JP4719515B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to an image forming apparatus capable of double-sided recording.

JP 2002-202638 A JP 2000-352889 A

  In a conventional image forming apparatus capable of double-sided recording, an image on one side (developed image) formed on an image carrier is transferred and fixed on a sheet, the sheet is reversed by a reversing path, and fed again. For this reason, a method of transferring and fixing an image on the other side (a visible image) on the back side of the paper has been widely used.

The double-sided recording by this method has the following problems.
1) A sheet on which an image has been formed once through a fixing device is easily curled, and is likely to be jammed during reversal or refeeding. Therefore, productivity decreases.
2) Since it is difficult to reverse a rigid sheet in the apparatus, the types of sheets that can be used are limited.
3) The image quality of the image surface that has been fixed twice is deteriorated. In particular, the graininess is remarkably deteriorated on the image surface that has been fixed twice.
4) The image surface that has been fixed twice is excessively glossy as compared to the image surface that is fixed only once.

  In order to solve such a problem, for example, in Patent Document 1 described above, double-sided recording can be performed with a single sheet passing by transferring images from the first intermediate transfer belt and the second intermediate transfer belt to both sides of the paper. There is disclosed an image forming apparatus that enables the above.

  Further, in Patent Document 2, two sets of image forming stations each including an image forming unit of each color and an intermediate transfer belt are provided, and an image formed at each image forming station is transferred to both sides of the sheet, thereby allowing one sheet to pass. Discloses an image forming apparatus capable of duplex recording.

However, those described in the above patent documents have a problem that a difference in image quality occurs between the front and back sides of the paper. In particular, there is a phenomenon that the glossiness of the image is greatly different between the front surface and the back surface of the paper. The inventor of the present application analyzed this phenomenon and found the following.
1) The glossy image, which is the surface property of the front and back surfaces, differs in the image of the image where the problem occurs, and the image quality gloss is deteriorated on the low gloss surface.
2) When the glossiness of the paper is low, the image gloss becomes excessively high and glare, and the image becomes poor in visibility.
3) The surface characteristics of the paper are detected by an optical sensor such as a media sensor, which is a conventionally known technique, but only on one side of the conventional paper.
4) In the detection of the surface characteristics, the image forming conditions are determined based on the result of only one side, and control is not performed assuming papers having different glossiness on each side.

  Incidentally, paper having different surface characteristics such as glossiness on each side is often used for the following purposes. In bookbinding printing in the light printing field, for example, it is a cover of a booklet or an illustration page of a photographic image. Usually, an image is often formed on the back surface (particularly, the surface having low glossiness).

  When using ink for normal offset printing or the like, an image gloss corresponding to the gloss of the paper is obtained, so the image gloss on the low gloss surface is a low gloss finish, and a natural image gloss is obtained with a mat close to the paper. On the other hand, when toner is used in electrophotography, the image gloss does not match the paper gloss due to the image thickness. In particular, when a paper having a rough surface and low gloss is used, only the image portion may become high gloss and glaring. This large gloss difference in the paper is recognized by humans as an unnatural glossiness, so that the quality of the image is impaired and the image lacks visibility and may become a defective image. This is a big problem peculiar to the electrophotographic system.

  The present invention solves the above-described problems in the conventional image forming apparatus, and even when sheets having different glossiness are used on the front and back sides, a difference in image quality between both sides of the sheet is small and a high-quality double-sided image can be obtained. It is an object to provide an image forming apparatus.

According to the present invention, there is provided an image forming apparatus capable of performing both-side recording by fixing images on both sides of a sheet by passing the paper through the fixing device once. Glossiness detection means for detecting glossiness is provided, and when performing duplex printing, the glossiness of each side of the paper detected by the glossiness detection means is compared. This can be solved by controlling the image forming conditions so that the toner adhesion amount on the paper surface becomes small .

  In order to solve the above problems, the present invention proposes that the glossiness detecting means is an optical sensor having a light emitting portion and a light receiving portion, and calculates the paper glossiness by the reflected light reflected on the paper. .

  In order to solve the above-described problems, the present invention is such that the light received by the light receiving portion of the optical sensor is specular reflection light, and the angle formed between the paper normal and the specular reflection light is not less than 60 degrees and not more than 85 degrees. Propose.

  In order to solve the above-described problem, the present invention provides a glossiness detection means for detecting the glossiness of one side of the paper and a glossiness detection means for detecting the glossiness of the other side of the paper. It is proposed that they are arranged so as not to face each other.

In order to solve the above problems, the present invention independently controls the toner adhesion amount on each side of the paper according to the glossiness of each side of the paper detected by the glossiness detecting means during double-sided printing. Propose that.

In order to solve the above problems, the present invention proposes that the toner adhesion amount is controlled by changing the developing potential in the image forming unit.
In order to solve the above problems, the present invention proposes that the development potential is controlled by changing the exposure energy of the exposure apparatus in the image forming unit.

In order to solve the above problems, the present invention proposes that the development potential is controlled by changing a DC voltage as a development bias in the image forming unit.
In order to solve the above problems, the present invention proposes that the toner adhesion amount is controlled by changing an AC voltage waveform as a developing bias in the image forming unit.

In order to solve the above problems, the present invention proposes that the toner adhesion amount is controlled by changing the toner density in the developing device in the image forming unit.
In order to solve the above-described problems, the present invention provides a first image forming station in which at least one image forming unit is provided around the first intermediate transfer member, and at least one around the second intermediate transfer member. A second image forming station provided with two image forming units, and each image formed by the two image forming stations is transferred from the first and second intermediate transfer members to each side of the sheet by one sheet passing. Suggest that double-sided recording is possible.

  In order to solve the above problems, the present invention provides an image forming station having at least one image forming unit provided around the first intermediate transfer member, and an image carried on the first intermediate transfer member. It is proposed to have a transferable second intermediate transfer member, and to perform double-sided recording by transferring each image carried by the first and second intermediate transfer members onto each side of the sheet with a single sheet passing. .

  In order to solve the above-described problem, the present invention provides the glossiness detection unit, wherein an image transfer position from the intermediate transfer member to the sheet is a quarter of the outer periphery of the intermediate transfer member along the sheet conveyance path. It is proposed to be arranged upstream of a distance of 1.

In order to solve the above-mentioned problems, the present invention proposes to transfer an image to the surface having the higher glossiness of each surface of the paper detected by the glossiness detecting means during single-sided recording.
Further, in order to solve the above-mentioned problems, the present invention provides a method in which the glossiness of each side of the paper detected by the glossiness detecting means is high when performing duplex printing where one side of the paper is a color image and the other side is a monochrome image. It is proposed that the color image be transferred to the surface.

In order to solve the above problems, the present invention proposes that the toner adhesion amount per unit area of a monochrome solid image is 0.7 mg / cm ² or less.
In order to solve the above problems, the present invention has a weight average particle diameter of 3 to 7 μm and a ratio (D4 / D1) of the weight average particle diameter (D4) to the number average particle diameter (D1) is 1.00. It is proposed to use toner in the range of ˜1.30.

  In order to solve the above problems, the present invention proposes to use a toner having a shape factor SF-1 in the range of 100 to 160 and a shape factor SF-2 in the range of 100 to 160.

  In order to solve the above-described problems, the present invention uses toner having at least a binder resin, a colorant, and a release agent, having a glass transition temperature of 45 to 65 ° C. and an outflow start temperature of 90 to 115 ° C. Propose.

Further, in order to solve the above-described problems, according to the present invention, the glossiness of each surface of the paper detected by the glossiness detection unit is G1, G2 (G1> G2), and each surface of the paper corresponding to G1 and G2 is used. When the toner adhesion amount per unit area is m1 and m2, respectively,
m2 / m1 ≦ 1-α × ΔG / G2
Where ΔG = G1-G2, α = 0.1
We propose to satisfy the relationship.
In order to solve the above-mentioned problems, the present invention proposes to use a sheet in which the difference between G1 and G2 is 20% or more.

  In order to solve the above problems, the present invention has an image area ratio detecting means for detecting an area ratio of an image to be formed on a sheet surface, and an area ratio of an image to be formed on each surface of the sheet at the time of duplex recording. Is detected by the image area ratio detection means, and the image having the lower area ratio among the detected images is detected as the lower glossiness of each side of the paper whose glossiness is detected by the glossiness detection means. Propose to record on paper.

  In order to solve the above problems, the present invention includes an image type detection unit that detects the type of an image to be formed on a paper surface, and the type of image to be formed on each surface of the paper during double-sided recording. When the type detecting unit detects the image type of each side of the paper sheet, the image type is a character image. It is proposed to record on the lower glossy side of the side.

According to the image forming apparatus of the present invention, it is possible to prevent the problem that image gloss of the low gloss paper surface when the glossiness Table soles with different paper is increased excessively, proper in accordance with the paper surface An image forming apparatus capable of obtaining a high-quality double-sided image having glossiness can be provided.

  According to the second aspect of the present invention, non-contact detection can be performed by calculating the glossiness of the paper from the reflected light using the optical sensor, and the degree of freedom of arrangement of the detection means is increased. In addition, detection can be performed at high speed during conveyance of the paper. Therefore, application to a high-speed output image forming apparatus is also possible.

  According to the configuration of claim 3, by using regular reflection light having an angle of 60 to 85 degrees as reflected light, it is easy to easily obtain a correlation with the glossiness on each side of the paper, and the glossiness on each side is improved. An excellent high-quality double-sided image can be obtained. Further, since the gloss level can be easily calculated, it is advantageous for a high-speed output image forming apparatus.

  According to the configuration of the fourth aspect, by disposing the glossiness detection means so as not to face each other with the sheet sandwiched therebetween, the optical sensor is not affected by the transmitted light of the sheet due to the light emission of the other optical sensor. The detection accuracy can be improved, and a high-quality double-sided image having excellent gloss on each side can always be obtained.

According to the configuration of the fifth aspect, the optimum toner adhesion amount corresponding to the glossiness of the paper is transferred to the paper, so that it is possible to always obtain a high-quality double-sided image having excellent glossiness on each side of the paper.

According to the configuration of the sixth aspect , since the toner adhesion amount can be controlled by changing the development potential, the toner adhesion amount can be directly changed. Therefore, a high-quality double-sided image excellent in glossiness on each surface. Can be definitely obtained.

According to the configuration of the seventh aspect , since the toner adhesion amount is controlled by changing the exposure energy of the exposure apparatus, it is possible to change only the toner adhesion amount while keeping the development conditions stable without changing. A high-quality double-sided image having excellent gloss on each side can always be obtained stably.

According to the configuration of the eighth aspect , the toner adhesion amount is controlled by changing the DC voltage applied to the developing roller, whereby the toner adhesion amount can be changed easily and at high speed. An excellent high-quality double-sided image can be obtained.

According to the configuration of the ninth aspect , the toner adhesion amount is controlled by changing an AC voltage waveform (for example, at least one parameter such as peak-to-peak voltage, frequency, and duty) applied to the developing roller. Since the toner adhesion amount can be changed dynamically, it is possible to obtain a high-quality double-sided image having excellent gloss on each side.

According to the structure of claim 10 , the toner adhesion amount is controlled by changing the toner replenishment amount to the developing device and changing the toner concentration of the developer in the developing device. Can be changed. In addition, with respect to continuous image formation on the same sheet that is frequently performed in practice, it is possible to stably increase the toner adhesion amount. Therefore, it is possible to obtain a high-quality double-sided image having excellent gloss on each side.

According to the configuration of the eleventh aspect , since the two image forming stations are provided, the detection result of the paper glossiness can be performed at high speed to control the toner adhesion amount on each paper surface, and the image forming productivity is lowered. It is possible to form a high-quality double-sided image with good glossiness. Further, since a developing device for controlling the toner adhesion amount is separately provided for each sheet surface, stable toner adhesion amount control is possible.

According to the configuration of the twelfth aspect , the detection result of the paper glossiness can be accurately fed back to the control of the toner adhesion amount, a high-quality double-sided image with good glossiness can be obtained on each side, and the size of the image forming apparatus can be obtained. Can be made compact.

According to the configuration of the thirteenth aspect , the detected glossiness is delayed by setting the arrangement position of the glossiness detection means on both sides of the paper to the upstream side of a distance corresponding to a quarter of the intermediate transfer body with respect to the transfer position. Therefore, it is possible to reliably feed back to the image forming conditions, and it is possible to stably obtain a high-quality double-sided image having good gloss on each surface without impairing productivity.

According to the configuration of claim 14 , when a single-sided image is printed, the image forming method is selected so that the toner image is transferred onto the paper surface having the higher glossiness, so that the user is automatically unaware. In addition, a high-quality image with high gloss and good appearance can be obtained more easily and no glare of the image on the low-gloss surface is generated.

