JP2016218294A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can improve separation of a recording sheet without reducing the amount of toner adhered to the recording sheet.SOLUTION: An image forming apparatus comprises: an image forming part that forms a toner image on a recording sheet by using a toner containing a wax; and a fixing part that conveys the recording sheet having the toner image formed thereon to be passed through a fixing nip to fix the toner image onto the recording sheet with application of heat and pressure. When forming a solid image as the toner image, the image forming apparatus performs processing of providing a solid white part at least in a predetermined area on a tip side in a conveyance direction of the solid image so as not to reduce the amount of toner per unit area.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a printer, a facsimile machine, and a copying machine.

  An image forming apparatus having a fixing device that fixes a toner image on a recording sheet by pressurization and heat treatment is used in, for example, a copying machine. In recent years, toners containing wax have become mainstream as toners used in such image forming apparatuses.

  The main role of the wax is to separate the recording paper from the fixing member at the outlet of the fixing device. That is, the toner image formed on the recording paper is pressurized and heated and melted in the fixing nip composed of the fixing member and the pressure member, and the wax is melted from the inside of the toner. The wax leaches out at the interface between the toner image and the fixing member to form a film, thereby reducing the adhesion between the toner image and the fixing member and facilitating separation of the recording paper from the fixing member. ing.

  In order for the wax in the toner to be leached out at the interface between the toner image and the fixing member, the wax is sufficiently dissolved until the toner resin is melted and the toners are united, and then the pressure is used as a driving force to bring the wax to the interface. Need to extrude. However, the melting point (softening point) of the resin is low in the low-temperature fixing toner, the toners are united by the time the wax moves, there is no moving path to the wax interface, and the wax cannot be sufficiently leached. did. This is the reason why it is difficult to separate the recording paper with the low-temperature fixing toner.

  As a technique for facilitating separation of recording paper, as exemplified in Patent Documents 1 and 2, for example, a method for solving the problem by reducing the toner adhesion amount at the leading edge of the solid image is known. The reason why the recording paper can be easily separated when the toner adhesion amount is reduced is presumed to be that the degree of adhesion of the toner to the fixing member is reduced. That is, if the amount of adhesion is small, the toner cannot follow the fine irregularities and undulations of the fixing member, resulting in a gap.

  Another reason is presumed to be the viscosity of the toner layer. In other words, the separation force of the recording paper acts on the separation of the recording paper, leading to peeling. However, if the toner layer is thick, the restoring force of the recording paper only extends the toner, and the toner image is peeled off. It is not considered. None of them are within the estimated range, but the technology to improve separation by lowering the toner adhesion amount is widely known, and the amount of solid image adhesion at the leading edge of the recording paper is reduced by devising it during exposure and transfer I am letting.

JP 2008-158463 A Japanese Patent Laid-Open No. 5-66628

  However, according to the above-described technique, the toner adhesion amount has to be reduced, and the density of the leading edge of the image located at the leading edge of the recording paper is inevitably reduced. As a result, the user may feel uncomfortable or the image information may be difficult to see.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of improving the separation of recording paper without reducing the toner adhesion amount.

  An image forming apparatus according to the present invention uses a toner containing wax to form an image forming unit that forms a toner image on a recording paper, and to transport the recording paper on which the toner image is formed to pass through a fixing nip. And a fixing unit that pressurizes and heat-fixes the toner image on the recording paper. When forming a solid image as the toner image, an amount of toner per unit area at least in a predetermined region on the front end side in the transport direction of the solid image In order to prevent the deterioration of the image, a process of providing a white portion is performed.

  According to this configuration, it is possible to improve the separation of the recording paper without reducing the toner adhesion amount. More specifically, as the above configuration, the process of providing the white portion may be a process of providing a predetermined number of white dots per unit area in the predetermined region.

  More specifically, the above-described configuration may be such that the white dots having a diameter size of 40 to 80 μm are provided at least in an area within 5 mm from the leading end in the transport direction of the solid image. In the above configuration, the fixing nip may be formed between the fixing member and the pressure member, and the fixing member and the pressure member may be driven to rotate so that there is a difference in surface speed between them. .

Further, in the above configuration, the fixing nip is formed between a fixing member and a pressure member, the fixing member has a belt configuration, and the pressure member is a roller having a reverse crown shape that is driven to rotate. The fixing member may be configured to follow the rotational drive of the pressure member. More specifically, the melting point of the wax may be 100 ° C. or lower, and the temperature at which the toner elastic modulus of the toner becomes 10 ⁴ Pa may be 110 ° C. or lower.

  More specifically, the configuration may be such that the thickness of the recording paper is detected, and whether or not the white dots are to be provided is determined based on the detection result. More specifically, the above configuration may be configured to determine whether or not to provide the white dots based on the position or width information of the solid image.

  According to the image forming apparatus of the present invention, it is possible to improve the separation of the recording paper without reducing the toner adhesion amount.

1 is a main part configuration diagram of an image forming apparatus according to Embodiment 1. FIG. It is explanatory drawing regarding a solid image. It is explanatory drawing regarding the area | region which provides a white dot. It is explanatory drawing regarding the reverse crown shape of a pressure roller. FIG. 6 is a configuration diagram in the vicinity of a fixing device according to a second embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. However, the content of the present invention is not limited to the embodiment.

1. First Embodiment First, a first embodiment which is an embodiment of the present invention will be described. FIG. 1 is a main part configuration diagram of an image forming apparatus (for example, a copying machine) according to the present embodiment. As shown in the figure, the image forming apparatus includes an image forming unit 1, a transfer belt 7, a roller 9, a ground roller 10, a secondary transfer roller 11, a transport roller 12, a discharge roller 13, a heating roller 14, a fixing belt 16, A pressure roller 17, a heater lamp 18, a fixing roller 19, and a discharge tray 20 are provided.

