JP6834320B2 - Transfer belt and image forming device - Google Patents

Description

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

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

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 moves from the transfer belt passing through the nip portion to the recording medium also passing through the nip portion, whereby the toner image is transferred to the recording medium in the secondary transfer portion. Become.

Various types of transfer belts have been proposed, but as a transfer belt that enables transfer to a recording medium having irregularities on the recording surface (for example, embossed paper), a transfer belt including an elastic layer is provided. It has been 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. A transfer belt provided is disclosed.

By using a transfer belt having such an elastic layer, when the transfer belt is pressed toward the recording medium at the nip portion of the secondary transfer portion, the surface side of the transfer belt is placed in a recess located on the surface of the recording medium. It will be deformed so that a part of it will enter, and the distance between the bottom surface of the recess of the recording medium and the surface of the transfer belt will be shortened. As a result, the action of the electric field is promoted, the toner is likely to move, and the transferability to a recording medium having irregularities on the recording surface is improved.

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

Here, even when a transfer belt having an elastic layer as described above is used, the elastic layer provided on the transfer belt is provided in order to realize high transferability for a recording medium having a deeper recess on the surface thereof. It is necessary to increase the thickness of the elastic layer and further reduce the hardness of the elastic layer.

However, when the transfer belt configured in this way is used as the intermediate transfer belt of the image forming apparatus, there is a problem that the recording medium is not separated from the intermediate transfer belt at the transfer nip outlet and a jam is generated.

Therefore, the present invention has been made to solve the above-mentioned problems, can realize high transferability even on a recording medium having irregularities on the surface, and can suppress the occurrence of jam on the recording medium. It is an object of the present invention to provide a transfer belt and an image forming apparatus equipped with the transfer belt.

As a result of repeating research by producing various belts including an elastic layer, the present inventor shows a predetermined characteristic behavior and displaces the surface when the belt is pressurized under a predetermined pressure condition. When this belt is used as a transfer belt, it can be used from a transfer belt such as thin paper or paper with strong tackiness while ensuring high transferability even for recording media having irregularities on the surface. It has been found that the separability from the transfer belt can be ensured even for a recording medium that is difficult to separate, and the present invention has been completed. Here, whether or not the belt is a belt whose surface exhibits a predetermined characteristic behavior and is displaced when pressurized under a predetermined pressurizing condition is a displacement amount devised by the present inventor, which will be described later. It can be evaluated by an evaluation method using a measuring device.

The transfer belt according to the present invention includes an elastic layer and has a toner image carried 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. It is intended to be transferred to a recording medium, has a curved ridge surface having a width of 20 [mm] and a radius of curvature of 20 [mm] on the upper surface, and a diameter at the top of the curved ridge surface. Upper side having a lower block provided with a hole having a displacement of 1.25 [mm] and a curved concave surface having a width of 20 [mm] and a radius of curvature of 20.3 [mm] on the lower surface. Using a block, the transfer belt is placed on the upper surface of the lower block so that the first main surface faces the upper surface of the lower block, and the upper block is lowered toward the lower block to lower the transfer belt. By sandwiching a part of the surface between the curved convex surface and the curved concave surface, the area under pressure which is a part of the transfer belt is 200 [kPa / ms] at a predetermined pressure rate [kPa / ms]. When the pressure of [kPa] is reached and then the pressure is constant at 200 [kPa], the displacement amount of the measurement region, which is the part corresponding to the hole in the first main surface. The maximum value of is a [μm], the displacement amount of the measurement region after the displacement of the measurement region has converged is b [μm], and 200 [kPa] is added from the time when the pressurization of the pressurized region is started. Assuming that the time to the time when the pressure is reached is t0 [s], E [-] and t0 calculated by (ab) / b using a and b are the displacement amount of the transfer belt. The curve is fitted by an exponential function of E = α × exp (−t0 / τ) using the time constant τ and the constant α, and the time constant τ satisfies the condition of 0.015 ≦ τ ≦ 0.1.

It is preferable that the transfer belt based on the present invention further includes a base layer and a surface layer in addition to the elastic layer, and the elastic layer is provided so as to cover the base layer and the surface layer is further provided so as to cover the elastic layer.

In the transfer belt based on the present invention, the hardness of the base layer is preferably higher than the hardness of the elastic layer.

The image forming apparatus based on the present invention is supported on an image-supporting portion and an intermediate transfer belt that support a toner layer, a primary transfer portion that transfers a toner image supported on the image-supporting portion to an intermediate transfer belt, and an intermediate transfer belt. It is provided with a secondary transfer unit that transfers the toner image to a recording medium. The secondary transfer portion includes a secondary transfer roller, an opposing roller facing the secondary transfer roller, and a nip portion formed by the secondary transfer roller and the opposing roller. The intermediate transfer belt is arranged so as to pass through the nip portion. In the image forming apparatus based on the present invention, the transfer belt based on the present invention is used as the intermediate transfer belt.

In the image forming apparatus based on the present invention, it is preferable that the hardness of the surface of the secondary transfer roller is higher than the hardness of the surface of the opposing roller.

By applying the present invention, it is possible to obtain a transfer belt capable of ensuring high transferability even on a recording medium having irregularities on the surface and ensuring separability of the recording medium, and an image forming apparatus provided with the transfer belt.

