JP6866689B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus including an intermediate transfer belt for transferring a carried toner image to a recording medium, and more particularly to an image forming apparatus including an intermediate transfer belt including an elastic layer.

Generally, in an image forming apparatus, a toner image formed on the surface of a photoconductor is transferred to the surface of an intermediate transfer belt in a primary transfer portion, so that the toner image is supported on the intermediate transfer belt. After that, the toner image supported on the intermediate transfer belt is transferred from the secondary transfer unit to a recording medium such as paper.

Normally, in the secondary transfer section, a predetermined electric field is formed between the secondary transfer roller and the opposing roller forming the nip section. Due to the action of the electric field, the toner image moves from the intermediate transfer belt passing through the nip portion to the recording medium also passing through the nip portion. As a result, the toner image is transferred to the recording medium in the secondary transfer unit.

Various types of intermediate transfer belts have been proposed. As an intermediate transfer belt that enables transfer to a recording medium having an uneven surface (for example, embossed paper or the like), an intermediate transfer belt including an elastic layer is known.

For example, in Japanese Patent Application Laid-Open No. 2014-855633 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2014-102384 (Patent Document 2), an elastic layer made of acrylic rubber or the like is provided on a base layer as an inelastic layer made of polyimide or the like. An intermediate transfer belt provided is disclosed.

By using the intermediate transfer belt having such an elastic layer, when the intermediate transfer belt is pressed toward the recording medium at the nip portion of the secondary transfer portion, the intermediate transfer belt is formed in a recess located on the surface of the recording medium. It is deformed so that a part of the surface side of the

As a result, the distance between the bottom surface of the recess of the recording medium and the surface of the intermediate transfer belt is reduced. This promotes the action of the electric field. By promoting this action, the toner is likely to move, and the transferability to a recording medium having irregularities on the surface is improved.

Japanese Unexamined Patent Publication No. 2014-85633 Japanese Unexamined Patent Publication No. 2014-102384

In order to obtain good transferability even for a recording medium having a deeper recess, it is necessary to increase the thickness or decrease the hardness of the intermediate transfer belt. However, if the thickness or hardness of the intermediate transfer belt is increased or the hardness is decreased, the elastic layer of the intermediate transfer belt is subjected to pressure and unnecessarily deformed at the primary transfer portion, resulting in distortion (roughness) of the toner image. It is more likely to occur.

By increasing the thickness or decreasing the hardness of the intermediate transfer belt having an elastic layer, the transferability to a recording medium having an uneven surface is improved in the secondary transfer portion, but in the primary transfer portion, The image quality deteriorates due to the roughening. Therefore, it has been difficult to ensure good image quality while achieving both good transferability on uneven paper and suppression of roughness.

An object of the present invention is to provide an image forming apparatus capable of suppressing rattling and ensuring good image quality while ensuring high transferability for a recording medium having a deep recess.

The image forming apparatus of the present invention includes an image carrier that supports a toner image, an intermediate transfer belt, a primary transfer roller, and a secondary transfer unit. The primary transfer roller transfers the toner image carried on the image carrier to the intermediate transfer belt. The surface hardness of the primary transfer roller is smaller than that of the image carrier. The secondary transfer unit transfers the toner image supported on the intermediate transfer belt to the recording medium. The secondary transfer unit includes a secondary transfer roller and an opposing roller. The opposing roller faces the secondary transfer roller and has a lower surface hardness than the secondary transfer roller.

The intermediate transfer belt contains at least an elastic layer, and records a toner image supported on the first main surface, which is one of a pair of exposed main surfaces composed of a first main surface and a second main surface located opposite to each other. Transcribe to.

A curved convex surface having a width of 20 [mm] and a radius of curvature of 20 [mm] is provided on the upper surface, and a hole having a diameter of 1.25 [mm] is provided at the top of the curved convex surface. The lower block and the upper block having a curved concave surface having a width of 20 [mm] and a radius of curvature of 20.3 [mm] on the lower surface are used, and the first main surface is the upper surface of the lower block. The intermediate transfer belt is placed on the upper surface of the lower block so as to face the lower block, and the upper block is lowered toward the lower block so that a part of the intermediate transfer belt has a curved convex surface and a curved concave surface. The area to be pressurized, which is a part of the intermediate transfer belt, reaches a pressing force of 200 [kPa] at a predetermined pressurizing rate [kPa / ms] by being sandwiched by and then 200 [kPa]. When the pressure is constant with the pressure of [kPa], a local peak occurs in the displacement of the measurement region, which is the part corresponding to the hole in the first main surface of the intermediate transfer belt. After that, the displacement starts to decrease with the passage of time, and finally gradually decreases to exhibit a displacement pattern that converges to a predetermined displacement amount.

The primary transfer nip is formed by the image carrier and the primary transfer roller. The secondary transfer nip portion is formed by the secondary transfer roller and the opposing roller. The belt transport speed of the intermediate transfer belt is V _sys [mm / s], the pressing force of the primary transfer roller pressing the image carrier is P1 [N], and the axial length of the primary transfer nip is L1. [Mm], the radius of the image carrier is r1 [mm], and γ1 [N / mm ² ] calculated by P1 / (L1 × r1) using P1, L1 and r1 is 2 × V _sys × γ1. ^{The condition of 2} + γ1 ≦ 0.0075 is satisfied.

The pressing force of the secondary transfer roller pressing the opposing roller is P2 [N], the axial length of the secondary transfer nip is L2 [mm], and the radius of the secondary transfer roller is r2 [mm. ^{], And γ2 [N / mm 2} ] calculated by P2 / (L2 × r2) using P2, L2 and r2 satisfies the condition of 5 × V _sys × γ2 ² + γ2 ≧ 0.088.

According to the above-mentioned image forming apparatus, it is possible to suppress rattling in the primary transfer section and secure good image quality while ensuring good transferability for a recording medium having a deep recess in the secondary transfer section.

When the predetermined pressurizing speed is 4 [kPa / ms], the maximum value of the displacement amount of the measurement area is a [μm], and the displacement amount of the measurement area after the displacement of the measurement area converges is b [ In the case of [μm], E [−] calculated by (ab) / b using a and b satisfies the condition of 0.2 ≦ E ≦ 3.0.

As a result, it is possible to suppress deterioration of image quality due to repeated use while ensuring high transferability to a recording medium having deep recesses.

In the above image forming apparatus, γ1 satisfies the condition of γ1 ≧ 0.00074. As a result, image unevenness in the axial direction can be suppressed.

In the above image forming apparatus, γ2 satisfies the condition of γ2 ≦ 0.028. As a result, crushing of thin lines can be suppressed.

By applying the present invention, it is possible to realize an image forming apparatus capable of suppressing rattling and ensuring good image quality while ensuring high transferability for a recording medium having deep recesses.

It is the schematic of the image forming apparatus in embodiment of this invention. It is a figure which shows the structure of the main functional block of the image forming apparatus shown in FIG. It is sectional drawing of the intermediate transfer belt shown in FIG. It is the schematic of the secondary transfer part shown in FIG. It is the schematic which shows the structure of the displacement amount measuring apparatus. It is the schematic which shows the operation of the pressurizing mechanism provided in the displacement amount measuring apparatus shown in FIG. FIG. 5 is a perspective view of the lower block of the displacement amount measuring device shown in FIG. 5 as viewed from above. FIG. 5 is a perspective view of the upper block of the displacement amount measuring device shown in FIG. 5 as viewed from below. It is a graph for demonstrating the evaluation method of the belt using the displacement amount measuring apparatus shown in FIG. FIG. 5 is an enlarged cross-sectional view of the vicinity of a hole in the lower block in a state where the belt is pressurized by using the displacement amount measuring device shown in FIG. It is a graph which shows the pattern of the displacement behavior of the measurement area of the belt obtained when the belt is evaluated by using the displacement amount measuring apparatus shown in FIG. It is the schematic which showed the state of the toner transfer from the intermediate transfer belt to the embossed paper when the intermediate transfer belt consisting only of a non-elastic layer is used. It is a graph which shows the relationship between the applied voltage and the transfer efficiency in the case of FIG. It is the schematic which showed the state of the toner transfer from the intermediate transfer belt to the embossed paper when the intermediate transfer belt including the elastic layer is used. It is a graph which shows the relationship between the applied voltage and the transfer efficiency in the case of FIG. It is a graph which shows the relationship between the overshoot rate E and ΔVadh. It is a graph which shows the relationship between the primary displacement rate k1 and ΔVadh. It is a graph which shows the relationship between the secondary displacement rate k2 and ΔVadh. It is a figure which shows the intermediate transfer belt in the concavely bent state in the primary transfer part. It is a figure which shows the intermediate transfer belt in the concave bending state in a secondary transfer part. It is a figure which shows the intermediate transfer belt in the convex bending state in a secondary transfer part. It is a figure which shows the intermediate transfer belt in a straight state in a secondary transfer part. It is an enlarged view of the region surrounded by XXIII in the nip part of FIG. It is a figure which shows the state which the intermediate transfer belt in a concave bending state is pressed. It is a graph which shows the relationship between the applied pressure in the belt A and the belt B, and the amount of deformation. It is a graph which shows the evaluation result of the roughness with respect to each applied pressure in the primary transfer part when the belt A and the belt B are used as the intermediate transfer belt of an image forming apparatus. It is a graph which shows the range of the applied pressure and the amount of deformation which can suppress the rattling while suppressing the occurrence of image unevenness in the axial direction. It is a graph which shows the evaluation result of the concave transferability with respect to each applied pressure in the secondary transfer part when the belt A and the belt B are used as the intermediate transfer belt of an image forming apparatus. It is a graph which shows the range of the applied pressure and the amount of deformation which can secure the good concave transferability while suppressing the crushing of a thin line. It is a graph which showed the range X which can suppress the rattling, and the range Y which can secure a good concave transferability while suppressing the occurrence of image unevenness in the axial direction and the crushing of fine lines. It is a graph which showed the time-dependent change of the displacement amount in the measurement area of the belt which exhibits overshoot deformation. It is a graph which showed four patterns of the pressure applied to a belt simply. It is a graph which showed the _{transient component ε t} in each case when the pressure of the pattern (1) to the pattern (4) was applied. It is a graph which shows the relationship between the pressurizing speed s and the increase amount Δε _t / Δp [μm / kPa] (the slope of a straight line in FIG. 33) of the _{transient component ε t} with respect to the increase amount of the maximum pressure p. It is a graph which showed the _{steady component ε s} in each case when the pressure of the pattern (1) to the pattern (4) was applied. It is a graph which shows the relationship between the pressurizing speed s and the increase amount Δε _s / Δp [μm / kPa] (the slope of a straight line in FIG. 35) of the _{steady component ε s} with respect to the increase amount of the maximum pressure p. It is a figure which showed how one roller presses against the other roller. It is a graph which shows the time change of the pressure which the intermediate transfer belt passing through a nip part receives when the pressing force P is set to PR1 and PR2. It is a graph which shows the relationship between a pressing force P and a transient component ε _t. It is a figure which shows the state of pressing one roller (radius r2) which has a relatively small radius against the other roller. It is a figure which shows the state of pressing one roller (radius r1) which has twice the radius (r2) of the roller shown in FIG. 40 against the other roller. It is a graph which shows the time change of the pressure which the intermediate transfer belt passing through a nip part receives when the roller of FIG. 40 and FIG. 41 is used. It is a graph which shows the relationship between the reciprocal 1 / r [mm ^-1 ] of the roller radius r, and the transient component ε _t. It is a graph which showed the relationship between P / r and the transient component ε _t. It is a graph which shows the relationship between P / r and the maximum displacement amount δ in the belts A and B which do not exhibit an overshoot deformation, and the belt P which exhibits an overshoot deformation. It is a schematic diagram of the inside of the image forming apparatus which showed how the intermediate transfer belt passes between rollers. It is a graph which shows the pressure distribution of the linear pressure in the transport direction of the intermediate transfer belt 21 in the nip part shown in FIG. It is a graph which shows the time change of the linear pressure which the intermediate transfer belt which passes through the nip part shown in FIG. 46 receives. It is a graph which shows the evaluation result of the roughness for each condition of a belt transport speed V _{sys, and a pressing force P1 in a primary transfer part.} It is a graph which shows the evaluation result of the concave transferability with respect to each condition of a belt transfer speed V _{sys, and a pressing force P2 in a secondary transfer part.} It is a graph which shows the image evaluation result for each condition when the belts of Example 1 to Example 7, Comparative Example 1 to Comparative Example 4, and Conventional Example 1 to Conventional Example 4 are used.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments shown below, the same or common parts are designated by the same reference numerals in the drawings, and the description thereof will not be repeated.

<Image forming device>
FIG. 1 is a schematic view of an image forming apparatus according to the present embodiment. First, the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. The image forming apparatus 1 in the present embodiment is a so-called digital multifunction device.

As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit 2, an image processing unit 3, an image forming unit 4, a paper conveying unit 5, and a fixing device 6.

The image reading unit 2 includes an automatic document feeding device 2a and a document image scanning device 2b (scanner). Of these, the document image scanning apparatus 2b is provided with a contact glass, various lens systems, and a CCD sensor 7. The CCD sensor 7 is connected to the image processing unit 3. The image processing unit 3 performs predetermined image processing on the input image.

The image forming unit 4 has an image forming unit 10 (10Y, 10M, 10C, 10K) that forms an image with each color toner of Y (yellow), M (magenta), C (cyan), and K (black). There is. Since all of these have the same configuration except for the toner to be stored, the symbol indicating the color will be omitted hereafter. The image forming unit 4 further has an intermediate transfer unit 20 and a secondary transfer unit 30.

The image forming unit 10 includes an exposure device 11, a developing device 12, a photoconductor drum 13, a charging device 14, and a drum cleaning device 15. The surface of the photoconductor drum 13 has photoconductivity, and is, for example, a negatively charged organic photoconductor. The photoconductor drum 13 is an image carrier that supports a toner image.

The charging device 14 is, for example, a corona charging device, but may be a contact charging device that charges a contact charging member such as a charging roller, a charging brush, or a charging blade by contacting the photoconductor drum 13. The exposure apparatus 11 is composed of, for example, a semiconductor laser.

The developing device 12 is, for example, a two-component developing type developing device, but may be a one-component developing type developing device that does not include a carrier.

The intermediate transfer unit 20 includes an intermediate transfer belt 21, a primary transfer roller 22 for pressing the intermediate transfer belt 21 against the photoconductor drum 13, a plurality of support rollers 23 including an opposing roller 24, and a belt cleaning device 25. ing.

The intermediate transfer belt 21 is an endless intermediate transfer belt. Here, the primary transfer roller 22 mainly constitutes a primary transfer unit that transfers the toner image carried on the photoconductor drum 13 to the intermediate transfer belt 21.

