JP2006072096A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where an amorphous silicon photoreceptor is loaded, in which the photoreceptor can be uniformly charged and stable picture quality can be obtained with no ghost and little production of ozone or NOx. <P>SOLUTION: The image forming apparatus is equipped with an image carrier, a charging means to charge the image carrier, an exposing means to form an electrostatic latent image on the surface of the image carrier, a developing means to convert the electrostatic latent image into a toner image, a transferring means to transfer the toner image onto a transfer material, a fixing means to thermally fix the toner image on a recording medium, and photo-destaticizing means to remove residual charges by exposing the surface of the image carrier to light. The image forming apparatus is characterized in that: the image carrier is made of amorphous silicon; and the exposure light quantity E of the photo-destaticizing means is controlled to the range indicated by an expression (1): Emin≤E≤5×Emin. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic method or an electrostatic recording method, and in particular, an image forming apparatus capable of forming a high-quality image with high speed and high durability. About.

  Electrophotographic technology is widely used in the fields of copiers, printers, and the like because it provides high speed and high print quality. Various electrophotographic photoreceptors (image carriers) used in these electrophotographic techniques have been proposed and put to practical use. Among them, the functionally separated organic laminated photoconductor (OPC photoconductor), in which a charge generation layer that generates a charge upon exposure and a charge transport layer that transports a charge is laminated, has an electron, sensitivity, chargeability, and repeated stability. It is excellent in terms of photographic characteristics, and various proposals have been made, leading to practical use.

  On the other hand, in the field of high-speed machines, an image forming apparatus using an amorphous silicon photoconductor has been proposed because it has higher durability and longer life than the OPC photoconductor (see, for example, Patent Document 1). . However, in an image forming apparatus using an amorphous silicon photoreceptor, a so-called ghost problem is often noticeable due to insufficient charging ability due to the high dielectric constant and low dark resistance of amorphous silicon.

In order to improve the above problems, there has been proposed an image forming apparatus in which the process speed is 300 to 400 mm / sec, the amount of neutralizing light is 5.0 to 8.0 μJ / cm ² , and the wavelength of neutralizing light is 500 to 700 nm (for example, , See Patent Document 2).

  However, in order to obtain a sufficient photosensitive member charging potential within the above-mentioned range of the amount of static elimination light, the wire current value (charging current value) of the scorotron, which is a corona charger, must be increased. Increasing the wire current value increases the generation amount of ozone and NOx, which is unfavorable for the environment, and the generation of these decreases the surface resistance of the photoreceptor and causes a so-called image flow problem.

Therefore, if the amorphous silicon photosensitive member is used with a large charging current, the problem of ghost generation can be avoided, but the conventional technique is insufficient when considering environmental problems and image flow problems.
Japanese Patent Publication No. 60-35059 JP-A-8-171319

The object of the present invention is to solve the above-mentioned problems of the prior art.
That is, according to the present invention, in an image forming apparatus equipped with an amorphous silicon photoconductor, the photoconductor can be uniformly charged, no ghost is generated, and a stable image quality with less ozone and NOx generation is obtained. An object is to provide a forming apparatus.

The above-mentioned subject is achieved by the following present invention. That is, the present invention
<1> At least an image carrier, charging means for uniformly charging the image carrier, exposure means for forming an electrostatic latent image on the surface of the image carrier, and developing the electrostatic latent image with toner Developing means for forming a toner image by developing with an agent, transfer means for transferring the toner image on the image carrier onto a transfer target, fixing means for thermally fixing the toner image on a recording medium, and after transfer In the image forming apparatus provided with a light neutralizing unit that exposes the surface of the image carrier to remove residual charges,
The image carrier is amorphous silicon, and E is set to a range represented by the following formula (1), where E (μJ / cm ² ) is the exposure light quantity of the light neutralizing means. Forming device.
Emin ≦ E ≦ 5 × Emin (1)

In the equation, Emin (μJ / cm ² ) is a value obtained when the attenuation of the image carrier potential is saturated in the relationship between the exposure light quantity and the image carrier potential when the image carrier charged to a constant potential is exposed. Represents exposure light quantity.

<2> The image forming apparatus according to <1>, wherein the charging unit is a corona charger, and a charging current value is in a range of 500 to 800 μA.

