Image forming apparatus and method for reducing airborne particles

An image forming apparatus has an airborne particle reduction structure located in an airflow passage and including a first L-shaped baffle and a second L-shaped baffle. The first L-shaped baffle and the second L-shaped baffle each include an overhang extending from a bent portion to a first end and a wind receiver extending from the bent portion to a second end. Additionally, the first end of the first L-shaped baffle and the first end of the second L-shaped baffle are both oriented toward an upstream position of the airflow passage. The second end of the first L-shaped baffle is attached to a first airflow surface of the airflow passage, and the second end of the second L-shaped baffle is attached to a second airflow surface opposing the first airflow surface and located downstream from the first L-shaped baffle.

BACKGROUND

Some image forming apparatuses may have a structure to exhaust, with an exhaust fan or the like, heat generated in the image forming apparatus to the outside of the apparatus, for stabilizing the formation of images. Because of this, airborne particles generated in the image forming apparatus due to developer or the like (i.e., particulate matters having a particle size of 30 to 300 nm, also termed UFP (Ultra Fine Particles)) are apt to be scattered outside the apparatus during heat exhaustion, potentially influencing the quality of indoor air around the image forming apparatus.

DETAILED DESCRIPTION

An image forming apparatus including an airborne particle reduction structure may be configured to reduce airborne particles without using air filters or the like that require maintenance. Particles retained within the image forming apparatus can be a cause of image forming failure. For example, when adhered to an exposure device such as a laser light transmitter, the particles may cause image failure. Also, the particles may cause such inconveniences as image control failure or contact failure when adhered to electric components, and may cause transport failure of transfer materials when adhered to a rubber transport roller for transporting transfer sheets, resulting in lower productivity. Such respective issues attributable to airborne particles tend to become more prominent due to increase in productivity and downsizing of image forming apparatuses.

An example image forming apparatus may include, in an airflow passage for airstream, an airborne particle reduction structure provided with at least a first L-shaped baffle and a second L-shaped baffle. The first L-shaped baffle and the second L-shaped baffle may each include an overhang extending from a flexure (e.g., a bent or curved portion of the baffle) to one end (e.g., a first end of the baffle) and a wind receiver extending from the flexure to the other end (e.g., a second end of the baffle). One end of the first L-shaped baffle and one end of the second L-shaped baffle may be oriented upstream or toward an upstream position of the airflow passage, the other end (e.g., second end) of the first L-shaped baffle may be attached to a first airflow surface of the airflow passage, and the other end (e.g., second end) of the second L-shaped baffle may be attached to a second airflow surface opposing the first airflow surface downstream from the first L-shaped baffle. With the provision of the airborne particle reduction structure, the image forming apparatus can reduce airborne particles generated within the image forming apparatus.

Such image forming apparatus may be a copier or multifunction machine, or any of other machines employing an electrophotographic system. For example, the imaging forming apparatus may be a printer, a component of an imaging system, or an imaging system. Additionally, the imaging forming apparatus may comprise a developing device used in an imaging system or the like. Further, any part within the image forming apparatus through which airstream flows can be considered an airflow passage in some examples, such that the airborne particle reduction structure can be disposed therein and airborne particles within the image forming apparatus can be reduced thereby.

In some example image forming apparatuses, the first L-shaped baffle and the second L-shaped baffle may each have a projection area of approximately 45 to 90%, and in some examples approximately 55 to 80%, of the cross sectional area of an air passing portion of the airflow passage in a front view from the upstream. Additionally, the length of the overhang of each of the first L-shaped baffle and the second L-shaped baffle may be approximately 85 to 120%, and in some examples approximately 95 to 110%, of the height of the wind receiver from the airflow surface. Further, the distance between the flexure of the wind receiver of the first L-shaped baffle and the flexure of the wind receiver of the second L-shaped baffle may be approximately 1.8 to 2.5 times, and in some examples approximately 2.0 to 2.3 times the height of the wind receiver of the first L-shaped baffle from the airflow surface. These ranges may be selected from the viewpoint of effectively reducing airborne particles. Further, in some examples, a transport passage for transfer materials may also serve as the airflow passage, and the image forming apparatus may be provided with a pair of mutually opposing side plates respectively abutting against side edges of the first L-shaped baffle and side edges of the second L-shaped baffle.

