Image forming apparatus and intermediate transfer member

Abstract: An image forming apparatus includes: a first image-bearing member, an intermediate transfer member for receiving an image formed on the first image-bearing member and transferring the image onto a second image-bearing member, pattern-forming means for forming a prescribed pattern on the intermediate transfer member, density detection means for detecting a density of the pattern, and control means for controlling image forming conditions based on the detected density. The intermediate transfer member is set to have a reflectance of 10 - 70 % for light having a wavelength in the range of 700 - 1500 nm at least in a region thereof for forming the prescribed pattern. As a result, the pattern density detection is suitably performed on the intermediate transfer member for all of yellow, magenta cyan and black, and the detected density data is used for controlling the image forming conditions.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to an image forming apparatus, particularly an image forming apparatus, such as a copying machine, a printer and a facsimile apparatus, of a type wherein an image formed on a first image-bearing member is once transferred to an intermediate transfer member (primary transfer), and then further transferred to a second image-bearing member (secondary transfer). The present invention further relates to an intermediate transfer member used in such an image forming apparatus. The above-mentioned type of image forming apparatus using an intermediate transfer member is effective as a multi-colour image forming apparatus for synthetically reproducing a multi-colour image product by sequentially transferring a plurality of component colour images in lamination based on multi-colour image data to form a multi-colour image free from deviation (colour deviation) among the respective component colour images. Figure 1 shows an outline of an example of image forming apparatus using a drum-shaped intermediate transfer member. The image forming apparatus shown in Figure 1 is a full-colour image forming apparatus (copying machine or laser beam printer) using an electrophotographic process and including an elastic roller 20 of a medium resistivity as an intermediate transfer member. The image forming apparatus further includes a rotating drum-type electrophotographic photosensitive member (hereinafter simply called "photosensitive member") repetitively used as a first image-bearing member, which is driven in rotation in an arrow direction at a prescribed peripheral speed (process speed). During the rotation, the photosensitive member 1 is uniformly charged to a prescribed potential of a prescribed polarity by a primary charger (corona discharger) 2 and then receives imagewise exposure light 3 from an imagewise exposure means (not shown) (such as a colour separation-focusing exposure optical system for a colour original image, or a scanning exposure optical system including a laser scanner for outputting a laser beam modulated corresponding to time-serial electrical digital image signals based on image data). As a result, an electrostatic latent image corresponding to a first colour component image (e.g., magenta component image) to an objective colour image is formed on the photosensitive member 1. Then, the electrostatic latent image is developed into a magenta component image (as a first colour component image) by a first developing device (magenta developing device). At this time, second to fourth developing devices, i.e., a cyan developing device 42, a yellow developing device 43 and a black developing device 44, are not operated, thus not acting on the photosensitive member 1, so that the first colour magenta component image is not affected by the second to fourth developing devices 42 - 44. An intermediate transfer member 20 includes a cylindrical support member 21 and an elastic layer 22 formed around the outer periphery thereof, and is driven in rotation in an indicated arrow direction at a peripheral speed identical to that of the photosensitive member 1. The first colour magenta component image formed on the photosensitive member 1 is sequentially primary-transferred to the outer periphery of the intermediate transfer member 20 while it passes through a nip between the photosensitive member 1 and the intermediate transfer member 20 under the action of an electric field formed by a primary transfer bias (voltage) applied to the intermediate transfer member 20. The surface of the photosensitive member 1 after transfer of the first colour magenta toner image is cleaned by a cleaning device 14. Thereafter, in similar manners, a second colour cyan component image, a third colour yellow component image and a fourth color black component image are sequentially transferred in superposition onto the intermediate transfer member 20 to form a full colour image corresponding to an objective colour image thereon. The transfer bias for sequentially transferring the first to fourth colour toner images from the photosensitive member 1 in superposition onto the intermediate transfer member 20 is of a polarity opposite to that of the toner and is applied from a bias supply 61. The applied voltage therefor is, e.g., in the range of +2 to +5 kV (or -2 to -5 kV). The image forming apparatus further includes a transfer roller 25, which is supported on a shaft in parallel with the intermediate transfer member 20 so as to contact the lower surface thereof. However, the transfer roller 25 and an intermediate transfer member cleaner 35 (described later) can be disposed in separation from the intermediate transfer member 20 during the steps for transferring the first to fourth color toner images from the photosensitive member 1 to the intermediate transfer member 20. The full-colour toner image superposedly transferred onto the intermediate transfer member 20 is secondary-transferred to a transfer(-receiving) material (second image-bearing member) 24 by causing the