It is the schematic of the image forming apparatus in embodiment of this invention. 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 and the operation of the pressurizing mechanism provided in the displacement amount measuring apparatus. It is a perspective view of the lower block and the upper block of the displacement amount measuring device shown in FIG. 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 using the displacement amount measuring apparatus shown in FIG. It is a schematic diagram and the graph for demonstrating the state of the toner transfer from the transfer belt to the embossed paper, and the relationship between the applied voltage and the transfer efficiency when the transfer belt consisting only of an inelastic layer is used. It is a schematic diagram and the graph for demonstrating the state of the toner transfer from the transfer belt to the embossed paper, and the relationship between the applied voltage and the transfer efficiency when the transfer belt including the elastic layer is used. 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 graph which shows the relationship between the pressurization time of the belt and the overshoot rate when the belt is pressurized by using the displacement amount measuring device. It is a graph which shows the behavior of the displacement of the belt with different time constants. It is a graph which shows the relationship of the overshoot rate, the primary displacement rate and the secondary displacement rate with respect to a time constant. It is a graph which shows the relationship between the time constant and the adhesive force reduction effect. It is a table which shows the evaluation result of the belt and the image evaluation result in an Example.

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 has an automatic document feeding device 2a and a document image scanning device 2b (scanner). Of these, the original image scanning device 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 device 11 is composed of, for example, a semiconductor laser.

The developing device 12 is, for example, a two-component developing method 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 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 drive roller among 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 belt 31 is stretched in a loop by the secondary transfer roller 33 and the support roller 32. The secondary transfer belt 31 travels in the direction of arrow B by rotating at least one of the plurality of support rollers 32. Here, the secondary transfer roller 33 and the opposing roller 24 mainly form a secondary transfer unit that transfers the toner image carried on the intermediate transfer belt 21 to the recording medium.

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

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.

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 to form 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 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 a toner having a high transfer rate is used, a cleaning device may not be used. The paper on which the toner image is transferred is conveyed toward the fixing device 6 by the secondary transfer belt 31.

It should be noted that 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.

Here, the toner is a binder resin containing a colorant, a charge control agent, a mold release agent, or the like, if necessary, and treated with an external additive, and is a commonly used known toner. Can be used. The volume average particle size of the toner 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. Good.

The shape coefficient SF-1 of the toner 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 "Luzex AP" (manufactured by Nireco). It is obtained from the average value of the shape coefficient (SF-1) derived by the formula.
SF-1 = [{(absolute maximum length of particles) ² / (projected area of particles)} × (π / 4)] × 100
Fine particles of metal oxides such as silica and titania are used as the toner externalizer, and those having a small particle size such as 30 [nm] to relatively large particles such as 100 [nm] are used. Toner. 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>
FIG. 2 is a cross-sectional view of the intermediate transfer belt shown in FIG. Next, the configuration of the intermediate transfer belt 21 will be described with reference to FIG. 2.

As shown in FIG. 2, 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 are included.

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, 10 8 ^[Ω · cm] More than 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 salt of organic boron complex, 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 may be added 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 21a and the elastic layer 21b can be measured using a micro rubber hardness tester (for example, manufactured by Polymer Meter 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 may 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 an evaluation method using a displacement amount measuring device described later, a part of its surface (that is, the first main surface 21s1) has a predetermined feature. It is displaced by showing a similar behavior, and the details will be described later.

<Structure of secondary transfer unit>
FIG. 3 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. In FIG. 3, the secondary transfer belt 31 is not shown.

As shown in FIG. 3, 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 arranged in parallel so as to face each other. A nip portion N 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 nip portion N, and a recording medium 1000 such as paper is also supplied so as to pass through the nip portion N.

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 nip portion N 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 at the nip portion N.

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 by a pressing mechanism (not shown) in the direction of arrow AR3 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 nip portion N, 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, since 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 33 and the opposing roller 24 can be measured using a micro rubber hardness tester (for example, manufactured by Polymer Meter 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. 1 Even if the 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. However, 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 described above will be described below.

<Displacement amount measuring device>
FIG. 4A is a schematic view showing the configuration of the displacement amount measuring device, and FIGS. 4B and 4C show the operation of the pressurizing mechanism provided in the displacement amount measuring device. It is a schematic diagram. 5 (A) is a perspective view of the lower block of the displacement amount measuring device shown in FIG. 4 (A) as viewed from above, and FIG. 5 (B) is a displacement amount measuring device shown in FIG. 4 (A). It is a perspective view which looked at the upper block of.

As shown in FIG. 4A, 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. 4 (A) and 5 (A), 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 is an upper surface in the width direction. A curved ridge surface 112 having a width of 20 [mm] is provided at the center of the 111. The radius of curvature of the curved convex surface 112 is 20 [mm].

Of the tops of the curved convex strips 112 located along the depth direction of the lower block 110, the central portion in the depth direction has a diameter of 1.25 [mm] (however, the tolerance is ± 0.02 [mm]. ]) Holes are 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. 4 (A) and 5 (B), 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 the lower surface 121 in the width direction. A curved concave surface 122 having a width of 20 [mm] is provided at the center of the surface. 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. 4A, 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. The cam 133, the shaft 134 connected to the cam 133, and the drive motor 135 for rotationally driving the shaft 134 are included.