In some examples, the image forming apparatus may further include a third L-shaped baffle disposed downstream from the second L-shaped baffle. The third L-shaped baffle may comprise at least an overhang extending from a flexure to one end and a wind receiver extending from the flexure to the other end; the one end of the third L-shaped baffle may be oriented upstream or toward an upstream position of the airflow passage, and the other end of the third L-shaped baffle may be attached to the first airflow surface. Further, the third L-shaped baffle may have a projection area of 45 to 90%, and in some examples approximately 55 to 80%, of the cross sectional area of the air passing portion of the airflow passage in a front view from the upstream, and the length of the overhang of the third L-shaped baffle may be approximately 85 to 120%, and in some examples approximately 95 to 110%, of the height of the wind receiver from the airflow surface. With the further provision of the third L-shaped baffle, the image forming apparatus can further reduce airborne particles generated within the image forming apparatus. Further, in some examples, a transport passage for transfer materials may also serve as the airflow passage, and the image forming apparatus may be provided with a pair of mutually opposing side plates respectively abutting against the side edges of the first L-shaped baffle, the side edges of the second L-shaped baffle, and side edges of the third L-shaped baffle.

The image forming apparatus may further include a water vapor generator for mixing water vapor with the airstream. With this, airborne particles generated within the image forming apparatus can be reduced more effectively. Then, in cases where an electrophotographic image forming apparatus is selected as the image forming apparatus, a fixing device for fixing a developer onto a transfer material under heat and pressure may also serve the role of the water vapor generator and the transport passage for transfer materials may also serve as the airflow passage. Further, a rate of supplying water vapor from the water vapor generator may be approximately 0.20 to 0.50 mg/min per 1 cm2of the cross sectional area of the air passing portion of the airflow passage.

An example method for reducing airborne particles in airstream passing through an airflow passage may be performed by an image forming apparatus including two or more L-shaped baffles each having an overhang and a wind receiver are alternately disposed on mutually opposing airflow surfaces in the airflow passage for producing, in the airstream passing through the airflow passage, a deceleration region formed between acceleration regions and at least one or more vortex flows in the deceleration region. In some examples, airborne particles in the airstream can be adhered and captured at the airflow surfaces of the airflow passage, and the overhangs and wind receivers of the L-shaped baffles. By producing the deceleration region formed between the acceleration regions in the airstream passing through the airflow passage, and by producing the at least one or more vortex flows in the deceleration region, the method can reduce airborne particles in the airstream passing through the airflow passage.

According to another example method, a plurality of vortex flows having different rotation directions may be produced in the deceleration region for effectively reducing airborne particles in the airstream. Further, water vapor may be mixed with the airstream. The water vapor may be supplied from a water vapor generator and a rate of supplying water vapor from the water vapor generator may be 0.20 to 0.50 mg/min per 1 cm2of the cross sectional area of the air passing portion of the airflow passage. By mixing water vapor with the airstream, the method can reduce airborne particles in the airstream more effectively.

In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. Additionally, the size, material and shape of components, as well as their relative arrangements and the like may be modified as appropriate.

FIG. 1illustrates, as an example image forming apparatus, a schematic construction of a multifunction color machine. Indicated at101is a full-color laser beam printer (hereinafter referred to as “printer”) illustrated as an example image forming apparatus,101A is a printer body (machine body), or an image forming machine body, and101B is an image forming section to form images on sheets. Indicated at102is an image reader disposed substantially horizontally on the top of the printer body101A, and a discharge space E for discharging sheets is formed between the image reader102and the printer body101A.

Indicated at130is a sheet feeding device including a paper feed cassette1, i.e., a sheet container attachably disposed in the printer body101A and containing sheets S, for feeding sheets S from the paper feed cassette1. The sheet feeding device130includes, for example, a pickup roller8to serve as a sheet feeder, and a separator having a feed roller9and a retard roller10for separating sheets S delivered from the pickup roller8.

For example, the image forming section101B employs a four-drum full-color system and is provided with a laser scanner110and four process cartridges111to form toner images of four colors, i.e., yellow (Y), magenta (M), cyan (C) and black (K). Each of the process cartridges111may comprise, for example, a photosensitive drum112, a charting unit or charger113, and a developing unit or developing device114. The image forming section101B may also include, for example, an intermediate transfer unit101C disposed above the process cartridges111, and a fixing unit120. Indicated at115is a toner cartridge for supplying toners to the developing devices114.