According to the configuration of claim 15 , by printing a color image with a large amount of toner adhesion on the paper surface having the higher glossiness, a high-quality color image having good glossiness automatically and more easily without being conscious of the user. Can be obtained. Further, by printing a monochrome image with a small amount of adhesion on a paper surface with a lower glossiness, occurrence of glare that is excessive image gloss can be suppressed.

According to the configuration of the sixteenth aspect , by defining the adhesion amount per unit area of a single color solid image to 0.7 [mg / cm 2] or less, sufficient fixability can be ensured even when multiple colors are superimposed on the paper. The gloss control range depending on the toner adhesion amount is widened. Further, since the image thickness (pile height) is small, the difference in gloss at the boundary of the image does not stand out.

The structure according to claim 17 , wherein the weight average particle diameter is 3 to 7 μm, and the ratio (D4 / D1) of the weight average particle diameter (D4) to the number average particle diameter (D1) is in the range of 1.00 to 1.30. By using the toner, the gap between the micro toners is reduced and the toner density in the toner image is increased (so-called solid filling is improved), so that a sufficient image density can be obtained with a smaller amount of adhesion. Therefore, it is possible to control a wide range of image gloss depending on the toner adhesion amount. In addition, it is possible to achieve high image quality, such as improvement in dot reproducibility with the reduction in particle size, stabilization of charge amount by sharpening of particle size distribution, and improvement of transfer rate by reduction in pile height.

According to the configuration of the eighteenth aspect , it is possible to prevent the deterioration of the image quality by using the toner having the shape factor SF-1 in the range of 100 to 160 and the shape factor SF-2 in the range of 100 to 160. If either of the shape factors SF-1 or SF-2 exceeds 160, the transfer rate is lowered and the image quality is significantly deteriorated.

According to the structure of claim 19 , good fixability can be obtained by using a toner comprising at least a binder resin, a colorant, and a release agent, having a glass transition temperature of 45 to 65 ° C and an outflow start temperature of 90 to 115 ° C. It is done.

  In general, it is known that the 1/2 outflow temperature (softening point) is related to the toner fixing property, but in the present invention, the 1/2 outflow temperature (softening point) is related. As a result, it has been clarified that good fixability can be obtained by using a toner satisfying both characteristics of a glass transition temperature of 45 to 65 ° C. and an outflow start temperature of 90 to 115 ° C. As a result, gloss control based on the toner adhesion amount can be performed widely.

According to the structure of the twentieth aspect , it is possible to set the toner adhesion amount according to the paper glossiness, and it is possible to obtain an appropriate image glossiness for various papers. At this time, the toner adhesion amount on the low glossy surface is set to be smaller as the glossiness G2 of the low glossy surface is smaller and as the glossiness difference of the paper surface is larger, so that the image on the lower glossy surface side of the paper is set. In this case, it is possible to prevent excessive gloss from occurring.
According to the structure of the twenty-first aspect, since a sheet having a gloss difference of 20% or more on each side of the sheet is used, it is possible to effectively prevent the occurrence of excessive gloss on the low-gloss surface.

According to the structure of the twenty-second aspect, the glossiness of the image can be automatically suppressed because the total toner adhesion amount is small on the low glossy surface paper. Further, since the image area ratio is low, the color reproducibility is not easily lowered, and it is possible to obtain a double-sided image that can simultaneously satisfy the suppression of glare due to excessive gloss and the ensuring of color reproducibility.

According to the structure of claim 23 , when a double-sided image is formed, an image containing a large number of character images is automatically formed on the paper surface having a lower glossiness, whereby the image glossiness is preferentially suppressed in the character images. Therefore, an image with excellent visibility can be obtained.

  First, FIG. 20 shows the relationship between the toner adhesion amount and the image glossiness. Here, two types of paper having different glossiness were used, and the paper glossiness was Ga and Gb as indicated by dotted lines. In each of the sheets, the image glossiness increases as indicated by the solid line as the toner adhesion amount increases, and the glossiness tends to be saturated at a certain adhesion amount. In order to bring the image glossiness close to the paper glossiness, it is necessary to set an optimum toner adhesion amount from the above relationship. It has been found that it is necessary to reduce the toner adhesion amount particularly in the case of low gloss paper. Based on this, an embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an example of an image forming apparatus according to the present invention. The image forming apparatus shown in this figure has two image forming stations of a first image forming station 11 and a second image forming station 12 inside a main body 100. Each of the image forming stations 11 and 12 is a so-called quadruple tandem type image forming station in which a plurality of (four in this example) image forming units are arranged along one side of the intermediate transfer belt. Therefore, the image forming apparatus of this example is a one-pass double-sided color image forming apparatus capable of recording full-color images on both sides of a sheet with a single sheet passing.

  In the first image forming station 11, the intermediate transfer belt 21 stretched around a plurality of support rollers is driven to rotate clockwise in the drawing. Along the belt upper side, four image forming units 30Y, 30C, 30M, 30Bk are arranged in parallel in the belt rotation direction at equal intervals. Each image forming unit 30 has the same configuration except for the color of the toner to be handled, and will be described with reference to FIG.

  As shown in FIG. 2, there are a scorotron charger 3, an exposure device 4, a developing device 5, a cleaning device 2, a photostatic device 6, and a potential sensor 7 around a photosensitive drum 1 as an image carrier. An image sensor 8 and the like are provided.

  As the photosensitive drum 1, for example, a photosensitive drum having an organic photosensitive layer (OPC) that is a photoconductive substance formed on an aluminum cylindrical surface having a diameter of about 30 to 120 mm can be used. In addition, a photoreceptor or the like on which an amorphous silicon (a-Si) layer is formed can be employed. Alternatively, a belt-like photoreceptor can be employed.

  As the charging means 3 for uniformly charging the surface of the photosensitive drum 1, a type that contacts the surface of the photosensitive member, for example, a charging roller can be employed in addition to the scorotron charger of this example.

  The exposure device 4 scans the surface of the photosensitive drum 1 with light corresponding to the image data for each color to form an electrostatic latent image. The exposure apparatus 4 in the illustrated example is an exposure apparatus that includes an LED (light emitting diode) array and an imaging element as light emitting elements, but uses a laser light source, a polygon mirror, etc., and beam light modulated according to image data to be formed. It is also possible to adopt a laser scanning type exposure apparatus.

  The developing device 5 includes a developing roller 5a, a layer thickness regulating blade 5b, stirring / conveying screws 5c and 5d, and toner detecting means 5e. In this example, the developing device uses a two-component developer composed of toner and carrier. is there. In this example, the electrostatic latent image for each color formed on the surface of each color photoconductor 1 by the exposure device 4 with respect to the negatively charged photoconductor 1 is a predetermined polarity having the same polarity (minus polarity) as the photoconductor charge polarity. A so-called reversal development is performed, which is developed with a color toner to form a visible image.

  When each color toner of yellow (Y), cyan (C), magenta (M), and black (Bk) is consumed by the developing device 5 that handles each color, it is detected by the magnetically permeable toner detecting means 5e to form an image. The toner of each color is supplied to each developing device 5 from a toner cartridge 86 provided in the toner cartridge housing portion 85 (FIG. 1) of the apparatus by a supply unit (not shown). As the toner supply means, a system using a known MONO pump can be adopted. According to this MONO pump, there are few restrictions on the installation location of the toner cartridge, which is advantageous for space allocation in the image forming apparatus. Further, since the toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in the developing device, and the developing device can be downsized.

  When the developing device 5 is mounted on the image forming apparatus 100, one end of the toner replenishing unit is connected to a part of the screw 5d. The toner is supplied to the developing roller 5a rotating in the clockwise direction in the drawing by the screw 5c, but the thickness of the toner layer on the surface of the developing roller 5a is regulated to a predetermined thickness by the blade 5b. The developing roller 5a is a cylinder made of stainless steel or aluminum, and is supported by the frame of the developing device 5 so as to be rotatable and a distance from the photosensitive member is properly secured, and a predetermined line of magnetic force is formed inside. Has a magnet.

  A transfer roller 22, which is an example of a primary transfer unit, is disposed inside the intermediate transfer belt 21 at a position facing the photosensitive drum 1 with the belt 21 interposed therebetween. The transfer roller 22 abuts on the back surface of the intermediate transfer belt 21 to ensure an appropriate transfer nip between the photosensitive drum 1 and the intermediate transfer belt 21. The transfer roller 22 is formed by coating the surface of a metal roller serving as a core metal with a conductive rubber material, and a bias is applied to the core metal portion from a power source (not shown). In the conductive rubber material, carbon is dispersed in urethane rubber, and the resistance is adjusted to a volume resistance of about 10E5 Ωcm. The transfer roller 22 is applied with a transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the photosensitive drum 1, in this example, a positive polarity. As a result, a transfer electric field is formed between the photosensitive drum 1 and the intermediate transfer belt 21, and the toner image on the photosensitive drum 1 is formed on the intermediate transfer belt 21 that is rotationally driven in synchronization with the photosensitive drum. Electrostatically transferred. As described above, the primary transfer unit 22 serves to electrostatically transfer the toner image on the photosensitive drum 1 onto the surface of the intermediate transfer belt 21.

  Transfer residual toner adhering to the surface of the photosensitive drum 1 after the toner image is transferred to the intermediate transfer belt 21 is removed by the cleaning device 2, and the surface of the photosensitive drum 1 is cleaned. The cleaning device 2 includes a cleaning brush 2a, a cleaning blade 2b, and a collecting member 2c, and removes and collects foreign matters such as toner remaining on the surface of the photosensitive drum 1.

  In each of the color image forming units 30Y, 30C, 30M, and 30Bk, yellow, cyan, magenta, and black color toners are applied to the electrostatic latent image formed on each photosensitive drum 1 from the developing device 5 of each color image forming unit. Thus, toner images of different colors are formed. The toner images of the respective colors formed on the respective color photoconductive drums 1 are electrostatically transferred onto the intermediate transfer belt 21 by being sequentially superimposed on the intermediate transfer belt 21 by the transfer rollers 22 arranged to face the respective photoconductive drums 1 of the respective color image forming units. The

  The intermediate transfer belt 21 as an image carrier is supported by a plurality of rollers 24, 25, 26 (two), 27, 28, 29 and runs in the clockwise direction in the figure. A belt cleaning device 23 is provided on the belt running side between the support rollers 28 and 29 for wiping off foreign matters such as unnecessary toner and paper dust remaining on the surface of the belt 21. A counter roller is provided in the belt loop at a position facing the blade of the belt cleaning device 23.

  Further, members related to the intermediate transfer belt 21 (support rollers 24 to 29, each transfer roller 22, belt cleaning device 23, and the like) are integrally configured as the first belt unit 20, and with respect to the apparatus main body 100. It is configured to be detachable.

  Next, the second image forming station 12 will be described. The configuration of the second image forming station 12 is basically the same as that of the first image forming station 11, and the tension of the intermediate transfer belt 41 and the orientations of the color image forming units 50Y, 50C, 50M, and 50Bk are the first image forming station. Only 11 is different. Therefore, the description will focus on the parts different from the first image forming station 11.

  As shown in FIG. 1, the intermediate transfer belt 41 stretched around a plurality of support rollers is driven to rotate counterclockwise in the drawing. Four image forming units 50Y, 50C, 50M, 50Bk are arranged in parallel in the belt rotation direction at equal intervals along the belt oblique side portion between the two support rollers 46, 46. Each image forming unit 50 has the same configuration except that the color of the toner to be handled is different. Each image forming unit 50 is the same as the image forming unit 30 except that it is configured symmetrically with the image forming unit 30 of the first image forming station described in FIG. As in the case of the first image forming station 11, toner is supplied to the developing device 5 of each image forming unit 50 from the toner cartridge 14 provided in the toner cartridge storage unit 13 (FIG. 1). The same toner and carrier are used.

  In addition, a transfer roller 42 as an example of a primary transfer unit is disposed inside the intermediate transfer belt 41 at a position facing the photosensitive drum 1 with the belt 41 interposed therebetween. Same as the case. The configuration of the transfer roller 42 is the same as that of the transfer roller 22 which is a primary transfer unit of the first image forming station 11. In the second image forming station 12, a belt cleaning device 43 is provided at a position facing the support roller 49.

  Further, each member such as the support rollers 44 to 49 related to the intermediate transfer belt 41, each transfer roller 42, and the belt cleaning device 43 is integrally formed as a second belt unit 40, and is connected to the apparatus main body 100. It is configured to be detachable.

