaning blade 5 cannot cope with these complicated changes in stress, and chatter occurs due to fine vibration. Cleaning blade 5
When the vibration starts, abnormal noise is generated at the vibration cycle.

Therefore, in the present embodiment, control for preventing chattering of the cleaning blade 5 at the time of deceleration and preventing abnormal noise is performed by simplifying the change in stress applied to the cleaning blade 5 at the time of deceleration as much as possible. I did it.

Hereinafter, control for preventing chattering of the cleaning blade 5 during deceleration in this embodiment will be described with reference to the flowchart of FIG.

The above-described image forming operation starts (start).
Then, primary transfer of image data of four colors is performed on the intermediate transfer belt 4 (step S1). At this time, if the transfer material P is OHT (step S3),
After the primary transfer of the color (black) is completed, a predetermined width (for example, about 1 cm) of laser exposure is performed from the exposure device 3 over the entire longitudinal direction of the photosensitive drum 1 (the entire area in the width direction of the image forming area) at a predetermined timing. Black toner is developed by the black developing device 3d, and a belt-shaped black image (hereinafter, referred to as a black belt image) of a predetermined width (for example, about 1 cm) is formed over the entire length of the photosensitive drum 1 (the entire area in the width direction of the image forming area). ) Is formed (Step S4).

In this operation, when the rotation speed of the photosensitive drum 1 and the intermediate transfer belt (intermediate transfer member) 4 is reduced, the black belt image forming position on the photosensitive drum 1 is changed to the photosensitive drum 1 and the intermediate transfer belt 4. At the timing corresponding to the contact portion (primary transfer nip portion N1) (step S5). At this time, the rotational speeds of the fixing roller 14a and the pressure roller 14b of the fixing device 14 are also reduced.

Then, as described above, the full-color toner image on the intermediate transfer belt 4 is transferred to the transfer material P at the secondary transfer nip N2 (secondary transfer), and is transferred at the fixing nip N3 of the fixing device 14. A full-color toner image is formed on a material P, and a fixing roller 14a and a pressure roller 14b whose rotational speed is reduced.
(Step S)
6).

In step S3, the transfer material P is
However, in the case of ordinary paper, a normal image forming operation is performed without changing the rotational speed of the photosensitive drum 1, the intermediate transfer belt 4, the fixing roller 14a, and the pressing roller 14b without changing the speed (step S7). , And the image forming operation is terminated (step S8).

In step S6, the intermediate transfer belt 4
After secondary transfer of the upper full-color toner image to the transfer material P, the secondary transfer roller 11 is separated from the intermediate transfer belt 4 to apply a bias to the black belt image transferred onto the intermediate transfer belt 4. The charged toner is recharged by the belt cleaning roller 12, transferred to the photosensitive drum 1 again, and collected by the cleaning blade 5.

As described above, in the present embodiment, when the transfer material P is OHT, when the rotation speed of the photosensitive drum 1 is reduced, the contact portion (primary contact) between the photosensitive drum 1 and the intermediate transfer belt 4 is reduced. Since the toner (black band image) is interposed in the transfer nip portion N1), the photosensitive drum 1 and the intermediate transfer belt 4
The friction coefficient of the abutting portion (primary transfer nip portion N1) between the photosensitive drum 1 and the intermediate transfer belt 4 is reduced.

For this reason, the change in stress on the cleaning blade 5 is approximately only a shock due to deceleration, which is considerably simplified. The cleaning blade 5 used in the present embodiment can absorb the shock sufficiently to such a degree of change because the tip side is formed of the polyurethane rubber 5a, so that the chatter at the time of deceleration can be considerably reduced. Become. Therefore, generation of abnormal noise can be sufficiently suppressed. Further, the fixing device 1
Since the rotation speeds of the fixing roller 14a and the pressure roller 14b are also reduced, thermal fixing can be performed well even in the case of an OHT having a large amount of heat.

In the present embodiment, the deceleration mode when OHT is passed has been described. However, the present invention can be similarly applied to glossy paper, glossy film, and thick paper which are transfer materials having a large heat capacity. .

