JP3129659B2 - Intermediate transfer belt for image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer, in which a toner image formed on an image carrier such as a photosensitive drum is temporarily received by electrostatic transfer in accordance with image information. Thereafter, the present invention relates to a belt-like intermediate transfer member for re-transferring this to a recording sheet, that is, an intermediate transfer member belt.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus for forming a recorded image using an intermediate transfer belt of this type, an image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 62-206567 is known.

Specifically, as shown in FIG. 1, after an unfixed toner image T corresponding to image information is formed on a latent image carrier 100 such as a photosensitive drum, first, a plurality of toner images T are formed. The toner image T is primarily transferred onto the intermediate transfer belt 101 wound around the rollers, and the toner image T is again transferred to the intermediate transfer belt 10.
It is configured such that a desired recording image is formed on the recording sheet 102 by performing secondary transfer from No. 1 to the recording sheet 102.

In particular, the illustrated image forming apparatus is provided with developing units 103 to 106 corresponding to black (Bk), yellow (Y), magenta (M), and cyan (C) around the latent image carrier 100. A non-fixed toner image T of each color sequentially formed on the latent image carrier 100 is transferred to the intermediate transfer belt 101 in a multiplex manner.
A composite image in which the toner images T overlap each other is formed on the intermediate transfer belt, and the composite image is collectively transferred to the recording medium 102 so that a full-color recorded image can be formed.

The primary transfer of the toner image from the latent image carrier 100 to the intermediate transfer belt 101 and the secondary transfer of the toner image from the intermediate transfer belt 101 to the recording sheet 102 are performed by an electrostatic transfer method. When a voltage having a polarity opposite to that of the toner is applied to the corona discharger 107 or the bias roll 108 disposed on the back side of the transfer target at each transfer position, the unfixed toner image is transferred from the latent image carrier 100 to the intermediate transfer. Transferred to the body 101 or the intermediate transfer body 101
Is transferred to the recording medium 102.

In transferring the toner image onto the intermediate transfer belt by such an electrostatic transfer method, it is important that the intermediate transfer belt has a predetermined surface resistivity. If the surface resistivity is too high, the intermediate transfer belt is remarkably charged at the time of transfer of the toner image, so that when the intermediate transfer belt is separated from the latent image carrier, a peeling discharge occurs, and the intermediate transfer belt is separated. While the toner image transferred to the belt is scattered due to the discharge, if the surface resistivity is too low, an excessive current flows between the intermediate transfer belt and the latent image carrier, so that the toner image is temporarily stopped. This is because a phenomenon called so-called retransfer occurs in which the toner image transferred to the intermediate transfer belt returns to the latent image carrier.

For this reason, conventionally, carbon black such as acetylene black, furnace black or channel black is added to a resin composition such as polyamide, polyimide, polyvinylidene fluoride (PVDF) and the like, and this is added to several tens to several hundreds μm. An intermediate transfer belt having a predetermined surface resistivity is obtained by molding the belt to a thickness of
1267, JP-A-5-170946, JP-A-6-228335, etc.).

[0008]

The carbon black, which adjusts the surface resistivity of the intermediate transfer belt, tends to bond in a chain in the resin composition to which the carbon black is added. Accordingly, the surface resistivity of the intermediate transfer member belt varies. That is, the longer the chain bond, the higher the conductivity of the intermediate transfer belt and the lower its surface resistivity, while the shorter the chain bond, the lower the conductivity and the higher its surface resistivity. Therefore, when carbon black forming a long chain bond is added to the resin composition, the surface resistivity of the intermediate transfer belt is lower than when carbon black forming a short chain bond is added in the same amount. It will change greatly.

Here, the length of the above-mentioned chain bond depends on the particle size, surface activity, etc. of the individual particles of carbon black, and one of the indicators indicating this is ASTM (American Standard Test Method) D2414. Has DBP oil absorption as defined at -6TT. The DBP oil absorption indicates the amount (ml) of dibutyl phthalate (DBP) absorbed by 100 g of carbon black, and it is considered that carbon black having higher DBP oil absorption forms a longer chain bond. ing.