The intermediate transfer unit101C may include, for example, an intermediate transfer belt116wrapped around a driver roller116aand a tension roller116b. Primary transfer rollers119are disposed inside the intermediate transfer belt116and abut against the intermediate transfer belt116at positions opposing the photosensitive drums112. The intermediate transfer belt116may rotate in the direction of an arrow, for example, by the driver roller116adriven by a driving unit.

Then, with the primary transfer rollers119, respective color images on the photosensitive drums are successively overlappingly transferred onto the intermediate transfer belt116. A secondary transfer roller117for transferring, for example, a color image formed on the intermediate transfer belt to a sheet S, is disposed at a position opposing the driver roller116aof the intermediate transfer unit101C. Further, the fixing unit120is arranged above the secondary transfer roller117, and a discharge roller pair125and a side reversing unit101D are arranged, for example, above the fixing unit120. The side reversing unit101D may include a reversibly rotatable reverse roller pair122and a re-transport passage R for once again transporting a sheet, which is formed with image on one side thereof, to the image forming section101B. InFIG. 1, indicated at160is a controller (operating unit) for controlling image forming operations, sheet feeding operations and others.

Next, an example image forming operation of the printer101is described. First, upon reading image information from a document, the image information is subjected to image processing and thereafter converted to electric signals to be transmitted to the laser scanner110of the image forming section101B. In the image forming section101B, the surfaces of the photosensitive drums112, which are uniformly charged with the chargers113to a predetermined polarity and potential, are successively exposed by laser light. Thereby, yellow, magenta, cyan and black electrostatic latent images are successively formed, for example, on the photosensitive drums of the process cartridges111.

After that, the electrostatic latent images may be developed and visualized, using color toners charged to a negative polarity, and the respective toner images on the photosensitive drums may be successively overlapped and transferred onto the intermediate transfer belt116, with the aid of a primary transfer bias (for example, 20 μA/+1.5-2 kV) of a positive polarity applied to the primary transfer rollers119. Toner images are thereby formed on the intermediate transfer belt116. In parallel with the toner image forming operation, a sheet S is delivered by the pickup roller8mounted to the sheet feeding device130. The delivered sheet S, which is separated one by one via the separator having the feed roller9and the retard roller10, may be transported to a registration roller pair140, and skewing may be corrected with the registration roller pair140.

After being corrected for skewing, the sheet S may be transported to the secondary transfer section by the registration roller pair140, and the toner images are collectively transferred onto the sheet S in the secondary transfer section, with the aid of a secondary transfer bias (for example, 30 μA/+1 kV) applied to the secondary transfer roller117. Next, the sheet S bearing the transferred toner images is transported to the fixing unit120, at which fixing unit120the color toners are melted and mixed under heat and pressure, and fixed onto the sheet S in the form of color image.

After that, the sheet S bearing the fixed image is discharged to the discharge space E by, for example, the discharge roller pair125disposed downstream from the fixing unit120, and stacked on a stacker123protruding from the bottom of the discharge space E. Indicated at F is a transport passage for transfer materials between the fixing unit120and the discharge roller pair125, through which a sheet S formed with a completed image is transported. If images are to be formed on both sides of the sheet S, after having been fixed with the image, the sheet S is transported by the reverse roller pair122to the transfer material reversal passage R, and once again transported to the image forming section101B.

As illustrated inFIG. 1, an example airborne particle reduction structure200disposed below the stacker123may include, within an airflow duct202, a first L-shaped baffle201aand a second L-shaped baffle201b.

The airborne particle reduction structure200may include in the vicinity of an inlet of the airflow duct202a water vapor generator230for supplying water vapor to airstream. The water vapor generator230may include a humidifying device231and a water supply tank232coupled to the humidifying device231. The inlet210of the airflow duct202may be disposed, for example, in the vicinity of the fixing unit120. Additionally, an outlet211of the airflow duct202may be provided with an axial flow blower203. The air in the space around the fixing unit120and in the space consecutive with that space may flow, in response to the operation of the axial flow blower203, from the inlet210to the outlet211via the first L-shaped baffle201aand the second L-shaped baffle201b.