As shown in FIGS. 4B and 4C, the drive motor 135 rotationally drives the shaft 134 in the direction of the arrow AR6 shown in the drawing, so that the cam 133 connected to the shaft 134 is shafted. It rotates together with the 134, and the pressurizing member 131 is pushed downward (in the direction of the 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. 4A, 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 the lower block 110 and the upper block 120. It is pulled out from between. 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. 6 is a graph for explaining a belt evaluation method using the displacement amount measuring device shown in FIG. 4 (A). Further, FIG. 7 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 shown in FIG. 4A.

The evaluation of the belt S is performed by the following procedure using the displacement amount measuring device 100 shown in FIG. 4 (A) 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 [kPa] ± 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. Regarding 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 be 35 [mm] or more and 300 [mm] or less, and is in the depth direction of the lower block 110 and the upper block 120. The corresponding 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).

Then, for 3 seconds from the start of pressurization, the position of the curved concave surface 122 of the upper block 120 of the portion facing the hole 113 of the lower block 110 is measured using the displacement meter 150, and this will be described later. Set as the baseline for measuring the displacement of 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. 6 and 7, 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. 6, 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.

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 of the belt S including the measurement region MR is compressed so that the portion of the belt S located around the portion is sandwiched between the lower block 110 and the upper block 120 and 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. 8 is a graph showing a pattern of displacement behavior in the measurement region of the belt.

As shown in FIG. 8, 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 it reaches (that is, t0 [s]), and then the displacement amount y of the measurement region MR of the belt S begins to decrease, and finally. It 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 transfer belt>
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. 8 (that is, that is, It exhibits a pattern having an overshoot portion).

This is because the present inventor prepared a plurality of types of belts and used each of them as an intermediate transfer belt of an image forming apparatus to form an image on embossed paper, as compared with a belt having no overshoot portion. 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 a transfer belt 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 above-mentioned overshoot portion.

Here, with reference to FIG. 8, the maximum value of the displacement amount y, which is a local peak of the displacement of the measurement region MR of the belt S, is defined as a [μm], and the displacement of the measurement region MR of the belt S converges. The convergence value, which is the amount of displacement y after the displacement, is defined as b [μm]. Further, the time from the start of pressurization to the time when the maximum value a [μm] is observed is defined as t1 [s], and the belt S is measured again after the maximum value a [μm] is observed from the start of pressurization. The time until the displacement amount y of the region MR 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)}.

In these overshoot rate E [−], primary displacement rate k1 [μm / s] and secondary displacement rate k2 [μm / s], the transfer belt was pressurized from the back surface (that is, the second main surface) side. In some cases, it is a parameter indicating how much the surface (that is, the first main surface) sways, and the more the surface of the transfer belt sways with a larger change, the larger these parameters take.

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

Here, 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 transfer belt is pressed from the back surface side, which is sufficient in terms of transferability. No effect can be expected. On the other hand, when the overshoot rate E [-] is 3 <E, the transfer belt 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. become.

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, and the image quality is deteriorated even after repeated use. Can be suppressed.

When the primary displacement rate k1 [μm / s] is k1 <60, the front surface does not sway too much even when the transfer belt is pressed from the back surface side, which is sufficient in terms of transferability. No effect can be expected. On the other hand, when the primary displacement rate k1 [μm / s] is 320 <k1, the transfer belt 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 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, and the image quality is deteriorated even after repeated use. Can be suppressed.

When the secondary displacement rate k2 [μm / s] is k2 <6, the front surface does not sway too much even when the transfer belt is pressed from the back surface side, and the transferability is improved. Sufficient effect cannot be expected. On the other hand, when the secondary displacement rate k2 [μm / s] is 30 <k2, the transfer belt 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 done.

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

<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 of an image forming apparatus will be described in detail.

FIG. 9 (A) is a schematic view showing the state of toner transfer from the transfer belt to the embossed paper when a transfer belt consisting of only an inelastic layer is used, and FIG. 9 (B) is a schematic view showing the state of toner transfer from the transfer belt to the embossed paper. It is a graph which shows the relationship between the applied voltage and transfer efficiency.

As shown in FIG. 9A, when the toner image is transferred to the recording medium 1000 which is the embossed paper by using the transfer belt 21'consisting only of the inelastic layer, the recess 1002 of the embossed paper is not located. The recording surface 1001 of the portion (hereinafter referred to as the convex portion 1003 for convenience) and the toner T located on the first main surface 21s1 of the transfer belt 21'are in contact with each other. On the other hand, the recording surface 1001 of the portion where the recess 1002 of the embossed paper is located and the toner T located on the first main surface 21s1 of the transfer belt 21'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, it is necessary to fly the toner T from the transfer belt 21'. In order for the toner T to fly from the transfer belt 21', the force received by the toner T from the electric field must overcome the adhesive force of the toner T on the transfer belt 21'. 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 transfer belt). ..

Here, the force F received by the toner T from the electric field is the distance between the embossed paper and the transfer belt 21', where the charge amount of the toner T is q and the potential difference between the embossed paper and the transfer belt 21'is dV. Is dx, 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 and the transfer belt 21', 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. 9B, 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. 9B, 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 (reference numeral c1002) is attached to the curve showing the relationship between the applied voltage and the transfer efficiency with respect to the concave portion 1002. 21') is attached.

Normally, in the image forming apparatus, the applied voltage is set near the applied voltage V0 at which the transfer efficiency is maximized at 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, and a high-quality image can be obtained. ..