The intermediate transfer belt 21 is stretched in a loop by a plurality of support rollers 23 and is movable. By rotating at least one of the plurality of support rollers 23, the intermediate transfer belt 21 travels at a constant speed in the direction of arrow A.

The secondary transfer unit 30 has an endless secondary transfer belt 31 and a plurality of support rollers 32 including a secondary transfer roller 33. The secondary transfer roller 33 faces the opposing roller 24. The secondary transfer roller 33 and the opposing roller 24 form a secondary transfer unit that transfers the toner image supported on the intermediate transfer belt 21 to the recording medium.

The secondary transfer belt 31 is stretched in a loop by the secondary transfer roller 33 and the support roller 32. By rotating at least one of the plurality of support rollers 32, the secondary transfer belt 31 travels in the direction of arrow B. The above-mentioned drive roller and a drive source for driving the roller constitute a transport belt drive mechanism 39 (see FIG. 2), which will be described later.

The fixing device 6 is for fixing the toner image transferred to the paper as a recording medium on the paper, and directs the fixing roller 6a for heating and melting the toner image on the paper and the paper toward the fixing roller 6a. It has a pressurizing roller 6b for pressing.

The paper transport unit 5 includes a paper feed unit 5a, a paper discharge unit 5b, and a transport path unit 5c. The paper feed tray units 5a1 to 5a3 constituting the paper feed unit 5a accommodate the papers identified based on the basis weight, size, and the like for each preset type. The transport path portion 5c has a plurality of transport roller pairs such as a resist roller pair 5c1. The paper ejection unit 5b is composed of a paper ejection roller 5b1.

The paper transfer speed in the transfer path unit 5c is determined by the control unit 8 as described later. The transfer path portion 5c includes a motor, a motor driver, a gear, and the like in addition to the secondary transfer belt 31 and a plurality of transfer roller pairs described above, and is a component for driving the secondary transfer belt 31 among them. However, it corresponds to the above-mentioned transport belt drive mechanism 39. These plurality of transport roller pairs, motors, motor drivers, gears, and the like transport paper by receiving electric signals from the control unit 8 and rotating various motors.

The members rotated by the various motors described above include, for example, the developing roller included in the developing device 12, the photoconductor drum 13, the intermediate transfer belt 21, the secondary transfer roller 33, the fixing roller 6a, the above-mentioned transport roller pair, and the like. However, these members may be driven centrally by one motor or may be driven separately by a plurality of motors. However, it is preferable that the outer peripheral surfaces of these members are driven at the same linear velocity (this linear velocity is generally referred to as a system velocity). The control unit 8 can change the system speed by switching the rotation speeds and gears of these various motors.

The present embodiment illustrates a case where a transport belt and a transport belt drive mechanism 39 for driving the transport belt are used as means for transporting the paper between the secondary transfer unit and the fixing device 6. The means may be configured by any means as long as the paper can be conveyed from the secondary transfer unit to the fixing device 6.

For example, the means may be configured by a transport roller pair that transports paper and a transport roller pair drive mechanism that drives the paper without using a belt, or by a secondary transfer roller 33 and an opposing roller 24. The means may be configured by these secondary transfer rollers 33 and the opposing rollers 24 and a roller drive mechanism for driving them so that the paper is directly conveyed to the fixing device 6.

FIG. 2 is a diagram showing a configuration of a main functional block of the image forming apparatus 1 shown in FIG. The control unit 8 is a part that controls the entire image forming apparatus 1, and as shown in FIG. 2, the control unit 8 includes a processor such as a CPU (Central Processing Unit) 8a, a ROM (Read Only Memory), and a RAM as main components. It includes a memory unit 8b such as (Random Access Memory). Typically, the CPU 8a executes various programs stored in the memory unit 8b to execute processing related to image formation in the image forming apparatus 1.

As shown in FIG. 2, in addition to the above-described configuration, the image forming apparatus 1 further includes a display operation unit 9a, a temperature / humidity sensor 9b, a paper sensor 9c, a pressing pressure adjusting mechanism 70, and a belt conveying speed adjusting mechanism 80. ing.

The display operation unit 9a displays the state of the image forming apparatus 1 or the like to the user based on the command of the control unit 8, or receives an operation on the image forming apparatus 1 by the user and inputs the operation to the control unit 8. It is a part to do.

The temperature / humidity sensor 9b is for detecting the temperature and humidity inside or around the image forming apparatus 1 and inputting the detection result to the control unit 8. The temperature / humidity sensor 9b is configured so as not to detect the temperature around the device such as the fixing device 6 which can be high due to the configuration of the image forming device 1 and the temperature of the exhaust gas of the image forming device 1. The temperature / humidity sensor 9b is most preferably configured to detect the temperature of the intermediate transfer belt 21.

The paper sensor 9c is a recording medium type information acquisition unit that acquires the recording medium type, and more specifically, the recording medium type used for image formation is smooth paper, thick paper, plain paper, or embossed paper. It is a part that identifies the presence or absence and acquires the recording medium type as information. Further, in the case of embossed paper, it is a part for identifying the embossed paper having a recess depth and the like and acquiring the recording medium type as information.

The paper sensor 9c is composed of, for example, an optical sensor capable of detecting the size of unevenness on the surface of the paper stored in the paper feeding unit 5a. In that case, the paper sensor 9c includes a light emitting element made of a light emitting diode or the like that obliquely irradiates visible light or infrared light with respect to the surface of the paper, and a photodiode or the like that receives the reflected light from the surface of the paper. It is composed of a light receiving element.

The paper sensor 9c detects the depth of the recess according to the amount of received light reflected from the paper, and outputs the detection result to the control unit 8. The control unit 8 acquires the above-mentioned recording medium type based on the detection result.

The paper sensor 9c is not limited to the use of the above-mentioned optical sensor, and other types of sensors capable of identifying the recording medium type can also be used. Further, the recording medium type information acquisition unit is not limited to the use of the paper sensor 9c described above, and the control unit 8 can be specified by the display operation unit 9a or the like to specify the recording medium type accommodated in the paper feed unit 5a. May be obtained.

The pressing force adjusting mechanism 70 adjusts the pressing force at which the primary transfer roller 22 presses the photoconductor drum 13 in the primary transfer unit. The pressing force adjusting mechanism 70 adjusts the pressing force at which the secondary transfer roller 33 presses the opposing roller 24 in the secondary transfer unit. The belt transfer speed adjusting mechanism 80 adjusts the belt transfer speed V _sys, which will be described later, in the intermediate transfer unit 20.

In the image forming apparatus 1 of the present embodiment, the control unit 8 can control the pressing pressure adjusting mechanism 70 and the belt transport speed adjusting mechanism 80 by receiving an input from the display operating unit 9a and the like.

Next, the process of image formation by the image forming apparatus 1 will be described. The document image scanning device 2b optically scans and reads the document on the contact glass. The reflected light from the document is read by the CCD sensor 7 and becomes input image data. The input image data is subjected to predetermined image processing by the image processing unit 3 and sent to the exposure apparatus 11. The input image data may be sent to the image forming apparatus 1 from an external personal computer, a mobile device, or the like.

The photoconductor drum 13 rotates at a constant peripheral speed. The charging device 14 uniformly charges the surface of the photoconductor drum 13 to a negative electrode property. The exposure apparatus 11 irradiates the photoconductor drum 13 with a laser beam corresponding to the input image data of each color component, and forms an electrostatic latent image on the surface of the photoconductor drum 13. The developing device 12 adheres toner to the surface of the photoconductor drum 13 to visualize the electrostatic latent image on the photoconductor drum 13. In this way, a toner image corresponding to the electrostatic latent image is formed on the surface of the photoconductor drum 13.

The toner image on the surface of the photoconductor drum 13 is transferred to the intermediate transfer belt 21 by the intermediate transfer unit 20. The transfer residual toner remaining on the surface of the photoconductor drum 13 after transfer is removed by the drum cleaning device 15 having a drum cleaning blade that is in sliding contact with the surface of the photoconductor drum 13. When the intermediate transfer belt 21 is pressed against the photoconductor drum 13 by the primary transfer roller 22, the toner images of each color are sequentially superimposed and transferred to the intermediate transfer belt 21.

The secondary transfer roller 33 is pressed against the opposing roller 24 via the intermediate transfer belt 21 and the secondary transfer belt 31. As a result, a transfer nip is formed. The paper is conveyed to the transfer nip by the paper transfer unit 5 and passes through the transfer nip. The correction of the inclination of the paper and the adjustment of the transfer timing are performed by the resist roller portion in which the resist roller pair 5c1 is arranged.

When the paper is conveyed to the transfer nip, a predetermined voltage is applied to the secondary transfer roller 33. By applying this voltage, the toner image supported on the intermediate transfer belt 21 is transferred to the paper. The transfer residual toner remaining on the surface of the intermediate transfer belt 21 is removed by the belt cleaning device 25 having a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 21. As for the belt cleaning device 25, a brush cleaning method may be adopted as long as it cleans the residual toner on the intermediate transfer belt 21. Further, when toner particles having a high transfer rate are used, there may be a mode in which a cleaning device is not used. The paper on which the toner image is transferred is conveyed toward the fixing device 6 by the secondary transfer belt 31.

The secondary transfer roller may be in direct contact with the paper without using the secondary transfer belt. In this case, the paper on which the toner image is transferred is sent toward the fixing device 6 by the rotation of the secondary transfer belt 31.

The fixing device 6 heats and pressurizes the paper on which the toner image is transferred and conveyed by the nip portion. In this way, the toner image is fixed on the paper. The paper on which the toner image is fixed is discharged to the outside of the machine by the paper ejection unit 5b provided with the paper ejection roller 5b1.

The toner particles are those in which a colorant, a charge control agent, a mold release agent, etc., if necessary, are contained in a binder resin and treated with an external additive, and commonly used known toner particles are used. can do. The volume average particle size of the toner particles is preferably particles in the range of 2 [μm] or more and 12 [μm] or less, and more preferably particles in the range of 3 [μm] or more and 9 [μm] or less in terms of image quality. Is good.

The shape coefficient SF-1 of the toner particles is preferably 100 to 140, but is not necessarily limited to this range.

The shape coefficient SF-1 is obtained by randomly capturing 100 toners taken at 5000 times with a scanning electron microscope with a scanner and analyzing them with an image processing analysis device "LuzexAP" (manufactured by Nireco). It is obtained from the average value of the shape coefficient (SF-1) derived from.
SF-1 = [{(absolute maximum length of particles) 2 / (projected area of particles)} × (π / 4)] × 100
As the external additive for toner particles, fine particles of metal oxides such as silica and titania are used, and those having a small particle size such as 30 [nm] to relatively large particles such as 100 [nm] are used. Will be done. Inorganic fine particles having an average primary particle size of 40 [nm] or less may be used for the purpose of powder fluidity, charge control, and the like.

Further, if necessary, in order to reduce the adhesive force, inorganic or organic fine particles having a larger diameter may be used in combination. Examples of the inorganic fine particles include alumina, metatitanic acid, zinc oxide, zirconia, magnesia, calcium carbonate, magnesium carbonate, calcium phosphate, cerium oxide, strontium titanate and the like, in addition to silica and titania. Further, in order to improve dispersibility and powder fluidity, the surface of the inorganic fine particles may be treated separately.

The carrier is not particularly limited, and a commonly used known carrier can be used, and a binder type carrier, a coat type carrier, or the like can be used. The carrier particle size is not limited to this, but is preferably 15 [μm] or more and 100 [μm] or less.

<Intermediate transfer belt 21>
Next, the configuration of the intermediate transfer belt 21 will be described with reference to FIG. FIG. 3 is a cross-sectional view of the intermediate transfer belt 21 shown in FIG.

As shown in FIG. 3, the intermediate transfer belt 21 is composed of a member having a pair of exposed main surfaces, a first main surface 21s1 and a second main surface 21s2, which are located relative to each other, and includes a base layer 21a and an elastic layer 21b. , The surface layer 21c and the like.

The elastic layer 21b is provided so as to cover the base layer 21a, and the surface layer 21c is provided so as to cover the elastic layer 21b. As a result, the above-mentioned first main surface 21s1 is defined by the surface layer 21c, and the above-mentioned second main surface 21s2 is defined by the base layer 21a.

The intermediate transfer belt 21 is for transferring the carried toner image to a recording medium such as paper as described above, and the toner image is supported on the first main surface 21s1 described above.

The base layer 21a is a layer for improving the mechanical strength of the intermediate transfer belt 21 as a whole, and is composed of, for example, a layer made of an organic polymer compound. Examples of the organic polymer compound constituting the base layer 21a include polycarbonate, fluororesin, polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, and styrene-acetic acid. Vinyl copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene -Octyl acrylate copolymer and styrene-phenyl acrylate copolymer, etc.), styrene-methacrylate copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methacrylate, etc.) Styrene-based resins such as phenyl copolymers, etc.), styrene-α-methyl chloroacrylate copolymers, styrene-acrylonitrile-acrylic acid ester copolymers, etc. (monopolymers or copolymers containing styrene or styrene substituents) , Methyl methacrylate resin, butyl methacrylate resin, ethyl acrylate resin, butyl acrylate resin, modified acrylic resin (silicone modified acrylic resin, vinyl chloride resin modified acrylic resin, acrylic / urethane resin, etc.), vinyl chloride resin, vinyl chloride -Vinyl acetate copolymer, rosin-modified maleic acid resin, phenol resin, epoxy resin, polyester resin, polyester polyurethane resin, polyethylene, polypropylene, polybutadiene, polyvinylidene chloride, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene- Examples thereof include ethyl acrylate copolymers, xylene resins and polyvinyl butyral resins, polyamide resins, styrene resins, modified polyphenylene oxide resins, modified polycarbonates, and mixtures thereof. The base layer 21a may be composed of a plurality of layers made of different materials.

A conductive agent may be added to the base layer 21a for adjusting the resistance value. As the conductive agent, only one type may be added, or a plurality of types may be added. The content of the conductive agent in the base layer 21a is preferably 0.1 part by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the base layer material, but is not limited thereto.

The elastic layer 21b is a layer for imparting elasticity to the intermediate transfer belt 21, and is composed of, for example, a layer made of an organic compound exhibiting viscoelasticity. Examples of the organic compound constituting the elastic layer 21b include butyl rubber, fluororubber, acrylic rubber, ethylene propylene rubber (EPDM), nitrile butadiene rubber (NBR), acrylonitrile butadiene styrene rubber, natural rubber, isoprene rubber, and styrene-butadiene. Rubber, butadiene rubber, ethylene-propylene rubber, ethylene-propylene terpolymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, silicone rubber, Fluorine rubber, polysulfide rubber, polynorbornene rubber, hydride nitrile rubber, thermoplastic elastomers (eg polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyamide, polyurea, polyester, fluororesin), and theirs. Examples thereof include a mixture of. The elastic layer 21b may be composed of a plurality of layers made of different materials.

