JP2004233914A - Multicolor image forming device - Google Patents

Abstract

Provided is a multicolor image forming apparatus in which a plurality of types of color toner images are superimposedly transferred on a transfer material, collectively pressed and fixed with good releasability, and excellent in fine line reproducibility.
In a quadruple tandem-type multicolor image forming apparatus, only a yellow toner contains a release agent Wax having a melting point of 100 ° C. or less in 7 parts by mass of a release agent, and the particle size of the toner is 10 μm. , A releasing agent is contained in 2 parts by mass, the toner particle size is 7 μm, and these four colors are combined. Then, the developing device loaded with the yellow toner is arranged at the most downstream in the sheet transport direction. At the time of printing, the control unit 75 of the electrical component unit 74 calculates the printing total coverage of the four colors so that the printing coverage is 5% in a portion where the printing coverage is 150% or more and the yellow coverage is 5% or less. Printing is performed by adding yellow independent dots.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multicolor image forming apparatus in which a plurality of types of color toner images are superimposedly transferred onto a transfer material and are collectively pressed and heat-fixed with good releasability and good fine line reproducibility.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the spread of computers as information devices centering on personal computers, printer devices have become widespread as one of the peripheral devices. Various types of color printers have been proposed for this printer. In particular, remarkable progress has been made in electrophotographic, thermal transfer, and ink jet printer systems, and the color images formed by these devices have been used in analog cameras that have been used for a long time in terms of beauty and resolution. It is comparable to salt photography and is an alternative to it.
[0003]
Among them, the electrophotographic tandem type multicolor image forming apparatus has a high processing speed because a plurality of toners are successively superimposed on a sheet and transferred and fixed in one process, so that a tandem type multicolor image forming apparatus has recently been developed. Image forming apparatuses are rapidly spreading.
FIG. 4 is a diagram schematically showing a configuration of a main part of such a conventional electrophotographic tandem-type multicolor image forming apparatus. As shown in FIG. 1, a tandem-type multicolor image forming apparatus 1 includes a paper feed cassette 2 in which paper P is stacked and stored, a paper feed roller (not shown) for taking out the paper P one by one from the paper feed cassette 2, A paper transport guide (not shown) for guiding the paper P fed by the paper feed roller as shown by an arrow A in the drawing, a pair of standby rollers (not shown) disposed at the end of the paper transport guide, and a pair of standby rollers And a transport belt 3 that circulates and transports the paper fed in synchronization with the printing timing in the counterclockwise direction in the figure, and drive rollers 4a and 4b that drive the transport belt 3.
[0004]
Further, four image forming units 5 (5-1, 5-2, 5-3, 5-4) are provided in a multi-stage manner from the upstream side to the downstream side in the paper transport direction in the vicinity of the paper transport surface of the transport belt 3. A fixing device 6 including a heat roller and a pressure roller is disposed downstream of the conveyance belt 3 in the sheet conveyance direction indicated by an arrow B in the drawing.
[0005]
Each of the four image forming units 5 has the same configuration, and has a cleaner 8, a charging unit 9, a recording head 10, a developing unit set 11, and a transport belt around the photosensitive drum 7 near its peripheral surface. The transfer devices 12 are sequentially arranged with 3 interposed therebetween. The developing device set 11 contains yellow (Y), magenta (M), and cyan (C) color toners, which are three subtractive primary colors, and black (K) toner, which is mainly dedicated to character portions. The developing roller 13 is disposed in the opening on the lower side surface.
[0006]
The cleaner 8, the charger 9, and the developing device set 11, except for the transport belt 3, the recording head 10, and the transfer device 12, form a detachable image forming unit in the main body of the multicolor image forming apparatus 1. are doing.
The photoreceptor drum 7 rotates clockwise as indicated by arrow C, and its peripheral surface is cleaned by a cleaner 8, and a uniform negative high charge is given to the cleaned peripheral surface by a charger 9. Initialized, the initialized peripheral surface is exposed by the recording head 10 to form an electrostatic latent image composed of a negative high potential portion due to the initialization and a negative low potential portion whose potential is attenuated by the exposure. You.
[0007]
The toner contained in the developing device set 11 is transferred to the negative low potential portion by the developing roller 13, and the electrostatic latent image is visualized (developed). The developed toner image is transferred onto the sheet P conveyed by the conveyor belt 3 by the transfer device 12 in a superimposed manner. The paper P on which the toner images of four colors are sequentially superimposed and transferred as described above is carried into a fixing device, where the toner image is fixed on the paper surface by heat and pressure, and is discharged out of the apparatus by a discharge roller (not shown). Is done. As a result, a color image is formed on the paper P by the combined color of the four toners.
[0008]
FIG. 5 is a side sectional view showing the image forming unit of the multicolor image forming apparatus in detail. As shown in FIG. 1, the image forming unit 15 includes a drum set 16 and the developing device set 11 described above. The drum set 16 includes a drum cover 17 in addition to the photosensitive drum 7, the cleaner 8, and the charger 9 described above, and has a horizontally long slot 18 in which the recording head 10 shown in FIG. ing.