FIG. 10 (A) is a schematic view showing the state of toner transfer from the transfer belt to the embossed paper when a transfer belt including an elastic layer is used, and FIG. 10 (B) is an applied voltage in that case. It is a graph which shows the relationship between and transfer efficiency.

As shown in FIG. 10A, when the transfer belt 21 "including the elastic layer is used, generally, a part of the transfer belt 21" on the first main surface 21s1 side in the recess 1002 of the embossed paper. The transfer belt 21 "is deformed so as to be inserted into the transfer belt 21", whereby the distance dx between the bottom surface of the recess 1002 of the embossed paper and the transfer belt 21 "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 transform effect.

On the other hand, when the transfer belt 21 "including the elastic layer exhibits the pattern having the overshoot portion described above, the first main surface 21s1 shakes significantly when the transfer belt 21" described above is deformed. As the first main surface 21s1 expands and contracts, the positional relationship between the transfer belt 21 "and the toner T adhering to the transfer belt 21" (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 transfer belt 21 ”is reduced. 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. 10B, the applied voltage V2 at which the transfer efficiency is maximized in the recess 1002 due to such a follow-up deformation effect or an effect of reducing the adhesive force in addition to the effect is the inelasticity described above. When the transfer belt 21'consisting of only layers 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. 10B, reference numeral c1002 (21 ") 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 transfer belt 21'consisting only of 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 density of the image in the concave portion 1002 and the convex portion 1003 of the embossed paper is increased. The difference becomes smaller, and a higher quality image can be obtained.

The adhesive force reducing effect is a particularly remarkable effect in a transfer belt that 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 transfer belt is primarily displaced at high speed in the early stage when the transfer belt passes through the nip portion, which is high. The effect of reducing the force of attachment will be obtained. When the overshoot rate E [-] described above is sufficiently large, the first main surface of the transfer belt is deformed at high speed and in a complicated manner in the middle stage where the transfer belt passes through the nip portion, resulting in high adhesive force. A reduction effect will be obtained. When the above-mentioned secondary displacement rate k2 [μm / s] is sufficiently large, the first main surface of the transfer belt is secondarily displaced at high speed at the final stage when the transfer belt passes through the nip portion, which is high. The effect of reducing the force of attachment will be obtained.

Here, with reference to FIG. 10B, 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 ΔVgap, and the reduction width of the applied voltage at which the transfer efficiency is maximized 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 transfer belt, but the values can be derived by experiments, and ΔVgap is measured by the belt evaluation method using the displacement amount measuring device 100 described above. It can be experimentally derived from the displacement amount y of the measurement region MR of the belt S. 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 made these into 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. 4A is used, and the belt to be measured and the embossed paper are sandwiched between the lower block 110 and the upper block 120. After applying a voltage to the lower block 110 and the upper block 120 so that a potential difference is generated between the lower block 110 and the upper block 120, the applied voltage is variously changed to obtain the best transfer efficiency. The voltage in this case was V2.

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

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. 11 is a graph showing the relationship between the overshoot rate E and ΔVadh. FIG. 12 is a graph showing the relationship between the primary displacement rate k1 and ΔVadh. FIG. 13 is a graph showing the relationship between the secondary displacement rate k2 and ΔVadh.

As can be understood from FIG. 11, 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, it was confirmed that ΔVadh tends to increase by more than 50 [V] as the value of the overshoot rate E increases, and a high adhesive force reducing effect can be obtained. ..

As can be understood from FIG. 12, 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. 13, 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 each of the first to third conditions. By satisfying the condition 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.

<Interrelationship between displacement parameters>
When the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2 are all sufficiently large, a very high adhesive force reducing effect is exhibited, and a recording medium having irregularities on the recording surface such as embossed paper is exhibited. High transferability can be ensured.

On the other hand, when a transfer belt exhibiting a pattern having an overshoot portion is used, the surface of the transfer belt completely follows the unevenness of the recording medium when the toner is transferred to a recording medium having a small uneven step such as non-embossed paper. It will be transformed to do. As a result, the contact area between the surface of the transfer belt and the surface of the recording medium becomes large, and as a result, the separability of the recording medium from the transfer belt tends to decrease.

However, when a transfer belt having a large secondary displacement rate k2 is used, even if the surface of the transfer belt is deformed so as to completely follow the unevenness of the recording medium at the central portion of the nip portion where the transfer pressure is maximum, the nip portion In the vicinity of the exit of, the transfer belt has already recovered from the deformation. Since the contact area between the surface of the transfer belt and the surface of the recording medium is small near the outlet of the nip portion, the recording medium is easily separated from the transfer belt. On the other hand, when a transfer belt having a small secondary displacement rate k2 is used, the surface of the transfer belt is deformed at the center of the nip so as to completely follow the unevenness of the recording medium, and then even near the outlet of the nip. This means that the deformation of the transfer belt has not been sufficiently eliminated. Therefore, the contact area between the surface of the transfer belt and the surface of the recording medium remains large, and it becomes difficult for the recording medium to be separated from the transfer belt.

Therefore, by increasing not only the overshoot rate E and the primary displacement rate k1 but also the secondary displacement rate k2 at the same time, the transferability to the recording medium having irregularities is ensured, and the separability of the recording medium from the transfer belt is ensured. It becomes possible to secure.