  The intermediate transfer belts 21 and 41 of the first and second image forming stations 11 and 12 are belts having, for example, a resin film or rubber having a base thickness of 50 to 600 μm as a base, and a photoreceptor of each image forming unit. 1 has a resistance value that enables electrostatic transfer of the toner image carried on the belt surface to the belt surface by a bias applied to the primary transfer rollers 22 and 42. As a specific example, carbon is dispersed in polyamide, and its volume resistance is adjusted to a resistance of about 10E6 to 10E12 Ωcm. Further, belt detent ribs for stabilizing the running of the belt are provided on one side or both ends of the belt. The belt circumference is 1500 mm.

  The transfer rollers 22 and 42 that are primary transfer means are, for example, a metal roller that is a core metal coated with a conductive rubber material, and a bias is applied to the core metal part from a power source (not shown). To give a specific example, in the conductive rubber material, carbon is dispersed in urethane rubber, and the resistance is adjusted to about 10E5 to 10E8 Ωcm.

  The image forming apparatus of this embodiment can form a full-color image, but of course, monochrome recording using only black toner is also possible. There are imaging units that are not used during monochrome recording. Therefore, not only does not operate the photosensitive drum 1 and the developing device 5 of the image forming unit (Y, C, M) that is not used, but also keeps the unused photosensitive member 1 and the intermediate transfer belts 21 and 41 in a non-contact state. It has a mechanism. In the present embodiment, the belt units 20 and 40 are provided with an internal frame (not shown) for supporting the support roller 26 (46) on the black image forming unit (Bk) side and the primary transfer roller 22 (42). By supporting the lens so as to be rotatable around a certain point and rotating it in a direction away from the photosensitive member, only the photosensitive member of the black image forming unit comes into contact with the image carrying belt 21 (41) to execute the image forming process. As a result, a black-and-white image is created with black toner. This configuration is advantageous in terms of improving the life of the photoreceptor.

  Further, a transfer roller 51, which is a first secondary transfer means, is provided at the lowermost part of the first image forming station 11 and on the outer side of the intermediate transfer belt 21 so as to face the support roller 28. The secondary transfer roller 51 is a metal roller that is a metal core, the surface of which is coated with conductive rubber, and a bias is applied to the metal core part from a power source (not shown). Carbon is dispersed in the rubber, and the volume resistance is adjusted to about 10E7 Ωcm. By applying a bias to the secondary transfer roller 51 while passing a recording medium (hereinafter referred to as paper P) between the intermediate transfer belt 21 and the secondary transfer roller 51, the toner image carried by the intermediate transfer belt 21 is transferred to the paper. Is done.

  In addition, a transfer charger 52 serving as a second secondary transfer unit is provided on the outermost side of the intermediate transfer belt 41 at the top of the second image forming station 12 and facing the support roller 44. The transfer charger 52 can be of a known type. A thin wire of tungsten or gold is used as a discharge electrode and is held by a casing, and a transfer current is applied to the discharge electrode from a power source (not shown). By applying a transfer current while passing the paper P between the intermediate transfer belt 41 and the transfer charger 52, the toner image carried by the intermediate transfer belt 41 is transferred to the paper P. The polarity of the transfer current applied to the transfer roller 51 and the transfer charger 52 as the secondary transfer means are both opposite to the polarity of the toner (plus in this example).

  On the right side of the apparatus main body 100, a paper feeding device 80 that accommodates paper is provided. The sheet feeding device 80 includes a plurality of stages of sheet feeding units. In this example, a sheet feeding tray 81 storing a large amount of sheets is arranged in the upper stage, and three stages of sheet feeding cassettes 82a to 82c are arranged below the sheet feeding tray 81. Yes. Each of the paper feed tray 81 and the paper feed cassettes 82a to 82c is configured to be able to be drawn out to the near right side (operation surface side) with respect to the paper surface. Of the sheets stored in the sheet feed tray 81 and the sheet cassettes 82a to 82c, the uppermost sheet is selectively separated and fed by the corresponding sheet feeding / separating means 83a to 83d to ensure that only one sheet is fed. Is sent to the recording paper conveyance paths 85 and 86 by a plurality of conveyance roller pairs 84.

  A pair of registration rollers 53 are provided in the recording paper conveyance path 86 in the apparatus main body 100 in order to take a feeding timing for feeding the paper to the secondary transfer position. Further, a jogger 54 for making the position perpendicular to the sheet conveyance direction a normal position is provided in the recording sheet conveyance path 86. The jogger 54 includes guide members that move from both sides toward the end of the paper in the paper conveyance direction, and the paper is aligned with a predetermined position by the guides pressing the paper for a moment from both sides of the running paper. .

  The sheet is conveyed from the registration roller pair 53 toward a transfer area which is a first transfer station including the intermediate transfer belt 21 and the secondary transfer roller 51 of the first image forming station. Thereafter, the sheet is transported toward a transfer area which is a second transfer station constituted by the intermediate transfer belt 41 and the transfer charger 52 of the second image forming station. The recording paper conveyance path 88 formed in the upper part of the paper feeding device 80 is provided with a plurality of conveyance roller pairs 84, and paper can be supplied from another paper feeding device 90 installed upstream in the conveyance direction. It has become.

  In the sheet feeding device 80, the uppermost sheet feeding surface of the sheet feeding tray 81 is arranged so that the uppermost sheet in the sheet feeding tray 81 is fed and then conveyed substantially horizontally without being bent. Therefore, even thick paper and highly rigid paperboard can be reliably fed. In addition, it is convenient to adopt an air paper feed made up of a vacuum mechanism so that the paper feed tray 81 can reliably feed papers having various characteristics stored therein. Although not shown, a sensor for detecting a sheet is provided at a key point of the recording sheet conveyance path, and serves as a trigger for various signals based on the presence of the sheet. A document reading device 89 equipped with an automatic document feeder is provided at the top of the sheet feeder 80.

  By the way, the image forming apparatus of the present embodiment includes glossiness detecting means (not shown in FIG. 1) for detecting the glossiness of both sides of the paper in the paper feeding device 80. The configuration of the glossiness detection means will be described later, but the glossiness of each of the front surface and the back surface of the paper can be detected during the conveyance of the paper. If the installation position of the glossiness detection means is too close to the transfer device, there is a possibility that the feedback to the image formation will not be in time after detection. It is necessary to arrange in the position. Specifically, it is preferable that the glossiness detecting means is disposed on the upstream side with respect to the transfer position at a distance of one quarter or more of the peripheral length of the intermediate transfer belts 21 and 41 along the sheet conveyance path.

  FIG. 3 shows an example of the glossiness detecting means. The glossiness detecting means 200 shown in this figure uses a reflected light sensor, and is composed of a pair of light projecting elements 201 and light receiving elements 202, which are arranged at the same angle θ from the perpendicular to the paper P. . This angle θ is preferably set in the range of 60 degrees to 75 degrees. The light emitted from the light projecting element 201 is reflected on the paper surface as shown in FIG. Here, in the reflected light, A is referred to as a regular reflection light (specular reflection light) component, and B is referred to as a diffuse reflection light component. Since the regular reflection light component is received by the light receiving element, the intensity of the regular reflection light can be detected. As the glossiness representing the surface state of the paper decreases, the specular reflection component becomes smaller. Therefore, it is possible to determine the glossiness of the paper using the intensity level of the specular reflection light received by the light receiving element. It becomes.

  Next, the arrangement of the glossiness detection means is shown in FIG. As shown in FIG. 5, the gloss detecting means 200a for the front side of the paper and the gloss level detecting means 200b for the back side of the paper are arranged at positions that do not face each other across the paper P (paper transport path). In addition, guides 203a and 203b with black surface layers are provided at positions facing the respective glossiness detecting means 200a and 200b with the sheet interposed therebetween, so that the sheet position is stabilized and the detection accuracy of reflected light is increased. If the glossiness detecting means 200a and 200b are arranged to face each other, the light from the light projecting element of the reflected light sensor is transmitted through the paper, so that the reflected light distribution on the opposite surface is affected, and the paper is independently supplied. It is not preferable because the glossiness of each surface cannot be detected.

Note that reference numeral 84 in FIG. 5 indicates a pair of conveyance rollers, but the glossiness detecting means 200a, 200b can be arranged on any of the horizontal conveyance path, the vertical conveyance path, and the inclined conveyance path.
Returning to the apparatus main body 100, on the extension of the recording paper transport path 86, the paper that has passed through the second transfer station is transported in a flat state to the fixing nip in the fixing device 15 provided downstream in the recording paper transport direction. For this purpose, a recording paper transfer means 55 is provided. The recording paper transport means 55 has a plurality of rollers that support a transport belt 56 that moves endlessly in the direction of the arrow. Outside the transport belt 56, a cleaning device 57 and a suction charger for attracting the recording paper to the belt. 58, a static elimination / separation charger 59 is provided.

  The conveying belt 56 that moves together with the recording paper while being in contact with the unfixed toner image is negatively charged by the suction charger 58 with the same polarity as the toner charging polarity. As the conveyance belt 56, a metal belt, a polyimide belt, a polyamide belt, or the like can be employed. The surface is provided with releasability from the toner and has a chargeable resistance value. The traveling speed of the belt 56 is matched with the traveling speed of the recording medium in the fixing device.

  A fixing device 15 having a heating unit is provided downstream of the recording paper transport unit 60 in the paper transport direction. As the fixing device 15, a type having a heater inside the roller, a belt fixing device that runs a heated belt, a fixing device that employs induction heating as a heating method, and the like can be used. In order to make the color and glossiness of the images on both sides of the paper the same, the material, hardness, surface properties, etc. of the fixing roller and fixing belt are made equal. Further, the fixing condition is controlled by a full-color and monochrome image, or single-sided or double-sided, or is controlled by a control unit (not shown) so as to obtain an optimal fixing condition according to the type of paper. A cooling roller pair 16 having a cooling function is provided in the conveyance path after fixing in order to cool the sheet after fixing and stabilize the unstable toner state at an early stage. A heat pipe structure roller having a heat radiating portion can be adopted as the cooling roller pair. The cooled sheet is discharged and stacked by a discharge roller pair 17 on a discharge stack unit 19 provided on the left side of the apparatus main body 100.

  The paper discharge stack unit 19 employs a mechanism in which a receiving member moves up and down according to a stack level by an elevator mechanism (not shown) so that a large amount of sheets can be stacked. It is also possible to pass the paper through the paper discharge stack unit 15 and transport the paper toward another post-processing apparatus. As another post-processing apparatus, an apparatus for bookbinding such as punching, cutting, folding, and binding can be mounted.

  In the toner cartridge storage portion 13 provided at the top of the apparatus main body 100, toner cartridges 14Y, 14C, 14M, and 14Bk for each color storing unused toner are detachably stored. Toner is supplied from the toner cartridge 14 to the developing device 5 of each image forming unit as necessary by toner conveying means (not shown). In the configuration of this example, the toner cartridge is common to the first and second image forming stations 11 and 12 arranged above and below, but can be separated. The toner cartridge 14Bk for black toner that is highly consumed can be set to have a particularly large capacity. The storage portion 13 is on the back side when viewed from the operation direction on the upper surface of the image forming apparatus, and a plane portion is secured on the front side of the upper surface of the image forming apparatus, so that it can be used as a work table.

  An operation / display unit 33 is provided adjacent to the toner cartridge housing 13. The operation / display unit 33 is provided with a keyboard and the like, and conditions for image formation can be input. The state of the apparatus is displayed on the display unit, so that information exchange between the operator and the image forming apparatus is easy. It shall be

  A waste toner storage unit 31 is provided inside the apparatus main body 100, and is connected to the cleaning device 2 of each image forming unit, the cleaning devices 23 and 43 of the intermediate transfer belts 21 and 41, and the cleaning device 57 of the conveyance belt 56. Collecting and storing foreign particles such as waste toner and paper dust in a lump. Since each of the cleaning devices does not include a large-capacity waste toner storage unit, each cleaning device can be reduced in size, and the waste toner disposal operability is good. The waste toner storage unit 31 is provided with a full sensor (not shown), and uses this to issue a warning such as toner disposal in the waste toner storage unit 31 or container replacement.

  An electrical / control device 32 is provided adjacent to the waste toner storage unit 31. In the electrical / control device 32, various power supplies, control boards, and the like are protected and housed in a sheet metal frame.

  The inside of the image forming apparatus becomes hot due to heat from the fixing device 15 and heat generated from the electrical device 32. As a countermeasure, a fan 18 is provided to prevent functional degradation due to internal heat. The fan 18 is coupled to the heat radiating portion of the cooling roller pair 16 to ensure the cooling effect of the cooling roller pair 16.