  The image forming unit 1 includes a photoreceptor 3, a charger 5, an exposure unit 4, a developing unit 2, a primary transfer roller 8, and a cleaning unit 6 disposed around the photoreceptor 3. Actually, there are a plurality of image forming units 1, and the portions not shown in FIG. 1 are vertically arranged directly below the image forming unit 1 shown in FIG. 1.

  The image forming apparatus operates to acquire image information to be printed (for example, image information obtained by scanning a document by a scanner (not shown)) and print it on the recording paper P. Specifically, the charger 5 uniformly charges the surface of the photoreceptor 3, and the exposure unit 4 exposes the surface according to image information to form an electrostatic latent image, which is developed by the developing device 2. Imaged.

  The visible image (toner image) formed on the surface of the photoreceptor 3 is electrostatically transferred to the transfer belt 7 by the primary transfer roller 8. Subsequently, the toner image on the transfer belt 7 is electrostatically transferred onto the recording paper P by the secondary transfer roller 11 and the earth roller 10. The recording paper P is transported by a transport roller 12 to a secondary transfer unit having a secondary transfer roller 11 and an earth roller 10. The recording paper P onto which the toner image has been transferred is nipped in a fixing nip N formed by a pressure roller 17 and a fixing roller 19 and is conveyed and fixed. Hereinafter, each component will be described in more detail.

[Photoreceptor]
The photoreceptor 3 is a negatively charged photoreceptor, and is configured by laminating an undercoat layer, a charge generation layer, a charge transport layer, and an overcoat layer in this order on an aluminum substrate.

[Exposure part]
An LED array having an element pitch of 0.02115 mm (1200 dpi) was used for the exposure unit 4. The emission wavelength is 685 ± 15 nm and the half width is 40 nm. The LED was driven so that the system speed was 200 mm / sec and the photosensitive member rotation direction was 1200 dpi. Adjustment of the irradiation energy to the surface of the photoreceptor 3 is performed by the light emission time (pulse width) of the LED, and the solid latent image potential can be freely changed.

[Developer]
The developing device 2 is a two-component developing device, and has a magnet roller 2 a that faces the photoreceptor 3. In the developing device 2, the developer is transported from the developing trough to the magnet roller 2a, and the toner is developed and visualized according to the developing bias and the latent image potential in the developing nip formed by the photoreceptor 3 and the magnet roller 2a. .

[Primary transfer section]
The primary transfer roller 8 is installed to face the photoconductor 3 and an appropriate pressure is applied with the intermediate transfer belt 7 interposed therebetween. Further, a transfer bias is applied between the primary transfer roller 8 and the photoreceptor 3 so that the toner is electrostatically transferred.

[Secondary transfer section]
The secondary transfer roller 11 is installed opposite to the earth roller 10 (rotatingly supporting the intermediate transfer belt 7 together with the roller 9), and an appropriate pressure is applied across the intermediate transfer belt 7. A transfer bias is applied to the secondary transfer roller 11 to electrostatically transfer the visible image on the intermediate transfer belt 7 to the recording paper P.

[Fixing part]
Next, the configuration of the fixing device (fixing unit) will be described. The fixing device includes a fixing belt 16 that is wound around the heating roller 14 and the fixing roller 19 and moves (runs) in the direction of arrow A, and a pressure roller 17 that presses the fixing belt 16 that is wound around the fixing roller 19. have. The fixing roller 19 is rotatably supported on a side plate (not shown).

  The heating roller 14 is biased in a direction away from the fixing roller 19 by a tension mechanism (not shown) using a spring or the like. As a result, a tension is applied to the fixing belt 16 wound around the fixing roller 19 and the heating roller 14. The pressure roller 17 is pressed against the fixing belt 16 with a predetermined pressure by a pressure mechanism (not shown) using a spring or the like, and a fixing nip N is secured between the two.

  The recording paper P onto which the toner image has been transferred is conveyed to the fixing nip N with the image surface facing the fixing belt 16. After passing through the fixing nip N, the recording paper P is discharged to the discharge tray 20 by the discharge roller 13. In this embodiment, the nip load of the fixing nip N is 50 to 500 N, the nip width (the length along the circumferential direction of the fixing belt 16) is 8 mm, and the nip length (the traveling direction of the fixing belt 16) is The length along the orthogonal width direction) is 320 mm.

  The heating roller 14 has, for example, a PTFE coat laminated on the outer peripheral surface (surface) of a cylindrical metal core 141, and has an outer diameter of 50 mm. The core metal 141 is made of an aluminum plate having a thickness of 1 mm. The heating roller 14 having such a configuration has a relatively small heat capacity.

  A plurality of heater lamps 18 for heating the heating roller 14 by an electric-heat conversion method are provided inside the heating roller 14. When the heating roller 14 is heated by any one or more of the heater lamps 18, the fixing belt 16 that is wound around the heating roller 14 is heated and passes through the fixing nip N by the heated fixing belt 16. The recording paper P to be heated is heated.

  The heater lamp 18 is constituted by, for example, a halogen heater lamp, and is arranged on a circumference with a constant radius centered on the axis of the heating roller 14 with each of the heating rollers 14 having an equal interval in the circumferential direction. It is arranged along the axis. The rated power of the heater lamp 18 is 1500 W in total.

  The heater lamp 18 is turned on (heat generation) when power is supplied, and heats the heating roller 14 with a heat generation amount substantially proportional to the supplied power. Each heater lamp 18 has the same length of 290 mm, and in order to ensure the fixability at each end on both sides of the fixing belt 16 in the width direction (direction perpendicular to the running direction) The light distribution (corresponding to the intensity of light and the heating intensity) at each end on both sides is larger than the light distribution at the center in the longitudinal direction. In the present embodiment, the light distribution of the 20 mm long portion at each end portion of each side of the heater lamp 18 is assumed to be 100% when the light distribution of the central portion of the 250 mm length other than the end portions on both sides is 100%. 115%.