[0009]
When the image forming unit 15 is detached from the main body apparatus (multicolor image forming apparatus 1) and is a single unit, the drum cover 17 is provided with two points in the drawing to protect the exposed lower portion of the photosensitive drum 7. The image forming unit 15 is moved to the right position shown by a chain line 17 'to shield the lower part of the photosensitive drum 7 from the outside, and when the image forming unit 15 is mounted on the main body apparatus, it is moved to the left position shown by the solid line in the figure. Moving.
[0010]
In the main unit, the photosensitive drum 7 rotates clockwise. The charger 9 applies a uniform charge to the peripheral surface of the photosensitive drum 7. The recording head 10 shown in FIG. 4, which is arranged with the head end portion inserted into the slot 18 and is arranged on the peripheral surface of the photosensitive drum 7, performs exposure in accordance with an image signal to form an electrostatic latent image.
[0011]
On the other hand, the developing device set 11 rotatably holds the developing roller 13 at a lower opening of a vertically long housing, and contains the toner 20 therein. A stirring member 21, a supply roller 22, and a doctor blade 23 are disposed below the toner 20 so as to be buried in the toner 20.
[0012]
The stirring member 21 rotates as shown by the broken line in the figure, and sends the toner 20 to the supply roller 22 while stirring the toner 20. The supply roller 22 presses against the developing roller 13 to press the toner 20 sent from the stirring member 21. The developer is supplied to the peripheral surface of the developing roller 13 so as to be rubbed. The doctor blade 23, which is in contact with the circumferential surface of the developing roller 13 in the rotation direction, applies a triboelectric charge to the toner 20 to assist the toner 20 to adhere to the developing roller 13, and regulates the adhered toner layer to a certain thickness. The developing roller 13 transfers the toner 20 supplied from the supply roller 22 and whose layer thickness is regulated by the doctor blade 23 to a low potential portion of an electrostatic latent image on the peripheral surface of the photosensitive drum 7 (for reverse development). Case), a toner image is formed.
[0013]
The four developing device sets 11 generally include a process color toner and a black toner for black plate made of a thermoplastic resin such as magenta, cyan, and yellow polyester, respectively, from the developing device set 11 on the upstream side in the sheet conveyance direction. The developer is sequentially accommodated in the developing device set 11 on the downstream side. The four color toner images formed on the paper by sequentially transferring these toner images are fixed on the paper surface by the fixing device 6 by the heat of the heat roller and the pressure of the pressure roller as described above.
[0014]
When a toner image is thermally fixed on a sheet, a phenomenon called offset, in which a part of the toner forming the toner image transfers from the toner image to the heat roller side, is likely to occur. In order to prevent this offset phenomenon, that is, to prevent toner from adhering to the heat roller, an oil application roller is usually provided in the fixing device, and the oil application roller rotates while rotating as the heat roller rotates. The roller is configured to supply oil for offset prevention to the roller.
[0015]
As described above, an oil application mechanism using an oil supply roller is a complicated and large-sized oil supply mechanism having a mechanism in which a low-viscosity silicon oil of about 10 mm ＾ / s is applied from the oil tank to the supply roller according to a required amount. In recent years, a silicone-urethane composite sponge impregnated with silicone oil of about 100 mm ＾ / s has been wrapped with a film having a microporous structure (Gore-Tex: trade name). The number of miniaturized ones using what is considered a roller is increasing.
[0016]
As described above, unless the amount of oil supplied from the oil application roller is supplied at a certain ratio or more, the effect of preventing the above-described offset phenomenon cannot be obtained. For example, when printing one sheet of A4 size paper, unless the oil supply rate is 1 mg or more, the effect of preventing the offset phenomenon cannot be obtained. For this reason, the above-mentioned oil supply rate is achieved by adjusting a film having a microporous structure.
[0017]
[Problems to be solved by the invention]
Incidentally, an oil application roller used in a conventional fixing device is specifically composed of, for example, 2 cm in diameter × 30 cm in length, and has an oil content of 30 g (1 cm of sponge). ³ 3.5 mg).
[0018]
Assuming that 20 g of the paper can be used (10 g remains in the roller until the end and cannot be used all), and when printing on one sheet of A4 size paper, as described above, if the oil is supplied at an oil supply rate of 1 mg or more, The life of the oil application roller is lost when printing up to 20,000 sheets. Therefore, assuming that the life of the fixing device (that is, the heat roller or the pressure roller) is 100,000 sheets, it is necessary to replace the oil application roller approximately four times before the life of the fixing device expires.
[0019]
However, this not only raises running costs, but also causes a problem that the operation of replacing the oil application roller is complicated for the user. To solve this problem, the only way to reduce or eliminate the number of replacements of the oil application roller is to use a large oil application roller having, for example, four times the oil content. There is a problem that it is not an essential solution because it is a solution that goes against the original purpose.
[0020]
In the oil application roller used in the conventional fixing device, oil is mainly supplied from the application roller when rotating, and is consumed on the heat roller when the paper passes through the fixing device. Even when the heat roller and the pressure roller are stopped and the heater for the heat roller is blinking, as in the case where the oil is applied, oil gradually seeps out of the oil application roller and accumulates on the heat roller. .