A conductive agent for exhibiting conductivity may be added to the elastic layer 21b. As the conductive agent, only one type may be added, or a plurality of types may be added. The content of the conductive agent in the elastic layer 21b is preferably 0.1 part by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the elastic layer material, but is not limited thereto. The content of the conductive agent in the elastic layer 21b, in its total amount, an amount to achieve a desired volume resistivity of the intermediate transfer belt 21, the volume resistivity of the intermediate transfer belt 21, for example, 1 × 10 8 ^[Ω · cm] or more and 1 × 10 ¹² [Ω · cm] or less.

The above-mentioned conductive agents include ionic conductive agents and electronic conductive agents. Ion conductive agents include silver iodide, copper iodide, lithium perchlorate, lithium trifluoromethanesulfonate, lithium salts of organic boron complexes, lithium bisimide ((CF ₃ SO ₂ ) ₂ NLi) and lithium trismethi. Do ((CF ₃ SO ₂ ) ₃ CLi) is included. Electronic conductive agents include metals such as silver, copper, aluminum, magnesium, nickel and stainless steel, and carbon compounds such as graphite, carbon black, carbon nanofibers and carbon nanotubes.

The elastic layer 21b may contain a non-fiber-shaped resin or a fiber-shaped resin in addition to the above-mentioned conductive agent.

Examples of the non-fiber-shaped resin include thermosetting resins such as phenol resins, thermosetting urethane resins, epoxy resins and reactive monomers, and thermoplastic resins such as polyvinyl chloride, polyvinyl acetate and thermoplastic urethane. Can be mentioned. The content of the non-fibrous resin in the elastic layer 21b with respect to the elastic layer material is preferably 20 parts by weight or more and 60 parts by weight or less with respect to 100 parts by weight of the elastic layer material, but is not limited thereto. ..

Examples of the fiber-shaped resin include resin-based fibers such as cotton, linen, silk, rayon, acetate, nylon, acrylic, vinylon, vinylidene, polyester, polystyrene, polypropylene, and aramid. The content of the fibrous resin in the elastic layer 21b is preferably 10 parts by weight or more and 40 parts by weight or less with respect to 100 parts by weight of the elastic layer material, but is not limited thereto.

The elastic layer 21b may further contain conventional additives such as a vulcanizing agent, a vulcanization accelerator, a vulcanization aid, a co-crosslinking agent, a softening agent, a plasticizer, and the like. These additives may be added alone or in combination of two or more.

Here, as the vulcanizing agent, for example, sulfur, an organic sulfur-containing compound, an organic peroxide, or the like can be used.

Examples of the co-crosslinking agent include ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, polyfunctional methacrylate monomer, triallyl isocyanurate, and metal-containing monomer as co-crosslinking agents using organic peroxides. .. The amount of the co-crosslinking agent added to the elastic layer 21b is preferably 5 parts by weight or less with respect to 100 parts by weight of the elastic layer material, but is not limited thereto.

The material of the surface layer 21c is not particularly limited, but it is preferable that the surface layer 21c has improved transferability by reducing the adhesive force of the toner to the intermediate transfer belt 21. From this point of view, the surface layer 21c uses, for example, polyurethane, polyester, epoxy resin or a mixture thereof as a base material, and the base material is a powder of, for example, fluororesin, fluorine compound, fluorocarbon, titanium dioxide, silicon carbide or the like. One type or two or more types of dispersed bodies or particles can be used. The surface layer 21c may be a modified surface of the elastic layer 21b.

Here, these powders and particles are materials for reducing the surface energy of the first main surface 21s1 to improve lubricity, and these powders and particles having different particle sizes are dispersed and used. You can also do it. Further, the surface energy of the first main surface 21s1 may be reduced by forming a fluorine-rich layer on the surface by performing heat treatment using a fluorine-based rubber material.

Here, the hardness of the base layer 21a is higher than the hardness of the elastic layer 21b. Since the elastic layer 21b is supported by the base layer 21a which is less deformable than the elastic layer 21b, the elastic layer 21b is less likely to be deformed toward the second main surface 21s2, and the elastic layer 21b becomes the first main surface 21s1 by that amount. It becomes easy to deform to the opposite side. The hardness of the base layer and the elastic layer can be measured using a micro rubber hardness tester (for example, manufactured by Polymer Instruments Co., Ltd .: MD-1).

The hardness of the surface layer 21c is higher than the hardness of the elastic layer 21b. The surface layer 21c, which is harder than the elastic layer 21b, can be formed by applying an uncured resin to the surface of the elastic layer 21b using a photocurable resin and curing the resin with ultraviolet rays. Alternatively, the surface layer 21c that is harder than the elastic layer 21b can be formed by a modification treatment such as hardening the vicinity of the surface of the elastic layer 21b.

The surface layer 21c does not necessarily have to be provided, and the intermediate transfer belt 21 can be composed of only the base layer 21a and the elastic layer 21b. Further, the intermediate transfer belt 21 may be formed only by the elastic layer 21b without providing the base layer 21a. Further, in addition to the above-mentioned base layer 21a, elastic layer 21b and surface layer 21c, another layer can be added to form the intermediate transfer belt 21 into four or more layers.

The ten-point average surface roughness Rz of the first main surface 21s1 of the intermediate transfer belt 21 is preferably 0.5 [μm] or more and 9.0 [μm] or less, and 3.0 [μm] or more and 6.0. It is still more preferable that it is [μm] or less. If the ten-point average surface roughness Rz is less than 0.5 [μm], there is a concern that it will adhere to the contact member, and if the ten-point average surface roughness Rz is larger than 9.0 [μm], unevenness will occur. Toner, paper dust, etc. tend to accumulate in the portion, and the image quality may deteriorate. The ten-point average surface roughness Rz is the surface roughness defined in JIS B0601 (2001).

Here, when the intermediate transfer belt 21 in the present embodiment is evaluated based on the evaluation method using the displacement amount measuring device 100 described later, a part of the surface (that is, the first main surface 21s1) is predetermined. It exhibits a characteristic behavior and is displaced, and the details will be described later.

<Structure of secondary transfer unit>
FIG. 4 is a schematic view of the secondary transfer unit shown in FIG. Next, the detailed configuration of the secondary transfer unit will be described with reference to FIG. 4. In FIG. 4, the secondary transfer belt 31 is not shown.

As shown in FIG. 4, the intermediate transfer belt 21 is arranged so as to pass through the secondary transfer portion of the image forming apparatus 1.

The secondary transfer unit includes a secondary transfer roller 33 and an opposing roller 24 which are arranged in parallel so as to face each other. A secondary transfer nip portion N2 is formed between the secondary transfer roller 33 and the opposing roller 24. The intermediate transfer belt 21 is arranged so as to pass through the secondary transfer nip portion N2, and a recording medium 1000 such as paper is also supplied so as to pass through the secondary transfer nip portion N2.

The secondary transfer roller 33 is made of a conductive material, and a secondary transfer power source 33c is connected to the secondary transfer roller 33. The opposing roller 24 includes a core metal 24a made of a conductive material and a conductive elastic portion 24b that covers the peripheral surface of the core metal 24a, of which the core metal 24a is grounded. As a result, a predetermined electric field is formed in the secondary transfer nip portion N2 by the secondary transfer roller 33, the opposing roller 24, and the secondary transfer power supply 33c.

The intermediate transfer belt 21 is arranged so as to pass through the facing roller 24 side of the recording medium 1000, and the recording medium 1000 is supplied so as to pass through the secondary transfer roller 33 side of the intermediate transfer belt 21. .. The intermediate transfer belt 21 is arranged so that its first main surface 21s1 faces the recording medium 1000 side (that is, the secondary transfer roller 33 side) and its second main surface 21s2 faces the opposite roller 24 side. There is. As a result, the first main surface 21s1 of the intermediate transfer belt 21 is arranged to face the recording surface 1001 of the recording medium 1000 in the secondary transfer nip portion N2.

The secondary transfer roller 33 is rotationally driven in the direction of arrow AR1 shown in the figure, and the opposing roller 24 is rotationally driven in the direction of arrow AR2 shown in the figure. Further, the secondary transfer roller 33 is pressed toward the arrow AR3 direction shown in the drawing when transferring the toner image, whereby the secondary transfer roller 33 and the opposing roller 24 are separated from each other by the secondary transfer belt 31 (see FIG. 1). ), The intermediate transfer belt 21 and the recording medium 1000 will be pressure-welded.

Based on the rotation of the secondary transfer roller 33 and the rotation of the opposing roller 24, the intermediate transfer belt 21 and the recording medium 1000 are conveyed in the directions of arrow AR4 and arrow AR5 shown in the drawings, respectively. At that time, when passing through the secondary transfer nip portion N2, the intermediate transfer belt 21 and the recording medium 1000 are sandwiched and brought into close contact with each other in a state of being pressurized by the secondary transfer roller 33 and the opposing roller 24.

Further, at that time, the predetermined electric field described above acts on the intermediate transfer belt 21 and the recording medium 1000 in the close contact portion. As a result, the toner adhering to the first main surface 21s1 of the intermediate transfer belt 21 adheres to the recording surface 1001 of the recording medium 1000, and the toner image is transferred.

Here, when the hardness of the surface of the secondary transfer roller 33 is higher than the hardness of the surface of the opposing roller 24, the intermediate transfer belt 21 and the recording medium 1000 of the portion sandwiched between the secondary transfer roller 33 and the opposing roller 24 Will be curved along the surface of the secondary transfer roller 33.

Therefore, a concave curved surface extending along the axial direction of the secondary transfer roller 33 is formed on the first main surface 21s1 of the intermediate transfer belt 21, and the toner image is transferred at this portion. Will be done. The hardness of the surfaces of the secondary transfer roller and the opposing roller can be measured using a micro rubber hardness tester (for example, manufactured by Polymer Instruments Co., Ltd .: MD-1).

Pressure acts on the intermediate transfer belt 21 at the secondary transfer section and the primary transfer section described above. When the intermediate transfer belt 21 is deformed by the action of pressure, the contact area between the first main surface 21s1 and the toner increases, and the adhesive force between the toner and the intermediate transfer belt 21 increases. However, since the intermediate transfer belt 21 has a hard surface layer 21c and the hardness of the first main surface 21s1 of the intermediate transfer belt 21 is high, the first main surface 21s1 is less likely to be deformed even when pressure is applied, or the first main surface 21s1 is not easily deformed. Even if 1 main surface 21s1 is deformed, it can be quickly restored to its original state.

Therefore, the increase in the contact area between the first main surface 21s1 and the toner is suppressed, and the increase in the adhesive force between the toner and the intermediate transfer belt 21 is suppressed, so that the toner image can be transferred more reliably. It has become.

The intermediate transfer belt 21 in the present embodiment is not limited to the case where plain paper or the like having no particular unevenness on the surface is used as the recording medium 1000 described above, and the case where embossed paper or the like having unevenness on the surface is used. In addition, good transferability can be ensured, but prior to explaining the mechanism and the like, the details of the evaluation method using the displacement amount measuring device 100 will be described below.

<Displacement amount measuring device 100>
FIG. 5 is a schematic view showing the configuration of the displacement amount measuring device 100, and FIG. 6 is a schematic view showing the operation of the pressurizing mechanism provided in the displacement amount measuring device 100 shown in FIG. FIG. 7 is a perspective view of the lower block of the displacement amount measuring device 100 shown in FIG. 5 as viewed from above, and FIG. 8 is a perspective view of the upper block of the displacement amount measuring device 100 shown in FIG. 5 as viewed from below. Is.

As shown in FIG. 5, the displacement amount measuring device 100 mainly includes a lower block 110, an upper block 120, a pressurizing mechanism 130, a tension applying mechanism 140, and a displacement meter 150.

As shown in FIGS. 5 and 7, the lower block 110 is made of an aluminum block having a width and a depth of 50 [mm] and a height of 20 [mm], and has a width at the center of the upper surface 111 in the width direction. Has a curved ridge surface 112 of 20 [mm]. The radius of curvature of the curved convex surface 112 is 20 [mm].

Of the tops of the curved convex surface 112 located along the depth direction of the lower block 110, the central part in the depth direction has a diameter of 1.25 [mm] (however, the tolerance is ± 0.02 [mm]. ]) Hole 113 is provided. The head portion 151 of the displacement meter 150 is arranged at a position retracted from the opening surface of the hole portion 113.

As shown in FIGS. 5 and 8, the upper block 120 is made of an aluminum block having a width and a depth of 50 [mm] and a height of 20 [mm], and has a width at the center of the lower surface 121 in the width direction. It has a curved concave surface 122 of 20 [mm]. The radius of curvature of the curved concave surface 122 is 20.3 [mm].

The tolerances between the upper surface 111 of the lower block 110 and the curved convex surface 112, and the surface tolerances of the lower surface 121 of the upper block 120 and the curved concave surface 122 are all 0.02 [mm].

As shown in FIG. 5, the upper surface 111 of the lower block 110 and the lower surface 121 of the upper block 120 are arranged so as to face each other. Here, the lower block 110 and the upper block 120 are positioned and arranged so that the curved convex strip surface 112 and the curved concave strip surface 122 described above are arranged so as to overlap each other in the vertical direction. ..

A pressurizing mechanism 130 is arranged above the upper block 120. The pressurizing mechanism 130 is arranged so as to be in contact with the pressurizing member 131, which is a block-shaped member, the spring 132 arranged between the pressurizing member 131 and the upper block 120, and the upper surface of the pressurizing member 131. It includes a cam 133, a shaft 134 connected to the cam 133, and a drive motor 135 for rotationally driving the shaft 134.

As shown in FIG. 6, the shaft 134 is rotationally driven by the drive motor 135 in the direction of the arrow AR6 shown in the drawing, so that the cam 133 connected to the shaft 134 rotates together with the shaft 134. The pressurizing member 131 is pushed downward (toward the direction of arrow AR7 shown in the figure). As a result, the upper block 120 is pushed down by the pressurizing member 131 via the spring 132, and a vertically downward load is applied to the upper block 120. The magnitude of the load is determined by the pushing down amount d of the pressing member 131, and the pushing down amount d of the pressing member 131 can be adjusted by the rotation amount of the cam 133.

As shown in FIG. 5, a belt S to be evaluated is arranged between the lower block 110 and the upper block 120, and both ends of the belt S are from between the lower block 110 and the upper block 120. It is pulled out toward the outside. Tension applying mechanisms 140 are connected to both ends of the belt S.