  A temperature sensor (not shown) for detecting the surface temperature of the fixing belt 16 wound around the heating roller 14 is provided in the vicinity of the heating roller 14. The temperature sensor is disposed so as to face the upstream portion of the fixing belt 16 wound around the heating roller 14 in the traveling direction. In this embodiment, a non-contact thermistor is used as the temperature sensor.

  The fixing roller 19 includes a cored bar 191 configured in a cylindrical shape with an outer diameter of 38 mm using iron having a thickness of 0.5 mm, and an elastic layer laminated on the outer peripheral surface (surface) of the cored bar 191. In this elastic layer, a silicone rubber having a thickness of 4 mm is formed on the outer peripheral surface of the metal core 191, and a silicone sponge having a thickness of 2 mm is formed on the outer peripheral surface. The fixing roller 19 has a hardness of 30 °. The fixing roller 19 having such a configuration has a relatively large heat capacity.

  The fixing belt 16 is laminated on a base material 161 formed in a cylindrical shape having an outer diameter of 80 mm with nickel having a thickness of 35 μm and a surface (outer peripheral surface) of the base material 161, as shown in a broken line frame in FIG. And the release layer 163 laminated on the surface (outer peripheral surface) of the elastic layer 162. The fixing belt 16 has an oval shape along the horizontal direction by being wound around the heating roller 14 and the fixing roller 19 with a predetermined tension.

  The elastic layer 162 of the fixing belt 16 is made of 200 μm thick silicone rubber, and the release layer 163 is made of 20 μm thick PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) tube. Has been. The fixing belt 16 having such a configuration has a relatively small heat capacity.

  The pressure roller 17 includes an iron (thickness 2.5 mm) cored bar 171 configured in a cylindrical shape with an outer diameter of 50 mm, an elastic layer 172 laminated on the outer peripheral surface (surface) of the cored bar 171, It has a release layer (not shown) stacked on the outer peripheral surface (surface) of the layer 172.

  The elastic layer 172 is made of, for example, silicone rubber having a thickness of 1.0 mm. The release layer is made of, for example, a PFA tube having a thickness of 30 μm. The hardness of the pressure roller 17 is, for example, 80 °. As described above, the pressure roller 17 is configured to have high rigidity by including the iron cored bar 171 having a thickness of 2.5 mm, and has a larger heat capacity than the fixing belt 16.

  The outer diameter of the pressure roller 17 has an inverted crown shape with a smaller diameter as it reaches the center in the longitudinal direction. As shown in FIG. 4, when the outer diameter of the end portion is D1 and the outer diameter of the central portion is D2, the difference between both (D1-D2) is the reverse crown amount. The reverse crown amount is set to about 0.1 to 0.8 mm.

  The pressure roller 17 is rotated at a predetermined surface speed (200 mm / s in this embodiment) by a drive motor (not shown). As a result, the fixing roller 19 that is in pressure contact with the pressure roller 17 with the fixing belt 16 interposed therebetween rotates following the pressure roller 17, and the fixing belt 16 is integrated with the fixing roller 19. And run. As described above, in this embodiment, the fixing member has a belt configuration (a configuration in which the fixing belt 16 is provided), and this fixing member is driven by the rotational drive of the pressure member (pressure roller 17).

  In this embodiment, a driving motor is connected to the pressure roller 17, but a driving motor may be connected to the fixing roller 19 separately. Alternatively, the driving force of the fixing roller 19 may be obtained from the driving motor of the pressure roller 17 through a gear, a driving belt, a chain, or the like. In such a case, the pressure roller 17 and the fixing roller 19 can be independently set for speed, and can be rotationally driven so that there is a difference in surface speed between them. These speed differences (vertical speed differences) may be about 0.1 to several percent of the system speed, for example.

〔toner〕
Next, the toner used in the image forming apparatus of this embodiment will be described. The toner contains toner base particles and at least a binder resin and a wax. The binder resin constituting the toner particles is not particularly limited, and various known resins can be used. Examples thereof include styrene resin, acrylic resin, styrene-acrylic resin, polyester resin, silicone resin, olefin resin, amide resin, and epoxy resin. The binder resin preferably contains a styrene-acrylic resin from the viewpoint of toner particle size, shape controllability and chargeability.

  Examples of the polymerizable monomer for obtaining a styrene-acrylic resin include styrene monomers such as styrene, methylstyrene, methoxystyrene, butylstyrene, phenylstyrene, chlorostyrene; methyl (meth) acrylate. , (Meth) acrylate ester monomers such as ethyl (meth) acrylate, butyl (meth) acrylate, and ethylhexyl (meth) acrylate; carboxylic acid monomers such as acrylic acid, methacrylic acid, and fumaric acid are used. be able to. These can be used alone or in combination of two or more.

  The glass transition point (Tg) of the binder resin is preferably 30 to 50 ° C, more preferably 35 to 48 ° C. When the glass transition point of the binder resin is in the above range, both low-temperature fixability and heat-resistant storage stability can be obtained. The glass transition point of the binder resin is measured using “Diamond DSC” (manufactured by PerkinElmer).

  As a measurement procedure, 3.0 mg of a sample (binder resin) is sealed in an aluminum pan and set in a holder. The reference used an empty aluminum pan. The measurement conditions were a measurement temperature of 0 ° C. to 200 ° C., a temperature increase rate of 10 ° C./min, a temperature decrease rate of 10 ° C./min, and heat-cool-heat temperature control. Perform analysis based on the data in Heat, draw a baseline extension before the rise of the first endothermic peak, and a tangent line indicating the maximum slope between the rise of the first peak and the peak apex, The intersection point is shown as the glass transition point.