The airflow duct202, as well as the first L-shaped baffle201aand the second L-shaped baffle201bare now further described in relation toFIG. 2.FIG. 2illustrates a cross section (hereinafter referred to as “longitudinal cross section” for convenience) of the airborne particle reduction structure200taken through a plane parallel with the flowing direction of airstream. In some examples, the airflow duct202is illustrated as having a rectangular cross section. However, the cross section of the airflow duct202is not limited to a rectangle and various shapes such as circle and ellipse may also be used.

In some examples, the first L-shaped baffle201ais disposed within the airflow duct202and the second L-shaped baffle201bis disposed downstream from the first L-shaped baffle201a. The first L-shaped baffle201aand the second L-shaped baffle201bhave, for example, the shape of letter L in a longitudinal cross section. Additionally, the first L-shaped baffle201ahas, for example, an overhang205a, which is a horizontal portion extending from a flexure208ato one end207a, and a wind receiver204a, which is a vertical portion extending from the flexure208ato the other end206a. The wind receiver204amay be disposed, for example at the other end206a, vertically to an airflow surface202aof the airflow duct202. The one end207aof the first L-shaped baffle201amay be oriented upstream or toward an upstream position of the airflow duct202. The second L-shaped baffle201balso has, for example, an overhang205b, which is a horizontal portion extending from a flexure208bto one end207b, and a wind receiver204b, which is a vertical portion extending from the flexure208bto the other end206b. The wind receiver204bmay be disposed, for example at the other end206b, vertically to an airflow surface202bof the airflow duct202, and the one end207bof the first L-shaped baffle201bis oriented upstream or toward an upstream position of the airflow duct202. The first L-shaped baffle201aand the second L-shaped baffle201bmay respectively make contact with other airflow surfaces which are perpendicular to the airflow surface202aand the airflow surface202bof the airflow duct202(e.g., corresponding to lateral surfaces of the airflow duct).

InFIG. 2, the height h1of the first L-shaped baffle201afrom the airflow surface202amay be adjusted such that the projection area in a front view from the upstream of the airflow duct202is, for example, approximately 45 to 90%, and in some examples approximately 55 to 80%, of the cross sectional area of an air passing portion of the airflow passage202. Further, the length w1of the overhang205amay have a length of approximately 85 to 120%, and in some examples approximately 95 to 110%, of the height h1. Likewise, the second L-shaped baffle201bmay be adjusted such that the height h2of the wind receiver204bfrom the airflow surface202bhas a projection area of approximately 45 to 90%, and in some examples approximately 55 to 80%, of the cross sectional area of an air passing portion of the airflow passage202, in a front view from the upstream of the airflow duct202. Further, the length w2of the overhang205bmay have a length of approximately 85 to 120%, and in some examples approximately 95 to 110%, of the height h2. The distance of separation a1between the flexure208aof the first L-shaped baffle201aand the flexure208bof the second L-shaped baffle201bmay be approximately 1.8 to 2.5 times, and in some examples approximately 2.0 to 2.3 times the height h1of the first L-shaped baffle201a.

Next, an example operation of the airborne particle reduction structure200is described. In response to the operation of the axial flow blower203, air containing airborne particles generated in the image forming apparatus forms airstream that proceeds into the inlet210. Part of the airstream is blocked from flowing by the first L-shaped baffle201a, and a deceleration region e1is produced in an area encompassed with the first L-shaped baffle201a. A vortex flow may be produced in the deceleration region e1. Further, airstream passing through a flow path (acceleration region b1) narrowed by the overhang205aof the first L-shaped baffle201amay be accelerated, while being rectified by the overhang205a. Then, if the length w1of the overhang205ais less than 85% of the height h1of the wind receiver204a, the overhang205amay not be unable to sufficiently rectify and accelerate the airstream, and also may have difficulty in maintaining the later-described spatial volume of the deceleration region, and the vortex flow produced in the deceleration region may become insufficient. Part of the accelerated airstream is once again blocked from flowing by the second L-shaped baffle201bdisposed to a surface opposite to that of the first L-shaped baffle201a. As a result, a deceleration region c1e2is created, comprising the region c1inFIG. 2and a region e2connected to the region c1and encompassed with the second L-shaped baffle201b. Vortex flows are produced in the region c1and the region e2, respectively. Further airstream passing through a flow path (acceleration region b2) narrowed by the overhang205bof the second L-shaped baffle201bmay produce a deceleration region f1downstream from the second L-shaped baffle201b, while being directed toward the outlet211. A vortex flow may be produced in the deceleration region f1. For example, the rotation direction of the vortex flow produced in the region c1may be opposite to the direction rotation of the vortex flow produced in the region e2(seeFIG. 5). It should be noted thatFIG. 5illustrates an airstream in the airborne particle reduction structure schematically, and it is to be understood that the illustrated flows of the airstream may vary in number, direction, size, etc. in other examples. Airborne particles carried in the airstream may be circulated and/or retained in the vortex flows, and become aggregated by repeatedly colliding with each other to gradually increase in particle size (coarsening). As it may be difficult for the coarsened airborne particles to remain within the vortex flows, they tend to adhere to airflow surfaces of the airflow duct202in the deceleration region c1, as well as surfaces of the first L-shaped baffle201aand the second L-shaped baffle201b. As such, by circulating/retaining the airstream containing airborne particles for coarsening the airborne particles for adhesion onto the airflow surfaces of the airflow duct and L-shaped baffle surfaces, airborne particles resident in the air proceeding into the inlet210can be reduced by the airborne particle reduction structure200according to the present disclosure.