[0021]
If the oil is supplied to the heat roller at an oil supply rate at which the effect of preventing the offset phenomenon can be sufficiently expected, the amount of oil seeping out when the main unit is stopped naturally increases. For this reason, conventionally, when printing is resumed after the main unit waits for at least one day, the oil accumulated in the contact portion between the heat roller and the oil application roller is transferred to the first printed paper and causes oil contamination. there were.
[0022]
The above problem is caused by adjusting the amount of oil leaching from the oil application roller so as to supply oil at an oil supply rate of 0.1 mg or less per A4 size sheet for printing, or omitting the oil application roller. To solve this problem, instead of reducing the oil supply, in order to increase the releasability of the toner in the toner, a low melting point Wax having a melting point of 100 ° C. or less, such as Carnauba Wax, is used as the toner mass ratio. More than 5%.
[0023]
However, when a large amount of the low melting point Wax is added, the Wax is pulverized from the localized portion at the time of the Wax pulverization, and the Wax tends to be exposed on the surface of the toner powder. The exposure of the Wax on the surface of the toner powder deteriorates the fluidity of the toner, and the charging of the toner when the toner passes through the doctor blade becomes uneven. Of the image to be printed (printed), and the reproducibility of the fine line of the printed image is deteriorated. In particular, when the particle size of the toner is reduced for the purpose of improving the image quality, this tendency becomes more remarkable, and the image quality is rather deteriorated.
[0024]
An object of the present invention is to provide a multicolor image forming method in which a plurality of types of color toner images are overlaid and transferred onto a transfer material, and are collectively pressed and heat-fixed with good releasability and good reproducibility of fine lines in view of the above conventional situation. It is to provide a device.
[0025]
[Means for Solving the Problems]
First, a multicolor image forming apparatus according to the first aspect of the present invention includes a plurality of image carriers arranged in parallel, and a plurality of electrostatic latent image forming means for forming an electrostatic latent image on the image carriers, respectively. A plurality of developing means for developing the electrostatic latent images formed on the surface of the plurality of image carriers into a color toner image with a predetermined color toner; and a transfer material for bringing the transfer material into contact with the plurality of image carriers. Transfer material conveying means for conveying, and a plurality of transfer means for transferring the color toner image to a transfer material which is arranged to constitute a transfer portion corresponding to the plurality of image carriers and is in contact with the image carrier And a heat roller contacting the color toner image side to fix the color toner image superimposedly transferred on the transfer material via the plurality of transfer means to the transfer material, and pressing the transfer material against the heat roller. The transfer material, which comprises a pressure roller arranged to be conveyed, and is conveyed. In a multicolor image forming apparatus having a pair of fixing rollers for nipping and transporting, the color toner used in the developing unit corresponding to the image carrier on the most downstream side in the transfer material transport direction is yellow, and the yellow color is The releasing agent Wax for the fixing roller pair contained in the toner has a melting point of 100 ° C. or less, and the content of the releasing agent Wax for the fixing roller pair is 5% or more based on the total mass ratio of the yellow color toner. It is constituted as.
[0026]
In this multicolor image forming apparatus, for example, the print coverage calculating means for calculating the print coverage of the toner image formed on the transfer material and the print coverage calculating means calculate the print coverage. A partial recognizing means for recognizing a portion having a print coverage of 150% or more and a print coverage of yellow toner in the print area of 5% or less, and printing of the yellow toner in the print area recognized by the partial recognition means; And yellow independent dot printing means for printing independent dots in the recognized printing area so that the coverage is 5%.
[0027]
The heat roller of the fixing roller pair may be configured such that the supply rate of the release auxiliary oil supplied from the oil application member as the toner image release auxiliary means is per A4 size transfer material printing as described in claim 3. It is configured such that the amount is 0.1 mg or less, and the oil application member as a toner image releasing assisting means is not disposed as an accessory.
[0028]
Next, according to a fifth aspect of the present invention, there is provided a multicolor image forming method, comprising: a plurality of image carriers arranged in parallel; and a plurality of electrostatic latent image forming means for forming an electrostatic latent image on each of the image carriers. A plurality of developing means for developing the electrostatic latent images formed on the surface of the plurality of image carriers into a color toner image with a predetermined color toner; and a transfer material for bringing the transfer material into contact with the plurality of image carriers. Transfer means for transferring the color toner image to a transfer material which is arranged to form a transfer portion corresponding to the plurality of image carriers and is in contact with the image carrier. Means, a heat roller contacting the color toner image side to fix the color toner image superimposedly transferred on the transfer material via the plurality of transfer means to the transfer material, and applying the transfer material to the heat roller. The transfer material, which comprises a pressure roller arranged to be pressed against and is conveyed. A multicolor image forming method in a multicolor image forming apparatus including a pair of fixing rollers for nipping and conveying, wherein a color of a color toner used in the developing unit corresponding to the image carrier on the most downstream side in the transfer material conveying direction Is yellow, the release agent Wax for the fixing roller pair contained in the yellow color toner has a melting point of 100 ° C. or less, and the content of the release agent Wax for the fixing roller pair is And the print coverage of the toner image formed on the transfer material is calculated, and the print coverage calculated by the calculation is 150% or more and the yellow toner in the print area is Steps of recognizing a portion having a print coverage of 5% or less and printing yellow independent dots in the recognized print area so that the print coverage of yellow toner in the recognized print area is 5% are included. In constructed.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side sectional view illustrating an internal configuration of an electrophotographic tandem-type multicolor image forming apparatus according to an embodiment. The multi-color image forming apparatus 25 shown in FIG. 1 is a color printer that performs printing for each cut sheet, and has a resource saving type double-sided printing mechanism. The multicolor image forming apparatus 25 includes an image forming unit 27 disposed above the inside of the main body 26, a double-sided printing transport unit 28 disposed below the center, and a supply unit disposed further below. The fixing unit 30 includes a paper unit 29 and a fixing unit 30 disposed downstream of the image forming unit 27 in the paper conveyance direction (left side in the drawing).