  As the wax contained in the toner, known waxes can be used. For example, polyolefin waxes such as polyethylene wax and polypropylene wax, branched hydrocarbon waxes such as microcrystalline wax, paraffin wax, and sazol wax. Long chain hydrocarbon wax, dialkyl ketone wax such as distearyl ketone, carnauba wax, montan wax, behenate behenate, trimethylolpropane tribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, Ester wax such as glycerin tribehenate, 1,18-octadecanediol distearate, tristearyl trimellitic acid, distearyl maleate, ethylenediamine Behenyl amides, amide-based waxes such as trimellitic acid tristearyl amide. Among these, branched hydrocarbon waxes such as microcrystalline wax are particularly preferable from the viewpoint of suppressing gloss unevenness.

  The melting point of the wax contained in the toner is preferably 70 to 100 ° C, more preferably 70 to 85 ° C. The melting point of the wax indicates the temperature at the top of the endothermic peak, and the differential scanning calorimeter “DSC-7” (manufactured by PerkinElmer) and the thermal analyzer controller “TAC7 / DX” (manufactured by PerkinElmer) DSC measurements are made by analysis.

  Specifically, 4.5 mg of a sample (wax) was sealed in an aluminum pan (KITNO.0219-0041), and this was set in a sample holder of “DSC-7”, and the temperature was raised at a measurement temperature of 0 to 200 ° C. Heating-cooling-heating temperature control is performed under the measurement conditions of a temperature rate of 10 ° C./min and a temperature-decreasing rate of 10 ° C./min, and analysis is performed based on the data in the second heating. However, an empty aluminum pan is used for the reference measurement. The content of the wax is preferably 1 to 30 parts by mass, more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the binder resin. When the content ratio of the wax is within the above range, fixing separation property can be obtained.

  When the toner particles contain a colorant, generally known dyes and pigments can be used as the colorant. As a colorant for obtaining a black toner, various known materials such as carbon black such as furnace black and channel black, magnetic materials such as magnetite and ferrite, dyes, and inorganic pigments containing nonmagnetic iron oxide are arbitrarily selected. Can be used. As the colorant for obtaining a color toner, known ones such as dyes and organic pigments can be arbitrarily used.

  The colorant for obtaining the toner of each color can be used singly or in combination of two or more for each color. It is preferable that the content rate of a coloring agent is 1-10 mass parts with respect to 100 mass parts of binder resin, More preferably, it is 2-8 mass parts.

  When the toner particles contain a charge control agent, a known positive charge control agent or negative charge control agent can be used. Specifically, as the positive charge control agent, for example, a nigrosine dye such as “Nigrosine Base EX” (manufactured by Orient Chemical Industries), “quaternary ammonium salt P-51” (manufactured by Orient Chemical Industries), “ Examples include quaternary ammonium salts such as “Copy Charge PX VP435” (manufactured by Hoechst Japan), alkoxylated amines, alkylamides, molybdate chelate pigments, and imidazole compounds such as “PLZ1001” (manufactured by Shikoku Kasei Kogyo). .

  Examples of the negative charge control agent include “Bontron S-22” (manufactured by Orient Chemical Industries), “Bontron S-34” (manufactured by Orient Chemical Industries), and “Bontron E-81” (Orient Chemical Industries, Ltd.). ), “Bontron E-84” (Orient Chemical Co., Ltd.), “Spiron Black TRH” (Hodogaya Chemical Co., Ltd.) and other metal complexes, thioindigo pigments, “Copy Charge NX VP434” (Hoechst Japan) Quaternary ammonium salts such as “Bontron E-89” (manufactured by Orient Chemical Industries), boron compounds such as “LR147” (manufactured by Nippon Carlit), magnesium fluoride, fluorinated carbon Fluorine compounds such as

  In addition to the metal complexes used as negative charge control agents, oxycarboxylic acid metal complexes, dicarboxylic acid metal complexes, amino acid metal complexes, diketone metal complexes, diamine metal complexes, azo group-containing benzene-benzene derivatives Examples thereof include those having various structures such as skeletal metal bodies and azo group-containing benzene-naphthalene derivative skeleton metal complexes. The content of the charge control agent is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

  The toner can be used as it is in the image forming method of the present embodiment, but it may be one to which an external additive is added in order to improve fluidity, chargeability, cleaning properties and the like. Examples of the external additive include inorganic oxide fine particles such as silica fine particles, alumina fine particles, and titanium oxide fine particles, inorganic stearate compound fine particles such as aluminum stearate fine particles and zinc stearate fine particles, strontium titanate, and zinc titanate. And inorganic fine particles such as inorganic titanic acid compound fine particles.

  These inorganic fine particles are preferably those subjected to surface treatment with a silane coupling agent, a titanium coupling agent, a higher fatty acid, silicone oil, or the like from the viewpoint of heat-resistant storage stability and environmental stability. The inorganic fine particles constituting the external additive preferably have an average primary particle size of 30 nm or less. When the external additive made of inorganic fine particles has the above particle size, the toner is less likely to be liberated during image formation. The additive amount of the external additive is 0.05 to 5% by mass, preferably 0.1 to 3% by mass in the toner.

  The toner used in the image forming method of the present embodiment can be used as a magnetic or nonmagnetic one-component developer, but is mixed with a carrier and used as a two-component developer. In the case where the toner is used as a two-component developer, the carrier may be a conventionally known material such as a ferromagnetic metal such as iron, a ferromagnetic metal and an alloy such as aluminum and lead, and a compound of a ferromagnetic metal such as ferrite and magnetite. In particular, ferrite particles are preferable.

  As the carrier, a coated carrier in which the surface of magnetic particles is coated with a coating agent such as a resin, a binder type carrier in which magnetic fine powder is dispersed in a binder resin, and the like can also be used. The coating resin constituting the coat carrier is not particularly limited, and examples thereof include olefin resins, styrene resins, styrene-acrylic resins, silicone resins, ester resins, and fluorine resins.