<3> The image forming apparatus according to <1> or <2>, wherein the polarity of the charging potential of the image carrier and the polarity of the transfer voltage in the transfer unit are the same.

  According to the present invention, in an image forming apparatus equipped with an amorphous silicon photoconductor, the photoconductor can be uniformly charged, ghosts are not generated, and an image with a stable image quality that generates less ozone and NOx is obtained. A forming apparatus can be provided.

Hereinafter, the present invention will be described in detail.
The image forming apparatus of the present invention includes at least an image carrier, a charging unit that uniformly charges the image carrier, an exposure unit that forms an electrostatic latent image on the surface of the image carrier, and the electrostatic latent image. Is developed with a developer containing toner to form a toner image, transfer means for transferring the toner image on the image carrier onto the transfer target, and the toner image is thermally fixed on a recording medium. In an image forming apparatus including a fixing unit and a photostatic discharge unit that exposes the surface of the image carrier after transfer to remove residual charges, the image carrier is amorphous silicon, and the amount of exposure light of the photostatic unit is An image forming apparatus, wherein E is set to a range represented by the following formula (1) where E (μJ / cm ² ).
Emin ≦ E ≦ 5 × Emin (1)

In the above formula, Emin (μJ / cm ² ) represents the exposure light amount at which the attenuation of the image carrier potential is saturated in the relationship between the exposure light amount and the image carrier potential with respect to the image carrier charged to a constant potential.

  Conventionally, when amorphous silicon is used as a photoconductor (image carrier), it is 7 kV or more (900 μA or more in charging current) in a non-contact type corona charger such as Scorotron because of its low charging ability. Therefore, the ghost based on the optical memory is hardly a problem, and the amount of static elimination in the photostatic elimination after transfer has not been studied in detail.

However, if the high bias application is continued with the corona charger as described above, the generation amount of ozone and NOx (corona product) increases, which causes an environmental problem. Also, the corona product causes discharge products to adhere to the surface of the photoreceptor, so-called image flow occurs.
Therefore, in order to suppress the occurrence of the above problem, it is desirable to reduce the applied bias for charging as much as possible.

When the charge application bias is lowered, the ghost is likely to be generated. Therefore, it is necessary to control the light removal amount within an appropriate range.
The present inventors have found the conditions for photostatic discharge under charging conditions in which the generation amount of corona product, which has not been clarified so far, has been completed, and the present invention has been completed.

Hereinafter, the configuration of the image forming apparatus of the present invention will be described first.
As described above, the image forming apparatus of the present invention includes at least an image carrier, a charging unit, an exposure unit, a developing unit, a transfer unit, a fixing unit, and a light neutralizing unit. A member may be provided, and for example, a cleaning unit for cleaning the surface of the photosensitive member after the toner image is transferred to the transfer target may be provided.

FIG. 1 is a schematic explanatory view showing an example of an image forming apparatus of the present invention.
The image forming apparatus includes a photoconductor (image carrier) 10, a charger (charging means) 11 that charges the surface of the photoconductor 10, a power source 12 for applying a voltage to the charger 11, and the photoconductor 10. An exposure unit (exposure unit) 13 that forms a latent image on the surface of the photosensitive member 10, a development unit (development unit) 14 that develops the electrostatic latent image on the surface of the photoconductor 10 to obtain a toner image, and the formed toner image on a sheet (Recording medium) 20 Transfer device (transfer means) 15 for transferring to the surface, cleaning device (cleaning means) 16 for removing residual toner and the like on the surface of the photoreceptor 10, and light removal for removing residual potential on the surface of the photoreceptor 10. It has an electric device (light neutralizing means) 17 and a fixing device (fixing means) 18 for fixing the toner image transferred on the surface of the paper 20 by heat and / or pressure.

The image forming process of the image forming apparatus will be briefly described as follows.
First, the surface of the drum-shaped photoconductor 10 rotating in the direction of the arrow is uniformly charged by the charger 11 to which a voltage is applied. An electrostatic latent image is written on the charged photoreceptor 10 by an exposure device 13 such as a laser optical system. The electrostatic latent image on the surface of the photoreceptor 10 is developed into a toner image by the developing device 14. Then, the toner image is transferred by the transfer unit 15 onto the paper 20 conveyed from a paper supply tray (not shown). After the transferred toner image is fixed on the paper 20 by the fixing device 18, the paper 20 is discharged out of the apparatus. Further, after the toner image is transferred to the paper 20, the toner remaining on the surface of the photoconductor 10 is removed by the blade of the cleaning device 16, and then is removed by the photostatic device 17 to prepare for the next image forming process.