transfer roller 25 to abut against the intermediate transfer member 20, supplying the transfer material 24 from a paper supply cassette 9 to the abutting position between the intermediate transfer member 20 and the transfer roller 25 at prescribed time and simultaneously by applying a secondary transfer bias to the transfer roller 25. The transfer material 24 bearing the transferred toner image is then introduced to a fixing device 15 for hot fixing of the toner image. After the completion of the image transfer onto the transfer material 24, a transfer residual toner on the intermediate transfer member 20 is cleaned by an intermediate transfer member cleaner 35 abutting the intermediate transfer member 20. The above-mentioned image forming apparatus using intermediate transfer member is advantageous compared to an image forming apparatus wherein images are transferred from a first image-bearing member onto a second image-bearing member attached onto or attracted by a transfer drum (e.g., as disclosed in Japanese Laid-Open Patent Application (JP-A) 63-301960) in the following respects: (a) Little colour deviation occurs during superposition of respective colour images. (b) As is understood from Figure 1, no means is required for processing or controlling the second image-bearing member (e.g., gripping by a gripper, attracting, providing a curvature, etc.), so that a wide variety of second image-bearing member can be used. For example, it is possible to use any paper from a thin paper of ca. 40 g/m 2 to a thick paper of ca. 200 g/m 2 equally as a second image-bearing member. Further, the transfer can be performed regardless of a difference in width and/or length of the second image-bearing member, so that it is applicable to even an envelop, a post-card or a label paper. Because of such advantages accompanying the use of an intermediate transfer member, the type of image forming apparatus using an intermediate transfer member has become commercially available as a colour copying machine or a colour printer. On the other hand, an electrophotographic image forming apparatus has been known to involve a difficulty that its performances are liable to change under different conditions of use or on continuation of use. These may be attributable to, for example, a change in humidity, a deterioration of a photoconductive material constituting the photosensitive member, an abrasion of the photosensitive member by the cleaning means, and a change in ability of triboelectrically charging the developer. In the case of a full-colour image forming apparatus using no intermediate transfer member, there has been known a technique of forming a characteristic pattern on an electrophotographic photosensitive member, etc., detecting a density of the pattern and feeding the detected data back for adjusting the toner replenishing quantity and the image forming conditions, such as a developing bias (voltage), to stabilize the image quality. More specifically, Figure 2 shows an outline of an example of a full-colour image forming apparatus using no intermediate transfer member. Laser light emitted from a laser (not shown) driven based on image signals is reflected by a rotating polygonal mirror 201 and a mirror 202 to be incident to a primarily charged photosensitive member 204. The photosensitive member 204 rotates in an indicated arrow direction during which the photosensitive member is exposed to scanning laser light in the above-described manner to form an electrostatic latent image sequentially thereon. The thus-formed electrostatic latent image is developed by a rotating developing device 203, and the developed toner image is then transferred onto a transfer(-receiving) paper 206 wound about a transfer drum 205. These steps are repeated in totally four cycles sequentially for Y (yellow), M (magenta), C (cyan) and BK (black), respectively, to form a full color image. After completion of the transfer, the transfer paper 206 is separated from the transfer drum 205, and subjected to fixing by a pair of fixing rollers 207 to form a full-colour image print. The above-mentioned pattern formed for controlling the image forming conditions is also obtained in the above-described manner. An LED 208 issuing near infrared rays (having a principal wavelength at ca. 950 nm) is used as an illumination means for illuminating the photosensitive member, and reflected light from the photosensitive member is read by a sensor 209. Based on the thus-obtained pattern density data, the image forming conditions may be controlled according to methods, e.g., as disclosed in U.S. Patents Nos. 4,312,589, 5,258,783 and 5,296,903, and JP-A 5-53402, thereby obtaining best full colour images under the respective conditions. In US-A-5 625 857, a black toner patch is measured with high accuracy. The priority apllications of this document were published in 1995. As described above, in the case of a colour electrophotographic image forming apparatus using no intermediate transfer member, it has become possible to adjust suitable image forming conditions by using a density detection device as described above. In the case of using a colour electrophotographic image forming apparatus using an intermediate transfer member, it is desirable to effect a density measurement as described above on the intermediate transfer member in order to obtain more accurate density data. There has been known a colour electrophotographic image forming apparatus using an intermediate transfer member wherein the toner amount detection is performed on the intermediate transfer member (Japanese Patent Publication (JP-B) 4-18310). However, in the apparatus, the toner amounts transferred onto the intermediate transfer member are measured with respect to three toners of yellow, magenta and cyan and not with respect to a black toner desirable to provide clearer full colour images, and moreover the toner amount detection is performed with respect to transmitted light through a sheet constituting the intermediate