  The toner particles according to the exemplary embodiment preferably have an average particle diameter of 3 to 9 μm, and more preferably 3 to 8 μm, for example, on a volume basis median diameter. This particle size can be controlled by the concentration of the coagulant used, the amount of organic solvent added, the fusing time, and the composition of the polymer, for example, when the emulsion coagulation method described later is employed. When the volume-based median diameter is in the above range, the transfer efficiency is increased, the image quality of halftone is improved, and the image quality of fine lines and dots is improved.

  The volume-based median diameter of the toner particles is measured and calculated using a measuring device in which “Multisizer 3” (manufactured by Beckman Coulter) is connected to a computer system equipped with data processing software “Software V3.51”. Is. Specifically, 0.02 g of a sample (toner particles) was added to 20 mL of a surfactant solution (for example, a surfactant obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water for the purpose of dispersing toner particles). Solution) and ultrasonically disperse for 1 minute to prepare a toner particle dispersion. This toner particle dispersion is placed in “ISOTONII” (manufactured by Beckman Coulter) in the sample stand. Pipette into a beaker until the displayed concentration of the measuring device is 8%.

  Here, a reproducible measurement value can be obtained by setting the concentration range. In the measurement apparatus, the measurement particle count is 25000, the aperture diameter is 50 μm, the frequency value is calculated by dividing the measurement range of 1 to 30 μm into 256, and the volume integrated fraction is 50 % Particle size is the volume-based median diameter.

  The toner particles according to the exemplary embodiment preferably have an average circularity of 0.930 to 1.000, more preferably 0.950 to 0.995, from the viewpoint of improving transfer efficiency. The average circularity of the toner particles is measured using “FPIA-2100” (manufactured by Sysmex).

Specifically, the sample (toner particles) is blended with an aqueous solution containing a surfactant, subjected to ultrasonic dispersion treatment for 1 minute to disperse, and then subjected to measurement conditions HPF by “FPIA-2100” (manufactured by Sysmex). In the (high magnification imaging) mode, photographing is performed at an appropriate density of 3,000 to 10,000 HPF detections, and the circularity is calculated according to the following formula (T) for each toner particle. Calculated by adding the circularity and dividing by the total number of toner particles.
Formula (T):
Circularity = (perimeter of a circle having the same projection area as the particle image) / (perimeter of the particle projection image)

The toner according to the exemplary embodiment preferably has a storage elastic modulus (G′170) at a temperature of 170 ° C. of 1 × 10 ² to 1 × 10 ³ (Pa) in terms of gloss stability and high-temperature offset resistance. . If the value of G′170 is smaller than 1 × 10 ² Pa, the change in the glossiness with respect to the temperature change is sharp, the glossiness changes easily at the leading and trailing edges of the image, a stable image cannot be obtained, and the high temperature offset is It is easy to happen. On the other hand, if the value of G′170 is larger than 1 × 10 ³ Pa, the toner is not sufficiently melted and the glossiness is insufficient. On the other hand, G ′ of the toner in the temperature range where the wax melts affects the leaching of the wax. The temperature Tb at which G ′ is 10 ⁴ (Pa) is preferably higher than the melting point of the wax.

The viscoelastic properties of the toner are measured using a viscoelasticity measuring device (rheometer) “RDA-II type” (manufactured by Rheometrics) under the following conditions.
Measuring jig: A parallel plate having a diameter of 10 mm is used.
Measurement sample: Toner is heated and melted and molded into a cylindrical sample having a diameter of about 10 mm and a height of 1.5 to 2.0 mm.
Measurement frequency: 6.28 radians / second Measurement strain setting: Initial value set to 0.1%, measured in automatic measurement mode Sample extension correction: Adjusted in automatic measurement mode

  The softening point (Tsp) of the toner is preferably 90 to 110 ° C. When the softening point (Tsp) is within the above range, the influence of heat applied to the toner during fixing can be further reduced. Therefore, since image formation can be performed without imposing a burden on the colorant, it is expected that a wider and more stable color reproducibility is expressed.

The softening point (Tsp) of the toner can be controlled by, for example, the following methods (1) to (3) alone or in combination.
(1) The kind and composition ratio of the polymerizable monomer for forming the binder resin are adjusted.
(2) The molecular weight of the binder resin is adjusted according to the type and addition amount of the chain transfer agent.
(3) Adjust the type and amount of wax.

The softening point (Tsp) of the toner is 1 by using a “flow tester CFT-500” (manufactured by Shimadzu Corp.), formed into a cylindrical shape with a height of 10 mm, and heated from a plunger while heating at a heating rate of 6 ° C./min. Apply pressure of 96 × 10 ⁶ Pa and push it out from a nozzle with a diameter of 1 mm and a length of 1 mm. This draws a curve (plunger flow curve) between the plunger drop amount and temperature of the flow tester. The temperature to be measured is measured by a method in which the melting start temperature is set, and the temperature with respect to the drop amount of 5 mm is set to the softening point temperature.

[Control to provide white dots on solid images]
As described above, the image forming apparatus according to the present embodiment includes the image forming unit (mainly the image forming unit 1) that forms a toner image on the recording paper P using the toner containing wax, and the formation of the toner image. And a fixing unit (including a pressure roller 17 and a fixing roller 19) that presses and heat-fixes the toner image onto the recording paper P by passing the recorded recording sheet P through a fixing nip.

  Further, the image forming apparatus according to the present embodiment includes a control unit (not illustrated) (for example, including a CPU) that controls each unit so that the apparatus operates appropriately. Then, when the solid image is formed as the toner image, the control unit has a toner amount per unit area (at the front end side in the conveyance direction of the recording paper P) at least on the solid image. The image forming apparatus is controlled to perform a process of providing a white portion (in this embodiment, a collection of white dots) so as not to reduce the average toner adhesion amount).

  That is, the control unit obtains image information to be printed on the recording paper P (for example, image information obtained by scanning a document by a scanner (not shown)), and when the image is recognized as a solid image, the control unit A white portion is provided in a predetermined area. Note that the control unit can recognize, for example, an image whose area exceeds a predetermined reference value as a solid image.