For this reason, when manufacturing the intermediate transfer belt, if only the carbon black having high DBP oil absorption is added to adjust the surface resistivity of the intermediate transfer belt, the amount of addition is slightly increased or decreased. However, the surface resistivity greatly changes, and there is a problem that the target surface resistivity cannot be given to the intermediate transfer belt unless the amount of carbon black added is strictly specified.

[0011] Further, the fact that the chain bond of carbon black is long is equivalent to the fact that more carbon black particles are agglomerated in one place, so that only carbon black having a high DBP oil absorption property is contained in the resin composition. When the carbon black is added, the interval between the chains of the carbon blacks adjacent to each other is widened, and as a result, the carbon blacks are dispersed in the resin composition. For this reason, even when a desired surface resistivity is given to the intermediate transfer belt, there is a problem that unevenness in resistance along the surface direction of the belt is noticeable in the surface resistivity.

On the other hand, if the surface resistivity of the intermediate transfer belt is adjusted by adding only carbon black having a low DBP oil absorbing property, the rate of change of the surface resistivity with the increase or decrease of the amount of addition is reduced. As a result, the carbon black is more uniformly dispersed in the resin composition than when only high-performance carbon black is added, so that both of the two problems described above can be avoided.

However, in such a case, in order to impart a desired surface resistivity to the intermediate transfer belt, it is necessary to add a larger amount of carbon black than when only carbon black having high DBP oil absorption is added. Since the compounding ratio of carbon black in the composition is increased, the strength of the intermediate transfer belt is reduced, and there is a problem that cracks are easily generated when the belt is driven.

The present invention has been made in view of the above problems, and has as its object to receive a toner image formed on an image carrier according to image information by electrostatic transfer. An intermediate transfer belt for an image forming apparatus for re-transferring the toner image onto a recording sheet, wherein a predetermined surface resistivity can be easily given to manufacture the belt, and the durability against use over time. Another object of the present invention is to provide an intermediate transfer belt having the above function.

Another object of the present invention is to provide an intermediate transfer member capable of providing a predetermined surface resistivity to an intermediate transfer belt and suppressing variations in surface resistivity along a surface direction of the belt. To provide a belt.

[0016]

In order to achieve the above object, an intermediate transfer belt of the present invention has a predetermined surface resistivity, and a toner image formed on an image carrier according to image information. Is an intermediate transfer belt of an image forming apparatus for re-transferring the toner image to a recording sheet after electrostatic transfer, wherein two types of carbon blacks having different DBP oil absorbing properties are added to a resin composition. Characterized by being formed by molding the resin composition.

According to such technical means, since two kinds of carbon blacks having different DBP oil absorbing properties are added to the resin composition, the amount of the carbon black having the lower DBP oil absorbing property is increased or decreased. The surface resistivity of the intermediate transfer belt can be adjusted little by little by
The surface resistivity can be easily adjusted to a desired value as compared with the case where only carbon black having a high oil absorbing property is added.

Further, since carbon black having high DBP oil absorption is added in addition to carbon black having low oil absorption of DBP, it is possible to obtain a desired surface resistivity as compared with the case where only the former is added. Since the total amount of required carbon black is reduced, it is possible to prevent the strength of the intermediate transfer belt from lowering.

The two types of carbon black added to the resin composition may be of any type as long as there is a difference between their DBP oil absorption properties. However, if the difference is too small. There is a concern that the same problem as when one kind of carbon black is added may occur. Therefore, the two types of carbon black in the present invention are DBP
It is preferable that the oil absorbency has a difference of at least a certain degree. Specifically, the carbon black having a higher DBP oil absorbency has a DBP oil absorption of 250 ml / 100 g or more, Black DBP
It is preferable that the oil absorption is 100 ml / 100 g or less.

The carbon blacks having high DBP oil absorbency include Lion Aguso Co., Ltd./Ketchen Black (DBP lubrication amount: 360 ml / 100 g), and Electrochemical Co., Ltd./granular acetylene black (DBP lubrication amount: 28).
8ml / 100g), manufactured by Cabot Corporation / Vulcan X
C-72 (DBP refueling amount 265 ml / 100 g), Asahi Carbon Co., Ltd./HS-500 (DBP refueling amount 447 m
l / 100g) etc., while DBP
Asahi Carbon Co., Ltd./Asahi Thermal FT (DBP lubrication amount 28 ml
/ 100g), manufactured by Asahi Carbon Co., Ltd./Asahi Thermal M
T (DBP refueling amount 35 ml / 100 g) or the like can be used.