In some example airborne particle reduction structures, the one end207aof the first L-shaped baffle201aand the one end207bof the second L-shaped baffle201bare directed upstream or toward an upstream position of the airstream. In some examples, when neither of the one end207aand the one end207bare directed upstream of the airstream, vortex flows may not be readily formed in the deceleration region c1e2and the aforementioned effect of reducing airborne particles may not be readily attained.

The airflow duct202, the first L-shaped baffle201aand the second L-shaped baffle201bmay be made of a material such as, for example, a thermoplastic resin, and they may be formed by way of injection molding. Further, to facilitate the adhesion of particles onto inner walls of the airflow duct and surfaces of the L-shaped baffles, the inner walls of the airflow duct and the surfaces of the L-shaped baffles may be subjected to a roughening treatment or fine processing. Further, the thicknesses of the wind receiver204aand the overhang205aof the first L-shaped baffle201a, and the thicknesses of the wind receiver204band the overhang205bof the second L-shaped baffle201bmay be, for example, approximately 0.5 to 2 mm. A thickness of the wind receiver2014B of less than 0.5 mm may affect the mold processing or strength of structure. Further, a thickness of the wind receiver2014B of greater than 2 mm may affect the ability to selectively control the pressure and sizing of the apparatus.

The airborne particle reduction structure200is provided with two L-shaped baffles, i.e., the first L-shaped baffle201aand the second L-shaped baffle201b, but the effect of reducing airborne particles can be further enhanced by appropriately additionally disposing L-shaped baffles having the same structure. For example, an airborne particle reduction structure300ofFIG. 3has a construction wherein, in addition to the first L-shaped baffle201aand the second L-shaped baffle201b, a third L-shaped baffle201cis disposed on the airflow surface202aopposing the airflow surface202bdownstream from the second L-shaped baffle201b.

The third L-shaped baffle201chas, for example, an overhang205c, which is a horizontal portion extending from a flexure208cto one end207c, and a wind receiver204c, which is a vertical portion extending from the flexure208cto the other end206c. The wind receiver204cmay be disposed, for example at the other end206c, vertically to the airflow surface202aof the airflow duct202. In some examples, the one end207cof the first L-shaped baffle201cis oriented upstream or toward an upstream position of the airflow duct202. In the same manner as the first L-shaped baffle201aand the second L-shaped baffle201b, the third L-shaped baffle201cmay also make contact with other airflow surfaces which are perpendicular to the airflow surface202aand the airflow surface202bof the airflow duct202(e.g., corresponding to lateral surfaces of the airflow duct).

As in the first L-shaped baffle or the second L-shaped baffle, the height h3of the third L-shaped baffle201cfrom the airflow surface202amay be adjusted, such that the projection area in a front view from the upstream of the airflow duct202is, for example, approximately 45 to 90%, and in some examples approximately 55 to 80%, of the cross sectional area of an air passing portion of the airflow passage202. Further, the length w3of the overhang205cmay have a length of approximately 85 to 120%, and in some examples approximately 95 to 110%, of the height h3. Further, the distance of separation a2between the flexure208bof the second L-shaped baffle201band the flexure208cof the third L-shaped baffle201cmay be approximately 1.8 to 2.5 times, and in some examples approximately 2.0 to 2.3 times the height h1of the first L-shaped baffle201a.