Next, the image forming operation in the image forming apparatus of this embodiment will be described separately for single-sided recording and double-sided recording.
First, the single-sided recording operation will be described. With the apparatus of this example, single-sided recording can be performed using either the first image forming station 11 or the second image forming station 12, and instructions can be selected from the operation unit 33. It has become. In the configuration of the image forming apparatus of this example, when the image carried on the intermediate transfer belt 21 of the first image forming station is transferred to one side of the sheet, the image is transferred to the upper surface of the sheet and to the intermediate transfer belt 41 of the second image forming station. When the carried image is transferred to one side of the paper, the image is formed on the lower surface of the paper. In the case where the data to be recorded is a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on the paper discharge stack unit 19. Here, a description will be given of an operation for performing single-sided recording using the first image forming station so as to perform page alignment in order from the image data of the last page (in reverse page order).

  When the start of image formation is instructed, the intermediate transfer belt 21 and the photoreceptor 1 in each of the image forming units 30Y to 30Bk rotate in the first image forming station 11. At the same time, the intermediate transfer belt 41 rotates in the second image forming station 12, but the photoreceptor 1 in each of the image forming units 50Y to 50Bk is separated from the intermediate transfer belt 41 and is not rotated. In a full-color image, image formation is started from the yellow image formation unit 30Y. By the operation of the exposure device 4 composed of an LED (light emitting diode) array and an imaging element, light corresponding to image data for yellow emitted from the LED is irradiated onto the surface of the photoreceptor 1Y uniformly charged by the charging device 3. Thus, an electrostatic latent image is formed. This electrostatic latent image is developed with yellow toner by the developing roller 5a to become a visible image, and is electrostatically primary-transferred onto the intermediate transfer belt 21 that moves in synchronization with the photoreceptor 1Y by the action of the primary transfer roller 22. The Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner at the other image forming units 30C, 30M, and 30Bk.

  As a result, yellow, cyan, magenta, and black toner images are carried on the intermediate transfer belt 21 as sequentially overlapping full-color toner images and are moved together with the intermediate transfer belt 21.

  On the other hand, the paper used for recording is fed out from the paper feed tray 81 or the paper feed cassettes 82a to 82c in the paper feed device 40 by one of the separation feeding means 83a to 83d for supplying the paper. 84 or the like is conveyed to the recording paper conveyance path 86. Before the leading edge of the paper is picked up by the registration roller pair 53, the jogger 55 operates so as to push both sides of the paper from the lateral direction on both sides with respect to the paper conveyance direction, and the lateral alignment of the paper is taken. . The registration roller pair 53 is still stationary, and the leading edge of the sheet is stationary while entering the nip of the registration roller pair 53, but the timing is set so that the position with the image on the intermediate transfer belt 21 is normal. As a result, the registration roller pair 53 rotates to feed the sheet to the transfer area.

  As described above, the full-color toner image carried on the intermediate transfer belt 21 is transferred to the upper surface of the sheet conveyed in synchronization with the intermediate transfer belt 21 under the action of the secondary transfer roller 51. In this example, the bias applied to the secondary transfer roller 51 has a positive polarity opposite to the charging polarity of the toner.

  Thereafter, the surface of the intermediate transfer belt 21 is cleaned by a belt cleaning device 23. Further, foreign matters such as toner remaining on the surface of the photosensitive drum 1 in each of the image forming units 30Y to 30Bk that have finished the primary transfer are removed from the surface of each photosensitive member by the cleaning brush 2a and the cleaning blade 2b of the cleaning device 2. . The surface of each photoconductor 1 is subjected to a discharging operation of residual potential by the discharging device 6 to prepare for the next image formation / transfer process. The removed foreign matter such as toner is sent to the collecting unit 31 by the collecting unit 2c. The sensors 7 and 8 detect whether the surface potential of the photosensitive member surface after exposure and the density of the toner adhering to the photosensitive member surface after the development process are appropriate, and appropriately set image forming conditions. Information is output to control means (not shown) for control.

  The sheet on which the toner image on the belt is transferred by being superimposed on the intermediate transfer belt 21 is transferred toward the fixing device 15 by the conveyance belt 56 of the conveyance device 55. The surface of the transfer belt 56 is charged in advance by a paper suction charger 58 so that the paper can be reliably transferred together with the transport belt 56. Further, a static elimination / separation charger 59 is provided so that the paper is separated from the transport belt 56 and reliably sent to the fixing device 15.

  Each color toner image transferred onto the paper is subjected to a fixing action by the heat and pressure of the fixing device 15 and is melted and mixed to form a complete color image. Since the toner is provided only on one side (here, the upper surface) of the paper, less heat energy is required for fixing compared to double-sided recording having toner on both sides. A control means (not shown) optimally controls the power used by the fixing device according to the image. Until the fixed toner is completely fixed on the paper, if it is rubbed against a guide member or the like in the conveyance path, the image may be lost or distorted. Cool down. Thereafter, the paper is discharged by the paper discharge roller 17 onto the paper discharge stack unit 19 with the image surface facing upward. In the paper discharge stack unit 19, since the image forming order is programmed so that the recorded matter of young pages is stacked so as to be sequentially stacked on top of each other, the page order is aligned.

  The single-sided recording operation using the second image forming station 12 is different in that image formation is performed from the first page (page order) so that the sheet is discharged to the paper discharge stack unit 19 in page order. Since this is the same as the image forming operation at the first image forming station, the description thereof will be omitted.

Next, the operation during double-sided recording in which images are formed on both sides of the paper will be described.
When the start of image formation is instructed, the image forming operation for each color is performed in the first image forming station 11 in the same manner as described in the above single-side recording operation (hereinafter, the image created in the first image forming station 11). The toner images of the respective colors sequentially formed by the respective image forming units 50Y to 50Bk of the second image forming station 12 are sequentially primary-transferred to the intermediate transfer belt 41 substantially in parallel with the first image. A process of carrying two images is performed. Since the apparatus configuration is as shown in FIG. 1, in order for the first image and the second image to coincide with each other at the leading edge in the sheet conveyance direction, the second image is formed after the start of the first image formation. Be started. Further, since the sheet is stopped and retransmitted by the registration roller pair 53, the sheet is fed in consideration of the time and is aligned by the jogger 54. The registration roller pair 53 conveys the sheet to a first transfer unit configured by a transfer roller 51 serving as a first secondary transfer unit and an intermediate transfer belt 21 at a timing. Here, a positive transfer current is applied to the transfer roller 51, and the first image is transferred from the intermediate transfer belt 21 to one side (here, the upper surface) of the sheet.

  The sheet on which the image (first image) is transferred on one side (upper surface) is continuously sent to the second transfer unit having the transfer charger 52 as the second secondary transfer unit by the conveying action of the transfer roller 51. When a positive polarity transfer current is applied to the charger, the full-color second image previously carried on the intermediate transfer belt 41 is collectively transferred to the lower surface of the sheet.

  The sheet having the full color toner image transferred on both sides in this manner is conveyed to the fixing device 15 by the conveying belt 56. The suction charger 58 charges the surface of the transport belt 56 with the same negative polarity as the polarity of the toner. Therefore, unfixed toner on the lower surface of the paper is prevented from transferring to the belt. Then, an AC voltage is applied to the charge removal / separation charger 59, and the sheet is separated from the belt 56 and transferred to the fixing device 15. The toner image on both sides of the sheet is melted and mixed by the fixing process by heat and pressure of the fixing device 15. The sheet subsequently passes through the cooling roller pair 16 and is discharged onto the discharge stack unit 19 by the discharge roller 17.

  When performing double-sided recording of a plurality of pages, if the image forming sequence is controlled so that the image of the young page is stacked on the paper discharge stack unit 19 when the image is placed on the bottom surface, The recorded material is one page in order from the top, two pages on the back, three pages on the second sheet, four pages on the back, and the page order is aligned. Such control of the image forming sequence and control such as increasing the power of the fixing device compared to single-sided recording are executed by a control means (not shown). Here, the single-sided recording and the double-sided recording operations have been described in the example of full-color recording, but monochrome recording using only black toner is also possible.

Here, the relationship between the development parameter and the toner adhesion amount on the photoreceptor in each image forming unit will be described.
In this example, the surface potential of the photosensitive member on which the electrostatic latent image is formed is as shown in FIG. 6, and the potential is changed only in the exposed image portion that is the electrostatic latent image. Here, the image is simply a solid image, and the surface potential of the photosensitive member at that time is VL, and the potential of the non-image portion is Vd (the arrow in the figure is in the minus direction). Next, this electrostatic latent image comes to the developing area (position facing the developing roller). The developing roller 5a rotates at a speed higher than the photosensitive member linear speed and conveys the developer containing toner to the developing area, and development is performed by applying a DC or AC voltage as a developing bias to the developing roller. As a result, the toner adheres to the electrostatic latent image portion on the photoconductor to form a visible image.

  At this time, the toner adhesion amount on the photosensitive member can be changed according to the magnitude of the developing potential | VB−VL | which is the absolute value of the difference between the developing bias VB and the latent image potential VL shown in FIG. This is shown in FIG. The graph of FIG. 7 represents the developing ability, the horizontal axis represents the development potential, and the vertical axis represents the toner adhesion amount M / A on the photoreceptor. Here, the case of a DC voltage is shown as the developing bias.

  As a method for changing the toner adhesion amount (M / A) on the photosensitive member, 1): increasing the exposure energy during exposure with the exposure device to lower the exposed portion potential VL (making it closer to the 0 direction), 2): The development bias VB is increased (away from VL), 3): 1) and 2) are both performed.

  The method 1) can be realized, for example, by increasing the lighting time of the exposure apparatus (LD and LED) or increasing the light emission intensity, and has an advantage that it is not necessary to change the development conditions. As the method 2), the toner adhesion amount can be increased without causing background contamination by keeping the difference between the non-image portion potential and the developing bias potential appropriate.

  On the other hand, an AC developing bias in which an AC voltage is superimposed on a DC voltage can be used as the developing bias. FIG. 8 shows the waveform as an example of the AC developing bias. The parameters of the waveform in this example are: average DC voltage VB0 = −500V, peak-to-peak voltage Vpp = 0.8 kV, frequency f = 4.5 kHz, duty (the direction in which toner is developed when one cycle is 100%) Ratio of time during which voltage is applied to) Duty = 35%. Here, the average DC voltage represents an average voltage of the waveform and is represented by the following equation (1).

  Here, V0 is the center value of the waveform. In the case of an asymmetric rectangular wave as in this example, the toner adhesion amount can be changed greatly by changing Vpp and Duty as parameters other than VB0. Note that this value does not define the waveform of the AC developing bias, and other values may be used. In addition to the asymmetric rectangular wave, a sine wave, a triangular wave, a pulse wave, or the like may be used.

  As another method for increasing the developing ability, it is also possible to increase the toner density in the developing device. The toner concentration represents the ratio of the toner weight to the developer weight among the toner and the carrier that are two-component developers in the developing device. By replenishing toner with the above-described toner replenishing device, the developing ability can be improved by increasing the amount of toner in the developing region by increasing the proportion of toner in the developer. For example, in FIG. 7, the developing ability is improved from line A to line B. Here, the increase in the toner density is performed within a range in which the problem of toner scattering in the developing device does not occur.

Now, a method for controlling the toner adhesion amount according to the detection result of the glossiness detection means 200 on both sides of the paper, which is a feature of the present invention, will be described below.
First, the glossiness of each surface of the paper detected by the glossiness detection means 200a, b on both sides of the paper is compared, and the toner adhesion amount corresponding to the paper surface having the lower glossiness is compared with the one having the higher glossiness. The control for making the paper surface smaller than that of the paper surface will be described with reference to the flowchart of FIG.

  In FIG. 9, first, the glossiness Ga and Gb of each side of the paper (referred to as side a and side b) is detected by the paper double-side glossiness detection means (S1). Next, it is determined whether or not the printing is duplex printing (S2). If the printing is not duplex printing, the process proceeds to S7 to perform normal image formation. On the other hand, in the case of duplex printing, it is determined whether or not the detected glossiness Ga and Gb of each side of the paper are equal (S3). If the glossiness on both sides of the paper is equal (Ga = Gb), the process proceeds to S7 and normal image formation is performed. On the other hand, if the glossiness of each side of the paper is different, it is determined in S4 whether the glossiness Ga of the a-side is lower than the glossiness Gb of the b-side (Ga <Gb). . When the glossiness of the b-side is high (Yes), the process proceeds to S5, and the image-forming conditions on the a-side are set so that the toner adhesion amount becomes small. On the other hand, when the glossiness of the a-side is high (No), the process proceeds to S6, and the image forming condition on the b-side is set so that the toner adhesion amount becomes small. In this way, image formation is performed. As described above, the setting of the toner adhesion amount according to the image forming conditions may be selected by changing the parameters of the latent image and the development condition, or by selecting a table of image forming conditions having different adhesion amounts by combining them.

  Next, the image forming apparatus includes a plurality of image forming modes having different toner adhesion amounts, and the image forming mode is independently determined for each glossiness of each side of the paper detected by the glossiness detecting unit 200 on both sides of the paper. A control method to which is applied will be described with reference to the flowchart of FIG.