  The above white portion corresponds to a portion penetrating to the surface of the recording paper P provided in the toner layer before fixing, and is provided in the toner layer in a stage until the solid image (toner image) is fixed on the recording paper P. This corresponds to the leaching path of the wax produced. For this reason, by appropriately providing a white portion, it is possible to promote sufficient wax penetration even for a solid image, and to easily separate the recording paper P from the fixing member at the exit of the fixing device.

Note that the control unit provides such white portions so that they are crushed and inconspicuous after fixing. In the present embodiment, a predetermined number of white dots (holes penetrating to the surface of the recording paper P) per unit area are provided as white portions. For example, the control unit causes a latent image to be formed on the photoconductor 3 so that minute white portions of several dots are generated in the solid image (toner image) before fixing. As the density, for example, as in Example 1 to be described later, the density of 4 × 4 dots white dots may be 10 / mm ² .

At this time, the control unit adjusts the latent image potential of the non-white portion (portion other than the white dot) so that the toner amount per unit area does not decrease. In other words, if a solid image is simply provided with white dots, the toner amount is reduced by that amount and the image density is lowered. In this embodiment, the toner amount of the non-white portion is reduced by this toner amount. Is increased so that the toner amount per unit area does not decrease. For example, as in Example 1 described later, the photosensitive member electrostatic potential corresponding to the non-white portion of the image portion may be adjusted so that the adhesion amount is about 4.0 g / m ² .

  Therefore, it is possible to suppress the density of the leading edge of the image on the leading edge side of the recording paper P as much as possible, and the problem that the user feels uncomfortable or the image information becomes difficult to see is solved. As described above, in the image forming apparatus of this embodiment, it is possible to improve the separation of the recording paper without reducing the toner adhesion amount.

  It should be noted that various control methods can be adopted for determining whether or not to provide the above-described white dots. As an example, the following control method can be employed.

  It has been found that the thinner the recording paper P is, the more difficult it is to separate the recording paper P at the fixing outlet (exit of the fixing unit). Therefore, whether or not white dots are provided in the leading edge region of the solid image may be determined based on the thickness of the recording paper P. For example, based on the selection information of the recording paper P in the operation unit of the image forming apparatus, white dots are provided when the recording paper P having a thickness equal to or less than a predetermined value is selected, and white dots are otherwise obtained. You may make it not provide an extraction dot. In addition, when the separation of various recording sheets is confirmed in advance, the recording sheet with poor separation is stored in the storage device of the control unit, and when the recording sheet with poor separation is selected, the leading edge of the solid image Alternatively, an aggregate of minute white dots may be formed.

  Further, based on the information on the position of the solid image, the size of the solid image, or the density (toner adhesion amount) of the solid image, it may be determined whether or not the white dot is provided in the leading end area of the solid image. For example, as the solid image is closer to the leading edge of the recording paper P, the separability becomes worse. Therefore, when the distance between the leading edge of the solid image and the leading edge of the recording paper P is equal to or less than a predetermined value, white dots are provided. In other cases, white dots may not be provided.

  In addition, when the width of the solid image (in the direction perpendicular to the conveyance direction) increases, the separability deteriorates. Therefore, white dots are provided when the width is equal to or greater than a predetermined value, and white dots are otherwise obtained. You may make it not provide a dot. Furthermore, since the separation becomes worse as the toner adhesion amount increases, white dots are provided when the adhesion amount is a predetermined value or more, and white dots are not provided in other cases. It may be.

2. Second Embodiment Next, another embodiment (second embodiment) of the present invention will be described. The second embodiment is basically the same as the first embodiment except for the portion related to the fixing device. In the following description, emphasis is placed on the description of parts different from the first embodiment, and description of common parts may be omitted.

  FIG. 5 is a configuration diagram in the vicinity of the fixing device according to the second embodiment. As shown in FIG. 5, the fixing device includes a fixing roller 21 and a pressure roller 17. The fixing roller 21 is rotatably supported by a side plate (not shown). The pressure roller 17 is pressed against the fixing roller 21 with a predetermined pressure by a pressure mechanism (not shown) using a spring or the like, and a fixing nip N is secured between the two.

  The recording paper P to which the toner image has been transferred is conveyed to the fixing nip N with the image surface directed toward the fixing roller 21, and then the recording paper P passes through the fixing nip N. The nip load of the fixing nip N is 50 to 500 N, the nip width (the length along the circumferential direction of the fixing belt 16) is 8 mm, and the nip length (the width direction orthogonal to the traveling direction of the fixing roller 21). (Length along) is 320 mm.

  The fixing roller 21 includes a cored bar 211 formed in a cylindrical shape having an outer diameter of 40 mm with aluminum having a thickness of 5 mm, and an elastic layer 212 laminated on the outer peripheral surface (surface) of the cored bar 211. The elastic layer 212 is formed by bonding a 10 mm thick silicone rubber on the outer peripheral surface of the cored bar 211 and a 30 μm thick PFA tube on the outer peripheral surface thereof. The fixing roller 19 has a hardness of 30 °.

  The outer diameter of the pressure roller 17 has an inverted crown shape with a smaller diameter toward the center in the longitudinal direction. The reverse crown amount is set to about 0.1 to 0.8 mm. The pressure roller 17 is rotated at a predetermined surface speed (200 mm / s in this embodiment) by a drive motor (not shown). As a result, the fixing roller 21 rotates following the pressure roller 17.

  On the other hand, a drive motor may be connected to the fixing roller 21 separately. Alternatively, the driving force of the fixing roller 21 may be obtained from the driving motor of the pressure roller 17 through a gear, a driving belt, a chain, or the like. In such a case, it is possible to set the speed of the pressure roller 17 and the fixing roller 21 independently. The vertical speed difference is about 0.1 to several percent with respect to the system speed.