transfer member. However, in view of the required performances of an intermediate transfer member, such as an accurate toner image transfer and a frequent contact with the first and second image-bearing members, the intermediate transfer member is required to have a preferred level of resistivity (1x10 4 - 1x10 13 ohm.cm) and a high mechanical strength. For this reason, the intermediate transfer member generally requires the inclusion of a large amount of filler, such as carbon black. The resultant intermediate transfer member becomes opaque and provides a lower reflectance to light, thus making difficult an accurate density measurement of a pattern formed thereon especially with respect to a black toner pattern. SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus allowing a better accuracy of pattern density measurement for controlling image forming conditions and capable of providing best images under available conditions. Another object of the present invention is to provide an image forming apparatus allowing a broader latitude for pattern density measurement designing. A further object of the present invention is to provide an intermediate transfer member suitable for use in an image forming apparatus as described above. The image forming apparatus of the present invention has, in common with that disclosed in United States Patent US-A-5103260, the following integers: a first image-bearing member whereon images of different colours can be formed, an intermediate transfer member for receiving images formed on the first image-bearing member in superposition and transferring the superposed image onto a second image-bearing member, pattern-forming means for forming a prescribed pattern in said different colours on the intermediate transfer member, density detection means for detecting a density of the pattern, and control means for controlling image forming conditions based on the detected density. According to the present invention, said image forming apparatus is characterised in that: the intermediate transfer member has a laminated structure including a layer containing a pigment for providing a reflectance of 10-70% for light having a wavelength in the range of 700-1500 nm at least in a region thereof for forming the prescribed pattern. In a full colour image-forming apparatus, toners for black, yellow, magenta and cyan can be used. In such a case, a large reflectance difference between the black toner (reflectance on the order of below 10%) and other colour toners (reflectance on the order of 80% or higher) is utilised, and the reflectance of the intermediate transfer member is adjusted to an intermediate level between the two levels to provide a good contrast with both a black toner pattern and other colour toner patterns, instead of providing different reflectance regions for different colour toners. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an illustration of an image forming apparatus including an intermediate transfer member. Figure 2 is an illustration of an image forming apparatus including no intermediate transfer member. Figures 3 - 6 are graphs showing spectral reflectance characteristics of yellow toner, magenta toner, cyan toner and black toner, respectively. Figures 7 - 9 are graphs each showing a spectral reflectance characteristic of an intermediate transfer member suitable for use in the invention. Figure 10 is a graph showing a spectral radiation intensity characteristic of light used for image density measurement. Figures 11 and 12 are respectively a diametrical sectional view of a drum-shaped intermediate transfer member used in the invention. Figure 13 is an illustration of an image forming apparatus including an intermediate transfer member in the form of an endless belt. Figures 14 - 16 are perspective illustrations of drum-shaped intermediate transfer members usable in the invention having specified reflectance portions in the form of a longitudinal stripe, a circumferential stripe and a square, respectively. Figures 17 - 20 are graphs showing spectral reflectance characteristic of intermediate transfer members prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2, respectively. Figures 21 and 22 are respectively an illustration of an embodiment of the image forming apparatus according to the invention. DETAILED DESCRIPTION OF THE INVENTION The image forming apparatus according to the present invention basically includes a first image-bearing member, and an intermediate transfer member for receiving an image formed on the first image-bearing member and transferring the image onto a second image-bearing member. The image forming apparatus further includes pattern-forming means for forming a prescribed pattern on the intermediate transfer member, density detection means for detecting a density of the pattern, and control means for controlling image forming conditions based on the detected density. Further, the intermediate transfer member is designed to have a reflectance of 10 - 70 % for light having a wavelength in the range of 700-1500 nm at least in a region thereof for forming the prescribed pattern. Ordinarily, yellow, magenta and cyan toners have spectral reflectance characteristic as shown in Figures 3 - 5, respectively, and show reflectance of at least 80 % for light having a wavelength in the range of 700 - 1500 nm. On the other hand, a black toner (e.g., a mono-component magnetic toner) has a spectral reflectance characteristic as shown in Figure 6 showing a reflectance of at most ca. 10 % for light having a wavelength in the range of 700 - 1500 nm. In the present invention, based on the above fact and the aforementioned concept of the present invention, the intermediate transfer member is designed to have a reflectance of 10 - 70 %, preferably 15 - 60 %, further preferably 15 - 35 %, at least in a pattern density-detection region thereof for light having a wavelength in the range of 700-1500 nm, e.g., at a near infrared wavelength of ca. 950 nm, thereby allowing the density