Second Embodiment The black band image shown in the first embodiment is a solid image and therefore has a large amount of toner. Therefore, there is a possibility that only the surface portion can be recharged by the belt cleaning roller 12 and that no charge is given to all the toner. This means that all of these toners cannot be collected on the photosensitive drum 1, resulting in contamination of the intermediate transfer belt 4. If this is left as it is, the uncleaned toner at that portion will be transferred onto the transfer material P at the time of the next image formation.

In order to prevent this, in the present embodiment,
Control described below is further performed on the control shown in the first embodiment.

As described in the first embodiment, when a black band image is formed during OHT sheet passing, the black band image is formed between the photosensitive drum 1 and the intermediate transfer belt 4 at the nip portion (primary transfer nip portion N1). Is applied, a negative DC bias having the same polarity as that of the toner is applied to the primary transfer roller 7. After the black band image has passed through the nip portion (primary transfer nip portion N1), an operation of collecting the secondary transfer residual toner on the photosensitive drum 1 must be performed.
, A normal positive DC bias is applied. Other controls are the same as in the first embodiment.

With this control, in the present embodiment, in addition to the effects obtained in the first embodiment, since the black band image is not transferred to the intermediate transfer belt 4, the contamination of the intermediate transfer belt 4 by the toner is eliminated. Can be reliably prevented.

In each of the above-described embodiments, the endless intermediate transfer belt is used as the intermediate transfer member. However, in the image forming apparatus using the drum-like intermediate transfer drum as the intermediate transfer member, the image forming apparatus is not limited. The present invention can also be applied to the present invention.

[0092]

As described above, according to the present invention,
Before the secondary transfer of the toner image primary-transferred to the intermediate transfer member to the transfer material by the secondary transfer member, each of the image carrier, the intermediate transfer member, and the pair of fixing rotators is performed according to the type of the transfer material. When the rotational speed of the image carrier is changed from the normal rotational speed, the image carrier, the intermediate transfer body, and the image carrier and the intermediate transfer The developing means performs development on the image carrier so that the toner is interposed in the primary transfer portion where the image carrier is in contact with, thereby cleaning the image carrier generated when the rotation speed of the image carrier changes (during deceleration). By simplifying the change in stress applied to the member,
Since chatter of the cleaning member can be significantly reduced, generation of abnormal noise can be suppressed within an allowable range.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a layer configuration of a photosensitive drum.

FIG. 3 is a schematic configuration diagram illustrating a developing device.

FIG. 4 is a schematic configuration diagram showing a cleaning blade.

FIG. 5 is a view for explaining a set angle and a penetration amount of a cleaning blade with respect to a photosensitive drum.

FIG. 6 is a diagram illustrating a shape factor SF1 of a toner.

FIG. 7 is a flowchart illustrating control according to the first embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 2 charging roller 3 developing device (developing means) 3a, 3b, 3c, 3d developing device 4 intermediate transfer belt (intermediate transfer member) 5 cleaning blade (cleaning member) 5a polyurethane rubber 6 exposure device 7 Primary transfer roller 11 Secondary transfer roller 12 Intermediate transfer belt cleaning roller 14 Fixing device (fixing means) 14a Fixing roller (fixing rotator) 14b Pressure roller (fixing rotator)

Continued on the front page F term (reference) 2H027 DC02 ED02 ED08 ED24 ED25 EE03 JA17 2H032 BA09 BA13 CA13 2H034 AA07 BF00 BF08

Claims (13)