  First, the glossiness of each side of the paper is detected by the paper double-sided glossiness detecting means (S11). Next, it is determined whether or not the printing is duplex printing (S12). If the printing is not duplex printing, the process proceeds to S14 to perform normal image formation. On the other hand, in the case of duplex printing, the process proceeds to S13, and a predetermined toner adhesion amount table is applied to each surface (a-side, b-side), and the a-side adhesion amount table Ta (Ga ) And b surface adhesion amount table Tb (Gb) are selected. In this way, image forming conditions for each surface are set independently, and double-sided image formation is performed.

Next, a control method in which image formation is performed on the paper surface having the higher glossiness during single-sided printing will be described with reference to the flowchart of FIG.
First, it is determined whether or not single-sided printing is performed (S21). If it is not single-sided printing, the process proceeds to S24 and normal double-sided printing is performed. On the other hand, in the case of single-sided printing, the glossiness Ga, Gb on each side of the paper is detected by the paper double-sided glossiness detection means (S22). Next, the glossiness of each surface is compared (S23). If Ga ≧ Gb, the process proceeds to S25, and image formation is performed so that one-side image formation is performed on the a-side of the sheet. On the other hand, if Ga <Gb, the process proceeds to S26, and image formation is performed so that one-side image formation is performed on the sheet b side.

  Next, a flowchart of FIG. 12 shows a control method for forming a color image on a paper surface having a higher glossiness when one side of the paper is a color image and the other side is a monochrome image during duplex printing. Will be described with reference to FIG. This control can be used when it is desired to output an image giving priority to the image quality of a color image.

  First, it is determined whether or not double-sided printing in which one side is a color image and one side is a monochrome image (S31). Otherwise, the process proceeds to S34 and normal image formation is performed. On the other hand, if this is the case, the glossiness Ga, Gb on each side of the paper is detected by the paper double-sided glossiness detection means (S32). Next, the glossiness of each surface is compared (S33), and if Ga ≧ Gb, the process proceeds to S35 and image formation is performed so as to form a color image on the a-side of the sheet. On the other hand, if Ga <Gb, the process proceeds to S36, and image formation is performed so as to form a color image on the sheet b side.

  The control described in the flowcharts of FIGS. 9 to 12 is performed independently on each sheet surface so that the image forming unit group in the first or second image station corresponding to each sheet surface side changes the toner adhesion amount. Operation becomes possible.

Note that it is preferable that the amount of adhesion per unit area of a monochromatic solid image is defined as 0.7 [mg / cm ² ] or less. By defining in this way, sufficient fixability can be ensured even when multiple colors are superimposed on the paper, and the gloss control range depending on the toner adhesion amount is widened. Further, since the image thickness (pile height) is small, the difference in gloss at the boundary of the image does not stand out. On the other hand, if the solid color adhesion amount is larger than 0.7 mg / cm ² , the fixing property may not be secured at the maximum adhesion amount at the time of color overlap, and sufficient gloss cannot be obtained. Further, since the pile height is conspicuous, the quality of the image is impaired.

Next, an example in which the present invention is applied to an image forming apparatus having a different apparatus configuration will be described.
In the image forming apparatus shown in FIG. 13, an image forming unit PU capable of forming a full-color image is disposed at a substantially central part of the apparatus main body. The image forming unit PU has four image forming units SU arranged in parallel with the belt 60 along the upper side of the intermediate transfer belt 60 stretched around the four rotating rollers 61, 62, 63, 64. . Above that, an exposure device 65 is disposed. Each image forming unit SU has the same configuration, and only the color of the toner to be handled is different. Therefore, one image will be described with reference to FIG.

  As shown in FIG. 14, in the image forming unit SU, a cleaning device 2, a charging device 3, a developing device 5, a static elimination device 6 and the like are disposed around the photosensitive drum 1. The developing device 5 of each image forming unit SU stores toners of cyan, magenta, yellow, and black, respectively, and applies each color toner to the electrostatic latent image formed on the photosensitive drum 1. A writing position is provided between the charging device 3 and the developing device 5, and the photosensitive member 1 is irradiated with the laser light L emitted from the exposure device 65. The exposure device 65 is a known laser system, and in this embodiment, the surface of the uniformly charged photoreceptor 1 is irradiated with light information corresponding to the color of the color-separated and developed toner as a latent image. . An exposure apparatus comprising an LED array and an image forming means can also be employed. Further, a transfer roller 66 is disposed so as to face the photosensitive drum 1 with the intermediate transfer belt 60 interposed therebetween. Reference numeral 67 denotes a backing roller. The toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 60 by the action of the transfer roller 66. Each device in the loop of the belt 60 is appropriately grounded to the apparatus frame except for the transfer unit.

  In forming a full color image, cyan, magenta, yellow, and black color toner images formed on the photosensitive drum 1 by the four image forming units SU are sequentially transferred onto the intermediate transfer belt 60 and transferred onto the belt 60. A full color image is formed. When forming a monochrome image, the toner image is formed only by the image forming unit SU that handles black toner, and the monochrome image is transferred onto the intermediate transfer belt 60.

  A belt-like intermediate transfer body 110 is disposed below the image forming unit PU. The intermediate transfer member 110 is stretched and supported by rotating rollers 111, 112, 113, 114 so as to be able to rotate counterclockwise in the drawing as shown in the figure. In the belt loop of the intermediate transfer body 110, a transfer roller 121 as a transfer unit is disposed to face the roller 63 that supports the intermediate transfer belt 60 of the image forming unit PU. A belt cleaning device 125 and a transfer charger 122 are disposed outside the belt loop. The intermediate transfer belt 60 and the intermediate transfer body 110 are brought into contact with each other by the transfer roller 121, the driven roller 114, and the roller 63 supporting the intermediate transfer belt 60, thereby forming a predetermined transfer nip. The devices in the belt loop of the intermediate transfer body 110 are appropriately grounded to the apparatus frame except for the transfer unit.

  Three-stage sheet feeding devices (sheet feeding cassettes) 126-1, 126-2, and 126-3 are disposed at the lower position of the apparatus. The uppermost sheet among the sheets stored in each cassette is fed one by one by the sheet feeding roller 127 and sent to the registration roller pair 128.

A fixing device 130 is provided on the left side of the intermediate transfer body 110.
In this embodiment, the toner image created by the image forming unit PU is carried on the intermediate transfer belt 60, and the toner image on the belt 60 is sent out by the belt surface of the intermediate transfer member 110 or the registration roller pair 128. It is transferred to one side of the paper.

  In this example, when images are obtained on both sides of the paper, the first side image created by the image forming unit PU is first transferred from the intermediate transfer belt 60 to the intermediate transfer body 110, and then the second side image is obtained by the image forming unit PU. create. The second side image is transferred from the intermediate transfer belt 60 to the second side of the sheet sent from the registration roller pair 128. The transfer of the second surface image is performed by the action of the transfer roller 121 disposed in the belt loop of the intermediate transfer body 110. At this time, the first-surface image previously transferred to the intermediate transfer member 110 is carried by the intermediate transfer member 110 and has made a full turn, and is superimposed on the first surface of the sheet. The sheet on which the second side image is transferred to one side and the first side image is superimposed on the other side is conveyed leftward by the intermediate transfer body 110, and the toner image (first side) on the intermediate transfer body 110 at the position of the transfer charger 122. 1 side image) is transferred to the first side of the sheet by the action of the transfer charger 122.

  In this way, the sheet having the image transferred on both sides of the sheet is separated by curvature by the roller 111, and the toner image is fixed on the sheet by the fixing device 30B. The sheet on which the toner image has been fixed is discharged to a discharge stack unit 40 on the upper surface of the apparatus or a discharge tray 44 on the side surface of the apparatus.

  On the other hand, when an image is obtained on one side of the sheet in this example, it is not necessary to transfer the image to the intermediate transfer body 110, and the image formed by the image forming unit PU is directly transferred from the intermediate transfer belt 60 onto the sheet. However, when the sheets are discharged to the sheet discharge tray 144 on the side surface of the apparatus, the image can be transferred to the lower surface of the sheet via the intermediate transfer body 110 in single-sided printing. As described above, in this example, the toner image created by the image forming unit PU is transferred from the intermediate transfer belt 60 to the sheet or the intermediate transfer body 110.

  Even in this example in which full-color images can be printed on both sides, when using stiff paper, paper can be fed from the manual feed tray 135 and ejected to the paper ejection tray 144, thereby transporting even thick, highly rigid paper. It is possible to obtain page-aligned double-sided printing without impairing the image quality. In the case of normal paper, paper can be fed from either the paper feed cassette 126 or the manual feed tray 135, and the paper discharge unit can be designated by either the stack unit 140 or the paper discharge tray 144. Of course, also in this case, it is possible to obtain double-sided printing with page alignment. Even in single-sided printing, when recording on stiff paper such as thick paper or OHP film, the paper surface is not reversed by specifying the paper discharge tray 144 using the manual feed tray 135, and is thick and highly rigid. Even in the case of a recording medium, single-sided printing with aligned pages can be obtained without impairing transportability.

  In the image forming apparatus of this example, in the case of special paper such as cardboard or envelope, transfer current (output of transfer bias applied to transfer means when transferring the toner image from the intermediate transfer belt 60 to the paper, intermediate transfer) The output of the transfer bias applied to the transfer means when transferring the toner image from the body 110 to the paper is increased by about 10 to 30% from that of the normal paper. In the case of special paper such as thick paper and envelopes, the temperature of the fixing rollers 118 and 119 is increased by about 10 to 30% from that of normal paper. Further, regarding the fixing temperature, more appropriate fixing property can be obtained by individually controlling the temperature of the fixing roller for each side of the paper in both cases of double-sided printing and single-sided printing. Further, a temperature detecting unit can be attached to each of the fixing rollers 118 and 119, and each fixing roller (fixing heater thereof) can be controlled based on the detection output of the temperature detecting unit.

  Also in the image forming apparatus of this example, glossiness detecting means 200 (FIG. 3) for detecting the glossiness of both sides of the paper is arranged on both sides of the paper transport path before the registration roller 128 (not shown). Then, the control of the toner adhesion amount according to the detection result of the glossiness detection means 200 is performed in the same manner as described with reference to the flowcharts of FIGS. Since the description is duplicated, it will be omitted. In the configuration of FIG. 13, since there is one image forming station, the toner adhesion amount is controlled by switching the image forming conditions of the image forming units SU for each sheet surface. ing.

  As described in the image forming apparatuses of the above two examples, the glossiness is different between the front and back in an image forming apparatus that forms a double-sided image by controlling the toner adhesion amount according to the detection result of the glossiness detecting means 200. Providing an image forming device that can prevent the problem of excessive increase in image gloss on low-gloss paper surfaces when using paper, and provide high-quality double-sided images with appropriate glossiness according to the paper surface can do.

  In other words, using the fact that the gloss characteristics can be controlled by the toner adhesion amount, the glossiness of each paper surface is detected, and the optimum toner adhesion amount is set so as to obtain an appropriate image glossiness according to the paper surface. By transferring it to a sheet, it is possible to obtain a high-quality double-sided image having appropriate gloss on each side. Appropriate glossiness refers to a state where the difference between the maximum and minimum gloss values in the paper is small, there is a natural glossiness corresponding to the paper, and there is little partial glare.

  In addition, since the image forming apparatus has a one-pass double-sided transfer configuration, it is possible to prevent the image gloss from being excessively increased since the sheet is not passed through the fixing device a plurality of times. In addition, the number of printing papers that are discarded due to poor image quality can be greatly reduced, and heat energy can be used efficiently for fixing double-sided images at a single time, making effective use of resources and carbon dioxide emissions. Since the amount can be reduced, it also leads to a reduction in environmental impact.

  Also, by calculating the glossiness of the paper from the reflected light using a plurality of optical sensors, non-contact detection can be performed, and the degree of freedom of arrangement of the detection means is increased. In addition, detection can be performed at high speed during conveyance of the paper. Therefore, application to a high-speed output image forming apparatus is also possible.

  In addition, by using regular reflection light having an angle of 60 to 85 degrees as reflected light used in the optical sensor, it is easy to easily obtain a correlation with the glossiness on each side of the paper, and the glossiness on each side is excellent. High-quality double-sided images can be obtained. Further, since the gloss level can be easily calculated, it is advantageous for a high-speed output image forming apparatus.

  Further, by disposing the glossiness detection means so as not to face each other with the sheet interposed therebetween, the optical sensor is not affected by the transmitted light of the sheet due to the light emission of the other optical sensor, and thus the detection accuracy of the optical sensor is improved. It is possible to obtain a high-quality double-sided image having excellent gloss on each side.