detection of all of black and colour images at an improved accuracy. The intermediate transfer member need not show an overall reflectance of 10 - 70 % for light having wavelengths ranging from 700 to 1500 nm. It is sufficient if the intermediate transfer member shows a spectral reflectance of 10 -70 % for a light fraction having a specific wavelength in the range of 700-1500 nm even if the intermediate transfer member shows a spectral reflectance of below 10 % (or above 70 %) at another wavelength in the same range as shown in Figure 7 (showing a spectral reflectance of ca. 23 % at 950 nm). In such a case, a stable and accurate image density is still possible by using a detection means including a light source issuing infrared rays having a principal or peak wavelength at or near the specific wavelength. On the other hand, an intermediate transfer member showing a spectral reflectance exceeding 70 % at some wavelength can also be used if it also shows a spectral reflectance in the range of 10 - 70 % at a specific wavelength in the range of 700 - 1500 nm as shown in Figure 8 (showing a spectral reflectance of ca. 33 % at 1000 nm). In this case, a stable and accurate density detection is also possible by using a photodetection system using infrared rays having a principal wavelength at or near the specific wavelength (1000 nm). It is of course possible to use an intermediate transfer member showing a reflectance of 10 - 70 % averagely in the wavelength range of 700-1500 nm for effecting a stable and accurate density detection by using infrared rays having a principal wavelength in the range. In the present invention, the light used for the density detection should have a principal wavelength in the range of 700 - 1500 nm as a matter of course but may preferably have a principal wavelength in the range of 800 - 1100 nm, particularly 900 - 1000 nm, in view of the stability of reflectance for the color toners. It is not always necessary that the optimum wavelength for the density detection should be the same as the principal wavelength of light actually used. This is because light having a principal wavelength at a specific wavelength, of, e.g., 950 nm, has a region showing a relative radiation intensity of ca. 0.6 - 0.8 near the principal wavelength, so that the density detection can be effected also in that region. The reflectances of toners and intermediate transfer members referred to herein are based on values measured by using a commercially available apparatus ("U-3400", available from Hitachi Seisakusho K.K.) equipped with a large sample chamber integrating sphere at scanning speeds of 300 nm/min for visible region and 600 nm/min for infrared region, a response level of medium, and band passes of 5.00 nm for visible region and servo (variable) for infrared region. The intermediate transfer member used in the present invention may have a structure including at least an electroconductive support and an elastic layer thereon comprising rubber, elastomer or resin, optionally further one or more coating layers thereon. The intermediate transfer member may have various shapes including drums or rollers as shown in Figures 11 and 12 and an endless belt (103) as shown in Figure 13, which may be arbitrarily selected depending on the purpose or necessity. Figures 11 and 12 show drum-shaped intermediate transfer members including a cylindrical electroconductive support 100 and an elastic layer 101, and further a coating layer 102. The endless belt-shaped intermediate transfer member 103 (Figure 13) may also have a similar lamination structure although the outer shape is different. In the present invention, the intermediate transfer member may preferably be in the form of a drum or roller in view of little colour deviation in superposition of colours and durability in repetitive use. The electroconductive support (100) may preferably comprise a metal or alloy, such as aluminium, iron, copper or stainless steel, or an electroconductive resin containing electroconductive carbon or metal particles. The support may have a shape of a drum or an endless belt as described above, inclusive of a drum equipped with a shaft piercing therethrough and a cylindrical bar. The elastic layer (101) and the coating layer (102) of the intermediate transfer member used in the present invention may comprise a rubber or elastomer, or a resin. Examples of the rubber or elastomer may include: styrene-butadiene rubber, high-styrene rubber, butadiene rubber, isoprene rubber, ethylenepropylene copolymer, nitrile-butadiene rubber, chloroprene rubber, butyl rubber, silicone rubber, fluorine-containing rubber, nitrile rubber, urethane rubber, acrylic rubber, epichlorohydrin rubber, and norbornene rubber. Examples of the resin may include: styrene-based resins (homopolymers and copolymers of styrene and substituted styrene, inclusive of polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrenemaleic acid copolymer), styrene-acrylate copolymers (such as styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, and styrene-phenyl acrylate copolymer), styrenemethacrylate copolymers (such as styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer and styrene-phenyl methacrylate copolymer), styrene-methyl α-chloroacrylate copolymer, and styrene-acrylonitrile-acrylate copolymers; vinyl chloride resin, styrene-vinyl acetate copolymer, rosin-modified maleic acid resin, phenolic resin, polyester resin, low-molecular weight polyethylene, low-molecular weight polypropylene, ionomer resins, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, and polyvinyl butyral resin. These rubbers or elastomers, and resins can also be used in combination of two or more species. The intermediate transfer member may preferably have a resistivity on the order of 1x10 4 -1x10 13 ohm.cm. For this purpose, the elastic layer or the coating layer may contain an electroconductive substance dispersed therein or comprise an electroconductive resin. Examples of the electroconductive substance may