The tension applying mechanism 140 includes a film 141, a tape 142, and a weight 143. The film 141 is made of a polyethylene terephthalate film having a thickness of 100 [μm], and the tape 142 is made of a polyimide adhesive tape having a thickness of 30 [μm]. One end of the film 141 is attached to the end of the belt S by the tape 142, and the weight 143 is attached to the other end of the film 141. Here, the tensile load by the weight 143 is adjusted to 44 [N / m]. If the belt S to be evaluated has a sufficient size, the weights 143 may be directly attached to both ends of the belt S without using the film 141 and the tape 142 described above.

The displacement meter 150 is for detecting the displacement of the surface of the belt S, and as described above, the head portion 151 of the displacement meter 150 is formed in the hole portion 113 of the lower block 110 so as to face the belt S. is set up. Here, as the displacement meter 150, a microhead type spectroscopic interference laser displacement meter (spectral unit (model: SI-F01U), head unit (model: SI-F01)) manufactured by KEYENCE Corporation is used.

<Evaluation method>
FIG. 9 is a graph for explaining a belt evaluation method using the displacement amount measuring device 100 shown in FIG. Further, FIG. 10 is an enlarged cross-sectional view of the vicinity of the hole portion of the lower block in a state where the belt is pressurized by using the displacement amount measuring device 100 shown in FIG.

The evaluation of the belt S is performed by the following procedure using the displacement amount measuring device 100 shown in FIG. 5 described above. The evaluation is performed in an environment of a temperature of 20 [° C.] and a humidity of 50 [%].

First, prior to setting the belt S on the displacement amount measuring device 100, the pressure distribution at the contact portion between the curved convex surface 112 of the lower block 110 and the curved concave surface 122 of the upper block 120 is measured. For the pressure distribution measurement, a tactile sensor (surface pressure distribution measurement system I-SCAN) manufactured by Nitta Corporation is used.

Specifically, the measuring unit of the tactile sensor is inserted between the lower block 110 and the upper block 120, the pressure member 131 is pushed down, and the pressure distribution after 30 seconds has passed is measured. This is repeated, and the pressure in the contact portion between the curved convex surface 112 and the curved concave surface 122 and its vicinity is adjusted so as to be within 200 ± 40 [kPa].

Prior to measurement, the belt S is stored in an environment of a temperature of 20 [° C.] and a humidity of 50 [%] for 6 hours or more. As for the size of the belt S to be evaluated, the length corresponding to the width direction of the lower block 110 and the upper block 120 is 60 [mm], and the length corresponding to the depth direction of the lower block 110 and the upper block 120 is 50. Let it be [mm]. The length corresponding to the width direction of the lower block 110 and the upper block 120 may have a size of 35 [mm] or more and 300 [mm] or less, and corresponds to the depth direction of the lower block 110 and the upper block 120. The length may be 50 [mm] or more and 150 [mm] or less. If the lengths of the lower block 110 and the upper block 120 corresponding to the width direction are insufficient, the weights 143 may be attached to both ends of the film 141 and the tape 142 described above.

Next, the tactile sensor is removed, the upper block 120 is lowered by the pressurizing mechanism 130 so that the lower block 110 and the upper block 120 are in light contact with each other, and then the upper block 120 is held for 30 seconds for contact. Stabilize the state. Then, the upper block 120 is pressed toward the lower block 110 by using the pressurizing mechanism 130. The pressurizing conditions here are the same as the pressurizing conditions of the belt S described later (for details, refer to the pressurizing conditions of the belt S described later).

Next, the position of the curved concave surface 122 of the upper block 120 of the portion of the lower block 110 facing the hole 113 is measured using the displacement meter 150 for 3 seconds from the start of pressurization, which will be described later. It is set as the baseline for measuring the displacement of the belt S.

Next, the upper block 120 is raised to release the contact between the lower block 110 and the upper block 120, and the belt S is placed on the upper surface 111 of the lower block 110. At this time, the first main surface Sa of the belt S is directed downward (that is, the lower block 110 side). When mounting the belt S, care should be taken not to allow foreign matter to enter between the belt S and the lower block 110 and between the belt S and the upper block 120.

Next, the upper block 120 is lowered by the pressurizing mechanism 130 so that the upper block 120 and the belt S are in light contact with each other, and then the state is held for 30 seconds to stabilize the contact state. Then, the upper block 120 is pressed against the belt S by using the pressurizing mechanism 130.

As shown in FIGS. 9 and 10, in the pressurization of the belt S, the pressurized region PR of the belt S to be sandwiched between the curved convex strip surface 112 and the curved concave strip surface 122 is predetermined. After reaching a pressing force of 200 [kPa] by pressurizing so that the pressing force increases at a pressurizing speed [kPa / ms], the pressurized region PR becomes a pressing force of 200 [kPa]. It is performed so that the state of being constantly pressurized is maintained.

With reference to FIG. 9, the time from the time when the pressurization to the pressurized region PR is started to the time when the pressurization of 200 [kPa] is reached is defined as t0 [s]. Then, when 3 seconds have passed from the start of pressurization, the pressurization on the belt S is released. In this embodiment, t0 = 0.05 [s] (pressurization speed 4 [kPa / ms]) was set.

At that time, the position of the measurement region MR, which is the portion corresponding to the hole 113 of the lower block 110 of the first main surface Sa of the belt S, is set for 3 seconds from the start of pressurization to the release of pressurization. The measurement is performed using a displacement meter 150. At that time, the portion including the measurement region MR of the belt S is compressed by sandwiching the portion of the belt S located around the portion by the lower block 110 and the upper block 120, so that the portion is directed toward the inside of the hole 113. It deforms so as to bulge, and the position of the measurement area MR changes with this deformation.

At the time of measuring the baseline and the position of the measurement area MR described above, the output of the displacement meter 150 is captured by the digital oscilloscope DL1640 manufactured by Yokogawa Electric Corporation. The sampling period at this time is 5 [ms].

Next, the displacement of the measurement region MR of the belt S is calculated as time series data by obtaining the difference between the measured position of the measurement region MR and the above-mentioned baseline.

The placement position of the belt S with respect to the lower block 110 is changed so that the position of the measurement region MR described above is different from that of the belt S to be measured, and the above description is performed 10 times in total. Make a measurement.

<Typical displacement pattern>
When various belts including an elastic layer are evaluated by applying the belt evaluation method using the displacement amount measuring device 100 described above, it is typically a pattern showing the displacement behavior of the belt measurement region. The following patterns can be confirmed. FIG. 11 is a graph showing a pattern of displacement behavior in the measurement region of the belt.

As shown in FIG. 11, the displacement amount y of the measurement region MR of the belt S increases as the pressing force for pressurizing the belt S increases after the start of pressurization, and the pressing force for pressurizing the belt S is 200 [kPa]. A local peak occurs in the displacement of the measurement region MR of the belt S near the time when the temperature reaches (that is, t0 [s]). After that, the displacement amount y of the measurement region MR of the belt S starts to decrease, and finally gradually decreases with the passage of time and converges to a predetermined displacement amount. That is, it can be said that the pattern has an overshoot portion in the transition of the displacement of the measurement region MR of the belt S.

In the following, the displacement in the phase where the displacement amount y of the measurement region MR of the belt S increases in the pattern is referred to as the primary displacement, and the displacement in the phase where the displacement amount y of the measurement region MR of the belt S decreases is referred to as the secondary displacement. Refer to.

<Displacement pattern of intermediate transfer belt 21>
The intermediate transfer belt 21 in the above-described embodiment is evaluated by applying the belt evaluation method using the displacement amount measuring device 100 described in detail above, and the pattern shown in FIG. 11 (that is, that is, It exhibits a pattern having an overshoot portion).

This is because when the present inventor prepared a plurality of types of belts and used each of them as the intermediate transfer belt 21 of the image forming apparatus 1 to form an image on embossed paper, the belt did not have an overshoot portion. In comparison, it is based on the finding that a belt having an overshoot portion has dramatically better transferability.

The reason why high transferability can be ensured in a belt having an overshoot portion is basically that even when the intermediate transfer belt 21 is pressed from the back surface (that is, the second main surface 21s2) side, its front surface (that is, the first main surface). This is due to the large shaking of 21s1). Therefore, in order to realize the intermediate transfer belt 21 capable of ensuring high transferability on a recording medium having irregularities on the recording surface such as embossed paper, it is preferable to pay attention to the overshoot portion described above.

With reference to FIG. 11, the maximum value of the displacement amount y, which is the local peak of the displacement of the measurement region MR of the belt S, is defined as a [μm], and after the displacement of the measurement region MR of the belt S has converged. The convergence value, which is the displacement amount y, is defined as b [μm]. The time from the start of pressurization to the time when the maximum value a [μm] is observed is defined as t1 [s], and after the maximum value a [μm] is observed from the start of pressurization, the measurement region MR of the belt S is measured again. The time until the displacement amount y of (a + b) / 2 reaches (a + b) / 2 is defined as t2 [s].

In addition, the overshoot rate E [-], the primary displacement rate k1 [μm / s], and the secondary displacement rate are parameters indicating the displacement behavior of the measurement region MR of the characteristic belt S having an overshoot portion. It is defined as k2 [μm / s].

The overshoot rate E [−] is a parameter indicating the magnitude of the overshoot, and is calculated by E = (ab) / b.

The primary displacement rate k1 [μm / s] is a parameter indicating the rate of increase in the primary displacement (that is, the rate of increase in the amount of displacement), which is the displacement until the above-mentioned local peak is reached, and k1 = a / t1. It is calculated.

The secondary displacement rate k2 [μm / s] is a parameter indicating the rate of decrease in the secondary displacement (that is, the rate of decrease in the amount of displacement), which is the displacement after reaching the above-mentioned local peak, and k2 = ( It is calculated by ab) / {2 × (t2-t1)}.

The overshoot rate E [-], the primary displacement rate k1 [μm / s], and the secondary displacement rate k2 [μm / s] are all pressurized by the intermediate transfer belt 21 from the back surface (that is, the second main surface) side. It is a parameter indicating how much the surface (that is, the first main surface) sways when the displacement is performed. The larger the change, the more the surface of the intermediate transfer belt 21 sways, the larger these parameters will be.

More specifically, when the overshoot rate E [−] takes a relatively large value, the surface of the intermediate transfer belt 21 is displaced more significantly. When the primary displacement rate k1 [μm / s] takes a relatively large value, the primary displacement of the intermediate transfer belt 21 occurs at a higher speed. When the secondary displacement rate k2 [μm / s] takes a relatively large value, the secondary displacement of the intermediate transfer belt 21 occurs at a higher speed.

The intermediate transfer belt 21 in the present embodiment satisfies the following first to third conditions.

The first condition is a condition in which the above-mentioned overshoot rate E [−] satisfies 0.2 ≦ E ≦ 3. By using the intermediate transfer belt 21 that satisfies the first condition, high transferability can be realized even on a recording medium having irregularities on the surface, and the image quality is deteriorated even after repeated use. Can be suppressed.

When the overshoot rate E [-] is E <0.2, the front surface does not sway too much even when the intermediate transfer belt 21 is pressed from the back surface side, which is a transferable surface. Can not be expected to have a sufficient effect. On the other hand, when the overshoot rate E [-] is 3 <E, the intermediate transfer belt 21 may be cracked or worn at an early stage due to repeated use, and there is a concern that the image quality may be deteriorated. Will be.

The second condition is a condition in which the above-mentioned primary displacement rate k1 [μm / s] satisfies 60 ≦ k1 ≦ 320. By using the intermediate transfer belt 21 that satisfies the second condition, high transferability can be realized even on a recording medium having irregularities on the surface. It is possible to prevent deterioration of image quality even after repeated use.

When the primary displacement rate k1 [μm / s] is k1 <60, the front surface does not sway too much even when the intermediate transfer belt 21 is pressed from the back surface side, which is a transferable surface. Can not be expected to have a sufficient effect. On the other hand, when the primary displacement rate k1 [μm / s] is 320 <k1, the intermediate transfer belt 21 may be cracked or worn at an early stage due to repeated use, resulting in deterioration of image quality. It will be a concern.

The third condition is a condition in which the above-mentioned secondary displacement rate k2 [μm / s] satisfies 6 ≦ k2 ≦ 30. By using the intermediate transfer belt 21 that satisfies the third condition, high transferability can be realized even on a recording medium having irregularities on the surface. It is possible to prevent deterioration of image quality even after repeated use.

When the secondary displacement rate k2 [μm / s] is k2 <6, even when the intermediate transfer belt 21 is pressed from the back surface side, the front surface does not sway too much, and the transferability is high. Sufficient effect cannot be expected in terms of surface. On the other hand, when the secondary displacement rate k2 [μm / s] is 30 <k2, the intermediate transfer belt 21 may be cracked or worn at an early stage due to repeated use, resulting in deterioration of image quality. Will be a concern.

The overshoot rate E [−], the primary displacement rate k1 [μm / s], and the secondary displacement rate k2 [μm / s] described above are the methods for evaluating the intermediate transfer belt 21 using the displacement amount measuring device 100 described above. , It is a value obtained by changing the position of the measurement area MR. It is obtained by calculating the average value of the remaining 4 values excluding 3 larger values and 3 smaller values among the values calculated from each of the 10 time series data in total.

<Relationship between displacement pattern and transferability>
Next, the reason why high transferability can be ensured when an image is formed on embossed paper by using a belt exhibiting a pattern having an overshoot portion as an intermediate transfer belt 21 of the image forming apparatus 1 will be described in detail.

FIG. 12 is a schematic view showing the state of toner transfer from the intermediate transfer belt 21A to the embossed paper when the intermediate transfer belt 21A composed of only the inelastic layer is used, and FIG. 13 is a schematic view showing the applied voltage in that case. It is a graph which shows the relationship between and transfer efficiency.

As shown in FIG. 12, when the toner image is transferred to the embossed paper 1000 using the intermediate transfer belt 21A composed of only the inelastic layer, the portion where the recess 1002 of the embossed paper 1000 is not located (for convenience, this is referred to as a portion). The recording surface 1001 (hereinafter referred to as the convex portion 1003) and the toner T located on the first main surface 21s1 of the intermediate transfer belt 21A are in contact with each other. On the other hand, the recording surface 1001 of the portion of the embossed paper 1000 where the recess 1002 is located and the toner T located on the first main surface 21s1 of the intermediate transfer belt 21A are in a non-contact state.

Therefore, in order to move the toner T to the bottom surface of the recess 1002 of the embossed paper 1000, it is necessary to fly the toner T from the intermediate transfer belt 21A. In order for the toner T to fly from the intermediate transfer belt 21A, the force received by the toner T from the electric field must overcome the adhesive force of the toner T on the intermediate transfer belt 21A. The adhesive force is the sum of the non-electrostatic adhesive force (Van der Waals force) and the electrostatic adhesive force (electrostatic attractive force due to the electric charge of the charged toner and the mirror image charge generated on the intermediate transfer belt 21). ..