(Time constant of transient displacement τ)
In general, there is a time constant as an index of the response speed of a transient phenomenon. When describing the strain deformation of a viscoelastic body such as rubber, the strain delay time, the stress relaxation time, and the like may be referred to as a time constant. The smaller the time constant, the faster the strain deforms and the faster the stress is relieved. The larger the time constant, the slower the deformation of the strain and the slower the relaxation of the stress. The time constant is an index showing the speed of deformation and the speed of return from deformation.

Therefore, the present inventor pays attention to what should be called the time constant of the transient displacement of the transfer belt, and by adjusting the time constant of the transient displacement of the transfer belt well, the overshoot rate E, the primary displacement rate k1 and the secondary displacement It has been found that any of the rates k2 can be designed to be appropriate. The time constant of transient displacement is defined as τ [s].

(Measurement method of time constant τ)
The time constant τ varies greatly depending on the belt. The time constant τ for the belt S can be obtained from the displacement amount of the belt S measured by using the displacement amount measuring device 100 described above.

According to the evaluation method described with reference to FIGS. 6 and 7, the displacement amount y is measured while changing the time from the start of pressurization to the arrival of the maximum pressure (that is, t0 described above) in the displacement amount measuring device 100. Then, the overshoot rate E is calculated from the maximum value a of the displacement amount y and the convergence value b. The series of measurement results obtained in this way are plotted with the horizontal axis representing the pressurization time t0 and the vertical axis representing the overshoot rate E.

FIG. 14 is a graph showing the relationship between the pressurization time t0 of the belt S and the overshoot rate E when the belt S is pressurized by using the displacement amount measuring device 100. As shown in FIG. 14, when the pressurizing time t0 is lengthened, that is, when the pressurizing speed is decreased, the internal stress is relaxed relatively quickly. Therefore, transient displacement (overshoot) due to concentration of internal stress becomes difficult, and the overshoot rate E becomes small.

As shown in FIG. 14, a series of measurement results are plotted so that the overshoot rate E decays exponentially as the pressurization time t0 is lengthened. These plots are curve-fitted to an exponential function such as the following equation using the time constant τ and the constant α [−] to obtain the time constant τ. The constant α is an arbitrary coefficient.
E = α × exp (−t0 / τ)

As shown in FIG. 14, when the time constant τ is small, the graph is such that the overshoot rate E rapidly attenuates as the pressurization time t0 is increased. If the time constant τ is large, the graph will be such that the overshoot rate E gradually attenuates as the pressurization time t0 is increased. The time constant τ is an index representing the relaxation time (relaxation rate) of the internal stress.

There is a positive correlation between the deformation rate of the belt and the relaxation rate of internal stress. That is, if the strain is deformed quickly, the stress is relaxed quickly, and if the strain is deformed slowly, the stress is relaxed slowly. Therefore, the time constant τ is an index of both the deformation rate of the belt and the relaxation rate of the internal stress.

(Relationship between time constant τ and displacement waveform)
FIG. 15 is a graph showing the behavior of displacement of belts having different time constants τ. A large number of belts were manufactured by variously adjusting the types and amounts of the resin, additives, cross-linking agents, etc. contained in the elastic layer 21b (FIG. 2). These belts have different elastic layer 21b compositions, resulting in different time constants τ. FIG. 15 shows the transition of the displacement amount with respect to the pressurizing time measured with respect to these belts by the evaluation method described with reference to FIGS. 6 and 7 using the displacement amount measuring device 100. In the graph (A), the graph (B), the graph (C), the graph (D), and the graph (E) shown in FIG. 15, the time constant τ increases in this order. As shown in FIG. 15, there is the following tendency between the time constant τ and the transient displacement waveform of the belt.

As shown in the graph (B) in FIG. 15, in a belt having a slightly small time constant τ, the deformation and relaxation of the belt are relatively fast, so that the primary displacement rate k1 and the secondary displacement rate k2 are large. The overshoot rate E is somewhat smaller.

As shown in the graph (D) in FIG. 15, in a belt having a slightly large time constant τ, the deformation and relaxation of the belt are relatively slow, so that the overshoot rate E is large, but the primary displacement rate k1 and the secondary are secondary. The displacement rate k2 is somewhat smaller.

In the graph (C) in FIG. 15, the time constant τ is between the graph (B) and the graph (D), and the overshoot rate E, the primary displacement rate k1, and the secondary displacement rate k2 are all balanced. It grows well.

As shown in the graph (A) in FIG. 15, when the time constant τ is further smaller than the graph (B), the overshoot rate E is further reduced. As a result of the overshoot rate E becoming smaller, the primary displacement rate k1 and the secondary displacement rate k2 are also reduced.

As shown in the graph (E) in FIG. 15, when the time constant τ becomes larger than the graph (D), the primary displacement rate k1 and the secondary displacement rate k2 become smaller, and the overshoot rate E tends to be saturated. It becomes.

Therefore, with a belt having an appropriate time constant τ as shown in the graph (B), the graph (C), or the graph (D) in FIG. 15, the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2 Both can be obtained sufficiently high.