  If the paper glossiness is low, the image glossiness is reduced by reducing the toner adhesion amount, and the glossiness of each detected paper surface is compared, and the lower glossiness of the paper surface is compared. By controlling the toner adhesion amount to be smaller than that of the paper surface with the higher glossiness, it is possible to suppress the appearance of excessive image glossiness on the low-gloss surface, and on the high-gloss surface. Since an appropriate image gloss according to the paper surface can be obtained, a good quality double-sided image with little difference in gloss between the paper and the image on each surface can be obtained simply and at high speed.

  Further, in a configuration including a plurality of image forming modes having different toner adhesion amounts, the image forming mode is selected independently for the first surface and the second surface according to the detected glossiness of each surface of the paper. Since the optimum toner adhesion amount corresponding to the glossiness of the paper is transferred to the paper, it is possible to always obtain a high-quality double-sided image having excellent glossiness on each side of the paper.

  In addition, the toner adhesion amount can be controlled by changing the development potential, so that the toner adhesion amount can be changed directly, so that a high-quality double-sided image with excellent glossiness can be reliably obtained on each side. Can do.

  In addition, the toner adhesion amount is controlled by changing the exposure energy of the exposure apparatus, so that only the toner adhesion amount can be changed while maintaining the development conditions without changing the development conditions. High-quality double-sided images can be always obtained stably.

  In addition, the toner adhesion amount is controlled by changing the DC voltage applied to the developing roller, so that the toner adhesion amount can be changed easily and at high speed. An image can be obtained.

  Also, the toner adhesion amount is controlled more dynamically by changing the AC voltage waveform (for example, at least one parameter such as peak-to-peak voltage, frequency, duty, etc.) applied to the developing roller. Therefore, it is possible to obtain a high-quality double-sided image having excellent gloss on each side.

  Further, the toner adhesion amount is controlled by changing the toner concentration of the developer in the developing device by changing the toner replenishment amount to the developing device, so that the toner adhesion amount can be changed by a simple method. it can. In addition, with respect to continuous image formation on the same sheet that is frequently performed in practice, it is possible to stably increase the toner adhesion amount. Therefore, it is possible to obtain a high-quality double-sided image having excellent gloss on each side.

  In addition, since the configuration of FIG. 1 includes two image forming stations, the detection result of the paper glossiness can be performed at high speed to control the toner adhesion amount on each paper surface, thereby reducing the productivity of image formation. It is possible to form a high-quality double-sided image with good glossiness. Further, since a developing device for controlling the toner adhesion amount is separately provided for each sheet surface, stable toner adhesion amount control is possible.

  Further, in the configuration of FIG. 13, the detection result of the paper glossiness can be accurately fed back to the control of the toner adhesion amount, a high-quality double-sided image with good glossiness can be obtained on each surface, and the size of the image forming apparatus can be increased. Can be made compact.

  Further, the glossiness detecting means on both sides of the paper is positioned upstream of the distance of one quarter of the toner carrying belt with respect to the transfer position, so that the detected glossiness can be ensured without delay. It is possible to feed back to the image forming conditions, and it is possible to stably obtain a high-quality double-sided image with good gloss on each side without impairing productivity.

  In addition, when a single-sided image is printed, an image forming method is selected so that the toner image is transferred onto the paper surface having the higher glossiness, thereby automatically and more easily without the user's awareness. A high-quality image with high gloss and good appearance can be obtained, and glare of the image on the low-gloss surface does not occur.

  Also, by printing a color image with a large amount of adhesion on the paper surface with the higher glossiness, a high-quality color image with good glossiness can be obtained automatically and more easily without the user's awareness. Further, by printing a monochrome image with a small amount of adhesion on a paper surface with a lower glossiness, occurrence of glare that is excessive image gloss can be suppressed.

  Next, an embodiment will be described in which the toner adhesion amount per unit area on each paper surface corresponding to the detected glossiness of each paper surface is set so as to satisfy a predetermined relationship. The present embodiment can be implemented by the image forming apparatuses of the above two examples.

  This embodiment prevents the problem that the image gloss of the low glossy paper surface increases excessively when using paper with different glossiness on the front and back when performing double-sided recording. A high-quality double-sided image with a high glossiness can be obtained.

  The inventor of the present application conducted an experiment to output images with different amounts of toner adhesion on a plurality of types of paper having different glossiness on each side of the paper and to evaluate the visibility of the glossiness of the image on each side of the paper. . The results are shown in Table 1 below. Here, seven types of papers A to G were evaluated.

  In the evaluation experiment, the paper glossiness on the high gloss surface side was G1, the toner adhesion amount per unit area was m1, and those on the low gloss surface side were G2 and m2. The toner adhesion amount was changed in m2 and the ratio (m2 / m1) was changed in four steps from 1 to 0.5.

  The visibility rank indicates a sense of discomfort in gloss when both sides are compared, and pays attention to the difference between the paper surface and the image gloss, glare of the image on the low gloss paper surface, and the like. Here, a three-step evaluation of ○, Δ, and × was made, and ○ was OK (good). At that time, the toner adhesion amount ratio, which is OK, was calculated from the data and used as the recommended toner adhesion amount ratio.

The recommended toner adhesion amount ratio decreases as the gloss difference ΔG increases on both sides of the paper (Examples 3 and 4), and the recommended toner adhesion amount as the paper glossiness on the low gloss side decreases. The following formula was derived by the decrease in the ratio (Examples 4, 5, etc.).
m2 / m1 = 1−α ′ × ΔG / G2
Transform the above equation,
α ′ = G2 / ΔG × (1−m2 / m1)
Table 1 shows the obtained α ′. Then, in the papers A to E (Examples 1 to 5), α was about 0.11.

Therefore, when α = 0.1 and (m2 / m1) is set as shown in the following formula (2), conditions for obtaining an image with good visibility and proper glossiness were obtained.

m2 / m1 ≦ 1-α × ΔG / G2 Equation (2)
Where ΔG = G1-G2, α = 0.1

  As shown in Comparative Examples 1 and 2 in Table 1, when the paper glossiness difference ΔG was small, good double-sided image visibility was obtained without changing the toner adhesion amount ratio. That is, when the paper glossiness difference ΔG is small to some extent, it is not necessary to change the toner adhesion amount ratio, and it has been found effective to control the toner adhesion amount when the paper glossiness difference is 20 or more. Further, it is not preferable to unnecessarily decrease the toner adhesion amount because of complicated control and impaired color reproducibility of an image.

  As described above, by setting (m2 / m1) so as to satisfy the condition expressed by the above formula (2), it is possible to set the toner adhesion amount according to the paper glossiness. Appropriate image gloss can be obtained. At this time, the toner adhesion amount on the low glossy surface is set to be smaller as the glossiness G2 of the low glossy surface is smaller and as the glossiness difference of the paper surface is larger, so that the image on the lower glossy surface side of the paper is set. In this case, it is possible to prevent excessive gloss from occurring.

  Further, image formation is performed by setting (m2 / m1) so as to satisfy the condition expressed by the above formula (2) using a sheet having a gloss difference of 20% or more between the first side and the second side of the sheet. Thus, it is possible to effectively prevent the occurrence of excessive gloss on the low gloss surface. Note that when a sheet having a gloss difference of less than 20% is used, an effective effect cannot be obtained even if the toner adhesion amount is reduced on the low gloss surface because the difference in gloss of the image portion is small. In addition, there is a concern that the color reproducibility is lowered due to a decrease in the toner adhesion amount. Therefore, in order to simplify the control and ensure color reproducibility, it is desirable to control the toner adhesion amount on a sheet having a gloss difference of 20% or more between the front and back sides.

  Next, an embodiment will be described in which the area ratio of an image to be formed on each side of a sheet is obtained, and an image having a lower image area ratio is formed on a sheet surface having a lower glossiness during duplex recording. . The present embodiment can be implemented by the image forming apparatuses of the above two examples. Further, it can be carried out together with the setting of (m2 / m1) based on the above formula (2).

  This embodiment prevents the problem that the image gloss of the low glossy paper surface increases excessively when using paper with different glossiness on the front and back when performing double-sided recording. A high-quality double-sided image with a high glossiness can be obtained.

  As an image area ratio calculation method, a method of calculating the area ratio of an image from the number of writing dots can be cited. The processing at that time will be described with reference to the block diagram of FIG. The image signal 71 color-separated for each color (C, M, Y, Bk) is input to the dot modulator 72. The dot modulation unit 72 is a part that modulates light emission of one dot in the exposure apparatus in accordance with an image signal and passes it to the exposure control unit 73. Specifically, the dot modulation unit 72 performs processing for changing the light emission time and the exposure intensity. Thereby, the light emission of one dot is modulated and emitted in the exposure unit 74 having a laser or the like. Further, the pixels at the time of dot emission in the image signal input to the dot modulation unit 72 are counted by the counter unit 75, integrated at a certain timing, and stored in the memory unit 76. This timing may be the timing for one sheet of paper or the timing per job. The image area ratio calculation unit 77 can calculate the input image area ratio from the ratio of the total number of pixels and the number of light emitting dots in that period.

FIG. 16 is a flowchart showing control for forming an image with a lower image area ratio on a paper surface with a lower glossiness during double-sided recording.
In the flowchart of FIG. 16, first, the glossiness of each surface of the paper is detected by the glossiness detection means 200a, b, and the surface with the high glossiness is the G1 surface and the surface with the low glossiness is the G2 surface (S41). Next, the image area ratio calculation unit 77 calculates the image area ratio of each surface. Here, the image area ratio of the G1 surface is A1, and that of the G2 surface is A2 (S42). Next, A1 and A2 are compared (S43). If A2 is equal to or less than A1, a command to create an image with an image area ratio of A2 on the G2 plane and an A1 image on the G1 plane (S43). S44), image output is performed (S46). On the other hand, if A2 is greater than A1, a command is issued to create an image with an image area ratio of A1 on the G2 plane and an A2 image on the G1 plane (S45), and image output is performed (S46). In this case, if the image is reversed using a paper reversing device after fixing (not shown), the printing order is not changed even for a plurality of jobs.

  In this way, when forming a double-sided image, the image with the lower image area ratio is formed on the paper surface with the lower glossiness. Gloss can be suppressed. In addition, since the image area ratio is low, deterioration in color reproducibility is not conspicuous, and it is possible to obtain a double-sided image that can simultaneously satisfy the suppression of glare due to excessive gloss and the securing of color reproducibility.

  Next, an embodiment will be described in which an image that is a character image is formed on a paper surface having a lower glossiness when images to be formed on each surface of the paper are a character image and an image image, respectively. To do. The present embodiment can be implemented by the image forming apparatuses of the above two examples. Further, it can be carried out together with the setting of (m2 / m1) based on the above formula (2).

  This embodiment prevents the problem that the image gloss of the low glossy paper surface increases excessively when using paper with different glossiness on the front and back when performing double-sided recording. A high-quality double-sided image with a high glossiness can be obtained. Here, a character image having a high ratio of character information is a character image, and an image having a high ratio of image images is an image. That is, the character image and the image image are not limited to only the character information or the image image.

  As a method for detecting an image type, there is a method for detecting an image type from an image mode selected from a plurality of image forming modes prepared in advance. From a plurality of image forming modes prepared in advance in the image forming apparatus, the operator can select one of these modes from the operation panel (reference numeral 33 in FIG. 1) or printer driver software on an external personal computer. It has become. The image forming mode is a plurality of print settings prepared according to the type and finish of the printed matter, and a character mode, a photo mode, a character / photo mixed mode, and the like are appropriately prepared. By changing the parameters of the image processing and the conditions of the image forming process according to the selected image forming mode, it is possible to obtain a finishing effect suitable for the printing type. Since these image forming modes are in accordance with the type of printing, it is possible to roughly predict how much character information the document contains. For example, it is possible to compare the amount of character information in association with the image forming mode such as character mode> character / photo mixed mode> photo mode. Accordingly, it is possible to easily detect the toner adhesion amount without counting pixels of image information every time.

Control based on the image type will be described with reference to the flowchart of FIG.
First, the glossiness of each side of the paper is detected by the glossiness detection means 200a, 200b, and the surface with high glossiness is designated as G1 and the surface with low glossiness is designated as G2 (S51). Next, the image type of each surface is detected by the above-described image type detection method (image type detection means). Here, the image type on the G1 plane is B1, and that on the G2 plane is B2 (S52). Then, B1 and B2 are compared with respect to the amount of character information (S53), and if B2 is B1 or more, an instruction to create an image of B2 as it is on the G2 surface and an A1 image on the G1 surface is issued. (S54), image output is performed (S56). On the other hand, if B1 is larger than B2 for character information, a command is made to create an image of B1 on the G2 surface and a B2 image on the G1 surface (S55), and image output is performed (S56). In this case, if the image is reversed using a paper reversing device after fixing (not shown), the printing order is not changed even for a plurality of jobs.