In the example airborne particle reduction structure300illustrated inFIG. 3, in addition to the airstream acceleration regions b1and b2and deceleration region c1e2formed in the airborne particle reduction structure200(FIG. 2), a deceleration region c2e3including a region e3connected to a region c2and encompassed with the third L-shaped baffle201c, and an acceleration region b3are created. Vortex flows are produced in the region c2and the region e3, respectively. Vortex flows are produced in the deceleration region c2e3, as in the deceleration region c1e2. However, the rotation direction of the vortex flow produced in the region c2may be opposite to the direction rotation of the vortex flow produced in the region c1. Due to the vortex flows produced in the deceleration region c2e3, airborne particles carried in the airstream may become aggregated and adhere to airflow surfaces of the airflow duct202, as well as surfaces of the second L-shaped baffle201band the third L-shaped baffle201c, as described above in connection with the deceleration region c1. Consequently, the airborne particle reduction structure300(FIG. 3) may further reduce airborne particles carried in the air, than in the case of the airborne particle reduction structure200(FIG. 2). Four or more L-shaped baffles can be provided for reducing airborne particles still further, and such may be appropriately selected in consideration of the size of the image forming apparatus, efficiency of exhaustion, etc.

In some examples, the airborne particle reduction structure200or300was described as being provided with the airflow duct202. However, other example airborne particle reduction structures may not be provided with such airflow duct. For example, an airflow duct may be a space in the image forming apparatus through which air within the apparatus may flow, and such space may be referred to as an airflow passage. In some examples, the transport passage (F inFIG. 1) for a transfer material formed with a completed image may also serve as such an airflow passage.

FIG. 4illustrates an example airborne particle reduction structure in the case where the transport passage (F inFIG. 1) also serves as an airflow passage.FIG. 4(a)is a simplified diagram in a view direction in which a sheet S moving through the transport passage is seen from the front, andFIG. 4(b)is a simplified side view thereof. The transport passage occupies a certain volume of space and communicates with the interior of the image forming apparatus.FIG. 4illustrates an example airborne particle reduction structure400in such space. InFIGS. 4(a) and (b), for example, with the aid of an axial flow blower, the air in the image forming apparatus may flow as airflow illustrated by a blank arrow and can be discharged to outside the image forming apparatus.

InFIG. 4(b), a sheet S formed with a completed image (illustrated in dotted lines) may proceed in the direction of the arrow, along a guide plate401. With the movement of the sheet S, the air in the vicinity of the surface of the sheet S may also move in the direction of the arrow. The airborne particle reduction structure400is provided with a first L-shaped baffle201aand a second L-shaped baffle201b, for example as described above in connection withFIG. 2. Also, the airborne particle reduction structure400is further provided with a pair of mutually opposing side plates403aand403brespectively abutting against side edges210aand211aof the first L-shaped baffle210aand side edges210band211bof the second L-shaped baffle201b. The side plate403amay be located in the vicinity of the sheet S and on the opposite side of the guide plate401across the sheet S. The side plate403bmay be located to oppose the side plate403aacross the first L-shaped baffle201aand the second L-shaped baffle201b. In the direction of movement of the sheet S, the side plates403aand403bmay have a length suitably accommodated in the space of the transport passage. Further, the above airborne particle reduction structure400may also be provided with a third L-shaped baffle201cas illustrated inFIG. 3, and the third L-shaped baffle201cmay have a relation in position as described above in connection withFIG. 3.

As illustrated inFIG. 4(a), the airborne particle reduction structure400may be installed by connecting side edges404aand404bof the side plate403a, side edges405aand405bof the side plate403b, the other end206aof the first L-shaped baffle201aand the other end206bof the second L-shaped baffle201bto component walls410and420, respectively, of the image forming apparatus. For example, the component wall410may be a rib or frame of the image forming apparatus. Further, the component wall420may be a door or the like for maintenance provided in the front of the image forming apparatus. Where the component wall420is a door, the airborne particle reduction structure400may not be connected to the door. In this case, the airborne particle reduction structure400may be adapted to make contact with the door.