As the photoreceptor 10, a drum-shaped amorphous silicon photoreceptor having a diameter of 84 mm is used. That is, as shown in the configuration cross-sectional view of FIG. 2, the photoconductor 10 includes a blocking layer 10d, a photoconductive layer (I) 10c, and a photoconductive layer (II) on a cylindrical substrate 10e made of, for example, aluminum as a conductive material. ) 10b and the surface layer 10a are sequentially laminated. The photoconductive layer (I) 10c and the photoconductive layer (II) 10b are formed mainly of an amorphous silicon material in which silicon atoms include hydrogen atoms and halogen atoms. The surface hardness of the photoconductor 10 is about 2000 kg / mm ² , and the charging device 11 and the transfer device 15 are corona chargers. Yes.

  A corona discharge type (non-contact charging type) charger (corona charger) 11 is disposed above the photoconductor 10 in the drawing, and the charger 11 is operated by a voltage supplied from a power source 12. In the present embodiment, the charger 11 is exemplified by a non-contact charging type, but a configuration using a so-called contact charging type charger that is in contact with the photosensitive member 10 such as a charging roll. However, it is preferable to use a corona charger in a high-speed machine having a linear speed of about 300 to 500 mm / sec.

  In this embodiment, a scorotron charger is used as the charger 11, and a voltage of +5 kV is applied to the wire of the charger and +520 V is applied to the grid (charging current: about 650 μA) at a peripheral speed of 350 mm / sec. The surface of the rotating photoconductor 10 is charged to about + 500V.

  The current value of the charging bias applied to the charger 11 is preferably in the range of 500 to 800 μA, more preferably in the range of 550 to 750 μA. If the current value is less than 500 μA, a sufficient charging potential may not be obtained. On the other hand, if it exceeds 800 μA, a corona product at a level that becomes a problem during operation of the image forming apparatus may be generated.

  As the exposure device 13, a known exposure means such as a combination of a semiconductor laser and a scanning device, a laser ROS comprising an optical system, an LED head, or a halogen lamp can be used. In order to realize a preferable mode in which the region of the exposure image, that is, the position of the surface of the photoreceptor on which the toner image is formed is changed as desired, it is preferable to use a laser ROS or an LED head. ROS is used.

  As the developing device 14, a conventionally known developing device can be used regardless of one-component system or two-component system as long as it has a function of forming a uniform toner image on the surface of the photoreceptor 10. In the present embodiment, the developing device 14 uses a two-component developer composed of a toner containing a styrene resin and a carrier, and the toner is charged to a positive polarity.

Examples of the method for producing the toner used in the present invention include a kneading and pulverizing method, a suspension polymerization method, an emulsion polymerization method, a dry granulation method in liquid, and the like. In order to obtain the toner, a polymerized toner such as a suspension polymerization method or an emulsion polymerization method is preferred, and a toner production method by emulsion polymerization is most desirable.
The toner used in the present invention preferably has a volume average particle diameter D _50v in the range of ₂ to 8 μm. The volume average particle diameter is measured, for example, with a measuring instrument such as Coulter Counter TAII (manufactured by Nikka Machine Co., Ltd.).

The toner shape factor SF1 in the present invention is preferably in the range of 100 to 140. Here, the shape factor SF1 is obtained by the following equation (2).
SF1 = (ML ² / A) × (π / 4) × 100 (2)
In the above formula (2), ML represents the absolute maximum length of the toner particles, and A represents the projected area of the toner particles.

  The SF1 is quantified mainly by analyzing a microscope image or a scanning electron microscope (SEM) image using an image analyzer, and can be calculated as follows, for example. That is, an optical microscope image of the toner scattered on the surface of the slide glass is taken into a Luzex image analyzer through a video camera, the maximum length and projected area of 100 or more toner particles are obtained, calculated by the above equation (2), and the average Obtained by determining the value.