[0030]
The image forming unit 27 includes four image forming units 31 (31-1, 3-2, 31-3, and 31-4) in a multi-stage manner from the upstream side (right side in the drawing) to the downstream side in the paper transport direction. (Tandem type) are arranged side by side, and a flat belt-shaped conveyance belt 32 is arranged substantially horizontally at the lower portion of the main body 26 along the sheet conveyance direction. ing.
[0031]
The four image forming units 31 have the same configuration except for the developer (color of toner) housed in the developing device. Hereinafter, the image forming unit 31-3 will be described as an example, and A description will be given with numbers. The image forming unit 31 surrounds the photosensitive drum 33 and the peripheral surface of the photosensitive drum 33 in a clockwise direction in the drawing, and includes a cleaner 34, a charger 35, a recording head 36, a developing device 37, a developing roller 38, and Various devices for the transfer sheet 39 are arranged with the transport belt 32 interposed therebetween.
[0032]
In the developing units 37 of the two image forming units 31-1 and 31-2 from the upstream side in the sheet transport direction, the magenta (M) and cyan (C) colors, which are two of the three subtractive primary colors, are provided. Non-magnetic toner is stored, and black (K) non-magnetic toner dedicated to black portions of characters and images is stored in the developing device 37 of the third image forming unit 31-3. A non-magnetic toner of yellow (Y), which is the remaining one of the three subtractive primary colors, is stored in the developing device 37 of the image forming unit 31-4 at the most downstream side. These four image forming units 31 are generally configured to form magenta (M), cyan (C), black (K), and yellow (Y) spectral images, respectively. The reason why the non-magnetic toner of yellow (Y) is stored in the most downstream image forming unit 31-4 will be described later.
[0033]
The developing roller 38 is rotatably supported by a lower opening of the developing device 37 and is in pressure contact with the photosensitive drum 33. The photoconductor drums 33 are disposed in contact with the upper circulating portion (paper transport surface) of the transport belt 32, respectively. The photoconductor drum 33 is formed by uniformly applying an organic photoconductive material on the peripheral surface of a conductive metal roller, and the metal roller portion is grounded. The photosensitive drum 33 rotates clockwise as indicated by the arrow in the figure.
[0034]
The transport belt 32 has a thickness of about 150 μm having a specific surface resistance and a volume resistance by adding carbon black to a fluororesin (tetrafluoroethylene copolymer (ETFE)) and adjusting the resistance. It is composed of a film-like member, is assembled to a frame of a belt unit (not shown), is stretched between a driving roller 41 and a driven roller 42, is driven by the driving roller 41, and as shown by arrows A and B in the drawing, Circulates counterclockwise.
[0035]
A pair of standby rollers 43 is disposed on the upstream side of the conveyor belt 32. The upstream side is further branched laterally and downward, and the paper supply roller 44, the separating member 45, and the open / close paper supply A tray 46 is provided.
Further, a feed path 47 composed of two guide plates is formed below, and a pair of transport rollers 48 is disposed at an intermediate portion extending below the feed path 47. Branches in the direction. A pair of paper feed rollers 49 and a paper guide roller 51 are disposed in the vertical direction, and a paper feed end of a paper cassette 52 of the paper feed unit 29 is located below the pair. Above the paper feed end of the paper feed cassette 52, a paper feed roller 53 having a half-moon cross section is disposed at a position substantially in line with the paper guide roller 51. A large number of sheets 54 are placed and stored in the sheet cassette 52.
[0036]
On the other hand, on the downstream side (left side in the drawing) of the conveyance belt 32 in the sheet conveyance direction, a sheet separation claw 55 is disposed in contact with an end thereof, and the above-described fixing unit 30 is disposed downstream thereof. The fixing unit 30 includes a heat-generating roller 57, a pressure roller 58, an oil application roller 59 in contact with the heat roller 57, and the like in a heat-insulating housing 56.