FIG. 16 is a graph showing the relationship between the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2 with respect to the time constant τ. In FIG. 16, the overshoot rate E and the primary displacement are measured by the evaluation method described with reference to FIGS. 6 and 7 using the displacement amount measuring device 100 for a large number of belts having different compositions of the elastic layer 21b. An approximate curve of the plot of the rate k1 and the quadratic displacement rate k2 and the time constant τ is shown.

The horizontal axis of the graph shown in FIG. 16 indicates the logarithmic time constant τ. The vertical axis of the graph shown in FIG. 16 shows the overshoot rate E, the primary displacement rate k1, and the secondary displacement rate k2. In the graph of FIG. 16, the scale of the vertical axis of the graph is appropriately adjusted with an emphasis on the comprehensibility of the drawing. In the graph of FIG. 16, the scale of the vertical axis is different for each of the overshoot rate E, the primary displacement rate k1, and the secondary displacement rate k2.

As shown in FIG. 16, the overshoot rate E becomes smaller as the time constant τ becomes smaller. When the time constant τ is small, the deformation of the belt and the relaxation of the internal stress occur at a very high speed, so that it becomes difficult for the strain of the belt to concentrate toward the hole 113 (FIG. 7) of the displacement amount measuring device 100. As a result, when the displacement at the center of the hole 113 is observed by the displacement meter 150, overshoot is less likely to occur, and the measured overshoot rate E becomes smaller.

The overshoot rate E increases as the time constant τ increases. As the time constant τ becomes larger, the deformation of the belt and the relaxation of the internal stress occur more slowly, so that the distortion of the belt is concentrated toward the center of the hole 113. As a result, an overshoot is likely to occur, and the measured overshoot rate E increases.

The overshoot rate E saturates when it increases to some extent. The overshoot rate E is saturated at the value when the belt distortion is concentrated to the maximum, and does not increase any more.

When the time constant τ is large, the primary displacement rate k1 becomes a small value because the belt deforms slowly. As the time constant τ becomes smaller, the belt deforms faster and the primary displacement rate k1 increases. When the time constant τ is further reduced, the primary displacement rate k1 becomes smaller again. The smaller the time constant τ, the higher the deformation speed of the belt, but if the time constant τ is small, the overshoot rate E becomes small, so the maximum value a of the displacement amount becomes small. As a result, the inclination of the displacement amount toward the maximum value a, that is, the rate of increase of the displacement also becomes small. In this way, the relationship of the primary displacement rate k1 with respect to the time constant τ becomes an upward convex shape such that the time constant τ has a peak at a certain value.

When the time constant τ is large, the secondary displacement rate k2 becomes a small value because the internal stress of the belt is slowly relaxed. As the time constant τ becomes smaller, the internal stress of the belt is relaxed faster, and the secondary displacement rate k2 becomes larger. When the time constant τ is further reduced, the secondary displacement rate k2 becomes smaller again. The smaller the time constant τ, the faster the relaxation rate of the internal stress of the belt, but the smaller the time constant τ, the smaller the overshoot rate E, so the difference between the maximum displacement amount a and the convergence value b becomes smaller. .. As a result, the inclination toward the convergence value b after the displacement amount reaches the maximum value a, that is, the reduction rate of the displacement also becomes small. In this way, the relationship of the secondary displacement rate k2 with respect to the time constant τ becomes an upward convex shape such that the time constant τ has a peak at a certain value.

Therefore, as shown in FIG. 16, there is an overlapping region in the range of the time constant τ in which each of the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2 becomes a large value.

In FIG. 16, the time constant τ corresponding to each of the graphs (A), (B), (C), (D), and (E) described with reference to FIG. 15 is shown on the horizontal axis.

(Relationship between time constant τ and adhesive force reduction effect)
FIG. 17 is a graph showing the relationship between the time constant τ and the adhesive force reducing effect. For a large number of belts having different elastic layer compositions described above, the time constant τ obtained by curve fitting described with reference to FIG. 14 and the time constant ΔVadh calculated based on the above-mentioned V1, V2 and ΔVgap are used. An approximate curve of the plot with τ as the horizontal axis and ΔVadh as the vertical axis is shown in FIG.

As shown in FIG. 17, the relationship of ΔVadh with respect to the time constant τ has an upward convex shape such that the time constant τ has a peak at a certain value. The lower limit of ΔVadh that can significantly improve the image quality is set to TH, and the range in which ΔVadh ≧ TH, that is, the range of the time constant τ that satisfies th1 ≦ τ ≦ th2 is ideal because a large adhesive force reducing effect can be obtained. You can see that.

In the embodiment, an image forming apparatus (digital printing machine: bizhub PRESS C8000) manufactured by Konica Minolta Co., Ltd. is used, and the intermediate transfer belt provided therein is replaced with various belts having a pattern having an overshoot portion. , Image formation was actually performed.

The secondary transfer roller of the image forming apparatus was a rigid body roller made of metal (material: SUS) having a diameter of 40 mm. The opposing roller 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 °. The pressure at the secondary transfer section was 200 kPa. The length in the nip axis direction was 340 mm.