Further, as described above, the intermediate transfer belt of the present invention is used by rotating and using the belt.
If the Young's modulus is small, the belt expands in the rotation direction due to the tensile stress applied during driving, resulting in a color shift in a composite image of the toner images of the respective colors superimposed on the intermediate transfer belt. Therefore, from this point of view, the higher the Young's modulus of the intermediate transfer belt, the better, preferably 35,000 kg / cm ² or more.

Examples of the resin composition having a Young's modulus of 35,000 kg / cm ² or more include those containing a thermosetting polyimide, a thermoplastic polyimide or the like as a main component. When forming into an endless belt shape by the film method, there is a problem that the evaporation of the solvent is likely to be non-uniform, and minute irregularities are likely to be generated on the surface of the formed intermediate transfer belt. Accordingly, from the viewpoint of maintaining the image quality of the toner image transferred to the intermediate transfer belt,
It is preferable to use a thermoplastic resin that can be formed into a belt shape by extrusion or injection molding.

On the other hand, the mixing ratio of carbon black having a high DBP oil absorption and that having a low DBP oil absorption in the resin composition is such as to provide a predetermined surface resistivity to the intermediate transfer belt. If the mixing ratio of the carbon black having a low DBP oil absorption is higher, the carbon black is more uniformly dispersed in the intermediate transfer belt. This makes it possible to suppress variations in the surface resistance.

On the other hand, as the total weight of carbon black added to the resin composition increases, the mechanical strength such as toughness of the intermediate transfer belt formed from the resin composition is lost.
Since cracks occur in the intermediate transfer belt in a short period of time, there is an upper limit to the total weight of carbon black that can be added to the resin composition in relation to such mechanical strength. For this reason, if the addition amount of carbon black having high DBP oil absorption is increased unnecessarily and the addition amount of carbon black having low DBP oil absorption is increased, it is necessary to give a predetermined surface resistivity to the intermediate transfer belt. Therefore, the total weight of the carbon black increases significantly, and the toughness of the intermediate transfer belt is impaired.

Therefore, from this viewpoint, first, the upper limit of the total weight of the carbon black that can be blended in the resin composition is determined from the relationship with the mechanical strength required for the intermediate transfer belt. It is preferable to adjust the surface resistivity of the intermediate transfer belt to a predetermined value while preferentially blending carbon black having a low DBP oil absorption over carbon black having a high DBP oil absorption.

Here, that the carbon black with low DBP oil absorption is preferentially mixed with the carbon black with high DBP oil absorption means that the former is added to the resin composition as much as possible while the intermediate transfer belt is added. Means that the total weight of carbon black, which has both low and high DBP oil absorbency, does not exceed the initially determined upper limit. In other words, DB
P means that, while adding two types of carbon blacks having different oil-absorbing properties to the resin composition, the compounding ratio is determined so that the total weight of these carboblacks approaches a predetermined upper limit as much as possible. .

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a toner image transfer device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a color electrophotographic copying machine to which the present invention is applied.
Reference numeral 1 denotes a photosensitive drum (latent image carrier), and an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum by a well-known electrophotographic process (not shown) with rotation in the direction of arrow A. Is done. That is, after the photosensitive drum 1 is charged to a predetermined dark potential by the charger 1a, exposure is performed according to an image signal by a light beam Bm emitted from a laser beam scanner (not shown). Further, developing devices 5 to 8 corresponding to black (Bk), yellow (Y), magenta (M) and cyan (C) are provided around the photosensitive drum 1.
Is provided, and the electrostatic latent image formed on the photosensitive drum 1 is developed by any one of the developing devices to form a toner image T. Therefore, if the electrostatic latent image written on the photosensitive drum 1 corresponds to yellow image information, this electrostatic latent image is developed by the developing device 6 containing yellow (Y) toner, and A yellow toner image is formed on the body drum 1.