[Claims] A rotatable image carrier for carrying an electrostatic latent image; a developing means for developing the electrostatic latent image to form a toner image on the surface of the image carrier; A rotatable intermediate transfer member that abuts at a primary transfer portion and temporarily transfers and carries the toner image formed on the image carrier, and transfers the toner image primarily transferred to the intermediate transfer member A secondary transfer member for secondary transfer to a material, and a leading end abutting on a downstream side in a rotation direction of the image carrier with respect to the primary transfer portion on the image carrier;
The intermediate transfer, comprising: a plate-shaped cleaning member for removing transfer residual toner remaining on the image carrier; and a fixing unit having a pair of rotatable fixing rotators abutting on each other at a fixing unit. The toner image primarily transferred to the body is
Before the secondary transfer to the transfer material is started by the next transfer member, the rotational speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators is set at a fixed rate according to the type of the transfer material. In the image forming apparatus, the toner image primary-transferred to the intermediate transfer member is subjected to secondary transfer to a transfer material by the secondary transfer member, according to the type of the transfer material. When changing the rotation speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators from a normal rotation speed, the image carrier, the intermediate transfer member, and the pair of fixing rotators are changed. At the timing when the rotation speed of each body changes, development on the image carrier is performed by the developing means such that toner is interposed in the primary transfer portion where the image carrier and the intermediate transfer body are in contact. Image forming apparatus 2. When the transfer material is not a normal transfer material but a specific transfer material, a secondary transfer of the toner image primarily transferred to the intermediate transfer member to the transfer material is started by the secondary transfer member. Before, the rotation speed of each of the image carrier, the intermediate transfer body, and the pair of fixing rotators is reduced at a substantially constant rate from a normal rotation speed at a fixed rate, and the transfer material is other than the specific transfer material. 2. The image forming apparatus according to claim 1, wherein in the case of (1), the rotation speed of each of the image carrier, the intermediate transfer member, and the pair of fixing rotators is not changed from a normal rotation speed. . 3. The image forming apparatus according to claim 2, wherein the specific transfer material is a transparent film used for an overhead projector. 4. The image forming apparatus according to claim 2, wherein the specific transfer material is a gloss film. 5. The image forming apparatus according to claim 2, wherein the specific transfer material is gloss paper. 6. The image forming apparatus according to claim 2, wherein the specific transfer material is thick paper. 7. The secondary transfer member abuts on the intermediate transfer member at the secondary transfer portion, and a surface that rotates at a substantially constant speed in a forward direction with respect to a rotation direction of the intermediate transfer member has elasticity. A secondary transfer roller having, before the secondary transfer of the toner image primary-transferred to the intermediate transfer member onto a transfer material by the secondary transfer roller, the image bearing member in accordance with the type of the transfer material. Body, the intermediate transfer body, when changing the rotation speed of each of the pair of fixing rotators from the normal rotation speed,
7. The image forming apparatus according to claim 1, wherein the rotation speed of the secondary transfer roller is changed accordingly. 8. The image forming apparatus according to claim 1, wherein the rotation speed of the intermediate transfer member is slightly higher than the rotation speed of the image carrier.
The image forming apparatus as described in the above. 9. The image bearing member, the intermediate transfer member, and the intermediate transfer member are separated from each other at a timing when the rotation speed of each of the pair of fixing rotators changes from a normal rotation speed. 5. The image forming apparatus according to claim 1, wherein the toner interposed in the abutting primary transfer unit is interposed over the entire developable longitudinal area of the image carrier. 9. The image forming apparatus according to 8. 10. The cleaning device according to claim 1, wherein at least a tip side of the cleaning member that contacts the image carrier is formed of polyurethane rubber.
10. The image forming apparatus according to 8 or 9. 11. A cleaning means for removing untransferred toner remaining on the intermediate transfer member downstream of the secondary transfer portion on the intermediate transfer member in the rotation direction of the intermediate transfer member. It is arrange | positioned so that it can contact and separate freely, The Claims 1, 2, 3, 4, 5, 6, 7,
11. The image forming apparatus according to 8, 9, or 10. 12. The image forming apparatus according to claim 1, wherein a bias having a polarity opposite to a charging polarity of the toner is applied to the intermediate transfer body to transfer the toner on the image carrier to the intermediate transfer body. 2, 3, 4, 5, 6, 7,
12. The image forming apparatus according to 8, 9, 10 or 11. 13. The image bearing member, the intermediate transfer member, and the intermediate transfer member are separated from each other at a timing at which a rotation speed of each of the pair of fixing rotators changes from a normal rotation speed. 13. The image forming apparatus according to claim 12, wherein a bias having the same polarity as the charged polarity of the toner is applied to the intermediate transfer body while the toner is interposed in the primary transfer unit that is in contact with the primary transfer unit. .