JP2006267949A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of a development ghost even when toner with a strong cohesiveness is used. <P>SOLUTION: A mean square value Rq is considered as 0.08 or less regarding waveform by performing surface shape measurement under conditions that arithmetic means roughness Ra measured by a measurement method based on JIS 1994 is considered as 1.3 μm or more in surface roughness of a development roll 20, measurement pitch of the surface roughness is considered as 0.15 μm and resolution in the height direction is considered as 0.01 μm, performing Fourier transform to the obtained cross-sectional shape waveform, cutting continuous frequency component more than toner particle diameter and performing five point weighted average to each point. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device that suppresses development ghosts (density unevenness due to image history) and an image forming apparatus using the same.

As a developing device that suppresses the development ghost, the developing devices disclosed in Patent Documents 1 to 4 are known. Patent Document 1 discloses a technology for preventing toner from being overcharged and suppressing ghosting by providing a resin layer having conductivity and surface lubricity composed of a phenol resin and carbon on a developer carrier. Is disclosed. In the developing device of Patent Document 2, the toner on the developed sleeve is removed by a magnetic roll arranged in non-contact with the sleeve, and the history is eliminated to suppress the development ghost. In the developing devices of Patent Documents 3 and 4, the toner on the sleeve after development is removed by a scraper to eliminate the history and suppress the development ghost.
JP-A-1-276174 JP-A-60-91373 Japanese Patent Laid-Open No. Sho 62-251771 JP-A-9-274383

  By the way, in recent years, a magnetic one-component toner using a polyester resin having good low-temperature fixability has been proposed from the viewpoint of increasing the printing speed. Further, for the purpose of improving the image quality, the toner particle diameter tends to be reduced.

  A magnetic one-component toner using a polyester resin and a toner having a reduced diameter have strong cohesive properties and are easily fixed on a developer carrying member. For this reason, in the non-image portion where the toner is not consumed, the toner is fixed on the developer carrier, and in the image portion where the toner is consumed, the toner is replaced with a new toner, so that the toner is not fixed on the developer carrier.

  When the toner is fixed on the developer carrier, the toner is difficult to be supplied to the image carrier, so that developability is deteriorated. On the other hand, the toner is not fixed on the developer carrier. Is easy to be supplied to the image bearing member, so that developability is good. This difference in developability appears as a development ghost (density unevenness due to image history).

  As described above, a toner having strong cohesion tends to have a difference in developability, so that a development ghost is likely to occur, and a development ghost may occur even when the developing devices of Patent Documents 1 and 2 are used. In the case of using the developing devices of Patent Documents 3 and 4, although there is an effect of suppressing the development ghost, scratches on the contact portion between the scraper and the developing roll, processing of the toner after peeling off, an increase in parts cost, etc. There's a problem.

  In view of the above fact, an object of the present invention is to suppress the development ghost even when a toner having high cohesion is used.

  A developing device according to a first aspect of the present invention is a developing device of a magnetic one-component development system in which toner is carried and conveyed by a developer carrying member, and the toner is supplied to the image carrying member for development. As for the surface roughness, the arithmetic average roughness Ra measured by a measuring method based on JIS 1994 is 1.3 μm or more, the measurement pitch of the surface roughness is 0.15 μm, and the resolution in the height direction is 0.01 μm. The surface shape is measured under the following conditions, the obtained cross-sectional shape waveform is Fourier transformed, a long frequency component equal to or larger than the toner particle diameter is cut, and a square average value Rq is 0 for a waveform obtained by weighted averaging of each point at five points. 0.08 μm or less.

  As described above, in the surface roughness of the developer carrier, the surface shape is measured under the condition that the measurement pitch of the surface roughness is 0.15 μm and the resolution in the height direction is 0.01 μm, and the obtained cross-sectional waveform is obtained. The square average value Rq is set to 0.08 μm or more with respect to a waveform obtained by performing Fourier transform, cutting a long frequency component equal to or larger than the toner particle diameter, and weighting and averaging each point at five points. Even when the toner is slippery and has strong cohesiveness, the toner is hardly fixed on the developer carrying member. For this reason, even in the portion of the developer carrying member where the toner has not been consumed continuously, the toner is not easily fixed on the developer carrying member, and there is a difference in developability from the portion where the toner has been consumed continuously. Since it is difficult, generation | occurrence | production of a development ghost can be suppressed.

  Further, as in the configuration of the first aspect, by setting the arithmetic average roughness Ra to 1.3 μm or more, the toner carrying property of the developing carrier is ensured, and sufficient toner is applied to the image carrier. Can be supplied and concentration does not decrease.

  According to a second aspect of the present invention, in the developing device according to the second aspect, a layer forming member for forming a thin toner layer is provided on the developer carrying member, and the layer forming member comprises a magnetic material. It is characterized by being.

  In this configuration, the binding force between the surface of the development carrier and the toner is weakened by increasing the magnetic binding force between the toners on the development carrier by the action of the magnetic member included in the layer forming member. For this reason, the toner is hardly fixed on the developer carrying member, and development ghost can be suppressed.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the developer carrying member has a resistance value of 20Ω or less by dispersing a conductive substance in the resin material. It has the adjusted resin layer, It is characterized by the above-mentioned. The resistance value was measured by a four-probe method using a Mitsubishi Oily Corporation Loresta.