  As the transfer device 15, for example, a charged toner is formed by creating an electric field between the photoreceptor 10 and the paper 20 using a conductive or semiconductive roller, brush, film, rubber blade, or the like to which a voltage is applied. Conventionally known means such as a means for transferring toner, a means for corona charging the back surface of the paper 20 with a corotron charger or a scorotron charger using corona discharge, and transferring a charged transparent toner can be used. it can.

Incidentally, the transfer means in the present invention transfers the toner image onto the transfer member. When an intermediate transfer member is present as the transfer member, the intermediate transfer member becomes the transfer member. When there is no intermediate transfer member as shown in the configuration, a recording medium such as paper becomes a transfer target.
In this embodiment, a transfer roll is used for the transfer device 15 and a voltage of −600 V is applied, and the developed toner image is transferred to the paper 20 by this electric field.

The toner image can be fixed on the paper 20 by using a known contact-type heat fixing device as the fixing device 18. Specifically, for example, the toner image has a rubber elastic layer on a core metal and is necessary. A heat roller fixing device having a fixing member comprising a heating roller having a fixing member surface layer and a pressure roller having a rubber elastic layer on the core and optionally having a fixing member surface layer. Alternatively, as the fixing member, a fixing device in which such a combination of a roller and a roller is replaced with a combination of a roller and a belt or a combination of a belt and a belt can be used. The fixing device may be provided with a release agent coating means such as silicone oil as necessary.
In the present embodiment, a heat roller fixing device including a heating roller and a pressure roller is used as the fixing device 18.

  Examples of the light neutralizer 17 include tungsten lamps and LEDs. Examples of the light quality used for the light neutralizer 17 include white light such as tungsten lamps and red light such as LED light. As the light static eliminator 17 of this embodiment, an LED having a wavelength of 660 nm is used as a light source, and the irradiation light intensity is five times the minimum exposure light amount at which the attenuation of the image carrier potential with respect to the exposure of the photoconductor 10 is saturated as will be described later. The output is set to be within.

Hereinafter, how the exposure light quantity range of the optical static eliminator in the present invention is determined will be described.
The lower limit value Emin of the exposure light amount of the light static eliminator is considered to be the minimum exposure light amount for making the photoreceptor surface potential after transfer substantially zero. Therefore, the relationship between the exposure light amount when the photosensitive member charged to a constant potential is exposed and the photosensitive member potential is examined, and the exposure light amount when the attenuation of the photosensitive member potential is saturated may be Emin.

  Here, “when the attenuation of the photoreceptor potential is saturated” refers to the position of the inflection point where the attenuation is stabilized at a constant value (almost zero) in the attenuation curve of the photoreceptor potential with respect to the exposure light quantity.

On the other hand, the upper limit value of the exposure light quantity of the light static eliminator is considered to be the exposure light quantity immediately before ghosting due to static elimination exposure starts when charging with the low charging bias.
The ghost is a kind of optical memory, and is generated when photocarriers are captured in a localized order in the band gap by static elimination exposure, and the carriers remain in the photoconductive layer. That is, among the photocarriers generated in a certain image forming process, the carriers remaining in the photoconductive layer are swept away by the electric field due to the surface charge at the next charging or after that, and the potential of the portion irradiated with the light is changed to the other. As a result, shading (ghost) occurs on the image.

  Accordingly, the amount of static elimination exposure light at which the ghost starts to occur can be obtained by plotting the charging potential when the photosensitive member is recharged after static elimination against the amount of exposure light, and examining the point at which the charging potential starts to decrease. .

Based on the above idea, the following experiment was conducted.
First, a surface potential meter is arranged immediately after the light neutralizer 17 (immediately before the charger 11) in the rotation direction of the photoconductor 10 of the image forming apparatus shown in FIG. Measure the surface potential of the photoconductor immediately after exposure without changing development, transfer, and cleaning, by changing the exposure light quantity from 0 to 5 μJ / cm ^2. The time-resolved measurement was performed. The measurement position of the surface electrometer corresponds to the position after 100 msec has elapsed after exposure.