include: electroconductive carbon black; and electroconductive materials inclusive of metals such as aluminium and nickel; electroconductive metal oxides, such as electroconductive titanium oxide, electroconductive tin oxide, electroconductive zinc oxide and electroconductive zinc oxide and electroconductive indium oxide; and electroconductive polymeric compounds, such as quaternary ammonium saltcontaining polymethyl methacrylate, polyvinylaniline, polyvinylpyrrole, polydiacetylene, polyethyleneimine, boron-containing polymers and polypyrrole. These may be used singly or in combination of two or more species. These are however not exhaustive. In the case of forming the surface layer(s) of the intermediate transfer member without using an electroconductive filter, the resultant intermediate transfer member is liable to have an excessively high transmittance so that it becomes also difficult to provide a sufficient density contrast with yellow toner, magenta toner and cyan toner having a high resistance. In this case, it is also effective to positively lower the reflectance of the intermediate transfer member. The intermediate transfer member may preferably contain a lubricating substance in its surface layer so as to exhibit an improved releasability. Examples of the lubricating substance (sometimes in the form of particles) may include: tetrafluoroethylene resin, trifluorochloroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, vinyl fluoride resin, vinylidene fluoride resin, difluorodichloro-ethylene resin, fluorinated carbon, silicone resin, silicone rubber, silicone elastomer, polyethylene (PE), polypropylene (PP), polystyrene (PS), acrylic resin, nylon resin, phenolic resin, epoxy resin, silica, and alumina. These may be used singly or in combination of two or more species. Among these, tetrafluoroethylene resin and tetrafluoroethylene-hexafluoropropylene copolymer resin are particularly preferred. The elastic layer (101) may preferably have a thickness of at least 0.5 mm, more preferably at least 1 mm, further preferably 1 - 10 mm. On the other hand, the coating layer (102) may preferably be thin so as to conduct the softness of the lower elastic layer to the surface of the intermediate transfer member and more specifically have a thickness of at most 3 mm, more preferably at most 2 mm, further preferably 20 µm - 1 mm. The intermediate transfer member is set to have a reflectance in the above-mentioned specific range by incorporating a reflectance-adjusting pigment into the coating layer and/or the elastic layer . Examples of the reflectance-adjusting pigment incorporated in the coating layer and/or the elastic layer may include; white pigments, such as titanium oxide (such as titanium white), barium sulfate, and zinc white; value pigments, such as phthalocyanine blue; red pigments, such as dimethylquinacridone, yellow pigments, such as disazo yellow, and black pigments, such as a relatively small amount of carbon black. Among these, white pigments are preferred because of colouring ability, and titanium white is particularly preferred because of colouring ability and dispersibility. The pigment may preferably be contained in a proportion of 0.2 - 10 wt. parts, particularly 1 - 3 wt. parts, per 100 wt. parts of the elastomer and the resin in the layer in which the pigment is contained. In the use of a black pigment, the pigment may preferably be contained in a proportion of 0.05 - 0.5 wt. part per 100 wt. parts of the elastomer and the resin in the layer concerned. Among the above-mentioned reflectance adjustment method, it is preferred to adopt the method of incorporating a pigment in a layer, which may preferably be not the uppermost surface layer but an intermediate layer so as to retain the required properties, such as strength, releasability, waterrepellency and electroconductivity, of the surface layer of the intermediate transfer member functioning to directly receive an image transferred thereto and transferring the received imaged to a second image-bearing member, unlike the transfer drum. Thus, it is preferred to control the reflectance by including the pigment in an intermediate layer so as to leave a broad latitude of designing to the surface layer. Further, as it is undesirable for a photosensitive layer to contain a colourant affecting the electrophotographic performances, the present invention controlling the reflectance of the intermediate transfer member is also effective in providing a broader latitude of designing to the photosensitive member, in addition to the provision of more accurate density data. The present invention does not require a special light source or a sensor with an extremely high accuracy compared with a system using an intermediate transfer member having a reflectance not satisfying the requirement of the present invention. Also, in this respect, a broad latitude of designing is provided. In the present invention, the intermediate transfer member need not have the specific reflectance over the entire surface thereof but it is sufficient that the intermediate transfers member has a surface region at least locally showing the specific reflectance where the pattern density is measured. For example, the intermediate transfer member may have a longitudinal stripe region (as shown in Figure 14), a circumferential stripe region (as shown in Figure 15) or a local pattern of, e.g., a square (as shown in Figure 16) showing the specific reflectance. However, in view of the convenience of production and so as not to result in locally different properties, the intermediate transfer member may preferably have the specific reflectance over the entire surface. In the present invention, the density measurement pattern-forming method, the shape of the pattern, the pattern density-measurement means, the control means for controlling image forming conditions based on the detected pattern density, the timing of the control, etc., need not be particularly limited, but may be selected according to the