(Evaluation of transferability of uneven paper)
For the evaluation of the quality of transferability, embossed paper manufactured by Tokushu Tokai Paper Co., Ltd., trade name Rezac 66 (Rezac is a registered trademark) was used. The basis weight of this embossed paper was 302 [g / m ² ]. The image to be formed was a solid image. At the time of determination, the reflection density of the sharp and deep concave portion (groove portion) and the reflection density of the convex portion were measured using a microdensitometer, and the difference between these concentrations was calculated. When the concentration difference is less than 0.15, it is judged as "excellent", and when the concentration difference is 0.15 or more and less than 0.25, it is judged as "good", and the concentration difference is When the permissible level was 0.25 or more and less than 0.40, it was judged as "acceptable", and when the concentration difference was 0.40 or more and less than the permissible level, it was judged as "impossible".

(Evaluation of paper separability)
For the evaluation of the quality of separability, plain paper manufactured by Konica Minolta Co., Ltd. and trade name J paper were used. The basis weight of this paper was 64 [g / m ² ]. In the determination, 1000 sheets of images having different densities were printed, and the number of paper jams due to poor separation of the secondary transfer portion during that period was counted. If the paper jam does not occur and it is good, it is judged as "good", if the paper jam is at an acceptable level of 3 times or less, it is judged as "OK", and the paper jam is at an unacceptable level of 4 times or more. In that case, it was judged as "impossible".

(Evaluation results)
A plurality of belts having different elastic layer compositions are evaluated using the displacement amount measuring device 100 described above based on the belt evaluation method described with reference to FIGS. 6 and 7, and the time constant τ and overshoot of each belt are evaluated. The rate E, the primary displacement rate k1 and the secondary displacement rate k2 were obtained. Using an image forming apparatus to which each of these belts is applied as an intermediate transfer belt, the temperature is 20 ° C., the humidity is 50%, and the linear velocity (system velocity) of the outer peripheral surfaces of the secondary transfer roller and the opposing roller is 200 [mm / s]. Under the conditions, image drawing evaluation on A4 size paper was performed. FIG. 18 is a table showing the evaluation results of the belt and the image evaluation results in the examples.

The belt types A to G shown in FIG. 18 are all manufactured by the present inventor, and the material of the base layer is polyimide and the material of the elastic layer is nitrile rubber. By preparing various types and amounts of resins, additives, cross-linking agents, etc. contained in the elastic layer in each belt, the composition of the elastic layer is different, and as a result, the time constant τ is different. On the other hand, the belt type X is not manufactured by the present inventor, but is an intermediate transfer belt used in a commercially available image forming apparatus, the base layer material is polyimide, and the elastic layer material is chloroprene rubber. ..

The belt type A used in Example 1 is a belt that can be expected to have the highest adhesive force reducing effect. When this belt was used, the effect of reducing the adhesive force was greatly exhibited, particularly good transferability was obtained in the recesses of the embossed paper, and the separability from the non-embossed paper was also good.

In Examples 1 to 5, the effect of reducing the adhesive force was greatly exhibited, particularly good transferability was obtained in the recesses of the embossed paper, and the separability from the non-embossed paper was also above an acceptable level. In the belts of Examples 1 to 5, the time constant τ is in the range of 0.015 ≦ τ ≦ 0.1. From this, the threshold value th1 which is the lower limit value of the time constant τ shown in FIG. 17 can be set to 0.015, and the threshold value th2 which is the upper limit value of the time constant τ can be set to 0.1. By managing the range of the time constant τ in this way and using an intermediate transfer belt in which the time constant τ satisfies the condition of 0.015 ≦ τ ≦ 0.1, the transferability to uneven paper and the paper separability can be improved. It can be compatible.

The belts used in Comparative Example 1 and Comparative Example 3 have a time constant τ of less than 0.015, and the time constant τ is outside the above range. In Comparative Example 1 and Comparative Example 3, none of the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2 were sufficiently high. Therefore, in Comparative Example 1 and Comparative Example 3, the effect of reducing the adhesive force was hardly exhibited, and good transferability was not obtained in the recesses of the embossed paper.

The belt used in Comparative Example 2 has a time constant τ larger than 0.1, and the time constant τ is outside the above range. In Comparative Example 2, a high value of the overshoot rate E was obtained, but a sufficiently high value was not obtained for the primary displacement rate k1 and the secondary displacement rate k2. For this reason, the effect of reducing the adhesive force was exhibited to some extent, and the transferability in the recesses of the embossed paper remained at a good level. Further, since the secondary displacement rate k2 is small for the large overshoot rate E, the surface of the transfer belt is deformed so as to completely follow the unevenness of the paper at the center of the nip portion where the transfer pressure is maximum. It is considered that the deformation is not sufficiently eliminated even in the vicinity of the outlet of the nip portion, and the contact area between the surface of the transfer belt and the surface of the paper remains large. As a result, it became difficult for the paper to be separated from the transfer belt, and the separability from the non-embossed paper became impossible.

In Comparative Example 1 and Comparative Example 3, the paper separability was good. In Comparative Example 1 and Comparative Example 3, the secondary displacement rate k2 is small, but the overshoot rate E is also small. At the center of the nip where the transfer pressure is maximum, the surface of the transfer belt is difficult to deform so that it completely follows the unevenness of the paper, and the amount of deformation itself is small, so the transfer belt is already near the exit of the nip. It is considered that the contact area between the surface of the transfer belt and the surface of the paper has become smaller after recovering from the deformation. It is believed that this allows the paper to be easily separated from the transfer belt.