3. Examples and Comparative Examples In order to evaluate the performance and the like of the image forming apparatus according to the present embodiment, each example (each example) according to the present embodiment in which various conditions were set was compared with each comparative example. . Hereinafter, various conditions and evaluation results will be described.

[Exposure pattern]
For the formation of a solid image, all the elements of the LED array were turned on, and the toner image was formed by lowering the photoreceptor image portion potential to −50V. The formation of minute white dots was made by stopping LED irradiation for 2 × 2 pixels and 4 × 4 pixels. The size of the small white dots was 2 × 2 pixels and the diameter was about 40 μm, and 4 × 4 pixels and the diameter was about 80 μm. The fine white dots are arranged at equal intervals, and the density existing in the solid image is 1 to 10 / mm ² . The density was adjusted at intervals of minute white dots.

[Toner used in Examples]
In the examples, the following three types of toners A to C were used.
Toner A: The melting point of the wax was about 70 ° C. The temperature at which G ′ was 10 ⁴ (Pa) was about 80 ° C.
Toner B: The melting point of the wax was about 85 ° C. The temperature at which G ′ was 10 ⁴ (Pa) was about 100 ° C.
Toner C: The wax had a melting point of about 70 ° C. The temperature at which G ′ was 10 ⁴ (Pa) was about 110 ° C.

[Pressure roller used in Examples]
In the examples, the pressure roller of the present embodiment described above was used. However, the following three types of pressure rollers a to c were obtained by changing the reverse crown amount.
Pressure roller a: reverse crown amount is 0.1 mm
Pressure roller b: Reverse crown amount is 0.6 mm
Pressure roller c: Reverse crown amount is 0 mm (no reverse crown)

〔Evaluation method〕
(1) Separation The apparatus shown in FIG. 1 is operated, 10 sheets of recording paper (A4 size) on which no image is formed are passed, and then a solid image is printed on the recording paper of A4 size as shown in FIG. And one sheet is passed through the fixing device. This cycle was repeated 10 times to evaluate the separability. Specifically, “X” indicates that the recording paper on which the solid image is formed is wound around the fixing belt and the number of times when the recording paper cannot be separated is 1 or more, while “○” indicates that the recording paper passes in a good state. Although it was difficult to say that it was in a good state, the case where it passed without trouble was marked as “Δ”.
(2) Density unevenness Density reduction at the leading edge of the solid image was visually evaluated. Specifically, “X” was assigned when the decrease in density could be confirmed, and “O” was assigned when the decrease in density could not be confirmed.
(3) Glossiness The glossiness of the solid image tip was visually evaluated. Specifically, if minute noise can be confirmed on the surface or if the gloss is uncomfortable, it will be marked as “X”, and if the gloss is good, it will be marked as “O”. The case was set as “△”.

[Effect confirmation 1]
First, an example in which a minute white dot group under conditions where ID reduction is likely to occur is created and covered with an increase in the amount of irradiation light other than the white portion, and a comparative example in which ID reduction occurs. Table 1 shows an outline of the conditions and evaluation results of the examples and comparative examples given here. Here, in both cases, the toner A described above was used as the toner, and the pressure roller b described above was used as the pressure roller.

In the first embodiment, as shown in FIG. 3, a solid image is created from a position 2 mm from the leading edge of the recording paper, and 4 × 4 dots of white dots are formed at 10 mm / mm ² from the leading edge of the solid image to 3 mm. Created with density. Further, the photosensitive member electrostatic potential of the image portion other than the white portion was adjusted so that the adhesion amount was about 4.0 g / m ² . Comparative Example 1 is a case where no white dots were created for Example 1. The amount of adhesion was the same as in Example 1. In Comparative Example 2, white dots having the same conditions as in Example 1 were created, but the amount of adhesion was not adjusted.

From the results of Example 1 and Comparative Example 1, it can be seen that when white dots having a diameter of about 80 μm are formed at a density of 10 pieces / mm ² within 3 mm of the leading edge of the solid image, the separability is improved. Even if the adhesion amount is not reduced, the separation is improved, so that it can be determined that the effect is obtained by forming the white dots. In Comparative Example 2, it can be presumed that the separability is improved by the effect of white dot formation, but the amount of adhesion is reduced, and density unevenness is confirmed. From the above results, it was shown that the separability can be improved by the present invention without causing a decrease in the adhesion amount. Since the amount of adhesion does not decrease, the image does not feel strange.

[Effect confirmation 2]
Next, it is verified how much dot diameter (diameter size) and density should be provided for the white dots. Table 2 shows an outline of the conditions and evaluation results of the examples given here. Here, in both cases, the toner A described above was used as the toner, and the pressure roller b described above was used as the pressure roller.

As in Example 1, a solid image was created from a position 2 mm from the front end of the recording paper, and white dots from 3 mm from the front end of the solid image were created. Further, the photosensitive member electrostatic potential of the image portion other than the white portion was adjusted so that the adhesion amount was about 4.0 g / m ² . From the results of Examples 2 to 4 and Example 1 described above, white dots of about 40 to 80 μm are not visually uncomfortable. When the thickness was 100 μm as in Example 5, a small amount of blur (fine noise) was seen on the solid image. From the results of Examples 2 to 4 and 6, it can be seen that the effect of white dots is better when the density is higher.

[Effect confirmation 3]
Next, it is verified to what position the white dots should be provided from the front end of the solid image. Table 3 shows an outline of the conditions and evaluation results of the examples and comparative examples given here. Here, in both cases, the toner A described above was used as the toner, and the pressure roller b described above was used as the pressure roller.

Similar to Example 1, a solid image was created from a position 2 mm from the leading edge of the recording paper, and the creation position of white dots was changed. Further, the photosensitive member electrostatic potential of the image portion other than the white portion was adjusted so that the adhesion amount was about 4.0 g / m ² . From the results of Examples 7 and 8 and Comparative Example 1, it can be seen that if white dots are formed in an area of at least 1 mm from the leading edge of the solid image, it is effective for separation.