The force F that the toner T receives from the electric field has the charge amount of the toner T as q, the potential difference between the embossed paper 1000 and the intermediate transfer belt 21A as dV, and the distance between the embossed paper 1000 and the intermediate transfer belt 21A. When dx is used, it is represented by F = q × dV / dx. As can be understood from this relationship, the force F is proportional to the potential difference dV between the embossed paper 1000 and the intermediate transfer belt 21A, so that the larger the distance dx, the more necessary for the toner T to fly. The applied voltage becomes large.

Therefore, as shown in FIG. 13, the applied voltage V1 at which the transfer efficiency is maximized at the concave portion 1002 is higher than the applied voltage V0 at which the transfer efficiency is maximized at the convex portion 1003. In FIG. 13, reference numeral c1003 is attached to a curve showing the relationship between the applied voltage and the transfer efficiency with respect to the convex portion 1003, and reference numeral c1002 (21A) is attached to the curve showing the relationship between the applied voltage and the transfer efficiency with respect to the concave portion 1002. It is attached.

Normally, in the image forming apparatus 1, the applied voltage is set in the vicinity of the applied voltage V0 at which the transfer efficiency is maximized in the convex portion 1003. Therefore, the higher the transfer efficiency in the concave portion 1002 in the vicinity of the applied voltage V0, the smaller the difference in image density between the concave portion 1002 and the convex portion 1003 of the embossed paper 1000, and a high-quality image can be obtained. Become.

FIG. 14 is a schematic view showing the state of toner transfer from the intermediate transfer belt 21B to the embossed paper when the intermediate transfer belt 21B including the elastic layer is used, and FIG. 15 shows the applied voltage and transfer in that case. It is a graph which shows the relationship with efficiency.

As shown in FIG. 14, when the intermediate transfer belt 21B including the elastic layer is used, a part of the intermediate transfer belt 21B on the first main surface 21s1 side generally enters the recess 1002 of the embossed paper 1000. As described above, the intermediate transfer belt 21B is deformed, whereby the distance dx between the bottom surface of the recess 1002 of the embossed paper 1000 and the intermediate transfer belt 21B is shortened. Therefore, the effect of lowering the applied voltage that maximizes the transfer efficiency in the recess 1002 can be obtained. This effect is a conventionally known effect, and here, it is referred to as a follow-up deformation effect.

On the other hand, when the intermediate transfer belt 21B including the elastic layer exhibits the pattern having the overshoot portion described above, the first main surface 21s1 shakes significantly when the intermediate transfer belt 21B described above is deformed. As the first main surface 21s1 expands and contracts, the positional relationship between the intermediate transfer belt 21B and the toner T adhering to the intermediate transfer belt 21B (that is, the distance between the toner T and the first main surface 21s1 and its contact area, etc. ) Changes, and the adhesive force of the toner T to the intermediate transfer belt 21B decreases. Therefore, the effect of further lowering the applied voltage at which the transfer efficiency is maximized in the recess 1002 can be obtained. This effect is not known from the past, but is an effect discovered by the present inventor, and here, this effect is referred to as an adhesive force reducing effect.

As shown in FIG. 15, the applied voltage V2 at which the transfer efficiency is maximized in the recess 1002 is obtained only from the above-mentioned inelastic layer by exerting such a follow-up deformation effect or an effect of reducing the adhesive force in addition to the effect. When the intermediate transfer belt 21A is used, the transfer efficiency is smaller than the applied voltage V1 at which the transfer efficiency is maximized in the recess 1002. In FIG. 15, reference numeral c1002 (21B) is attached to a curve showing the relationship between the applied voltage and the transfer efficiency with respect to the recess 1002.

Therefore, as compared with the case of using the intermediate transfer belt 21A composed of only the non-elastic layer described above, the transfer efficiency in the concave portion 1002 becomes higher in the vicinity of the applied voltage V0, and the image in the concave portion 1002 and the convex portion 1003 of the embossed paper 1000 The density difference becomes small, and a higher quality image can be obtained.

The adhesive force reducing effect is particularly remarkable in the intermediate transfer belt 21 which exhibits a pattern having an overshoot portion in the transition of the displacement amount measured by using the displacement amount measuring device 100. The degree of effect obtained is largely related to the overshoot portion of the pattern described above.

That is, when the above-mentioned primary displacement rate k1 [μm / s] is sufficiently large, the first main surface of the intermediate transfer belt 21 is primarily displaced at high speed in the early stage when the intermediate transfer belt 21 passes through the nip portion. Therefore, a high adhesive force reducing effect can be obtained. When the overshoot rate E [−] described above is sufficiently large, the first main surface of the intermediate transfer belt 21 is deformed at high speed and in a complicated manner in the middle stage where the intermediate transfer belt 21 passes through the nip portion. , A high adhesive force reducing effect can be obtained.

When the above-mentioned secondary displacement rate k2 [μm / s] is sufficiently large, the first main surface of the intermediate transfer belt 21 is secondarily displaced at high speed at the final stage when the intermediate transfer belt 21 passes through the nip portion. Therefore, a high adhesive force reducing effect can be obtained.

Here, with reference to FIG. 15, the difference between the applied voltage V1 and the applied voltage V2 described above is defined as ΔVtotal, and the reduction width of the applied voltage at which the transfer efficiency is maximized in the recess 1002 due to the following deformation effect described above is defined as ΔVgap. When the reduction width of the applied voltage that maximizes the transfer efficiency in the recess 1002 due to the above-mentioned adhesive force reducing effect is ΔVadh, the relationship of ΔVtotal = ΔVgap + ΔVadh is established.

Since ΔVtotal is represented by V1-V2 as described above, ΔVadh is represented by V1-V2-ΔVgap. Both V1 and V2 have unique values for each intermediate transfer belt 21, but the values can be derived experimentally. ΔVgap can be experimentally derived from the displacement amount y of the measurement region MR of the belt S measured in the evaluation method of the intermediate transfer belt 21 using the displacement amount measuring device 100 described above. Therefore, it is possible to calculate ΔVadh from these values.

<Experiment confirming the relationship between the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2, and ΔVadh>
The present inventor has produced a large number of belts having different elastic layer compositions by preparing various types and amounts of resins, additives, cross-linking agents, etc. contained in the elastic layer, and these are used in the displacement amount measuring device 100 described above. Each belt was evaluated based on the evaluation method of the belts, and the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2 of each belt were obtained.

From these, a plurality of belts having different overshoot rates E, a primary displacement rate k1 and a secondary displacement rate k2 were selected, and the transfer efficiency for the recesses of the embossed paper was experimentally measured using the selected multiple belts. By doing so, the value of V2 of each belt was obtained. Here, when measuring the V2, the displacement amount measuring device 100 shown in FIG. 5 is used, and the belt to be measured and the embossed paper are sandwiched between the lower block 110 and the upper block 120 and arranged on the lower side. A voltage is applied to the lower block 110 and the upper block 120 so that a potential difference is generated between the block 110 and the upper block 120, and then the applied voltage is variously changed to obtain the highest transfer efficiency. Was V2.

Further, the same measurement is performed using an inelastic belt to obtain the value of V1 and from the displacement amount of the measurement region MR of each belt measured in the evaluation method of the intermediate transfer belt 21 using the displacement amount measuring device 100. ΔVgap was calculated by calculation.

Based on the data of each of these belts, the relationship between the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2, and ΔVadh was organized. FIG. 16 is a graph showing the relationship between the overshoot rate E and ΔVadh. FIG. 17 is a graph showing the relationship between the primary displacement rate k1 and ΔVadh. FIG. 18 is a graph showing the relationship between the secondary displacement rate k2 and ΔVadh.

As can be understood from FIG. 16, in the relationship between the overshoot rate E and ΔVadh, ΔVadh is less than 50 [V] in the range of 0 ≦ E <0.2, and the effect of reducing the adhesive force is almost obtained. I was able to confirm that there was no such thing. On the other hand, in the range of 0.2 ≦ E, ΔVadh tends to increase by more than 50 [V] as the value of the overshoot rate E increases, and it was confirmed that a high adhesive force reducing effect can be obtained. ..

As can be understood from FIG. 17, in the relationship between the primary displacement rate k1 and ΔVadh, ΔVadh is less than 50 [V] in the range of 0 ≦ k1 <60, and the effect of reducing the adhesive force is hardly obtained. Was confirmed. On the other hand, in the range of 60 ≦ k1, it was confirmed that ΔVadh tends to increase by more than 50 [V] as the value of the primary displacement rate k1 increases, and a high adhesive force reducing effect can be obtained.

As can be understood from FIG. 18, in the relationship between the secondary displacement rate k2 and ΔVadh, ΔVadh is less than 50 [V] in the range of 0 ≦ k2 <6, and the effect of reducing the adhesive force is hardly obtained. I was able to confirm that. On the other hand, in the range of 6 ≦ k2, ΔVadh tends to increase by more than 50 [V] as the value of the secondary displacement rate k2 increases, and it was confirmed that a high adhesive force reducing effect can be obtained.

The above results are the basis for determining the lower limit values of the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2 under the first to third conditions described above, and are the basis for determining the lower limit values of the first to third conditions. By satisfying any of the conditions on the lower limit value side, it is shown that a sufficient adhesive force reducing effect can be obtained in addition to the above-mentioned follow-up deformation effect.

<Effect of bending the intermediate transfer belt 21>
When an image is formed using the intermediate transfer belt 21 exhibiting a pattern having an overshoot portion, the intermediate transfer belt 21 is bent in a specific direction at the nip portion, so that an overshoot is likely to occur. That is, the transferability changes greatly depending on the bending state of the intermediate transfer belt 21. The bending state of the intermediate transfer belt 21 has three patterns: concave bending, convex bending, and straight bending. Hereinafter, three patterns in the bent state of the intermediate transfer belt 21 will be described.

(Concave bent state)
FIG. 19 is a diagram showing an intermediate transfer belt 21 in a concavely bent state in the primary transfer portion. In the primary transfer portion, the primary transfer nip portion N1 is formed by the photoconductor drum 13 and the primary transfer roller 22. The concave bending state in the primary transfer portion means that in the primary transfer nip portion N1, the first main surface 21s1 (toner supporting surface) on the side close to the photoconductor drum 13 contracts, and the second side close to the opposing roller 24. This is a state in which the main surface 21s2 is bent so as to extend.

When the hardness of the surface of the photoconductor drum 13 is higher than the hardness of the surface of the primary transfer roller 22, the intermediate transfer belt 21 of the portion sandwiched between the photoconductor drum 13 and the primary transfer roller 22 is the surface of the photoconductor drum 13. It will be curved along. The hardness of the surfaces of the photoconductor drum 13 and the primary transfer roller 22 can be measured using a micro rubber hardness tester (for example, manufactured by Polymer Instruments Co., Ltd .: MD-1).

FIG. 20 is a diagram showing an intermediate transfer belt 21 in a concavely bent state in the secondary transfer portion. In the secondary transfer portion, the secondary transfer nip portion N2 is formed by the secondary transfer roller 33 and the opposing roller 24. The concave bending state in the secondary transfer portion means that in the secondary transfer nip portion N2, the first main surface 21s1 (toner supporting surface) on the side close to the secondary transfer roller 33 contracts, and the side close to the opposing roller 24. This is a state in which a second main surface 21s2 is bent so as to extend.

The secondary transfer roller 33 is pressed against the opposing roller 24 via the recording medium 1000 and the intermediate transfer belt 21. By pressing the secondary transfer roller 33 toward the opposing roller 24 having the elastic portion 24b on the outer layer, a part of the secondary transfer roller 33 bites into the opposing roller 24 via the recording medium 1000 and the intermediate transfer belt 21. It may take the form of. As a result, the intermediate transfer belt 21 in the secondary transfer nip portion N2 is in a concavely bent state.

(Convex bent state)
Hereinafter, the convex bending state in the secondary transfer unit will be described. The description of the convex bending state in the primary transfer section will be omitted because it can be described in the same manner as the convex bending state in the secondary transfer section.

FIG. 21 is a diagram showing an intermediate transfer belt 21 in a convexly bent state in the secondary transfer portion. In the convex bending state, in the secondary transfer nip portion N2, the first main surface 21s1 (toner supporting surface) on the side close to the secondary transfer roller 33 extends, and the second main surface 21s2 on the side close to the opposing roller 24. Is a state in which is bent so as to contract.

When a roller having an elastic portion 33b in the outer layer is used as the secondary transfer roller 33, the secondary transfer roller 33 is pressed toward the opposing roller 24 so that a part of the opposing roller 24 is an intermediate transfer belt. It may be in the form of biting into the secondary transfer roller 33 via the 21 and the recording medium 1000. As a result, the intermediate transfer belt 21 in the secondary transfer nip portion N2 is in a convex bending state.

(Straight state)
FIG. 22 is a diagram showing an intermediate transfer belt 21 in a straight state in the secondary transfer section. The straight state is a state in which the intermediate transfer belt 21 is a straight line or a substantially straight line in the secondary transfer nip portion N2. The straight state is a state between the concave bending state and the convex bending state.

When both the secondary transfer roller 33 and the opposing roller 24 are rollers having an elastic portion in the outer layer and the diameter and hardness of both rollers are substantially the same, the intermediate transfer belt 21 is straight or straight in the secondary transfer nip portion N2. , Almost straight.

Even if there is a difference in hardness between the secondary transfer roller 33 and the opposing roller 24, the straight state may be obtained. For example, when the secondary transfer roller 33 is a rigid roller but has a very large diameter, the intermediate transfer belt 21 has a concave bending shape that is almost straight at the secondary transfer nip portion N2. Is also regarded as a straight state.

<Effect of concave bending>
FIG. 23 is an enlarged view of the region surrounded by XXIII in the secondary transfer nip portion N2 of FIG. 20. The direction along the first main surface 21s1 in the figure is defined as the in-plane direction DR1. In the concave bending state, a force is applied in the direction in which the first main surface 21s1 is compressed in the in-plane direction DR1 due to the difference in curvature between the first main surface 21s1 and the second main surface 21s2. That is, the length of the second main surface 21s2 (double-headed arrow A in FIG. 23) remains unchanged, and a force is applied so that the length of the first main surface 21s1 (double-headed arrow B in FIG. 23) is compressed.

Since rubber is generally an incompressible object, it tends to deform in a direction that maintains its volume when pressure is applied. Therefore, when the first main surface 21s1 is subjected to a force in the direction of being compressed in the in-plane direction DR1 due to the concave bending, if there is a recess on the surface of the recording medium 1000, the direction in which the elastic layer 21b swells toward the recess ( It becomes easy to be deformed as shown by the arrow C) in FIG.