known techniques. For example, the pattern may include a succession of square images having several density levels, which may be provided for the respective colours. The optical system for density detection may for example include a light source of, e.g., an LED emitting light having a principal wavelength around 950 nm, and a sensor of, e.g., silicon photo-diode. Based on the detected pattern density, it may be possible to control, e.g., the developing bias, the spot diameter of exposure light for exposing the first image-bearing member, and the quantity of replenished toner. The first image-bearing member used in the present invention may suitably comprise an electrophotographic photosensitive member, of which the structure and composition need not be particularly limited. The second image-bearing member used in the present invention may include various types of paper and OHP sheets. Hereinbelow, the present invention will be described more specifically based on Examples and Comparative Examples. Example 1 (Elastic layer compound) 100 wt. parts of EPDM (ethylene-propylenediene copolymer rubber), 5 wt. parts of zinc oxide, 1 wt. part of higher fatty acid, 5 wt. parts of electroconductive carbon, 10 wt. parts of paraffin oil, 2 wt. parts of sulphur, and totally 4 wt. parts of vulcanization promoters (1 wt. part of 2-mercaptobenzothiazole (MBT), 1.5 wt. parts of tetramethylthiuram disulfide (TMTD) and 1.5 wt. parts of zinc dimethyldithiocarbamate (ZnMDD)) were blended by a two roll mill under cooling for 20 min. to prepare a compound. (Surface layer paint) 50 wt. parts of polyurethane prepolymer, 3 wt. parts of titanium white (colourant), 40 wt. parts of electroconductive titanium oxide, 5 wt. parts of dispersion aid, 100 wt. parts of toluene, 50 wt. parts of curing agent and 100 wt. parts of PTFE (polytetrafluoroethylene) particles, were blended and dispersed for 30 min. in a beads mill to prepare a surface layer paint. (Preparation and evaluation of intermediate transfer member) On an aluminium cylinder (outer diameter = 182 mm, length = 320 mm, thickness = 5 mm), the elastic layer compound was transfer-molded and vulcanized to form a 5 mm-thick elastic layer, which was then coated with the surface layer paint by spray coating to form a 40 µm-thick surface layer, thereby obtaining an intermediate transfer member. The reflectance of the thus-obtained intermediate transfer member was measured according to the above-described manner to obtain a spectral reflectance characteristic as shown in Figure 17. The intermediate transfer member was incorporated in an electrophotographic photosensitive member (shown in Figure 21) having a structure generally as shown in Figure 1, and also including a density detection circuit 53 for detecting a density of pattern formed on the intermediate transfer member and a control circuit 54 for controlling the image forming conditions, particularly for controlling a developing bias generating circuit 55 in this example, whereby the pattern formation and the pattern density measurement were performed. The density measurement pattern included a succession of 5 squares at 5 density levels from a maximum density to a minimum density for each of yellow, magenta, cyan and black. The light source 51 for the pattern density measurement was an LED (light emission device) emitting light having a principal wavelength of 950 nm. The density levels of the thus-formed pattern were measured by using a silicon photodiode 52, whereby totally 20 density levels (5 levels for each of the four colours of yellow, magenta, cyan and black) were accurately measured and the measured density levels were satisfactorily used for controlling the developing bias voltages. Example 2 (Elastic layer compound) 100 wt. parts of EPDM, 5 wt. parts of zinc oxide, 5 wt. parts of titanium white (colourant), 150 wt. parts of electroconductive titanium oxide, 10 wt. parts of paraffin oil, 2 wt. parts of sulphur, and totally 4 weight parts of vulcanization promoters (1 wt. part of MBT, 1.5 wt. parts of TMTD and 1.5 wt. parts of ZnMDC) were blended by a two-roll mill under cooling for 20 min to prepare a compound. (Surface layer paint) 50 wt. parts of polyurethane prepolymer, 20 wt. parts of electroconductive aluminium borate whisker, 5 wt. parts of dispersion aid, 50 wt. parts of curing agent, and 100 wt. parts of PTFE particles, were blended and dispersed for 30 min. in a beads mill to prepare a surface paint. (Preparation and evaluation of intermediate transfer member) An intermediate transfer member was prepared in the same manner as in Example 1 except for using the above-prepared elastic layer compound and surface layer paint. As a result, the intermediate transfer member showed a spectral reflectance characteristic as shown in Figure 18. The intermediate transfer member was incorporated in the same electrophotographic image forming apparatus as in Example 1 and evaluated in the same manner as in Example 1, whereby all the density levels for the respective colours were accurately measured, and the control of the developing biases was satisfactorily performed. Example 3 (Elastic layer compound) 33 wt. parts of SBR, 67 wt. parts of EPDM, 1.5 wt. parts of sulfur, 2 wt. parts of zinc white (vulcanization aid), totally 2.2 wt. parts of vulcanization promoters (1 wt. part of MBT and 1.2 wt. parts of TMTM), 25 wt. parts of electroconductive carbon black, 1 wt. part of stearic acid and 40 wt. parts of plasticizer (naphthene-based process oil), were blended by a two-roll mill under cooling for 20 min. to prepare a compound. (Surface layer paint) A surface layer paint was prepared in the same manner as in Example 1 except that the amount of PTFE particles were reduced to 50 wt. parts. (Preparation and evaluation of intermediate transfer member) The elastic layer compound was vulcanized in a mould at 150 °C for 50 min. to form an endless belt having an outer diameter of 150 mm, a width of 230 mm and a thickness of 0.9 mm. On the outer surface of the