FIG. 3 shows the relationship between the amount of static exposure light and the photoreceptor potential in the measurement system. As shown in FIG. 3, the photoreceptor potential is attenuated as the exposure light amount is increased, and the attenuation is saturated to almost 0 V when the exposure light amount is 0.7 μJ / cm ² . From this, Emin in the present embodiment was determined to 0.7μJ / cm ^2.

  Next, the surface charge of the photoconductor was measured in the same manner as described above, with the amount of charge for static elimination exposure changed and without developing, transferring, or cleaning. Here, the charging voltage applied to the wire of the charger 11 was performed at two levels of +5 kV (charging current: 650 μA) and +7 kV (charging current: 900 μA). The measurement position of the surface electrometer is the same position as described above.

FIG. 4 shows the relationship between the amount of static elimination exposure light and the charging potential in the measurement system. As shown in FIG. 4, when the charging voltage is +7 kV, no decrease in the charging potential was observed within the range of the amount of static elimination exposure light that was changed this time. On the other hand, when the charging voltage is +5 kV, a charging potential of +500 V can be obtained up to a static elimination exposure light amount of 3.5 μJ / cm ² . When an image was actually produced using the developing device 14 and the transfer device 15, a ghost was generated when the amount of exposure light exceeded 3.5 μV / cm ² .

As a result, the upper limit of the amount of charge for exposure to static electricity when the charging bias is as low as +5 kV is obtained as 3.5 μJ / cm ² , and this value is five times the 0.7 μJ / cm ² obtained as Emin. Therefore, in the image forming apparatus according to the present embodiment, the range of the exposure light amount E (μJ / cm ² ) of the optical static eliminator 17 that can sufficiently eliminate static electricity without generating a ghost is the range of the following formula (1). I understood.
Emin ≦ E ≦ 5 × Emin (1)

  The exposure light quantity E of the light neutralizer 17 is preferably 2 × Emin ≦ E ≦ 4.5 × Emin. If the exposure light quantity E is less than Emin, a ghost in which an afterimage of image exposure in the previous image forming process is generated on the image occurs. On the other hand, when the exposure light amount E exceeds 5 × Emin, a ghost based on the photocarriers remaining in the photoconductive layer due to exposure occurs.

  The image forming apparatus of the present invention has been described by taking the case of reversal development in which the toner is developed on the exposed portion by the exposure device 13 on the photosensitive member as an example, but in the normal development in which the toner is developed on the non-exposed portion. Since the voltage (transfer voltage) applied to the photoconductor 10 by the transfer device 15 has the same polarity as the photoconductor charging potential, transfer ghosts and leaks that occur when the photoconductor is charged to the opposite polarity. This is also advantageous.

  Therefore, for example, when a negatively charged toner containing a polyester resin is used as the toner and the normal development is performed on the positively charged photoreceptor 10, the applied voltage of the transfer device 15 has the same polarity as the photosensitive body charging potential + It is preferable because it can be polar. In this case, it is preferable to apply a voltage of about +600 V to the transfer unit 15.

In the present invention, the charging unit, the exposure unit for forming the electrostatic latent image, the developing unit, the transfer unit, the photostatic unit, and the fixing unit are not limited to the configuration of the present embodiment, and any configuration conventionally used. Can also be used.
The image forming apparatus of the present invention is an image forming apparatus of any specification such as a light lens type copying machine, a laser beam printer that emits light in the near infrared light or visible light, a digital copying machine, an LED printer, and a laser facsimile. Also good.

<Test example>
In order to confirm the operation of the above embodiment, the following comparative test was performed.
(Evaluation equipment)
As an image forming apparatus, a modified DocuCenter 719CP manufactured by Fuji Xerox Co., Ltd. as described below was used. Specifically, the photosensitive drum is changed to an amorphous silicon photosensitive drum having the same outer diameter (a photoconductive layer having a thickness of 35 μm formed of two photoconductive layers and a surface layer formed on an aluminum substrate), A voltage was applied to the scorotron as a charger from an external power supply, a developing bias was set to +150 V, a transfer bias was set to +600 V, and an LED having a wavelength of 660 nm was provided as a light static eliminator.
In this evaluation apparatus, Emin was measured in the same manner as described above, and as a result, it was 0.7 μJ / cm ² .