FIG. 24 is a diagram showing a state in which the intermediate transfer belt 21 in the concavely bent state is pressurized. Due to the pressure contact between the secondary transfer roller 33 and the opposing roller 24, pressure is applied so that the intermediate transfer belt 21 is pressed against the recording medium 1000, and the elastic layer 21b facing the convex portion 1003 of the recording medium 1000 having irregularities (FIG. 24). Strong pressure is applied to the double-headed arrow D) inside.

On the other hand, since the elastic layer 21b facing the concave portion 1002 of the recording medium 1000 having unevenness does not receive direct pressure, the elastic layer 21b is a portion facing the concave portion 1002 from the elastic layer 21b facing the convex portion 1003 of the recording medium 1000. (Arrow E in FIG. 24), resulting in the elastic layer 21b bulging toward the recess 1002 (arrow F in FIG. 24).

Therefore, when the pressure is applied in the concavely bent state, the vicinity of the first main surface 21s1 facing the concave portion 1002 is pressurized in a state of being easily deformed, and the internal stress momentarily causes a large strain to cause the concave portion. The elastic layer 21b, which concentrates toward the portion facing the 1002 and faces the recess 1002, momentarily swells greatly. By applying pressure in the concavely bent state in this way, overshoot is likely to occur.

<Both suppression of roughness in the primary transfer section and good concave transferability in the secondary transfer section>
In the secondary transfer section, the elastic layer of the intermediate transfer belt having an elastic layer is deformed to follow the recesses of the paper with respect to paper such as embossed paper having irregularities on the surface, so that the transferability to the recesses of the paper is enhanced. .. When forming an image on a paper such as embossed paper having an uneven surface, it is necessary to apply a relatively high pressure at the secondary transfer portion to greatly deform the elastic layer.

On the other hand, in the primary transfer section, when the intermediate transfer belt having the elastic layer is pressed against the photoconductor drum by the primary transfer roller, the surface of the photoconductor drum is smooth, so that it looks like a recess of paper in the secondary transfer section. , There is no space to absorb the deformation of the elastic layer of the intermediate transfer belt. Therefore, the elastic layer when pressure is applied from the primary transfer roller is deformed toward the space before and after the primary transfer nip portion.

When the elastic layer of the intermediate transfer belt is excessively deformed, the toner image transferred to the intermediate transfer belt is disturbed or the amount of charge of the toner changes. Therefore, in the primary transfer portion, it is desirable to relatively reduce the pressure applied to the intermediate transfer belt to suppress the deformation of the elastic layer.

When a conventional intermediate transfer belt is used, it is difficult to achieve both transferability to recesses in paper such as embossed paper having irregularities on the surface and suppression of roughness. The reason for this will be described in detail below.

<Conventional elastic belt>
FIG. 25 is a graph showing the relationship between the applied pressure on the belt A and the belt B and the amount of deformation. The hardness of the elastic layer of the belt A and the belt B is different. The hardness of the belt A is larger than the hardness of the belt B. Belt A is less likely to be deformed than Belt B.

The amount of deformation on the vertical axis is the amount of displacement measured after a sufficient time has passed after applying pressure, unlike the normal displacement amount measurement using the displacement amount measuring device 100 described with reference to FIG. The applied pressure was changed to 50 kPa, 100 kPa, 150 kPa, and 200 kPa, and the amount of deformation of the belt with respect to each applied pressure was recorded.

The straight line in FIG. 25 is obtained by fitting the measurement plot of the amount of deformation with respect to each applied pressure to a straight line passing through the origin. The amount of deformation is proportional to the applied pressure. The amount of change in the amount of deformation (inclination of the straight line in FIG. 25) with respect to the amount of change in the applied pressure is larger than that of the belt A because the belt B, which is a soft belt, is more easily deformed.

(Relationship between applied pressure and roughness in the primary transfer section)
Using the above belts A and B as intermediate transfer belts, the relationship between the applied pressure and the roughness was investigated while changing the applied pressure in the primary transfer portion of the image forming apparatus.

An image forming apparatus (digital printing machine: bizhub PRESS C8000) manufactured by Konica Minolta Co., Ltd. was used for the evaluation of the roughness, and the intermediate transfer belt provided in the image forming apparatus (digital printing machine: bizhub PRESS C8000) was replaced with the above-mentioned belts A and B in the primary transfer unit. Image formation was actually performed by changing the applied pressure. A solid image was printed, and the roughness of the solid image was observed.

By setting the conditions (pressure, bias, etc.) in the secondary transfer section to the optimum conditions so that the toner image can be transferred onto the paper without disturbing the toner image, the roughness caused by the primary transfer section was evaluated.

As the paper, coated paper manufactured by Oji Paper Co., Ltd., OK Top Coat + was used. The basis weight of this coated paper was 104.7 [g / m ² ].

FIG. 26 is a graph showing the evaluation results of roughness with respect to the respective applied pressures in the primary transfer unit when the belt A and the belt B are used as the intermediate transfer belts of the image forming apparatus. On the graph showing the relationship between the applied pressure and the amount of deformation in the belt A and the belt B described with reference to FIG. 25, the evaluation result of the roughness at each applied pressure is indicated by ○ (permissible level or higher) or × (impossible level). There is.

For example, when the applied pressure of the belt A is 50 [kPa], the amount of deformation measured by the displacement amount measuring device 100 is about 2 [μm]. When the belt A was used as the intermediate transfer belt of the image forming apparatus in which the applied pressure in the primary transfer unit was set to 50 [kPa], the evaluation result of the roughness was above the permissible level. In this case, the positions of x = 50 [kPa] and y = 2 [μm] in FIG. 26 are marked with a circle. From the evaluation result of the roughness in FIG. 26, it can be said that it is necessary to suppress the deformation amount to about 5 [μm] or less in order to suppress the roughness.

In order to suppress the roughness, it is better to suppress the amount of deformation as much as possible, and therefore it is better to set the applied pressure to be small. However, when the applied pressure is reduced, the pressure contact state becomes unstable at the primary transfer nip portion, and image unevenness tends to occur in the axial direction of the photoconductor drum. Under the image output condition, when the applied pressure is less than 48 [kPa], image unevenness in the axial direction is likely to occur.

FIG. 27 is a graph showing a range of applied pressure and deformation amount that can suppress roughness while suppressing the occurrence of image unevenness in the axial direction. The range indicated by the shaded area U, in which the amount of deformation is 5 [μm] or less and the applied pressure is 48 [kPa] or more, is a suitable condition.

(Relationship between applied pressure in secondary transfer section and concave transferability)
Using belt A and belt B as intermediate transfer belts, the relationship between the applied pressure and the transferability of the uneven paper to the recesses (recess transferability) was investigated while changing the applied pressure in the secondary transfer section of the image forming apparatus. It was.

FIG. 28 is a graph showing the evaluation results of the recess transferability with respect to the respective applied pressures in the secondary transfer section when the belt A and the belt B are used as the intermediate transfer belts of the image forming apparatus. On the graph showing the relationship between the applied pressure and the amount of deformation in the belt A and the belt B described with reference to FIG. 25, the evaluation result of the recess transferability at each applied pressure is indicated by ○ (permissible level or higher) or × (impossible level). Shown.

An image forming apparatus (digital printing machine: bizhub PRESS C8000) manufactured by Konica Minolta Co., Ltd. was used for the evaluation of the concave transferability, and the intermediate transfer belt provided therein was replaced with the above-mentioned belts A and B to perform secondary printing. Image formation was actually performed by changing the applied pressure in the transfer section.

The paper used was embossed paper manufactured by Tokushu Tokai Paper Co., Ltd., and the product name Rezac 66 (Rezac is a registered trademark). The basis weight of this embossed paper was 302 [g / m ² ].

A solid image is printed on this paper, and when making a judgment, the reflection density of the sharp and deep recesses (grooves) and the reflection density of the protrusions are measured using a microdensitometer, and the difference between these densities is measured. Calculated. If the concentration difference is less than 0.25, it is judged as "good", and if the concentration difference is 0.25 or more and less than 0.40, it is judged as "OK", and the concentration difference is When it was an unacceptable level of 0.40 or more, it was judged as "impossible".

By setting the conditions (pressure, bias, etc.) in the primary transfer section to the optimum conditions so that the toner image can be transferred onto the intermediate transfer belt without disturbing the toner image, the transfer to uneven paper caused by the secondary transfer section is performed. Sexual evaluation was performed.

From the evaluation result of the concave transferability of FIG. 28, it can be said that the deformation amount needs to be about 19 [μm] or more in order to secure good concave transferability.

In order to ensure good concave transferability, it is better to increase the amount of deformation as much as possible, and for that purpose, it is better to increase the applied pressure. However, when the applied pressure is increased, fine line crushing is likely to occur. Under the image output condition, when the applied pressure exceeds 350 [kPa], fine line crushing is likely to occur.

FIG. 29 is a graph showing a range of applied pressure and deformation amount that can secure good concave transferability while suppressing thin line crushing. The range shown by the shaded portion V in FIG. 29, in which the deformation amount is 19 [μm] or more and the applied pressure is 350 [kPa] or less, is a suitable condition.

(Area of optimum conditions for image formation)
FIG. 30 is a graph showing a range X in which roughness can be suppressed and a range Y in which good recess transferability can be ensured while suppressing the occurrence of image unevenness in the axial direction and crushing of fine lines.

The upper limit of the amount of deformation that can suppress rattling in the primary transfer section is indicated by εth1. The shaded portion X in FIG. 30 in which the amount of deformation is εth1 or less and is surrounded by the lower limit applied pressure for suppressing the occurrence of image unevenness in the axial direction and the upper limit applied pressure for suppressing thin line crushing. Is the region where the conditions of the primary transfer unit can be set.

The lower limit of the amount of deformation that can secure the concave transferability in the secondary transfer is indicated by εth2. The shaded portion Y in FIG. 30 in which the amount of deformation is εth2 or more and is surrounded by the lower limit applied pressure for suppressing the occurrence of image unevenness in the axial direction and the upper limit applied pressure for suppressing fine line crushing. Is the region where the conditions of the secondary transfer unit can be set.

When the belt A, which is relatively hard and hard to be deformed, has an overlapping portion W1 in the region of X, the condition of the applied pressure in the primary transfer portion is set in the range of W1 by using the belt A. Roughness can be suppressed while suppressing the occurrence of image unevenness in the axial direction in the transfer nip portion.

However, when the belt A is used, there is no overlapping portion in the region of Y. Therefore, in the secondary transfer section, it is not possible to set the conditions of the applied pressure so that the concave transferability can be ensured while suppressing the crushing of fine lines.

On the other hand, when the belt B, which is relatively soft and easily deformed, has an overlapping portion W2 in the Y region, the applied pressure in the secondary transfer portion is set in the range of W2 by using the belt B to make a thin line. Good recess transferability can be ensured without causing crushing.

However, when the belt B is used, there is no overlapping portion in the region of X. Therefore, it is not possible to set the conditions in the primary transfer section so as to suppress the roughness while suppressing the occurrence of image unevenness in the axial direction in the primary transfer nip section.

As described above, when the conventional elastic belts A and B are used, only one of the conditions of ensuring good recess transferability and suppressing roughness can be satisfied, and both conditions are satisfied. Could not be set.

<Belt exhibiting overshoot deformation in the present invention>
The present inventor appropriately utilizes the peculiar property of the intermediate transfer belt 21 exhibiting the pattern having the overshoot portion shown in FIG. 11, to suppress the roughness in the primary transfer portion and to perform good concave transfer in the secondary transfer portion. I found that it is possible to achieve both sex. The "displacement amount" in the following description means the displacement amount when the belt is measured by using the displacement amount measuring device 100.

FIG. 31 is a graph showing the time course of the displacement amount in the measurement region of the belt exhibiting overshoot deformation. The maximum displacement amount δ [μm] (maximum value a of the displacement measurement in the displacement amount measuring device 100 in FIG. 11) can be considered as the sum of _{the transient component ε t} [μm] and the stationary component ε _{s [μm].}

The steady-state component ε _s can be obtained as the convergence value b of the displacement measurement in the displacement amount measuring device 100 of FIG. The transient component ε _t can be obtained as the difference between the maximum value a and the convergence value b of the displacement measurement in the displacement amount measuring device 100 of FIG.

(Transient component ε _t )
FIG. 32 is a graph simply showing four patterns of pressure applied to the belt. Four patterns are applied in which the maximum pressure is p1 [kPa] or p2 [kPa] and the pressurization rate (increase in pressure per unit time) is s1 [kPa / ms] or s2 [kPa / ms]. Consider the case.

The reference is the pattern (1), the maximum pressure is p1 and the pressurizing speed is s1. In the pattern (2), the pressurizing speed is s1 which is the same as that of the pattern (1), and the maximum pressure is p2 (twice the p1). In the pattern (3), the maximum pressure is p1 which is the same as the pattern (1), and the pressurizing speed is s2 (twice the s1). In the pattern (4), the maximum pressure is p2 and the pressurizing speed is s2.

FIG. 33 is a graph showing the _{transient component ε t} in each case when the pressures of the patterns (1) to (4) are applied. The transient component ε _t increases in proportion to the maximum pressure p. Since the maximum pressure of the pattern (2) is twice that of the pattern (1), the transient component ε _t is also twice that of the pattern (1). Since the maximum pressure of the pattern (4) is twice that of the pattern (3), the transient component ε _t is also twice that of the pattern (3).

Further, the transient component ε _t increases or decreases depending on the pressurization rate s. The patterns (1) and (2) and the patterns (3) and (4) have pressurizing speeds s1 and s2, respectively. _{The transient component ε t} becomes larger when the pressures of the patterns (3) and (4) having a higher pressurizing speed s are applied than when the pressures of the patterns (1) and (2) are applied. The transient component ε _t increases or decreases in proportion to the maximum pressure p, and increases or decreases depending on the pressurizing speed s.

FIG. 34 is a graph showing the relationship between the pressurizing speed s and the increase amount Δε _t / Δp [μm / kPa] (slope of a line in FIG. 33) of the _{transient component ε t} with respect to the increase amount of the maximum pressure p. .. Δε _t / Δp increases or decreases in proportion to the pressurizing speed s.

As shown in FIG. 33, transients epsilon _t since transients epsilon _t is proportional to the maximum pressure p is expressed by equation (1).

ε _t = k × p (k: coefficient) ・ ・ ・ (1)
As shown in FIG. 34, since Δε _t / Δp (that is, the coefficient k of the equation (1)) is proportional to the pressurizing speed s, k is expressed as the equation (2).

k = α × s (α: coefficient) ・ ・ ・ (2)
The equation (1) and the equation (2) can be summarized as the equation (3).

ε _t = α × s × p ・ ・ ・ (3)
The transient component ε _t is proportional to the product of the maximum pressure p and the pressurizing speed s. Therefore, as both the maximum pressure p and the pressurizing speed s are increased, ε _t increases quadratically. For example, in the pattern (4), the maximum pressure p is doubled and the pressurizing speed s is doubled with respect to (1). Therefore, the transient component ε _t of the pattern (4) is the pattern (1). ) Is four times the transient component ε _t.