endless belt, the above-prepared surface layer paint was applied by spray coating to form a 30 µmthick surface layer, thereby obtaining an intermediate transfer member. As a result of reflectance measurement, the intermediate transfer member showed a reflectance in the range of 10 - 70 % (somewhat lower level than in Figure 17) in the range of 700 - 1500 nm. The intermediate transfer member was incorporated in an electrophotographic image forming apparatus shown in Figure 22 (generally similar to one shown in Figure 13 but further including an LED 51, a silicon photodiode 52, a density detection circuit 53, a control circuit 54 and a developing bias supply 55 similar to those used in Example 1), whereby all the density levels for the respective colours were accurately measured, and the control of the developing bias voltages was satisfactorily performed. Comparative Example 1 (Preparation and evaluation of intermediate transfer member) An intermediate transfer member was prepared in the same manner as in Example 1 except that surface layer paint was replaced by the one of Example 2 to form a 25 µm-thick surface layer. The resultant intermediate transfer member showed a spectral reflectance characteristic as shown in Figure 19 showing a reflectance of below 10 % over the range of 700 nm to 1500 nm. The intermediate transfer member was incorporated in the same electrophotographic image forming apparatus as in Example 1 and evaluated in the same manner as in Example 1, whereby all the density levels could be measured for yellow, magenta and cyan but the pattern density detection was impossible for black because of too low a spectral reflectance difference. Comparative Example 2 (Elastic layer compound) Same as in Example 2. (Surface layer paint) 50 wt. parts of polyurethane prepolymer, 10 wt. parts of titanium white (colourant), 40 wt. parts of electroconductive titanium oxide, 5 wt. parts of dispersion aid, 100 wt. parts of toluene, 50 wt. parts of curing agent and 100 wt. parts of PTFE particles, were blended and dispersed for 30 min. in a beads mill to prepare a surface layer paint. (Preparation and evaluation of intermediate transfer member) An intermediate transfer member was prepared in the same manner as in Example 1 except that the elastic layer compound and the surface layer paint were replaced by those described above. The resultant intermediate transfer member showed a spectral reflectance characteristic as shown in Figure 20 showing a reflectance of ca. 80 - 90 % over the range of 700 nm to 1500 nm. The intermediate transfer member was incorporated in the same electrophotographic image forming apparatus as in Example 1 and evaluated in the same manner as in Example 1, whereby all the density levels could be measured for black but the pattern density detection was impossible for yellow, magenta or cyan because of the excessively high reflectance of the intermediate transfer member.

Claims: Image forming apparatus, comprising: a first image-bearing member (1) whereon images of different colours can be formed, an intermediate transfer member (20) for receiving images formed on the first image-bearing member in superposition and transferring the superposed image onto a second image-bearing member (24), pattern-forming means (41-44) for forming a prescribed pattern in said different colours on the intermediate transfer member, density detection means (51-53) for detecting a density of the pattern, and control means (54) for controlling image forming conditions based on the detected density, characterised in that : the intermediate transfer member (20) has a laminated structure (21,22; 100,101; 100-102) including a layer (22;101) containing a pigment for providing a reflectance of 10-70% for light having a wavelength in the range of 700-1500 nm at least in a region thereof for forming the prescribed pattern. Apparatus according to claim 1 wherein: said first image-bearing member (1) is one wherein respective different colour images of yellow, magenta, cyan and black can be formed; said pattern-forming means (41-44) is adapted for forming a prescribed pattern with toners in four colours of yellow, magenta, cyan and black on the intermediate transfer member; said density detection means (51-53) is adapted for detecting densities of said prescribed pattern by illuminating the intermediate transfer member with light having a principal wavelength in said range of 700-1500 nm and measuring reflected light quantities from the intermediate transfer member; said control means (54) is adapted for controlling the image forming conditions for images of the four colours; and said layer (22) of said laminated structure (21,22) of said intermediate transfer member (20) contains said pigment for providing said reflectance of 10-70% for the illuminating light. Apparatus according to either of claims 1 or 2, wherein the first image-bearing member (1) comprises an electrophotographic photosensitive member. Apparatus according to any of claims 1 to 3, wherein the intermediate transfer member (20) has a reflectance of 15-60% for light having a wavelength of 700-1500 nm at least in said region thereof for forming the prescribed pattern. Apparatus according to claim 4, wherein the intermediate transfer member (20) has a reflectance of 15-35% for light having a wavelength of 700-1500 nm at least in said region thereof for forming the prescribed pattern. Apparatus according to any preceding claim, wherein the density detection means (51-53) uses light having a principal wavelength in the range 800-1100 nm. Apparatus according to claim 6, wherein the density detection means (51-53) uses light having a principal wavelength in the range 900-1000 nm. Apparatus according to any preceding claim, wherein the intermediate transfer member (20) has a localised region of its surface which shows the defined reflectance. Apparatus according to claim 8, wherein the localised region is a longitudinal shape. Apparatus according to claim 8, wherein the localised region