Reference numeral 2 denotes an intermediate transfer member belt arranged so as to be in contact with the surface of the photosensitive drum 1, and is stretched around a plurality of rolls and rotates in the direction of arrow B. The unfixed toner image T formed on the photosensitive drum 1 is transferred from the photosensitive drum 1 to the surface of the intermediate transfer belt 2 at a primary transfer position where the photosensitive drum 1 contacts the intermediate transfer belt 2. . At this primary transfer position, a corona discharger 9 is disposed on the back side of the intermediate transfer belt 2,
An unfixed toner image T on the photosensitive drum 1 is electrostatically attracted to the intermediate transfer belt 2 by applying a voltage having a polarity opposite to the charged polarity of the toner to the corona discharger 9.

When a monochromatic image is formed, the unfixed toner image T primarily transferred to the intermediate transfer belt 2 is secondarily transferred to the recording sheet 3 immediately, but a color image in which a plurality of color toner images are superimposed. Is formed, the process of forming the toner image on the photosensitive drum 1 and the primary transfer process of this toner image are repeated by the number of colors. For example, when forming a full-color image in which four color toner images are superimposed,
An unfixed toner image T of black, yellow, magenta, and cyan is formed on the photoreceptor drum 1 for each rotation, and these unfixed toner images T are sequentially transferred to the intermediate transfer belt 2.
Is primary-transferred. On the other hand, the intermediate transfer belt 2 rotates at the same cycle as the photosensitive drum 1 while holding the black unfixed toner image T that has been firstly transferred, and the intermediate transfer belt 2 moves on the intermediate transfer belt 2 every one rotation thereof. The unfixed toner image T of yellow, magenta, and cyan is replaced with the unfixed toner image T of black.
Is transcribed on top of

The unfixed toner image T primarily transferred to the intermediate transfer belt 2 in this manner moves to a secondary transfer position facing the conveyance path of the recording sheet 3 as the intermediate transfer belt 2 rotates. Conveyed. At the secondary transfer position, a semiconductive bias roll 10 is in contact with the intermediate transfer belt 2, and the recording sheet 3 carried out of the tray 12 at a predetermined timing by the feed roller 11 is separated from the bias roll 10 and the intermediate transfer member. It is sandwiched between the belt 2.
On the back side of the intermediate transfer belt 2 at the secondary transfer position, a backup roll 4 serving as an opposite electrode of the bias roll 10 is provided. Is applied,
The unfixed toner image T carried on the intermediate transfer belt 2 is electrostatically transferred to the recording sheet 3 at the secondary transfer position.

Then, the recording sheet 3 to which the unfixed toner image has been transferred is peeled off from the intermediate transfer belt 2 by the peeling claw 13 and sent to a fixing device (not shown) to fix the unfixed toner image. You. On the other hand, the intermediate transfer belt 2 on which the secondary transfer of the unfixed toner image has been completed is
As a result, residual toner is removed.

In the above configuration, the bias roll 10, the peeling claw 13, and the cleaner 15 are disposed so as to be able to freely contact and separate from the intermediate transfer belt 2, and when a color image is formed, the final color is not determined. These members are separated from the intermediate transfer belt 2 until the applied toner image is primarily transferred to the intermediate transfer belt 2.

Next, the intermediate transfer belt 2 used in this embodiment will be described. Intermediate transfer member belt 2 of the present embodiment
Is a thermoplastic polyimide (Mitsui Toatsu Chemical Co., Ltd./NE
W-TPI) in the form of a belt having a width of 100 mm and a thickness of 125 μm. In order to adjust the surface resistivity of the belt to about 10 ¹⁰ to 10 ¹³ Ω / □, the above resin composition is used. Two types of carbon black having different DBP oil absorbing properties are added therein.

As the carbon black, carbon black having a DBP oil absorption of 288 ml / 100 g (manufactured by Denki Kagaku Co., Ltd./granular acetylene black) and carbon black having a DBP oil absorption of 28 ml / 100 g (manufactured by Asahi Carbon Co., Ltd.) Asahi Thermal FT), 10 parts by weight of the former was added to 100 parts by weight of the resin composition, and 5 to 10 parts by weight of the latter was added.