[0037]
A discharge roller pair 61 and a switching flap 62 are provided downstream of the fixing unit 30. The switching flap 62 rotates up and down between a lower position indicated by a solid line and an upper position indicated by a broken line in FIG. Above the switching flap 62, a pair of transport rollers 63 and a paper discharge path 64 which is inverted from the upper direction to the front are formed. At the end of the paper discharge path 64, an upper paper discharge port in which a paper discharge roller pair 65 is disposed. Reference numeral 66 denotes an opening above the rear part of the upper paper discharge tray 67. A discharge roller pair 68 is disposed in the horizontal direction downstream of the switching flap 62, and a rear discharge port 69 opens to the outside downstream of the pair.
[0038]
Further, below the switching flap 62, a return transport path 71 for returning the paper of the duplex printing transport unit 28 exclusively to the upstream side is provided with five reverse transport roller pairs 72 (72a, 72b,..., 72e). ) And a reverse transport path 73 (73 a, 73 b,..., 73 e) disposed between the reverse transport roller pair 72. The terminal end 73 e of the return transport path 71 joins the feed path 47.
[0039]
An electrical unit 74 to which a predetermined number of circuit boards can be mounted is provided between the feed-back transport path 71 and the paper cassette 52. A control device including a plurality of electronic components is mounted on a circuit board provided in the electrical component 74.
Here, using the multicolor image forming apparatus having the above-described configuration, in order to realize printing performance with excellent image quality with good releasability even with a small amount of oil applied, no offset, and good fine line reproducibility. Next, the relationship between the print coverage of the toner, the amount of wax contained in the toner, and the state of occurrence of offset was examined and examined. For this purpose, various toners of four colors having various sizes having different particle diameters and varying amounts of the wax to be contained were prepared.
[0040]
As such a toner, 100 parts by mass of a polyester resin CBClOO (manufactured by Kao Corporation: weight average molecular weight 37,000) and C.I. I. (International color index) 2.4 parts by mass of Pigment Yellow 17 and C.I. I. Pigment Blue 15-3 (3.6 parts by mass) and C.I. I. And 3.6 parts by mass of CI Pigment Red 57-1.
In addition, as each of the charge control agents, 1.2 parts by mass of "LR-147" (manufactured by Nippon Carlit Co., Ltd .: organoboron compound), and "Carnauba wax No. 1 powder" having a melting point of 100 ° C. or less as a release agent (Kato) After mixing 7.0 parts by mass using a Henschel mixer, melt kneading with a twin screw extruder, pulverizing and classifying with an impact plate type pulverizer, and then obtaining a mass average particle size. The above three colored fine particles of about 10 μm were obtained.
[0041]
To 100 parts by mass of the obtained colored fine particles, 0.3 parts by mass of silica “TG810G” (manufactured by CABOT) and 1.4% by mass of “RY50” (manufactured by Nippon Aerosil Co.) were added as external additives. The mixture was mixed with a Henschel mixer to obtain three color toners Ml, C1, and Yl.
[0042]
Similarly, 4.4 parts by mass of “BLACK PEARS-L” (Cabot Corporation: carbon black for toner) as a black colorant, and “T-77” (iron compound made by Hodogaya Chemical Co., Ltd.) as a charge control agent. Using 2 parts by mass, a black toner Kl was obtained.
Further, toners M2, C2, Y2, and K2 of four colors each having 2 parts by mass of “Carnauba wax No. 1 powder” (imported by Kato Yoko Co., Ltd.) were prepared in the same manner as described above. Four-color toners M3, C3, Y3, and K3 each having 4 parts by mass of “Carnauba wax No. 1 powder” (imported by Kato Yoko Co., Ltd.) were prepared. Toners M4, C4, Y4, and K4 each having 10 parts by mass of the toner M4, C4, Y4, and K4.
[0043]
Next, the oil application roller 59 is removed from the fixing unit 30 of the multi-color image forming apparatus 25 having the above-described configuration of the present example, and the positions of the developing units for loading the toners of the four colors for each of the mass parts are variously changed. As a result of observing the occurrence of the offset while changing the printing ratio in various ways, the following was found.
[0044]
{Circle around (1)} First, when the print coverage was 150% or less, no offset occurred even when printing was performed using any combination of toners from M1, Cl, Y1, K1 to M4, C4, Y4, and K4.
(2) However, when the print coverage exceeds 150%, an offset occurs in printing of M2, C2, Y2, K2 and a combination of M3, C3, Y3, K3 with a release agent Wax content of 4 parts by mass or less. did.
[0045]
{Circle around (3)} However, when the last toner to form an image has a release agent Wax content of 7 parts by mass or more and a printing rate of 5% or more, an offset occurs even if the printing coverage exceeds 150%. Did not.
Considering various reasons why the above results were obtained, when the printing rate is low, the thickness of the melted toner layer is small, so that the anchor effect that the melted toner enters the paper acts on a large proportion of the entire toner layer. It is thought to be from.
[0046]
On the other hand, when the printing rate is high, the relatively strong anchor effect is considered to work in the same manner as in the above case where the printing rate is low, but the amount of the molten toner that does not enter the paper increases, and the anchor effect is also reduced. The offset must be prevented mainly by the cohesive force of the toner itself because it does not act on the entire toner layer.However, the low cohesive force of the toner is dominant, and the toner in the fused toner layer is moved to the heat roller side. It is considered that this causes the offset to occur easily.