(Standing component ε _s )
FIG. 35 is a graph showing the _{steady-state component ε s} in each case when the pressures of the patterns (1) to (4) are applied. The steady component ε _{s is} also proportional to the maximum pressure p, like the transient component ε _t. Since the maximum pressure of the pattern (2) is twice that of the pattern (1), the steady-state component ε _s is also twice that of the pattern (1). Since the maximum pressure p of the pattern (4) is twice that of the pattern (3), the steady-state component ε _s is also twice that of the pattern (3).

The steady-state component ε _s does not increase or decrease depending on the pressurization rate s. Regardless of whether the pressurizing speed s is s1 or s2, the steady-state component ε _{s with} respect to the maximum pressure p is substantially the same.

FIG. 36 is a graph showing the relationship between the pressurizing speed s and the increase amount Δε _s / Δp [μm / kPa] (slope of a line in FIG. 35) of the _{steady component ε s} with respect to the increase amount of the maximum pressure p. .. The steady-state component ε _s increases and decreases in proportion to the maximum pressure p, but _{unlike the case of the transient component ε t} , it does not depend on the pressurizing speed s.

As shown in FIG. 35, the steady-state component ε _s is proportional to the maximum pressure p and does not depend on the pressurizing speed s, and is therefore expressed by the equation (4).

ε _s = β × p (β: coefficient) ・ ・ ・ (4)
From equations (3) and (4), the maximum displacement amount δ is expressed as in equation (5).

δ = ε _t + ε _s
= Α × s × p + β × p (α, β: coefficient determined by rubber viscoelasticity, film thickness, etc.) ・ ・ ・ (5)
Since the transient component ε _t is proportional to the product of p and s, the maximum displacement amount δ increases or decreases in a quadratic function. The image quality can be kept good by adjusting the maximum pressure p and the pressurizing speed s and adjusting the maximum displacement amount δ.

(Parameters for adjusting the maximum displacement amount δ (pressing pressure P, roller radius r))
FIG. 37 is a diagram showing how one roller presses against the other roller. As a parameter in the image forming apparatus 1, attention was paid to the ratio (P / r) of the pressing force P [N] and the roller radius r [mm]. P is the pressing force between the rollers, and r is the radius of the harder roller.

In the primary transfer unit, the pressing force when the primary transfer roller 22 is pressed against the photoconductor drum 13 is P, and the radius of the photoconductor drum 13 is r. In the secondary transfer unit, the pressing force when the secondary transfer roller 33 is pressed against the opposing roller 24 is P, and the radius of the secondary transfer roller 33 is r.

The present inventors have found that the maximum displacement amount δ increases or decreases quadratically with respect to P / r within a range in which the image forming apparatus 1 can be preferably used. The reason will be explained below.

FIG. 38 is a graph showing the time change of the pressure received by the intermediate transfer belt 21 passing through the nip portion when the pressing force P is set to PR1 and PR2. Let p1 be the maximum pressure when the pressing pressure P is PR1, and p2 be the maximum pressure when the pressing pressure P is PR2. PR2 is twice as much as PR1 and p2 is twice as much as p1. When the roller radius r is fixed and the pressing force P is doubled (PR1 to PR2), the maximum pressure p is approximately doubled (p1 to p2). And the pressurization speed s (inclination of the thick line in FIG. 38) is also about doubled. The pressurization rate in this case is the pressurization rate between 20% of the maximum pressure p and the maximum pressure p. Since both the maximum pressure p and the pressurizing speed s are approximately doubled, the transient component ε _t is approximately quadrupled from Eq. (3).

FIG. 39 is a graph showing the relationship between the pressing force P and the transient component ε _t. The transient component ε _t increases or decreases quadratically with respect to the pressing force P. This is because the maximum pressure p and the pressurizing speed s both increase or decrease as the pressing force P increases or decreases.

FIG. 40 is a diagram showing how one roller (radius r2) having a relatively small radius is pressed against the other roller. FIG. 41 is a diagram showing a state in which one roller (radius r1) having a radius twice the radius (r2) of the roller shown in FIG. 40 is pressed against the other roller. FIG. 42 is a graph showing the time change of the pressure received by the intermediate transfer belt 21 passing through the nip portion when the rollers of FIGS. 40 and 41 are used. Let p1 be the maximum pressure p when the roller radius r is r1, and p2 be the maximum pressure p when the roller radius r is r2. r2 is half of r1 and p2 is twice as much as p1.

When the pressing force P is fixed and the roller radius r is halved (r1 to r2), the pressure is concentrated in the center, so that the maximum pressure p is about doubled and the pressurizing speed s is also about doubled. Since both the maximum pressure p and the pressurizing speed s are approximately doubled, the transient component ε _t is approximately quadrupled from Eq. (3).

FIG. 43 is a graph showing the relationship between the reciprocal 1 / r [mm ^-1 ] of the roller radius r and the transient component ε _t. The transient component ε _t increases or decreases quadratically with respect to the reciprocal 1 / r of the roller radius r. This is because the maximum pressure p and the pressurizing speed s both increase or decrease as the roller radius r increases or decreases.

FIG. 44 is a graph showing the relationship between P / r and the transient component ε _t. When the roller radius r is fixed, the transient component ε _t increases or decreases in proportion to the square of the pressing force P, and when the pressing force P is fixed, it increases or decreases in proportion to the square of the reciprocal 1 / r of the roller radius r. To do. Therefore, the transient component ε _t increases or decreases in proportion to the square of P / r.

<Comparison between belts with overshoot deformation and belts without overshoot deformation>
(Belt that does not exhibit overshoot deformation)
FIG. 45 is a graph showing the relationship between P / r and the maximum displacement amount δ in the belts A and B that do not exhibit overshoot deformation and the belt P that exhibits overshoot deformation. Let εth1 be the upper limit maximum displacement amount δ for suppressing rattling, and εth2 be the lower limit maximum displacement amount δ for ensuring good recess transferability. P1 / r1 is a lower limit value for suppressing image unevenness in the axial direction. P2 / r2 is an upper limit value for suppressing thin line crushing.

In a belt that does not show overshoot deformation, the transient component ε _t is approximately zero. Therefore, from the equation (5), the maximum displacement amount δ is expressed only by the _{steady component ε s as in the following equation (6).}

δ ≒ ε _s
= Β × p ・ ・ ・ (6)
As described with reference to FIG. 25, the amount of deformation (maximum displacement amount δ) of the belts A and B that do not exhibit overshoot deformation is proportional to the maximum pressure p. As shown in FIGS. 38 and 42, the maximum pressure p is substantially proportional to the pressing force P and substantially proportional to 1 / r, and therefore is substantially proportional to P / r. Belts A and B that do not exhibit overshoot deformation exhibit a characteristic that the maximum displacement amount δ changes so as to be substantially proportional to P / r.

As shown in FIG. 45, the maximum displacement amount δ is εth1 or less, and the region of the shaded area X in FIG. 45 surrounded by P1 / r1 and P2 / r2 is the condition-settable region in the primary transfer unit. is there. The region of the shaded area Y in FIG. 45 surrounded by P1 / r1 and P2 / r2 when the maximum displacement amount δ is εth2 or more is a condition-settable region in the secondary transfer unit.

As described with reference to FIG. 30, in the belts A and B that do not show overshoot deformation, in relation to the amount of deformation (maximum displacement amount δ) with respect to the applied pressure, both suppression of rattling and ensuring good recess transferability are achieved. It was not possible to set the conditions for such an appropriate applied pressure.

Similarly, the relationship of the maximum displacement amount δ with respect to P / r cannot be set to an appropriate condition that both suppresses rattling and secures good recess transferability.

(Belt exhibiting overshoot deformation)
In the belt P exhibiting overshoot deformation, as shown in FIG. 44, the transient component ε _t increases / decreases in a quadratic function with respect to P / r. That is, the maximum displacement amount δ (= transient component ε _t + steady component ε _s ) also increases or decreases in a quadratic function.

As shown in FIG. 45, the belt P exhibiting overshoot deformation has a small increase in the maximum displacement amount δ with respect to an increase in P / r in a region where P / r is small, and P in a region where P / r is large. It shows a non-linear characteristic that the amount of increase in the maximum displacement amount δ with respect to the amount of increase in / r is large.

Due to the above characteristics, it is possible to sufficiently suppress the maximum displacement amount δ in the primary transfer portion and suppress the roughness while the condition is P / r so that the image unevenness in the axial direction can be suppressed. Further, the maximum displacement amount δ can be increased in the secondary transfer portion to ensure good recess transferability, even though the condition is P / r so that the fine line crushing can be suppressed.

As described with reference to FIG. 14, the belt exhibiting overshoot deformation has an adhesive force reducing effect. When the belt exhibits overshoot deformation, the surface of the belt expands and contracts significantly in a short time, so that the adhesive force of the toner is reduced. As a result of reducing the adhesive force of the toner, the toner is easily moved to the concave portion of the paper. Due to this effect, it is possible to secure good recess transferability with a smaller amount of deformation as compared with a conventional belt that does not exhibit overshoot deformation.

As shown in FIG. 45, when the belt P exhibiting overshoot deformation is used, the maximum displacement amount δ of the lower limit for ensuring good recess transferability is more than εth2 due to the adhesive force reducing effect described above. Is also small εth2A.

Therefore, a condition for ensuring good recess transferability even in the shaded area Z in FIG. 45 surrounded by P1 / r1 and P2 / r2 when the maximum displacement amount δ is εth2A or more and εth2 or less. The setting becomes possible, and the condition-settable area for ensuring good concave transferability in the secondary transfer portion is expanded.

When a belt P exhibiting overshoot deformation is used, the value of P / r in the primary transfer portion and the secondary transfer portion is set within the range of the overlapping portion W1 in the region of X and the overlapping portion W3 in the region of Z. By doing so, it is possible to achieve both suppression of roughness and good concave transferability.

(Parameters in the image forming apparatus 1 for adjusting the maximum displacement amount δ (linear pressure P _x , belt transport speed V _sys ))
FIG. 46 is a schematic view of the inside of the image forming apparatus 1 showing how the intermediate transfer belt 21 passes between the rollers. FIG. 47 is a graph showing the pressure distribution of the linear pressure of the intermediate transfer belt 21 in the transport direction DR2 at the nip portion N shown in FIG. FIG. 48 is a graph showing the time change of the linear pressure received by the intermediate transfer belt 21 passing through the nip portion N shown in FIG.

As shown in FIG. 46, the nip portion N is formed by the roller. The value obtained by dividing the pressing force P by the length L [mm] of the nip portion N in the roller axial direction DR3 is defined as the linear pressure P _x (= P / L) [N / mm]. As shown in FIGS. 47 and 48, the distance of 20% and a position of the maximum line pressure P _x in the nip portion N to the position of the maximum line pressure P _x in the nip portion N and w [mm], between w Let N [s] be the time for the intermediate transfer belt 21 to pass through. Further, the belt transfer speed, which is the transfer speed of the intermediate transfer belt 21, is set to V _sys [mm / s].

Assuming that the pressurizing speed at the linear pressure is sa, the pressurizing speed sa at the linear pressure is represented by the following equation (7).

sa = (P _x −0.2 × P _x ) / N
= (0.8 × P _x ) / (w / V _sys ) ・ ・ ・ (7)
Here, since it can be regarded as w∝r, it becomes sa∝V _sys × 0.8 × P _× / r.

Further, it can be regarded as sa ∝ s, and since it is p ∝ P _x / r, the maximum displacement amount δ at the actual nip portion is expressed by the following equation (8).

δ = ε _t + ε _s
= Α × s × p + β × p
= Α × c × V _sys × (P _x / r) × (P _x / r) + β × d × (P _x / r) (c, d: coefficient)
= Α × c × V _sys × γ ² + β × d × γ ・ ・ ・ (8) (γ = P _x / r)
As shown in equation (8), the maximum displacement amount δ is expressed as a function of the parameter γ (= P _{x / r) consisting of the linear pressure P x} and the roller radius r and the belt transport speed V _sys.

_{(Indicator value ε c} indicating the degree of influence on image quality)
Here, if the index in which the contribution of the transient component ε _t and the steady component ε _s to the quality (roughness, concave transferability) is taken as δ _j , δ _j is expressed by the equation (9).

δ _j = α × c × e × V _sys × γ ² + β × d × f × γ (e, f: coefficients representing the contribution of the _{transient component ε t} and the steady component ε _{s, respectively) (9)}
Dividing both sides of the equation (9) by β × d × f and summarizing the coefficients by A (= α × c × e / (β × d × f)), the following equation (10) is obtained.

δ _j / (β × d × f) = A × V _sys × γ ² + γ
ε _c = A × V _sys × γ ² + γ (ε _c = δ _j / (β × d × f)) ・ ・ ・ (10)
The left side ε _c of the formula (10) is an index value indicating the degree of influence on the image quality (roughness, concave transferability, etc.). The upper limit of _{ε c} is determined for the suppression of rattling in the primary transfer section.

Assuming that the pressing force of the primary transfer roller 22 pressing the photoconductor drum 13 is P1, the length of the primary transfer nip portion N1 in the roller axial direction DR3 is L1, and the radius of the photoconductor drum 13 is r1, the upper limit of _{ε c is} , Coefficient A, belt transport speed V _sys , and γ1 (= P1 / (L1 × r1)) of the primary transfer unit.

Since r1∝W1 (W1: primary transfer nip width), γ1 obtained by dividing the pressing force P1 by the product of the length L1 and the radius r1 of the photoconductor drum 13 corresponds to the surface pressure in the primary transfer nip portion N1. ..

The lower limit of _{ε c} is determined for the concave transferability in the secondary transfer section. Assuming that the pressing force with which the secondary transfer roller 33 presses the opposing roller 24 is P2, the length of the secondary transfer nip portion N2 in the roller axial direction DR3 is L2, and the radius of the secondary transfer roller 33 is r2, the lower limit of _{ε c.} The value is a function of the coefficient A, the belt transport speed V _sys , and γ2 (= P2 / (L2 × r2)) of the secondary transfer unit.

Since r2∝W2 (W2: secondary transfer nip width), γ2 obtained by dividing the pressing force P2 by the product of the length L2 and the radius r2 of the secondary transfer roller 33 is the surface pressure in the secondary transfer nip portion N2. Corresponds to.

The first term on the right side of the above equation (10) _{is a quantity representing the degree of influence of the transient component ε t on} the quality (roughness, concave transferability, etc.). A is a coefficient that determines the degree of contribution of the transient component ε _{t to} the quality (how many times it is likely to affect _{the steady component ε s} of the same displacement amount). It is considered that A is determined in relation to the viscoelasticity and film thickness of the elastic belt, the surface shape (surface roughness), and the like.