The evaluation conditions were as follows.
(Developer)
As the toner, a black toner (volume average particle diameter: 6.5 μm, shape factor SF1: 120) prepared by an emulsion polymerization method using polyester as a binder resin is used. A two-component developer obtained by mixing a carrier having a volume average particle diameter of 45 μm coated with a polymethyl methacrylate copolymer having carbon black dispersed as a conductive agent on the surface so that the toner concentration (TC) is 8% by weight. (Toner is -polar).

(Printing conditions)
As an apparatus, voltages of +5 kV and +7 kV were applied to a scorotron as a charger from an external power source, and various printing was performed under each condition. The test environment was a high-temperature and high-humidity environment (28 ° C., 85% RH) in which image flow tends to occur.

(Evaluation methods)
-Ghost-
The applied voltage to the charger is +5 kV, various filters are inserted on the irradiation surface of the LED, which is a static eliminator, the exposure light quantity is changed from 0.5 to 8 μJ / cm ² , and each halftone image is output. The ghost was evaluated. Further, the same evaluation was performed with the applied voltage to the charger being +7 kV.
○: No unevenness is observed in the image.
X: Unevenness is clearly seen in the image.
The results are shown in Table 1.

-Corona product generation, image flow-
500 sheets of continuous printing is performed with the applied voltage of the charger being +5 kV and the amount of static elimination exposure light being 3 μJ / cm ^2. The NOx concentration meter (manufactured by Shimadzu Corporation, CLAD-1000) was used. The image forming apparatus after printing 500 sheets was left as it was in a high temperature and high humidity environment for a whole day and night, and then a standard image including characters and pictures was output to check for the occurrence of image flow. Further, the same test was performed with the applied voltage of the charger set to +7 kV.
Table 2 shows the measurement results of ozone concentration and NOx concentration.

As shown in Table 1, when the charging voltage is +7 kV, no ghost is generated at the charge removal exposure light amount equal to or higher than Emin. Ghost did not occur only in the range of ² . However, as shown in Table 2, when the charging voltage is +7 kV, ozone is generated 4 times or more and NOx is generated 2 times or more compared to the case of +5 kV, which is not preferable in terms of environment. Further, due to the difference in the generation amount of ozone and the like, when the charging voltage was +7 kV, image flow occurred in the image after being left.
From this result, it was confirmed that even when the charging voltage was lowered, an image free from ghosting and image flow could be obtained by performing photostatic elimination within the exposure light quantity range defined in the present invention.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention. It is a schematic sectional drawing which shows the structural example of an amorphous silicon photoconductor. It is a figure which shows the relationship between static elimination exposure light quantity and electric potential attenuation | damping. It is a figure which shows the relationship between static elimination exposure light quantity and a charging potential.

Explanation of symbols

10 Photoconductor (image carrier)
11 Charger (charging means)
12 Power supply 13 Exposure unit (exposure means)
14 Developer (Developing means)
15 Transfer device (transfer means)
16 Cleaning device 17 Static eliminator (light static eliminator)
18 Fixing device (fixing means)
20 paper (recording medium)

Claims (3)

At least an image carrier, charging means for uniformly charging the image carrier, exposure means for forming an electrostatic latent image on the surface of the image carrier, and developing the electrostatic latent image with a developer containing toner A developing means for forming a toner image, a transferring means for transferring the toner image on the image carrier onto a transfer medium, a fixing means for thermally fixing the toner image on a recording medium, and an image carrier after transfer. In an image forming apparatus provided with a light neutralizing means that exposes the body surface to remove residual charges,
The image carrier is amorphous silicon, and E is set to a range represented by the following formula (1), where E (μJ / cm ² ) is the exposure light quantity of the light neutralizing means. Forming equipment.
Emin ≦ E ≦ 5 × Emin (1)
(Where Emin (μJ / cm ² ) is when the attenuation of the image carrier potential is saturated in the relationship between the amount of exposure light and the image carrier potential when the image carrier charged to a constant potential is exposed. Represents the amount of exposure light.)   The image forming apparatus according to claim 1, wherein the charging unit is a corona charger, and a charging current value is in a range of 500 to 800 μA.   The image forming apparatus according to claim 1, wherein the polarity of the charging potential of the image carrier and the polarity of the transfer voltage in the transfer unit are the same polarity.

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