[0047]
Also, it is considered that when a large amount of the release agent is introduced into the toner even at a high printing ratio, a large amount of the release agent Wax is interposed between the heat roller and the molten toner layer when the toner is melted, so that the offset hardly occurs. Can be In general, it has already been known that a release agent Wax having a melting point of 100 ° C. or less is effective for securing good releasability from a heat roller.
[0048]
In addition, as a condition for securing good release properties, the release agent Wax is effective for preventing offset only when present between the heat roller and the molten toner layer in a toner-molten state. If a large amount of the release agent Wax is contained even in the toner on the uppermost surface of the paper that melts in a portion near the toner layer, the amount of the release agent Wax contained in the other toners is particularly large. Even if it is not, it is considered that the same effect can be obtained as when a large amount of the release agent Wax is added to all the toners.
[0049]
The above effect can be expected if the toner printing rate on the uppermost surface is at least 5%. Therefore, in order to avoid hindrance to the obtained image, it is preferable to use yellow that is close to white as the color, and the above object can be achieved by setting the printing rate to 5%. it is conceivable that.
[0050]
Next, various printings were attempted by changing the average particle diameters of the toners Ml, Cl, Yl, Kl to M4, C4, Y4, and K4.
FIG. 2 is an evaluation chart showing observation results (visual evaluation of dust and fine line reproducibility) obtained by executing printing while changing the average particle diameter of the toner as described above. In the figure, from the top to the bottom in the left column, the combinations of the toners are “M2, C2, K2, Y2”, “M3, C3, K3, Y3”, “M1, C1, K1, Y1”, and “M4, C4”. , K4, Y4 "in that order. The arrangement order of each of M, C, K, and Y indicates the color of the toner in the developing device arranged in order from upstream to downstream in the sheet conveyance direction. Also, in the same figure, the average particle diameter of the toner is shown in the order of 7 μm, 8 μm, 9 μm, and 10 μm from left to right corresponding to the combination of the toners in the left column.
[0051]
As shown in this evaluation chart, the set of Ml, Cl, Kl, and Yl and the set of M4, C4, K4, and Y4, each containing 7 parts by mass or more of the release agent Wax, have a reduced average particle size. It was found that no improvement in image quality was observed.
Considering the cause, first, when a large amount of the low melting point Wax is added, the Wax is crushed from the localized portion at the time of the Wax pulverization and mixing, and the Wax tends to be exposed on the toner powder surface. Be able to be seen. When Wax is exposed on the surface of the toner powder, the transferability of the toner is deteriorated. As a result, the charging of the toner when the toner passes through the doctor blade becomes non-uniform. Image quality is deteriorated. In particular, when the particle size of the toner is reduced for the purpose of improving the image quality, this tendency becomes more remarkable, and it is considered that the image quality deteriorates.
[0052]
Here, when printing was performed by combining only the yellow toner with Yl (7 parts by mass of the release agent: particle size of 10 μm) and the other toners as M2, C2, and K2 (2 parts by mass of the release agent: particle size of 7 μm), characters were obtained. And a good image with excellent fine line reproducibility was obtained.
[0053]
This is because the L value (CIE L * a * b *) of the yellow toner itself is originally high (that is, close to white), and the contrast with the paper is small. This is probably because only the image characteristics of magenta, cyan, and black, which are excellent in reproducing thin lines with less color, are now recognized.
[0054]
Summarizing the above, first, the yellow color toner is transferred to the most downstream image carrier (photosensitive member) in the transfer material (paper) transport direction so that the yellow toner is transferred to the uppermost surface of the toner image on the paper. (A body drum). Then, a release agent Wax having a melting point of 100 ° C. or less for the fixing roller pair is contained in the yellow color toner. Then, the amount of the release agent Wax contained in the yellow color toner is set to 5% or more by mass ratio.
[0055]
When the printing is executed, the printing coverage of the toner image formed on the paper is calculated, and the printing coverage calculated by this calculation is 150% or more and the printing area is not changed. A portion where the print coverage of the yellow toner is 5% or less is searched for. Then, control is performed so as to print the yellow independent dots so that the print coverage of the yellow toner in the found print area is 5%.
[0056]
Then, the same printing method as when printing an image with good releasability, no dust, and good fine line reproducibility among the results of the various tests described above can be always realized. Further, if the printing is performed in such a manner, it is already known that good results can be obtained in the above-described experiment in which the oil application roller is removed. Need not be accompanied by an oil application member as a toner image release assisting means.
[0057]
Also, even if an oil application roller is attached for the sake of design, the supply rate of the release auxiliary oil supplied from the oil application roller is set to be 0.1 mg or less per A4 size transfer material printing. It is easy to see that there is no problem even if the setting is small.
FIG. 3 shows the printing of fine lines with good releasability and good releasability by using the arrangement of the developing unit and the structure of the fixing unit configured based on the results obtained by the above various experiments. FIG. 2 is a block diagram showing a circuit configuration of a control device for performing
As shown in the figure, the control device 75 includes a color separation unit 76, a color correction circuit 77, a color correction value integration circuit 78, a base color removal unit 79 (79-1, 79-2, 79-3), a K gain It comprises an adjustment unit 81, a set value unit 82, a calculation unit 83, a Y gain adjustment unit 84, and a line buffer 85.