is a circumferential shape. Apparatus according to claim 8, wherein the localised region is a square. Apparatus according to any of claims 1 to 7, wherein the whole surface of the intermediate transfer member (20) shows the defined reflectance. Apparatus according to any preceding claim, wherein the intermediate transfer member (20) has a resistivity of 1 x 10 4 to 1 x 10 13 ohm.cm. Apparatus according to any preceding claim, wherein the intermediate transfer member (20) includes an elastic layer (101) and a coating layer (102) thereon, and the elastic layer contains the pigment. Apparatus according to any preceding claim, wherein the pigment is a white pigment. Apparatus according to claim 15, wherein the pigment comprises titanium white. Apparatus according to any preceding claim, wherein the surface layer (102) of the intermediate transfer member (100-102) contains a lubricating agent. An apparatus according to any preceding claim, wherein the intermediate transfer member (20) is in the form of a drum. Use of an intermediate transfer member in an image forming apparatus comprising: a first image-bearing member (1) wherein images of different colours can be formed, an intermediate transfer member (20) for receiving images formed on the first image-bearing member in superposition and transferring the superposed image onto a second image-bearing member (24), pattern-forming means (41-44) for forming a prescribed pattern in said different colours on the intermediate transfer member, density detection means (51-53) for detecting a density of the pattern, and control means (54) for controlling image forming conditions based on the detected density; characterised in that : the intermediate transfer member (20) has a laminated structure (21,22; 100,101; 100-102) including a layer (22;101) containing a pigment for providing a reflectance of 10-70% for light having a wavelength in the range of 700-1500 nm at least in a region thereof for forming the prescribed pattern. Use according to claim 19 wherein: said first image-bearing member (1) is one wherein respective different colour images of yellow, magenta, cyan and black can be formed; said pattern-forming means (41-44) is adapted for forming a prescribed pattern with toners in four colours of yellow, magenta, cyan and black on the intermediate transfer member; said density detection means (51-53) is adapted for detecting densities of said prescribed pattern by illuminating the intermediate transfer member with light having a principal wavelength in said range of 700-1500 nm and measuring reflected light quantities from the intermediate transfer member; said control means (54) is adapted for controlling the image forming conditions for images of the four colours; and said layer (22) of said laminated structure (21,22) of said intermediate transfer member (20) contains said pigment for providing said reflectance of 10-70% for the illuminating light. Use according to either of claims 19 or 20, wherein the intermediate transfer member (20) has a reflectance of 15-60% for light having a wavelength of 700-1500 nm at least in said region thereof for forming the prescribed pattern. Use according to claim 21, wherein the intermediate transfer member (20) has a reflectance of 15-35% for light having a wavelength of 700-1500 nm at least in said region thereof for forming the prescribed pattern. Use according to any preceding claim 19 to 22, wherein the intermediate transfer member (20) has a localised region of its surface which shows the defined reflectance. Use according to claim 23, wherein the localised region is a longitudinal shape. Use according to claim 23, wherein the localised region is a circumferential shape. Use according to claim 23, wherein the localised region is a square. Use according to any of claims 19 to 22, wherein the whole surface of the intermediate transfer member (20) shows the defined reflectance. Use according to any preceding claim 19 to 27, wherein the intermediate transfer member (20) has a resistivity of 1 x 10 4 to 1 x 10 13 ohm.cm. Use according to any preceding claim 19 to 28, wherein the intermediate transfer member (20) includes an elastic layer (101) and a coating layer (102) thereon, and the elastic layer contains the pigment. Use according to any preceding claim 19 to 29, wherein the pigment is a white pigment. Use according to claim 30, wherein the pigment comprises titanium white. Use according to any preceding claim 19 to 31, wherein the surface layer (102) of the intermediate transfer member (100-102) contains a lubricating agent. Use according to any preceding claim 19 to 32, wherein the intermediate transfer member (20) is in the form of a drum. Use according to any of claims 19 to 33 wherein the first image-bearing member (1) comprises an electrophotographic photosensitive member. Use in colour image forming apparatus of an intermediate transfer member (20) having a laminated structure (21,22; 100,101; 100-102) including a layer (22;101) containing a pigment for providing a reflectance of 10-70% for light having a wavelength in the range of 700-1500 nm to permit feedback control of the image forming conditions based on a detected image density for a black image and for yellow, magenta and cyan images. An intermediate transfer member for use in colour image forming apparatus, said intermediate transfer member (20) having a laminated structure (21,22; 100,101; 100-102) including a layer (22;101) containing a pigment for providing a reflectance of 10-70% for light having a wavelength in the range of 700-1500 nm to permit feedback control of the image forming conditions based on a detected image density for a black image and for yellow, magenta and cyan images.

Inventors: ASHIBE TSUNENORI, KOBAYASHI HIROYUKI, KUSABA TAKASHI, NAKAZAWA AKIHIKO, TANAKA ATSUSHI, ASHIBE, TSUNENORI, KOBAYASHI, HIROYUKI, KUSABA, TAKASHI, NAKAZAWA, AKIHIKO, TANAKA, ATSUSHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1996
Main classification: G03G15
IPC codes: G03G15