As a specific molding method, the thermoplastic polyimide to which the carbon black was added was uniformly mixed with a Banbury mixer or the like, and then first molded into resin pellets using a twin-screw extruder. The resin pellets are extruded into a sheet using a T-die single screw extruder under the conditions of a die temperature of 400 ° C. and a screw rotation speed of 100 rpm, and this is cast on a roll having a surface temperature of 200 ° C. Then, a film was formed in a belt shape.

FIG. 2 shows the results when the amount of carbon black having low DBP oil absorption was changed between 5 and 10 parts by weight.
5 is a graph showing a change in surface resistivity of the intermediate transfer belt 2. As apparent from this graph, the surface resistivity of the intermediate transfer member when 5 parts by weight of carbon black having low DBP oil absorption was added was 13.2 (logΩ / □), and the surface resistivity when 7 parts by weight was added. Is 11.5 (logΩ /
□) The surface resistivity is 9.8 when 10 parts by weight are added.
(Log Ω / □), and the decrease in surface resistivity with respect to the increase of 5 parts by weight of the low DBP oil-absorbing carbon black was 4.
It was reduced to four digits.

On the other hand, FIG. 3 shows that only carbon black having high DBP oil absorption was added to 100 parts by weight of the resin composition made of thermoplastic polyimide, and the amount of addition was 5 to 5.
Intermediate transfer belt 2 when changed between 13 parts by weight
5 is a graph showing a change in surface resistivity of the sample (hereinafter, referred to as a comparative example). The method of forming the intermediate transfer belt is exactly the same as that described above. As is apparent from this graph, the surface resistivity of the intermediate transfer belt 2 sharply changes around the time when the amount of carbon black having high DBP oil absorption exceeds 12 parts by weight. The surface resistivity was reduced by four orders of magnitude even if the amount of added was increased by only 2 parts by weight.

That is, according to these graphs, DB
The intermediate transfer belt of the present example in which two kinds of carbon blacks having different P oil absorbing properties were added to the resin composition,
It is apparent that the surface resistivity of the belt is easier to be set within the target numerical range than the intermediate transfer belt of the comparative example in which only the high DBP oil absorbing carbon black is added to the resin composition.

On the other hand, Table 1 below shows the results of measuring the variation in the surface resistivity of both the intermediate transfer belt of the present embodiment and the intermediate transfer belt of the comparative example. For such measurement, width 100mm, length 300m
The surface resistivity was measured for 12 points of each test piece using the test pieces of the intermediate transfer belt formed into a film having a thickness of 125 μm, and the average value, standard deviation, and maximum value of the variation were obtained. . In addition, as the intermediate transfer belt of the present embodiment, three types of carbon black (Asahi Thermal FT) having a low DBP oil absorption and different amounts of 5 parts by weight, 7 parts by weight, and 10 parts by weight are used. As the intermediate transfer belt of the comparative example, a belt having 13 parts by weight of carbon black (acetylene black) having high DBP oil absorption was used.

[0040]

[Table 1]

As is apparent from the results, the intermediate transfer belt of the comparative example has the maximum value of the variation of the surface resistivity within one digit in logarithmic value in the intermediate transfer belt of the present embodiment. The maximum value of the variation was as large as 1.5 digits in logarithmic value.

From this fact, when carbon black having high DBP oil absorption is mixed with carbon black having high DBP oil absorption and added to the resin composition, carbon black having only high DBP oil absorption is added to the resin composition. Also, it was confirmed that the variation of the surface resistivity along the surface direction of the intermediate transfer member belt was reduced.

When the three types of intermediate transfer belts of the present embodiment were compared, the surface resistance was better when a large amount of low DBP oil absorbing carbon black was blended with a fixed amount of high DBP oil absorbing carbon black. It was also found that the variation in rate was small.

However, it has been confirmed by the present inventor that if the total weight of carbon black added to 100 parts by weight of the thermoplastic polyimide exceeds 20 parts by weight, mechanical properties such as the toughness of the intermediate transfer belt will be reduced. It has been found that the durability is significantly reduced, for example, the initial strength is impaired and cracks are generated early.