[0058]
In the drawing, input pixel data as an image signal is input as an RGB signal from an external host device to a color separation unit 76. The input image signal is separated into three colors of magenta, cyan, and yellow by a color correction circuit 77 and output to a color correction value integration circuit 78 and a background removal unit 79, respectively.
[0059]
The color correction value accumulating circuit 78 outputs a gray component (black plate) extracted from the three input colors of magenta, cyan, and yellow to the K gain adjusting unit 81 and the three base removing units 79, and The integrated value of the magenta, cyan, yellow, and gray components is output to the calculation unit 83.
[0060]
In the setting value section 82, a value of 150% corresponding to the entire printing rate and a value of 5% corresponding to the yellow printing rate are set in advance. These set values are output to the calculation unit 83.
Based on these set values and the integrated value input from the color correction value integrating circuit 78, the set value portion has a print coverage of 150% or more and a print coverage of yellow toner in the print area of 5%. The following portion is recognized, and data indicating the additional Y component is output to the Y gain adjusting section 84 so that the printing coverage of the yellow toner in the recognized printing area becomes 5%.
[0061]
The K gain adjusting section 81 outputs a black print signal Dk to the line buffer based on the gray component input from the color correction value accumulating circuit 78, and the base removing section 79-1 outputs the magenta print signal input from the color correcting circuit 77. The base is removed from the signal Dm based on the gray component from the color correction value integrating circuit 78, and the magenta print signal Dm is output to the line buffer.
[0062]
The background removal unit 79-2 removes the background from the cyan print signal Dc input from the color correction circuit 77 based on the gray component from the color correction value integration circuit 78, and outputs the cyan print signal Dc to the line buffer. The background removal unit 79-3 removes the background from the yellow print signal Dy input from the color correction circuit 77 based on the gray component from the color correction value integration circuit 78, and outputs the yellow print signal Dy to the line buffer. I do.
[0063]
The Y gain adjustment unit 84 receives the additional Y component data input from the calculation unit 83 when there is a portion where the print coverage is 150% or more and the print coverage of the yellow toner in the print area is 5% or less. , The overall print coverage is 150% or more and the print coverage of the yellow toner in the print area is 5% with respect to the yellow print signal Dy output from the background removal unit 79-3 to the line buffer. The print signal of the yellow independent dot is added to the print signal of the following portion. The printing of the yellow independent dots by the added print signal is performed so as to be uniformly distributed in a portion where the print coverage of the yellow toner is 5% or less.
[0064]
As described above, in the quadruple tandem-type multicolor image forming apparatus, a combination of only the yellow toner having a particle size of 10 μm with 7 parts by mass of the release agent and the other color toner having a particle size of 7 μm with 2 parts by mass of the release agent, The developing device loaded with the yellow toner is disposed at the most downstream in the paper transport direction, and the total printing coverage of the four colors is calculated, and the printing coverage of 5% or less in the portion where the printing coverage is 150% or more and the yellow coverage is 5% or less is calculated. %, Printing by adding yellow independent dots so that a clear color image with good releasability and fine line reproducibility can be printed without the need for an oil coating device in the fixing device.
[0065]
【The invention's effect】
As described above, according to the present invention, it is possible to print a clear color image with good releasability and fine line reproducibility without the need for an oil application device in the fixing device. Since the apparatus can be reduced in size and the replacement work of the oil application apparatus becomes unnecessary, it is possible to provide a multicolor image forming apparatus which is inexpensive in both selling price and running cost and easy to use.
[Brief description of the drawings]
FIG. 1 is a side sectional view illustrating an internal configuration of an electrophotographic tandem-type multicolor image forming apparatus according to an embodiment.
FIG. 2 is an evaluation chart showing observation results (visual evaluation of dust and fine line reproducibility) obtained by executing printing while changing the average particle size of various toners.
FIG. 3 is a control apparatus for executing printing with good releasability and fine line reproducibility using the arrangement of the developing device and the configuration of the fixing unit based on the results obtained by various experiments. FIG. 2 is a block diagram showing a circuit configuration of FIG.
FIG. 4 is a diagram schematically illustrating a configuration of a main part of a conventional electrophotographic tandem-type multicolor image forming apparatus.
FIG. 5 is a side sectional view showing in detail an image forming unit of a conventional electrophotographic tandem type multicolor image forming apparatus.