The effect of the transient component ε _{t is proportional to the belt transport speed V sys} and proportional to the square of γ. As a result, _{the effect of the transient component ε t} becomes relatively small for a small γ, and as γ increases, the effect of the _{transient component ε t} increases quadratically in proportion to the square of the γ. At this time, it can be seen _{that the larger V sys} is, the larger _{the contribution of the transient component ε t is.}

The second term on the right side is a quantity representing the degree of influence of the displacement amount on the quality (roughness, concave transferability, etc.) _{of the constant component ε s.} However, since both sides are divided by the coefficient and arranged, the second term on the right side is γ itself. The influence of the steady-state component ε _s is proportional to the pressing force P, and is inversely proportional to the length L of the nip portion N in the roller axial direction DR3 and the roller radius r.

In the image forming apparatus 1, the relationship between the roughness and the concave transferability was investigated while changing _{the belt transport speed V sys, the pressing force P, and the like.} Specifically, an image forming apparatus 1 (digital printing machine: bizhub PRESS C8000) manufactured by Konica Minolta Co., Ltd. is used, and the intermediate transfer belt 21 provided therein is replaced with a belt exhibiting a pattern having an overshoot portion. , Image formation was actually performed.

The primary transfer roller 22 of the image forming apparatus 1 is a roller having a diameter of 24 mm in which an elastic layer made of rubber is provided around a core metal having a diameter of 12 mm. The hardness of the elastic layer measured with a micro rubber hardness tester (MD-1 manufactured by Polymer Meter Co., Ltd.) was 40 degrees. The axial length of the primary transfer pressure contact portion was set to 335 mm.

The secondary transfer roller 33 of the image forming apparatus 1 is a rigid body roller made of metal (material is SUS). The opposing roller 24 was a roller having a diameter of 40 mm in which an elastic layer made of sponge and rubber was provided around a core metal having a diameter of 24 mm. The hardness of the elastic layer measured with a micro rubber hardness tester (MD-1 manufactured by Polymer Meter Co., Ltd.) was 40 degrees. The axial length of the secondary transfer pressure contact portion was set to 340 mm.

The paper used for the evaluation was embossed paper manufactured by Tokushu Tokai Paper Co., Ltd., and the trade name Rezac 66 (Rezac is a registered trademark). The basis weight of this embossed paper was 302 [g / m ² ]. The image to be formed was a solid image.

(Roughness evaluation result due to the primary transfer part)
FIG. 49 is a graph showing the evaluation results of roughness for each condition of the belt transport speed V _{sys and the pressing force P1 in the primary transfer unit.} Similar to the case described with reference to FIG. 26, the conditions (pressure, bias, etc.) in the secondary transfer section are caused by the primary transfer section by setting the optimum conditions so that the toner image can be transferred onto the paper without disturbing the toner image. We evaluated the quality of the paper.

In the visual evaluation, ○ is indicated when the roughness is at a good level, Δ is indicated when the level is acceptable, and × is indicated when the level is not acceptable. From this result, when the boundary where the roughness changes from ○ to Δ or × is investigated, it is found that the roughness changes from ○ to × with the curve represented by the following equation (11) as the boundary.

2 × V _sys × γ ² + γ = 0.0075 ... (11)
That is, the coefficient A that determines the degree of contribution of the transient component ε _{t to} the roughness is A = 2, and the index value ε _c 1 at _{this time is ε c} 1 = 0.0075. _{ε c 1 = 2 × V sys} × ε c 1 represented by the gamma ^{2 +} gamma is, when satisfying the following equation (12), good image quality is obtained coarseness is suppressed.

ε _c 1 ≤ 0.0075 ... (12)
(Evaluation result of concave transferability due to secondary transfer part)
FIG. 50 is a graph showing the evaluation results of the recess transferability under each condition of the belt transfer speed V _{sys and the pressing force P2 in the secondary transfer unit.} Similar to the case described with reference to FIG. 28, the conditions (pressure, bias, etc.) in the primary transfer section are caused by the secondary transfer section by setting the optimum conditions so that the toner image can be transferred onto the paper without disturbing the toner image. The concave transferability was evaluated.

In the visual evaluation, ○ is indicated when the concave transferability is at a good level, Δ is indicated when the concave transferability is at an acceptable level, and × is indicated when the concave transferability is at an impossible level. The concave transferability was evaluated while changing the belt transfer speed V _sys and the secondary transfer section pressing force P2.

From this result, when the boundary where the concave transferability changes from ○ to Δ or × was investigated, it was found that the concave transferability changed from ○ to × with the curve represented by the following equation (13) as the boundary. ..

5 × V _sys × γ ² + γ = 0.088 ... (13)
That is, the coefficient A that determines the degree of contribution of the transient component ε _t to the recess transferability is A = 5, and the index value ε _c 2 at _{this time is ε c} 2 = 0.088. _{It was found that when ε c} 2 represented by ε _c 2 = 5 × V _sys × γ 2 + γ satisfies the following equation (14), good image quality with recessed transferability is ensured.

ε _c 2 ≧ 0.088 ・ ・ ・ (14)
Summarizing the above, when the following equation (15) is satisfied, rattling can be suppressed in the primary transfer portion, and when the following equation (16) is satisfied, good recess transferability is ensured in the secondary transfer portion. be able to.

2 × V _sys × γ1 ² + γ1 ≦ 0.0075 ・ ・ ・ (15) (γ1 = P1 / (L1 × r1))
5 × V _sys × γ2 ² + γ2 ≧ 0.088 ... (16) (γ2 = P2 / (L2 × r2))
FIG. 51 is a graph showing image evaluation results for each condition when the belts of Examples 1 to 7, Comparative Example 1 to Comparative Example 4, and Conventional Example 1 to Conventional Example 4 are used. Visual evaluation shows that the image quality is good (good), acceptable (possible), and unacceptable (impossible). The evaluation was carried out using the belt P in Examples 1 to 7 and Comparative Examples 1 to 4, and the belts A and B in the conventional examples 1 to 4.

The belt type P is manufactured by the present inventor, and the material of the base layer is polyimide and the material of the elastic layer is nitrile rubber. On the other hand, the belt types A and B are not manufactured by the present inventor, but are intermediate transfer belts used in a commercially available image forming apparatus. In the belt type A, the material of the base layer is polyimide and the material of the elastic layer is chloroprene rubber. In the belt type B, the material of the base layer is polyimide and the material of the elastic layer is acrylic rubber.

(Examples 1 to 7)
In each of Examples 1 to 5, a belt P showing E = 1.0 is used, and _{a pressing force is applied so that ε c} 1 and ε _c 2 satisfy the equations (12) and (14). P, roller radius r, and belt transfer speed V _sys are set. The image evaluation results of the belts P of Examples 1 to 5 are "OK" or higher in all of the items of roughness, concave transferability, axial image unevenness, and fine line crushing.

Even if the image is evaluated using the belt showing E = 0.2 shown in Example 6 and the belt showing E = 3.0 shown in Example 7, E = 1.0 shown in Examples 1 to 5 As in the case of using the belt showing the above, all of the items of roughness, concave transferability, axial image unevenness, and fine line crushing are “OK” or higher.

Even in the belt showing E = 0.2 and E = 3.0, the pressing force P, the roller radius r, and the belt so that _{ε c} 1 and ε _{c 2 satisfy the equations (12) and (14).} Good image quality can be ensured by setting the transport speed V _sys.

On the other hand, when a belt showing E = 3.5 was used, there was no problem with the transferability of uneven paper, but image noise was likely to occur after printing 10,000 sheets, and durability during repeated use was difficult. was there.

By setting the belt that satisfies 0.2 ≦ E ≦ 3 as the intermediate transfer belt 21, it is possible to prevent the image quality from being deteriorated even by repeated use while ensuring good concave transferability.

(Comparative Example 1 to Comparative Example 4)
As can be seen from Comparative Example 1 to Comparative Example 4, even when a belt P exhibiting overshoot deformation is used, if ε _c 1 or ε _c 2 deviates from the appropriate range, rattling, recess transferability, and axial direction are observed. It was not possible to achieve high image quality due to either image unevenness or thin line crushing.

From the results of Example 4 and Comparative Example 3, it can be seen that when γ1 satisfies the following equation (17), image unevenness in the axial direction can be suppressed.

γ1 ≧ 0.00074 ・ ・ ・ (17)
Further, from the results of Example 5 and Comparative Example 4, it can be seen that when γ2 satisfies the following equation (18), fine line crushing can be suppressed.

γ2 ≦ 0.028 ・ ・ ・ (18)
(Conventional Example 1 to Conventional Example 4)
A belt A having a relatively hard elastic layer that does not exhibit overshoot deformation is used, _{and images are drawn under conditions such that ε c} 1 and ε _c 2 satisfy equations (12) and (14) as in the conventional example 1. When it was taken out, good concave transferability could not be secured. Although the pressing force P2 in the secondary transfer section was increased, fine line crushing occurred when P2 = 210 [N] (conventional example 2). At this time, the concave transferability was not improved either.

A belt B having a relatively soft elastic layer that does not exhibit overshoot deformation is used, _{and images are drawn under conditions such that ε c} 1 and ε _c 2 satisfy equations (12) and (14) as in the conventional example 3. When it was put out, good concave transferability could be secured, but roughening occurred. Image evaluation was performed by reducing the pressing force P1 in the primary transfer unit, but image unevenness in the axial direction occurred when P1 = 9 [N] (conventional example 4). At this time, the roughness was not improved either.

As described above, when the belt A and the belt B, which do not exhibit overshoot deformation, are used as the intermediate transfer belts, it is not possible to achieve both suppression of rattling and good recess transferability.

Further experiments were repeated, and a large number of belts having a hardness intermediate between the belt A and the belt B were prototyped and examined. I couldn't.

From the above, it is good to set the pressing force P, the roller radius r, and the belt transport speed V _{sys so that ε c} 1 and ε _c 2 are appropriate using the belt P exhibiting overshoot deformation. It is possible to achieve both recess transferability and suppression of roughness. That is, it is possible to realize an image forming apparatus capable of suppressing rattling and ensuring good image quality while ensuring high transferability for a recording medium having a deep recess.

In the present embodiment described above, the case where the present invention is applied to a so-called digital multifunction device or digital printing machine as an image forming apparatus has been described as an example, but the present invention is applied to other image forming apparatus. Of course, it is possible to do so.

As described above, the above-described embodiments and examples disclosed this time are exemplary in all respects and are not restrictive. The technical scope of the present invention is defined by the claims and is intended to include all modifications within the meaning and scope equivalent to the claims.

1 image forming apparatus, 13 image carrier, 21 intermediate transfer belt, 21s1 first main surface, 21s2 second main surface, 22 primary transfer roller, 24 opposed roller, 24b elastic part, 33 secondary transfer roller, 33b elastic part, 70 Push pressure adjustment mechanism, 80 Belt transfer speed adjustment mechanism, 100 Displacement amount measuring device, 110 Lower block, 111 upper surface, 112 curved convex surface, 113 hole, 120 upper block, 121 lower surface, 122 curved concave surface, 1000 embossed paper, recording medium, 1001 recording surface, 1002 concave part, 1003 convex part, DR1 in-plane direction, DR2 transport direction, DR3 roller axial direction.

Claims (4)

An image carrier that supports a toner image and
A toner image supported on the first main surface, which includes at least an elastic layer and is one of a pair of exposed main surfaces composed of a first main surface and a second main surface located opposite to each other, is transferred to a recording medium. With an intermediate transfer belt for
A primary transfer roller having a surface hardness smaller than that of the image carrier, which transfers the toner image supported on the image carrier to the intermediate transfer belt.
An image forming apparatus including a secondary transfer unit that transfers a toner image supported on the intermediate transfer belt to a recording medium.
The secondary transfer unit includes a secondary transfer roller and an opposing roller facing the secondary transfer roller and having a surface hardness smaller than that of the secondary transfer roller.
A curved convex surface having a width of 20 [mm] and a radius of curvature of 20 [mm] is provided on the upper surface, and a hole having a diameter of 1.25 [mm] is provided at the top of the curved convex surface. The lower block and the upper block having a curved concave surface having a width of 20 [mm] and a radius of curvature of 20.3 [mm] on the lower surface are used, and the first main surface is the lower side. A part of the intermediate transfer belt is placed on the upper surface of the lower block so as to face the upper surface of the block, and the upper block is lowered toward the lower block. Is sandwiched between the curved convex surface and the curved concave surface so that the area under pressure, which is a part of the intermediate transfer belt, is pressed at a predetermined pressure rate [kPa / ms]. When the pressing force of 200 [kPa] is reached and then the pressing force of 200 [kPa] is applied to keep the pressure constant.
A local peak occurs in the displacement of the measurement region of the intermediate transfer belt, which is a portion of the first main surface corresponding to the hole, and then the displacement starts to decrease with the passage of time, and finally. It presents a displacement pattern that gradually decreases and converges to a predetermined displacement amount.
The primary transfer nip portion is formed by the image carrier and the primary transfer roller, and the primary transfer nip portion is formed.
The secondary transfer nip portion is formed by the secondary transfer roller and the opposing roller, and the secondary transfer nip portion is formed.
The belt transport speed of the intermediate transfer belt is V _sys [mm / s], the pressing force with which the primary transfer roller presses the image carrier is P1 [N], and the axial direction of the primary transfer roller of the primary transfer nip portion. Is L1 [mm], the radius of the image carrier is r1 [mm], and γ1 [N / mm ^{2) calculated by P1 / (L1 × r1) using the P1, the L1 and the r1.} ] Satisfies the condition of 2 × V _sys × γ1 ² + γ1 ≦ 0.0075.
The pressing force of the secondary transfer roller pressing the opposing roller is P2 [N], the axial length of the secondary transfer nip portion of the secondary transfer roller is L2 [mm], and the length of the secondary transfer roller is L2 [mm]. ^{The radius is r2 [mm], and γ2 [N / mm 2} ] calculated by P2 / (L2 × r2) using the P2, the L2, and the r2 is 5 × V _sys × γ2 ² + γ2 ≧ 0. An image forming apparatus that satisfies the condition of 088. When the predetermined pressurizing speed is 4 [kPa / ms], the maximum value of the displacement amount of the measurement region is set to a [μm], and the displacement of the measurement region after the displacement of the measurement region converges. When the amount is b [μm], E [−] calculated by (ab) / b using the above a and the said b satisfies the condition of 0.2 ≦ E ≦ 3.0. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1 or 2, wherein the γ1 satisfies the condition of γ1 ≧ 0.00074. The image forming apparatus according to any one of claims 1 to 3, wherein the γ2 satisfies the condition of γ2 ≦ 0.028.

Images