The airborne particle reduction structure200may further reduce airborne particles carried in the airstream when the water vapor generator230is provided to supply water vapor to the airstream in the vicinity of the inlet of the airflow duct202. The inclusion of water vapor in the airstream may help facilitate the coarsening of airborne particles in the airstream, and the adherence to airflow surfaces of the airflow duct, surfaces of the L-shaped baffles and other surfaces.

The humidifying device231applicable to the water vapor generator230may include a small humidifying device of steam type, ultrasonic type, atomization (heaterless) type or hybrid type. Further, when the image forming apparatus is an electrophotographic type, a heat and pressure fixing device disposed in the image forming apparatus may be used as the water vapor generator230. In some examples, moisture contained in the transfer material vaporizes at the fixing unit120. Thereby, the image forming apparatus may not include the water supply tank232and/or the humidifying device231.

A rate of supplying water vapor from the water vapor generator230to the vicinity of the inlet of the airflow duct202may be approximately 0.20 to 0.50 mg/min per 1 cm2of the cross sectional area of the airflow duct through which the airstream flows. If the rate of supplying water vapor is less than 0.20 mg/min, the effect of supplying water vapor may not be sufficient and, if it exceeds 0.50 mg/min, dew condensation may occur inside the airflow duct202.

In some examples, the rate of supplying water vapor may be defined as a value obtained by dividing a transpiration amount of water supplied to the humidifying device by an operating time of the humidifying device. Further, when a fixing device also serves as the humidifying device, a value obtained by dividing a moisture content of transfer material, which is lost during passage through the fixing device, by a printing time may be used as the rate of supplying water vapor. The moisture content of transfer material, which is lost during passage through the fixing device, may be calculated beforehand from a moisture content of an unused transfer material and a moisture content of the transfer material immediately after passing through the fixing device without bearing any image (e.g., solid white). The moisture content of transfer material may be measured with, for example, a resistance-type paper moisture sensor HK-300 available from KETT Electric Laboratory.

When a fixing device is also used as a humidifying device, a humidifying rate can be adjusted by way of a heating temperature of the fixing device, and the humidifying rate may be increased by increasing the heating temperature. For example, when a temperature/humidity sensor is mounted beforehand in an upstream part of airstream, the supply rate of water vapor supplied to the airflow duct202can be automatically adjusted without depending on the type of transfer material and the moisture content thereof. In some examples, the airstream may be introduced into the airflow duct202for calculating an absolute moisture content from measurements of the temperature/humidity sensor to be fed back to a heater controller of the fixing device.

The inventors have modified a commercially available electrophotographic multifunction color machine and installed the airborne particle reduction structure200(seeFIG. 1) for studying the state of emission of airborne particles, so as to quantitatively demonstrate the effect of the aforementioned airborne particle reduction structure. The airborne particle reduction structure200used in this study was verified in advance by visualization observation with laser sheet irradiation that, when aerosol is mixed in airstream and passed in the same rate as the multifunction color machine, a deceleration region sandwiched between acceleration region is formed within the airflow duct202and vortex flows having different rotation directions are produced at two locations in the deceleration region. As an emission amount of airborne particles, the number of particles emitted per 10 minutes of printing was calculated in accordance with a method described in Appendix S-M to RAL-UZ 171 of Germany. A compact SMPS (Scanning Mobility Particle Sizer) of TSI, Inc. (Model 3910) was used for measuring changes in number of airborne particles.

The results show that, while the amount of emission of airborne particles was 12×1011before the modification (before installing the airborne particle reduction structure200), the emission amount of airborne particles was reduced to 1.9×1011after the installation of the airborne particle reduction structure200(reduction rate; 84%). A comparison of particle size profiles of airborne particles emitted during the measurements shows that, while airborne particles emitted before the modification had an average particle diameter of 49 nm (FIG. 6(a)), the average particle diameter of emitted airborne particles was coarsened to 87 nm (FIG. 6(b)) after the modification.

Further, when the airborne particle reduction structure200was replaced by installing the airborne particle reduction structure300, the emission amount of airborne particles was reduced to 1.5×1011(reduction rate; 88%). As such, it has been confirmed that, with the airborne particle reduction structure provided with a plurality of L-shaped baffles, airborne particles emitted from the image forming apparatus can be reduced without using air filters or the like that require maintenance.