Based on the above results, it was found that if the time constant τ is less than 0.015 or the time constant τ is more than 0.1, both transferability to uneven paper and paper separability cannot be achieved. By appropriately managing the time constant τ so as to satisfy the condition of 0.015 ≦ τ ≦ 0.1, it is possible to obtain sufficiently high values for all of the overshoot rate E, the primary displacement rate k1 and the secondary displacement rate k2. Therefore, it was shown that both transferability to uneven paper and paper separability can be achieved.

Therefore, by appropriately managing the time constant τ of the transient displacement of the intermediate transfer belt 21 so as to satisfy the condition of 0.015 ≦ τ ≦ 0.1, the transferability is high even for a recording medium having irregularities on the surface. It is possible to suppress the deterioration of image quality even with repeated use, and it is surely separated even for recording media that are difficult to separate from the intermediate transfer belt such as thin paper and paper with strong tackiness. It is possible to provide an image forming apparatus capable of suppressing the risk of occurrence of jam.

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 and a transfer belt and an intermediate transfer belt provided therein has been illustrated and described. However, it is naturally possible to apply the present invention to other image forming apparatus and the transfer belt provided therein.

As described above, the above-described embodiment disclosed this time is an example in all respects and is not limiting. The technical scope of the present invention is defined by the scope of claims and includes all modifications within the meaning and scope equivalent to the description of the scope of claims.

1 Image forming device, 2 Image reading unit, 2a Automatic document feeding device, 2b Original image scanning device, 3 Image processing unit, 4 Image forming unit, 5 Paper transport unit, 5a Paper feeding unit, 5a1-5a3 Paper feed tray unit 5b Paper ejection unit, 5b1 Paper ejection roller, 5c Transport path unit, 5c1 Resist roller pair, 6 Fixing device, 6a fixing roller, 6b Pressurizing roller, 7 Sensor, 10 Image forming unit, 11 Exposure device, 12 Developing device, 13 Photoreceptor drum, 14 Charging device, 15 Drum cleaning device, 20 Intermediate transfer unit, 21 Intermediate transfer belt, 21a base layer, 21b elastic layer, 21c surface layer, 21s1 first main surface, 21s2 second main surface, 22 primary transfer roller , 23, 32 Support roller, 24 Opposing roller, 24a core metal, 24b Elastic part, 25 Belt cleaning device, 30 Secondary transfer unit, 31 Secondary transfer belt, 33 Secondary transfer roller, 33c Secondary transfer power supply, 100 displacement Quantity measuring device, 110 lower block, 111 upper surface, 112 curved convex surface, 113 hole, 120 upper block, 121 lower surface, 122 curved concave surface, 130 pressurizing mechanism, 131 pressurizing member, 132 spring, 133 cam , 134 shaft, 135 drive motor, 140 tensioning mechanism, 141 film, 142 tape, 143 weight, 150 displacement meter, 151 head part, 1000 recording medium, 1001 recording surface, 1002 concave part, 1003 convex part.

Claims (5)

A toner image supported on the first main surface, which is one of a pair of exposed main surfaces including an elastic layer and is composed of a first main surface and a second main surface located opposite to each other, is transferred to a recording medium. It is a transfer belt for
A curved ridge 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 ridge surface. A lower block made of the material and an 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. A part of the transfer belt is formed by placing the transfer belt on the upper surface of the lower block so as to face the upper surface of the side block and lowering the upper block toward the lower block. By being sandwiched between the curved convex surface and the curved concave surface, the area to be pressurized, which is a part of the transfer belt, is 200 [kPa / ms] at a predetermined pressure rate [kPa / ms]. When the pressing force of [kPa] is reached and then the pressing force of 200 [kPa] is applied to the constant pressure, the measurement region of the first main surface corresponding to the hole portion. The maximum value of the displacement amount is a [μm], the displacement amount of the measurement area after the displacement of the measurement area is converged is b [μm], and 200 from the time when the pressurization of the pressurized area is started. Assuming that the time until the time when the pressing force of [kPa] is reached is t0 [s], E [-] and t0 calculated by (ab) / b using the a and the b . The plot with t0 on the horizontal axis and E on the vertical axis is an index of E = α × exp (−t0 / τ) using the time constant τ [s] and the constant α [−] with respect to the displacement amount of the transfer belt. A transfer belt that is curve-fitted by a function and whose time constant τ satisfies the condition of 0.015 ≦ τ ≦ 0.1. In addition to the elastic layer, a base layer and a surface layer are further included.
The transfer belt according to claim 1, wherein the elastic layer is provided so as to cover the base layer, and the surface layer is further provided so as to cover the elastic layer. The transfer belt according to claim 2, wherein the hardness of the base layer is higher than the hardness of the elastic layer. An image-carrying part and an intermediate transfer belt that support the toner layer,
A primary transfer unit that transfers the toner image supported on the image-supporting unit to the intermediate transfer belt, and
A secondary transfer unit that transfers a toner image supported on the intermediate transfer belt to a recording medium is provided.
The secondary transfer portion includes a secondary transfer roller, an opposing roller facing the secondary transfer roller, and a nip portion formed by the secondary transfer roller and the opposing roller.
The intermediate transfer belt is arranged so as to pass through the nip portion.
An image forming apparatus in which the transfer belt according to any one of claims 1 to 3 is used as the intermediate transfer belt. The image forming apparatus according to claim 4, wherein the hardness of the surface of the secondary transfer roller is higher than the hardness of the surface of the opposing roller.

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