  In this way, when a double-sided image is created, an image containing a large number of character images is automatically created on the lower glossy paper surface, so that the image glossiness can be preferentially suppressed for character images. Therefore, an image with excellent visibility can be obtained.

Finally, a toner that can be suitably used in an image forming apparatus to which the present invention is applied will be described.
In order to reproduce minute dots of 600 dpi or more, the toner preferably has a weight average particle diameter of 3 to 7 μm. In this range, since the toner particles have a sufficiently small particle size with respect to the minute latent image dots, the dot reproducibility is excellent.

  When the weight average particle diameter (D4) is less than 3 μm, phenomena such as a decrease in transfer efficiency and a decrease in blade cleaning properties tend to occur. When the weight average particle diameter (D4) exceeds 7 μm, it is difficult to suppress scattering of characters and lines.

  Moreover, it is preferable that ratio (D4 / D1) of a weight average particle diameter (D4) and a number average particle diameter (D1) exists in the range of 1.00-1.30. The closer (D4 / D1) is to 1.00, the sharper the particle size distribution. With such a toner having a small particle size and a narrow particle size distribution, the toner charge amount distribution is uniform, a high-quality image with little background fogging can be obtained, and the electrostatic transfer method has a high transfer rate. can do.

Next, a method for measuring the particle size distribution of toner particles will be described.
Examples of the measuring device for the particle size distribution of toner particles by the Coulter counter method include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter). The measurement method is described below.

  First, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an aqueous electrolytic solution. Here, the electrolytic solution is a solution prepared by preparing a 1% NaCl aqueous solution using primary sodium chloride. For example, ISOTON-II (manufactured by Coulter) can be used. Here, 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the measurement device is used to measure the weight and number of toner particles or toner using a 100 μm aperture as an aperture. Calculate weight distribution and number distribution. From the obtained distribution, the weight average particle diameter (D4) and the number average particle diameter (D1) of the toner can be obtained.

  As channels, 2.00 to less than 2.52 μm; 2.52 to less than 3.17 μm; 3.17 to less than 4.00 μm; 4.00 to less than 5.04 μm; 5.04 to less than 6.35 μm; 6 Less than 35 to 8.00 μm; less than 8.00 to less than 10.08 μm; less than 10.08 to less than 12.70 μm; less than 12.70 to less than 16.00 μm; less than 16.00 to less than 20.20 μm; Uses 13 channels of less than 40 μm; 25.40 to less than 32.00 μm; 32.00 to less than 40.30 μm, and targets particles having a particle size of 2.00 μm to less than 40.30 μm.

  The toner shape factor SF-1 is preferably in the range of 100 to 160, and the shape factor SF-2 is preferably in the range of 100 to 160. FIG. 18 is a diagram schematically illustrating the shape of the toner in order to explain the shape factor SF-1 and the shape factor SF-2. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following mathematical formula (3). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.

SF-1 = {(MXLNG) ² / AREA} × (100π / 4) (3)
When the SF-1 value is 100, the shape of the toner is a true sphere, and becomes larger as the SF-1 value increases.

  The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following mathematical formula (4). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner onto the two-dimensional plane by the figure area AREA and multiplying by 100 / 4π.

SF-2 = {(PERI) ² / AREA} × (100 / 4π) (4)
When the SF-2 value is 100, unevenness does not exist on the toner surface, and as the SF-2 value increases, the unevenness of the toner surface becomes more prominent.

  Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated.

  When the shape of the toner is close to a spherical shape, the contact state between the toner and the toner or the toner and the photoconductor becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity increases, and the toner and the photoconductor The attraction force becomes weaker and the transfer rate becomes higher. If either of the shape factors SF-1 and SF-2 exceeds 160, the transfer rate is lowered, which is not preferable.

  Many toner characteristics related to toner fixing properties are known, and in particular, it is known that a ½ outflow temperature (softening point) is related. For the fixing device of the present invention, a ½ outflow temperature is known. (Softening point) No relationship was found in the fixability, and a toner satisfying both characteristics of a glass transition temperature (described later) of 45 to 65 ° C. and an outflow start temperature (described later) of 90 to 115 ° C. is used. It was revealed that good fixability can be obtained.

  When the glass transition temperature is lower than 45 ° C., offset may occur during fixing. Conversely, when the glass transition temperature is higher than 65 ° C., sufficient fixing property cannot be obtained, and the image is easily peeled off from the transfer paper. There is.

  If the outflow start temperature is lower than 90 ° C, offset may occur during fixing. Conversely, if it is higher than 115 ° C, sufficient fixability cannot be obtained, and the image tends to peel off from the transfer paper. There is.

About glass transition point (Tg) The measuring method of Tg is outlined. As an apparatus for measuring Tg, a TG-DSC system TAS-100 manufactured by Rigaku Corporation was used.

  First, about 10 mg of a sample is placed in an aluminum sample container, which is placed on a holder unit and set in an electric furnace. Then, after heating from room temperature to 150 ° C. at a rate of temperature increase of 10 ° C./min, the sample was allowed to stand at 150 ° C. for 10 minutes, and the sample was cooled to room temperature and left for 10 minutes. DSC measurement was performed by heating at / min. Tg was calculated from the tangent of the endothermic curve near the Tg and the base line using the analysis system in the TAS-100 system.

About the outflow start temperature The outflow start temperature of the toner can be measured using a flow tester. An example of a flow tester is an elevated flow tester CFT500D manufactured by Shimadzu Corporation. The flow curve of this flow tester becomes the data shown in FIGS. 19A and 19B, from which each temperature can be read. In the figure, TGb is the outflow start temperature, and the melting temperature in the 1/2 method is the T1 / 2 temperature. The measurement conditions are: load: 5 kg / cm ² , heating rate: 3.0 ° C./min, die diameter: 1.00 mm, and die length: 10.0 mm.

Further, as the binder resin used for the toner, those having the following composition can be used as long as they satisfy the characteristics of the toner.
For example, homopolymers of styrene such as polyester, polystyrene, poly p-chlorostyrene, polyvinyltoluene and the like; and styrene-p-chlorostyrene copolymers, styrene-propylene copolymers, styrene-vinyltoluene copolymers. Styrene-vinyl naphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate Copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, Styrene-vinyl ethyl acetate Ter copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester Examples thereof include styrene copolymers such as copolymers.

Moreover, the following resin can also be mixed and used.
Polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyacrylic resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or Examples thereof include alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffin, and paraffin wax.

  Among these, a polyester resin is particularly preferable in order to obtain sufficient fixability. The polyester resin is obtained by condensation polymerization of alcohol and carboxylic acid, and the alcohol used is polyethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butane. Diols such as diol, neopentyl glycol, 1,4-butenediol, 1,4-bis (hydroxymethyl) cyclohexane, bisphenol A, hydrogenated bisphenol A, polyexethylenated bisphenol A, polyoxypropylenated bisphenol A, etc. And a divalent alcohol simple substance obtained by substituting these with a saturated or unsaturated hydrocarbon group having 3 to 22 carbon atoms, and other divalent alcohol simple substance.

  Examples of the carboxylic acid used to obtain the polyester resin include maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, Adipic acid, sebacic acid, malonic acid, divalent organic acid monomers in which these are substituted with a saturated or unsaturated hydrocarbon group having 3 to 22 carbon atoms, acid anhydrides, lower alkyl esters and linolenic acid Dimers and other divalent organic acid monomers can be mentioned.

  In order to obtain a polyester resin to be used as a binder resin, it is also preferable to use not only a polymer with only the above bifunctional monomer but also a polymer containing a component with a trifunctional or higher polyfunctional monomer. It is. Examples of the polyhydric alcohol monomer having three or more valences that are such polyfunctional monomers include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sarbitane, pentaesitol, dipenta. Esitol, tripentaerythritol, sucrose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol , Trimethylolethane, trimethylolpropane, 1.3.5-trihydroxymethylbenzene, and others.

  Examples of the trivalent or higher polyvalent carboxylic acid monomer include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2 -Methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, embol trimer acid, acid anhydrides thereof, and the like.

  Further, the toner can contain a release agent for the purpose of improving the releasability of the toner on the surface of the fixing belt at the time of fixing. As the release agent, all known ones can be used, and in particular, defree fatty acid type carnauba wax, montan wax, oxidized rice wax, and ester wax can be used alone or in combination.

  The carnauba wax is preferably a microcrystalline one, having an acid value of 5 or less and a particle size of 1 μm or less when dispersed in a toner binder. The montan wax generally refers to a montan wax refined from minerals, and like a carnauba wax, it is microcrystalline and preferably has an acid value of 5 to 14. The oxidized rice wax is obtained by air-oxidizing rice bran wax, and the acid value is preferably 10-30.

  When the acid value of each wax is less than the respective range, the low temperature fixing temperature rises and the low temperature fixing becomes insufficient. On the contrary, when the acid value exceeds each range, the cold offset temperature rises and the low-temperature fixing becomes insufficient. The added amount of the wax is 1 to 15 parts by weight, preferably 3 to 10 parts by weight with respect to 100 parts by weight of the binder resin. If it is less than 1 part by weight, the releasing effect is thin and the desired effect is difficult to obtain. On the other hand, when the amount exceeds 15 parts by weight, problems such as significant spent on the carrier occur.

  Further, for the purpose of imparting charge to the toner, a charge control agent can be contained. Any conventionally known charge control agent can be used. Examples of positive charge control agents include nigrosine, basic dyes, lake dyes of basic dyes, quaternary ammonium salt compounds, etc., and examples of negative charge control agents include metal salts of monoazo dyes, salicylic acid, naphthoic acid, dyes, and the like. Examples include carboxylic acid metal complexes and the like.

  The amount of the polarity control agent used is determined by the toner production method including the type of binder resin, the presence or absence of additives used as necessary, and the dispersion method, and is not limited uniquely. Is used in an amount of 0.01 to 8 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the binder resin. If it is less than 0.01 part by weight, the effect is small with respect to the fluctuation of the charge amount Q / M when the environment changes, and if it exceeds 7 parts by weight, the low-temperature fixability is inferior.

  Further, as the metal-containing monoazo dye to be used, a chromium-containing monoazo dye, a cobalt-containing monoazo dye, and an iron-containing monoazo dye can be used alone or in combination. By adding these, the rising of the charge amount Q / M in the developer (time until saturation) becomes more excellent.

  The amount used is determined by the toner production method including the type of binder resin, the presence or absence of additives used as necessary, and the dispersion method as in the case of the polar control agent, and is uniquely limited. However, it is used in the range of 0.1 to 10 parts by weight, preferably 1 to 7 parts by weight with respect to 100 parts by weight of the binder resin. If the amount is less than 0.1 parts by weight, the effect is small, and if the amount exceeds 10 parts by weight, the saturation level of the charge amount is lowered.

  In addition, it is particularly preferable to use a metal salt of a salicylic acid derivative for the color toner, but if necessary, a transparent or white substance that does not impair the color tone of the color toner is added to stabilize the charging property of the toner. Can be granted. Specifically, organic boron salts, fluorine-containing quaternary ammonium salts, calixarene compounds and the like are used, but are not limited thereto.

  Further, the toner can further contain a magnetic material and can be used as a magnetic toner. Magnetic materials contained in the magnetic toner include iron oxides such as magnetite, hematite and ferrite, metals such as iron, cobalt and nickel, or aluminum of these metals, cobalt, copper, lead, magnesium, tin, zinc, antimony, Examples include alloys of metals such as beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, vanadium, and mixtures thereof.

  These ferromagnetic materials preferably have an average particle size of about 0.1 to 2 μm. The amount of the ferromagnetic material to be contained in the toner is about 20 to 200 parts by weight, particularly preferably 100 parts by weight of the resin component, with respect to 100 parts by weight of the resin component. 40 to 150 parts by weight per part.

As the colorant, all known colorants can be used.
As the black colorant, for example, carbon black, aniline black, furnace black, lamp black and the like can be used. Examples of cyan colorants include phthalocyanine blue, methylene blue, Victoria blue, methyl violet, aniline blue, and ultramarine blue. As the magenta colorant, for example, rhodamine 6G lake, dimethylquinacridone, watching red, rose bengal, rhodamine B, alizarin lake and the like can be used. Examples of yellow colorants include chrome yellow, benzidine yellow, hansa yellow, naphthol yellow, molybdenum orange, quinoline yellow, and tartrazine.