[Explanation of symbols]
1 Tandem type multicolor image forming apparatus
2 Paper cassette
P paper
3 Conveyor belt
4a, 4b drive roller
5 (5-1, 5-2, 5-3, 5-4) Image forming unit
6 Fixing device
7 Photoconductor drum
8 Cleaner
9 Charger
10 Recording head
11 Developing device
12 Transfer device
13 Developing roller
15 Image forming unit
16 Drum set
17 Drum cover
18 slot
20 Toner
21 Stirring member
22 Supply roller
23 Doctor Blade
25 Multicolor Image Forming Apparatus
26 Body
27 Image forming unit
28 Double-sided printing transport unit
29 Paper feed unit
27 Image forming unit
30 Fixing unit
31 (31-1, 31-2, 31-3, 31-4) Image forming unit
32 conveyor belt
33 Photoconductor drum
34 Cleaner
35 Charger
36 Recording Head
37 Developing device
38 Developing roller
39 Transfer sheet
41 Drive roller
42 driven roller
43 Standby roller pair
44 Paper feed roller
45 Handling member
46 Openable paper tray
47 Feeding route
48 Transport Roller Pair
49 Paper Feed Roller Pair
51 Paper Guide Roller
52 paper cassette
53 Feed Roller
54 paper
55 Paper separation claw
56 housing
57 Heating roller
58 Press roller
59 Oil application roller
61 Paper Delivery Roller Pair
62 Switching flap
63 transport roller pair
64 paper ejection path
65 paper ejection roller pair
66 Upper paper exit
67 Upper output tray
68 paper ejection roller pair
69 Rear paper exit
71 Send-back transport path
72 (72a, 72b, ..., 72e) Reverse transport roller pair
73 (73a, 73b, ..., 73e) Reverse transport path
74 electrical components
75 Control device
76 color separation unit
77 color correction circuit
78 Color Correction Value Integration Circuit
79 (79-1, 79-2, 79-3) base removal section
81 K gain adjustment unit
82 Set value section
83 Calculation section
84 Y gain adjustment unit
85 line buffer

Claims (5)

A plurality of image carriers arranged side by side, a plurality of electrostatic latent image forming means for forming an electrostatic latent image on each of the image carriers, and an electrostatic latent image formed on the surface of the plurality of image carriers. A plurality of developing means for developing a color toner image with a predetermined color toner; a transfer material transporting means for transporting the transfer material to bring the transfer material into contact with the plurality of image carriers; A plurality of transfer means for transferring the color toner image to a transfer material which is arranged to form a transfer unit and is in contact with the image carrier; and a plurality of transfer means for transferring the color toner image to the transfer material via the plurality of transfer means. A heat roller that contacts the color toner image side to fix the transferred color toner image to the transfer material, and a pressure roller that is disposed to press the transfer material against the heat roller, and is conveyed. Multicolor image formation with a pair of fixing rollers for nipping and conveying the transfer material In the location,
The color of the color toner used for the developing unit corresponding to the image carrier on the most downstream side in the transfer material transport direction is yellow,
The release agent Wax for the fixing roller pair contained in the yellow color toner has a melting point of 100 ° C. or less,
The content of the release agent Wax for the fixing roller was set to 5% or more based on the total mass ratio of the yellow color toner.
A multicolor image forming apparatus characterized by the above-mentioned. Print coverage calculating means for calculating the print coverage of the toner image formed on the transfer material,
Partial recognition means for recognizing a portion where the print coverage calculated by the print coverage calculation means is 150% or more and the print coverage of yellow toner in the print area is 5% or less;
Yellow independent dot printing means for printing independent dots in the recognized printing area so that the printing coverage of yellow toner in the printing area recognized by the partial recognition means is 5%;
The multicolor image forming apparatus according to claim 1, further comprising: The heat roller of the fixing roller pair has a supply rate of a release auxiliary oil supplied from an oil application member as a toner image release auxiliary means of 0.1 mg or less per A4 size transfer material printing. 3. The multicolor image forming apparatus according to claim 1, wherein: 3. The multi-color image forming apparatus according to claim 1, wherein the heat roller of the fixing roller pair is not provided with an oil application member as a toner image release assisting unit. A plurality of image carriers arranged side by side, a plurality of electrostatic latent image forming means for forming an electrostatic latent image on each of the image carriers, and an electrostatic latent image formed on the surface of the plurality of image carriers. A plurality of developing means for developing a color toner image with a predetermined color toner; a transfer material transporting means for transporting the transfer material to bring the transfer material into contact with the plurality of image carriers; A plurality of transfer means for transferring the color toner image to a transfer material which is arranged to form a transfer unit and is in contact with the image carrier; and a plurality of transfer means for transferring the color toner image to the transfer material via the plurality of transfer means. A heat roller that contacts the color toner image side to fix the transferred color toner image to the transfer material, and a pressure roller that is disposed to press the transfer material against the heat roller, and is conveyed. Multicolor image formation with a pair of fixing rollers for nipping and conveying the transfer material A multicolor image forming method of location, and the yellow color of the color toner used in the developing unit corresponding to the image carrier on the most downstream side of the transfer material conveying direction,
The release agent Wax for the fixing roller pair contained in the yellow color toner has a melting point of 100 ° C. or less,
The content of the release agent Wax for the fixing roller pair is set to 5% or more based on the total mass ratio of the yellow color toner,
Calculate the print coverage of the toner image formed on the transfer material,
Recognizing a portion where the print coverage calculated by the calculation is 150% or more and the print coverage of yellow toner in the print area is 5% or less,
A multicolor image forming method, wherein yellow independent dots are printed in the recognized print area so that the print coverage of yellow toner in the recognized print area is 5%.

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