Therefore, in forming the intermediate transfer belt of this embodiment, carbon black is added in a range where the sum of the high DBP oil-absorbing carbon black and the low DBP oil-absorbing carbon black does not exceed 20 parts by weight. It is necessary to mix more carbon black having low DBP oil absorption within this range, and to make the surface resistivity of the intermediate transfer belt conform to the range of 10 ¹⁰ to 10 ¹³ Ω / □. Ideal.

That is, in Table 1 described above, the surface resistivity of the intermediate transfer belt of the present embodiment in which 10 parts by weight of acetylene black and 7 parts by weight of Asahi Thermal FT are blended is 11.5 (logΩ / □). If 9 parts by weight of acetylene black and 11 parts by weight of Asahi Thermal FT can be mixed to obtain the same surface resistivity, the variation in the surface resistivity can be reduced.

The surface resistivity of the intermediate transfer belt in the present specification was measured using an HR probe of Hiresta IP manufactured by Mitsubishi Yuka. In particular,
After applying a voltage of 500 V to the intermediate transfer belt, a current value I after 30 seconds was measured, and R = 500
The resistance was determined from / I.

[0048]

As described above, according to the intermediate transfer belt of the image forming apparatus of the present invention, since two kinds of carbon blacks having different DBP oil absorbing properties are added to the resin composition, By increasing or decreasing the amount of carbon black having low DBP oil absorption, a predetermined surface resistivity can be easily given to the intermediate transfer belt,
By adjusting the amount of carbon black having high DBP oil absorption, the total amount of carbon black required to obtain a desired surface resistivity can be reduced, and the durability against use over time can be increased. It becomes possible.

Further, according to the method of manufacturing an intermediate transfer belt of the present invention, carbon black which can be added to a resin composition predetermined in consideration of the mechanical strength required for the intermediate transfer belt is used. DBP within the total weight
By adjusting the surface resistivity of the intermediate transfer belt to a predetermined value while preferentially blending carbon black having low oil absorbency with carbon black having high oil absorbency of DBP, the carbon black along the surface direction of the intermediate transfer belt is adjusted. It is possible to minimize the variation in the surface resistivity that occurs as much as possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a color image forming apparatus using an intermediate transfer belt of the present invention.

FIG. 2 is a graph showing a change in surface resistivity of the intermediate transfer belt when the amount of carbon black exhibiting low DBP oil absorption is changed in the intermediate transfer belt according to an example.

FIG. 3 is a graph showing a change in surface resistivity of the intermediate transfer belt with respect to a change in the amount of carbon black when only carbon black exhibiting high DBP oil absorption is added.

FIG. 4 is a schematic view showing a conventional color image forming apparatus using an intermediate transfer belt.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum (latent image carrier), 2 ... Intermediate transfer belt, 3 ... Recording sheet, T ... Toner image

Claims (4)

(57) [Claims] An image forming apparatus having a predetermined surface resistivity, receiving a toner image formed on an image carrier according to image information by electrostatic transfer, and retransferring the toner image to a recording sheet. an intermediate transfer belt of the apparatus, a DBP oil absorption of different two types of carbon black were added in the resin composition with each other, it by molding the resin composition
Ri, DBP oil absorption of carbon black having a higher DBP oil absorption
The amount is 250ml / 100g or more and DBP oil absorption
DBP oil absorption of lower carbon black is 100ml
/ 100 g or less, intermediate transfer belt. 2. The intermediate transfer belt according to claim 1, wherein
The intermediate transfer belt having a Young's modulus of 35,000 kg / cm ² or more . 3. The method according to claim 1 or 2, wherein
An image forming apparatus using the intermediate transfer belt . 4. The production of the intermediate transfer belt according to claim 1.
Method, wherein the relationship with the mechanical strength required for the intermediate transfer belt
The total amount of carbon black that can be blended in the above resin composition
After determining the upper limit of the weight, DBP oil absorption within this range
Low carbon black with high DBP oil absorption
While adding the black toner in preference to black,
A method for manufacturing an intermediate transfer belt, wherein the surface resistivity of the belt is adjusted to a predetermined value .