  As the colorant used in the toner of the present invention, dyes and pigments capable of obtaining toners of yellow, magenta, cyan and black colors can be used. For example, carbon black, lamp black, ultramarine, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, Rogmin 6G, rake, chalcoil blue, chrome yellow, quinacridone, benzidine yellow, rose bengal, triallylmethane dye, etc. Any conventionally known dyes and pigments such as dyes and pigments can be used alone or in combination.

  Further, as an external additive, for the purpose of improving the fluidity of the toner, a hydrophobic silica, titanium oxide, alumina, or the like, and a fatty acid metal salt, polyvinylidene fluoride, or the like may be added as necessary.

  Further, when the toner is used as a two-component developer, all known carriers can be used. Examples thereof include magnetic powders such as iron powder, ferrite powder, and nickel powder, glass beads, and the like. The thing which processed these surfaces with resin etc. is mentioned.

  Examples of the resin powder that can be coated on the carrier include a styrene-acrylic copolymer, a silicone resin, a maleic acid resin, a fluorine resin, and a polyester resin epoxy resin. In the case of a styrene-acrylic copolymer, those having a styrene content of 30 to 90% by weight are preferred. In this case, when the styrene content is less than 30% by weight, the development characteristics are low, and when it exceeds 90% by weight, the coating film becomes hard and easily peeled, and the life of the carrier is shortened.

Moreover, the resin coating of the carrier in the present invention may contain an adhesion-imparting agent, a curing agent, a lubricant, a conductive material, a charge control agent and the like in addition to the resin.
The carrier core particles coated with the silicone resin may be conventionally known particles, and examples thereof include ferromagnetic metals such as iron, cobalt and nickel; alloys and compounds such as magnetite, hematite and ferrite; and glass beads. The average particle diameter of these core particles is usually 10 to 1000 μm, preferably 30 to 500 μm. In addition, the usage-amount of a silicone resin is 1 to 10 weight% normally with respect to a carrier core particle.

  The silicone resin may be any conventionally known silicone resin such as KR261, KR271, KR271, KR272, KR275, KR280, KR282, KR285, KR251, KR155 manufactured by Shin-Etsu Silicone Co., Ltd., which are commercially available. , KR220, KR201, KR204, KR205, KR206, SA-4, ES1001, ES1001N, ES1002T, KR3093 and SR2100, SR2101, SR2107, SR2110, SR2108, SR2109, SR2115, SR2400, SR2410, SR2411, made by Toray Silicone, SH806A, SH840, etc. are used. As a method for forming the silicone resin layer, a silicone resin may be applied to the surface of the carrier core particles by means of a spraying method, a dipping method or the like, as in the past. The carrier has a volume average particle size of about 25 μm to 60 μm.

  As described above, the weight average particle diameter is 3 to 7 μm, and the ratio (D4 / D1) of the weight average particle diameter (D4) to the number average particle diameter (D1) is in the range of 1.00 to 1.30. It is preferable to use toner. By having such toner characteristics, voids between micro toners are reduced and the toner density in the toner image is increased (so-called solid filling is improved), so that a sufficient image density can be obtained with a smaller amount of adhesion. . Therefore, it is possible to control a wide range of image gloss depending on the toner adhesion amount. In addition, it is possible to achieve high image quality, such as improvement in dot reproducibility with the reduction in particle size, stabilization of charge amount by sharpening of particle size distribution, and improvement of transfer rate by reduction in pile height.

  On the other hand, when the toner characteristics are in a range other than the above, it is difficult to control the gloss by the toner adhesion amount. If (D4) is less than 3 μm, problems such as a decrease in transfer efficiency and a decrease in blade cleaning properties are likely to occur. When (D4) exceeds 7 μm, it is difficult to suppress scattering of characters and lines. When (D4 / D1) exceeds 1.30, the toner charge amount distribution becomes broad, and problems such as background fog are likely to occur.

  Further, it is preferable to use toner having a shape factor SF-1 in the range of 100 to 160 and a shape factor SF-2 in the range of 100 to 160. If either of the shape factors SF-1 or SF-2 exceeds 160, the transfer rate is lowered and the image quality is significantly deteriorated.

Further, it is preferable to use toner having at least a binder resin, a colorant, and a release agent and having a glass transition temperature of 45 to 65 ° C. and an outflow start temperature of 90 to 115 ° C.
In general, it is known that the 1/2 outflow temperature (softening point) is related to the toner fixing property, but in the present invention, the 1/2 outflow temperature (softening point) is related. As a result, it has been clarified that good fixability can be obtained by using a toner satisfying both characteristics of a glass transition temperature of 45 to 65 ° C. and an outflow start temperature of 90 to 115 ° C. As a result, gloss control based on the toner adhesion amount can be performed widely.

  On the other hand, when the glass transition temperature is lower than 45 ° C., offset may occur at the time of fixing. Conversely, when the glass transition temperature is higher than 65 ° C., sufficient fixing property cannot be obtained, and the image is easily peeled off from the transfer paper. There is a case. Further, when the outflow start temperature is lower than 90 ° C., offset may occur at the time of fixing. Conversely, when it is higher than 115 ° C., sufficient fixing property cannot be obtained, and the image is easily peeled off from the transfer paper. There is a case.

  Although the present invention has been described above with reference to the illustrated examples, the present invention is not limited to this and can be modified as appropriate. For example, the number of image forming units in the image forming station is arbitrary, and a color image forming apparatus using three image forming units and a monochrome apparatus using a single image forming unit are also possible. Further, the configuration of the glossiness detection means is not limited to the illustrated example, and an appropriate system can be adopted.

1 is a cross-sectional view illustrating a schematic configuration in an example of an image forming apparatus according to the present invention. 2 is a cross-sectional view illustrating a schematic configuration of an image forming unit of the image forming apparatus. FIG. It is a cross-sectional block diagram which shows an example of a glossiness detection means. It is a schematic diagram for demonstrating the reflected light component in the glossiness detection means. It is a schematic diagram which shows arrangement | positioning of a glossiness detection means. FIG. 6 is a schematic diagram illustrating a surface potential of a photoreceptor on which an electrostatic latent image is formed. It is a graph for demonstrating developing ability. It is a wave form diagram which shows an example of an alternating current developing bias. 6 is a flowchart illustrating an example of toner adhesion amount control based on paper glossiness. 6 is a flowchart illustrating another example of toner adhesion amount control based on paper glossiness. 10 is a flowchart illustrating still another example of toner adhesion amount control based on paper glossiness. 10 is a flowchart illustrating still another example of toner adhesion amount control based on paper glossiness. 1 is a cross-sectional configuration diagram illustrating an image forming apparatus having a different configuration to which the present invention is applied. It is a side view which shows the image formation unit. It is a block diagram which shows the structure of an image area ratio calculation part. 6 is a flowchart illustrating control for forming an image having a lower image area ratio on a paper surface having a lower glossiness during duplex recording. It is a flowchart which shows the control which forms an image containing much character information on the paper surface of a low glossiness. FIG. 6 is a diagram schematically illustrating the shape of a toner in order to explain the shape factor SF-1 and the shape factor SF-2. It is a graph which shows the flow curve of the tester which measures the outflow start temperature of a toner. 6 is a graph showing a relationship between toner adhesion amount and image glossiness.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 11,12 Image forming station 20,40 Belt unit 21,41 Intermediate transfer belt 22,42 Primary transfer roller 30,50 Image forming unit 33 Operation part 51 Secondary transfer roller 52 Secondary transfer charger 60 First intermediate Transfer belt 80 Paper feed device 100 Device main body 110 Second intermediate transfer belt 200 Gloss degree detecting means 201 Light emitting portion 202 Light receiving portion 203 Guide member PU Image forming portion SU Image forming unit

Claims (23)

In an image forming apparatus capable of performing both-side recording by fixing images on both sides of a sheet with a single sheet passing through a fixing device,
Glossiness detection means for detecting the glossiness of each of the one side surface and the other side surface of the paper,
When printing on both sides, the glossiness of each side of the paper detected by the glossiness detection means is compared. If the glossiness of each side of the paper is different, the amount of toner adhesion on the lower glossy side is reduced. An image forming apparatus that controls image conditions . The image forming apparatus according to claim 1, wherein the glossiness detection unit is an optical sensor having a light emitting portion and a light receiving portion, and calculates the paper glossiness based on the reflected light reflected on the paper. 3. The image forming apparatus according to claim 2, wherein the light received by the light receiving unit of the optical sensor is specularly reflected light, and an angle formed by the sheet perpendicular and the specularly reflected light is not less than 60 degrees and not more than 85 degrees. . The glossiness detecting means for detecting the glossiness of the one side of the paper and the glossiness detecting means for detecting the glossiness of the other side of the paper are arranged so as not to face each other across the paper, The image forming apparatus according to claim 1. The image formation according to claim 1 , wherein during double-sided printing, the toner adhesion amount on each side of the paper is controlled independently according to the glossiness of each side of the paper detected by the glossiness detecting unit. apparatus. The image forming apparatus according to claim 1, wherein the toner adhesion amount is controlled by changing a developing potential in an image forming unit. The image forming apparatus according to claim 6 , wherein the development potential is controlled by changing an exposure energy of an exposure apparatus in an image forming unit. The image forming apparatus according to claim 6 , wherein the developing potential is controlled by changing a DC voltage as a developing bias in the image forming unit. The image forming apparatus according to claim 1, wherein the toner adhesion amount is controlled by changing an AC voltage waveform as a developing bias in the image forming unit. The image forming apparatus according to claim 1, wherein the toner adhesion amount is controlled by changing a toner density in the developing device in the image forming unit. A first image forming station having at least one image forming unit provided around the first intermediate transfer member; and a second image forming station having at least one image forming unit provided around the second intermediate transfer member. The double-sided recording is possible by transferring each image formed by the two image forming stations from each of the first and second intermediate transfer bodies to each side of the paper by one sheet passing. The image forming apparatus according to 1. An image forming station provided with at least one image forming unit around the first intermediate transfer member, and a second intermediate transfer member capable of transferring an image carried on the first intermediate transfer member, 2. The image forming apparatus according to claim 1, wherein each of the images carried by the first and second intermediate transfer members is transferred onto each side of the sheet by one pass and recording on both sides is possible. The glossiness detecting means is disposed upstream of a distance of a quarter of the outer periphery of the intermediate transfer body along the sheet conveyance path with respect to the image transfer position from the intermediate transfer body to the paper. The image forming apparatus according to claim 11 or 12 . The image forming apparatus according to claim 1, wherein an image is transferred to a surface having a higher glossiness of each side of the sheet detected by the glossiness detecting unit during single-sided recording. When performing double-sided printing in which one side of the paper is a color image and the other side is a monochrome image, the color image is transferred to the higher glossy side of each side of the paper detected by the glossiness detecting means. The image forming apparatus according to claim 1. 2. The image forming apparatus according to claim 1, wherein the toner adhesion amount per unit area of the monochrome solid image is 0.7 mg / cm <2> or less. A toner having a weight average particle diameter of 3 to 7 μm and a ratio (D4 / D1) of the weight average particle diameter (D4) to the number average particle diameter (D1) in the range of 1.00 to 1.30 is used. The image forming apparatus according to claim 1. In the range of the shape factor SF-1 of 100-160 and a shape factor SF-2 is characterized by using a toner in the range of 100 to 160, the image forming apparatus according to claim 1 or 17. At least a binder resin, a colorant, consists release agent, a glass transition temperature of 45 to 65 ° C., flow beginning temperature is characterized by using a toner of 90 to 115 ° C., more of claims 1, 17, 18 The image forming apparatus according to claim 1. The glossiness of each side of the paper detected by the glossiness detection means is G1, G2 (G1> G2), and the toner adhesion amount per unit area of each side of the paper corresponding to G1, G2 is m1, m2, respectively. When
m2 / m1 ≦ 1-α × ΔG / G2
Where ΔG = G1-G2, α = 0.1
The image forming apparatus according to claim 1, wherein the relationship is satisfied. 21. The image forming apparatus according to claim 20 , wherein a sheet having a difference between G1 and G2 of 20% or more is used. An image area ratio detecting means for detecting an area ratio of an image to be formed on the paper surface;
The area ratio of the image to be formed on each side of the sheet at the time of double-sided recording is detected by the image area ratio detecting means, and the image having the lower area ratio among the detected images is detected by the glossiness detecting means. The image forming apparatus according to any one of claims 1, 20 and 21 , wherein recording is performed on a surface of the detected sheet having a lower glossiness. Image type detection means for detecting the type of image to be formed on the paper surface;
The type of image to be formed on each side of the paper during double-sided recording is detected by the image type detection means, and when the detected image type on each side of the paper is a character image and an image image, an image, characterized in that the recording on the sheet surface of the lower gloss of the sheet surfaces of detecting the glossiness in the glossiness detection means, to any one of claims 1, 20, 21 The image forming apparatus described.

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