[Effect confirmation 4]
Next, it is verified whether the effect changes depending on the difference in the reverse crown amount of the pressure roller 17. Table 4 shows an outline of the conditions and evaluation results of the examples given here. In all cases, the toner A described above was used as the toner, the dot diameter of the white dots was 40 μm, and the dot density was 2 / mm ² .

  From the results of Examples 9 and 3, it is considered that the reverse crown shape of the pressure roller 17 is preferably set so that the crown amount is about 0.1 mm to 0.6 mm.

[Effect confirmation 5]
Next, the effect of the fixing device of the upper and lower independent drive system will be verified. Table 5 shows an outline of the conditions and evaluation results of the examples given here. In all cases, the toner A described above is used as the toner, the dot diameter of the white dots is 40 μm, the dot density is 2 / mm ² , and the dot creation site is 3 mm from the top of the image. The pressure roller c described above as the pressure roller was adopted as the region.

In Examples 10 and 11, a driving motor was also connected to the fixing roller 19 in Embodiment 1, and the speed was increased with respect to the surface speed of the pressure roller 17. The pressure roller 17 uses a pressure roller c that is not an inverted crown shape. In Example 12, no speed difference is provided. On the other hand, Examples 13 and 14 use the upper and lower roller type fixing device shown in the second embodiment (see FIG. 5). The pressure roller c which is not a reverse crown shape was also used for these pressure rollers. The solid image was provided with a white dot diameter of 40 μm at a density of 2 pieces / mm ^{2 up} to the solid image tip of 3 mm. In Example 15, no speed difference is provided. From these results, it can be seen that it is important to provide a speed difference as the vertical drive.

[Effect confirmation 6]
Next, the effect of the difference in toner type will be verified. Table 6 shows an outline of the conditions and evaluation results of the examples and comparative examples given here. Here, in any case, the pressure roller b is adopted in the first embodiment.

  As shown in Table 6, it was verified whether the effects of the present invention can be obtained with the three types of toners A to C described above. As a result, it was confirmed that any toner can be effective.

4). Summary The image forming apparatus described above includes an image forming unit (mainly the image forming unit 1) that forms a toner image on the recording paper P using toner containing wax, and the recording paper P on which the toner image is formed. And a fixing unit (including a pressure roller 17 and a fixing roller 19) for pressurizing and heating the toner image onto the recording paper P by passing the toner image through the fixing nip. In forming the image, a process of providing a whitened portion is performed so as not to reduce the toner amount per unit area in at least a predetermined region on the front end side in the conveyance direction of the solid image. Therefore, it is possible to improve the separation of the recording paper without reducing the toner adhesion amount.

In the present embodiment, the process of providing the white portion is a process of providing a predetermined number of white dots per unit area in the predetermined area. Considering the evaluation results of the above-described embodiment, it is preferable to provide white dots having a diameter of 40 to 80 μm in at least a region within 5 mm from the leading end in the conveyance direction of the solid image. Regarding the wax and toner used in this embodiment, the melting point of the wax is 100 ° C. or less, and the temperature at which the toner elastic modulus (G ′) of the toner becomes 10 ⁴ Pa is 110 ° C. or less. Is preferred.

  In the present embodiment, the fixing nip is formed between the fixing member and the pressure member. The fixing member and the pressure member may be rotationally driven so that there is a difference in surface speed between them. In addition, the fixing member may have a belt configuration, the pressure member may be a roller having a reverse crown shape that is rotationally driven, and the fixing member may be configured to be driven by the rotational driving of the pressure member.

  As mentioned above, although the specific example was given and demonstrated about embodiment of this invention, this invention is not limited to the content. The present invention can be implemented in various specific forms without departing from the spirit of the present invention.

  The present invention is applicable to an image forming apparatus such as a copying machine.

DESCRIPTION OF SYMBOLS 1 Image formation unit 2 Developer 3 Photoconductor 4 Exposure part 5 Charger 6 Cleaning unit 7 Transfer belt 8 Primary transfer roller 9 Roller 10 Earth roller 11 Secondary transfer roller 12 Conveyance roller 13 Discharge roller 13 Heating roller 16 Fixing belt 17 Pressure roller 18 Heater lamp 19 Fixing roller 20 Discharge tray

Claims (8)

An image forming unit for forming a toner image on a recording paper using toner containing wax;
A fixing unit that conveys the recording paper on which the toner image is formed and passes the recording paper through a fixing nip to press and heat-fix the toner image on the recording paper;
In forming a solid image as the toner image,
An image forming apparatus, wherein a process of providing a whitened portion is performed so as not to reduce a toner amount per unit area at least in a predetermined region on the leading end side in the conveyance direction of the solid image.   The image forming apparatus according to claim 1, wherein the process of providing a white portion is a process of providing a predetermined number of white dots per unit area in the predetermined region.   The image forming apparatus according to claim 2, wherein the white dots having a diameter size of 40 to 80 μm are provided at least in an area within 5 mm from the leading end in the transport direction of the solid image. The fixing nip is formed between a fixing member and a pressure member,
The image forming apparatus according to claim 3, wherein the fixing member and the pressure member are rotationally driven so that there is a difference in surface speed between them. The fixing nip is formed between a fixing member and a pressure member,
The fixing member has a belt configuration;
The pressure member is a roller having an inverted crown shape that is driven to rotate,
The image forming apparatus according to claim 3, wherein the fixing member is driven by rotation of the pressure member. The melting point of the wax is 100 ° C. or less,
The image forming apparatus according to claim 2, wherein a temperature at which a toner elastic modulus of the toner becomes 10 ⁴ Pa is 110 ° C. or less. Detecting the thickness of the recording paper,
The image forming apparatus according to claim 2, wherein whether or not to provide the white dots is determined based on the detection result.   The image forming apparatus according to claim 2, wherein whether or not to provide the white dots is determined based on position or width information of the solid image.