According to a fourth aspect of the present invention, there is provided the developing device according to the first aspect, further comprising a layer forming member that contacts the developer carrying member and forms a thin layer of toner on the developer carrying member. The developer carrying member has a charging capability Q / S of 10 μC / cm ² or more, and the layer forming member has a hardness of 40 degrees or less when measured with a JIS-K6301 spring type A, and the contact pressure is The linear pressure is 60 gf / cm or less.

In this way, by setting the charging capacity Q / S of the developer carrier to 10 μC / cm ² or more, the force in the electric development direction (force to adhere to the image carrier) due to the developing electric field acting on the toner is increased. Therefore, even if the toner has high cohesiveness, sufficient toner can be supplied to the image carrier, and high developability can be obtained.

  In addition, the layer forming member that contacts the developer carrier and forms a thin layer of toner on the developer carrier has a hardness of 40 degrees or less when measured with a JIS-K6301 spring type A. When the contact pressure is 60 gf / cm or less in linear pressure, the charge-up phenomenon that occurs when the hardness and contact pressure are high is unlikely to occur, and after solid black output (hereinafter referred to as “black after”), solid white output. Since the charge distribution of the later toner layer (hereinafter referred to as “after white”) can be made substantially the same, the developability after white after black can be made the same, and the development ghost can be suppressed.

  According to a fifth aspect of the present invention, there is provided the developing device according to the fourth aspect, wherein the layer forming member is curved so that a surface facing the developer carrier is a straight shape or along the developer carrier. It is characterized by being.

  In the case where the layer forming member is curved to the opposite side with respect to the developer carrying member, the contact width cannot be effectively obtained, and the layer forming member is in contact with the developer carrying member in a stretched state. Substantially the same effect as the layer forming member having a hardness equal to or higher than the material hardness abuts against the developer carrying member is brought about.

  On the other hand, in the configuration according to claim 5, the side surface on the opposite side to the developer carrier is curved so as to be straight or along the developer carrier. The effect of claim 4 in which the hardness is set to 40 degrees or less and the contact pressure is set to 60 gf / cm or less in terms of linear pressure is reliably exhibited.

  An image forming apparatus according to a sixth aspect of the present invention includes the developing device according to any one of the first to fifth aspects.

  Since the present invention has the above-described configuration, it is possible to suppress development ghost even when a toner having strong cohesion is used.

Hereinafter, embodiments of a developing device of the present invention and an image forming apparatus using the developing device will be described with reference to the drawings.
[First Embodiment]
First, a first embodiment of the present invention will be described. As shown in FIG. 1, an image forming apparatus 10 according to the present embodiment includes a photosensitive drum 12 that rotates in one direction (A direction in FIG. 1). In the vicinity of the photosensitive drum 12, a developing device 14 is provided for supplying the single-component developer D made of magnetic toner onto the photosensitive drum 12 for development.

  The developing device 14 includes a housing 24 including a developer accommodating chamber 18 that accommodates the developer D and a developing roll accommodating chamber 22 that accommodates the developing roll 20. The housing 24 is formed with an opening 16 that allows the developer storage chamber 18 and the developing roll storage chamber 22 to communicate with each other. The stirring member 26 passes through the opening 16 from the developer storage chamber 18 to the developing roll storage chamber 22. The stirred developer D is supplied.

  The upper side of the developing roll storage chamber 22 is opened, and the developing roll 20 faces the photosensitive drum 12 in this open area. A power source (not shown) for applying a developing bias to the developing roll 20 is connected to the developing roll 20.

  The developing roll 20 is provided with a magnet roll 28 that is fixed so as not to rotate and in which a plurality of magnetic poles are alternately arranged, and around the magnet roll 28 in one direction (direction B in FIG. 1). A non-magnetic cylindrical developing sleeve 30 is provided.

  A layer forming blade (layer forming member) 32 that contacts the surface of the developing sleeve 30 and forms a thin layer of the developer D on the developing sleeve 30 is attached to the housing 24. The layer forming blade 32 includes a leaf spring material 34 having one end fixed to the housing 24 and a rubber member 36 attached to the other end of the leaf spring material 34. As the rubber member 36, for example, silicon rubber, urethane rubber or the like is used.

  The developing sleeve 30 was made of aluminum as a base material, subjected to a blasting process for forming a substantially spherical dimple as a surface treatment, and then anodized to deposit nickel.

In the blast treatment, by adjusting the size of the glass beads to be blown, the arithmetic average roughness Ra measured by the measuring method based on JIS 1994 is set to 1.3 μm or more, preferably 1.5 μm or more. In addition, by adjusting the nickel deposition conditions, the surface shape is measured under the condition that the measurement pitch of the surface roughness is 0.15 μm and the resolution in the height direction is 0.01 μm, and the obtained cross-sectional waveform is Fourier transformed. The square mean value Rq (hereinafter, simply referred to as “microscopic surface roughness Rq”) is preferably set to 0.08 μm or less with respect to a waveform obtained by cutting a long frequency component larger than the toner particle diameter and weighting and averaging each point at five points. Is 0.045 μm or less. The 5-point weighted average is obtained by the following equation.

  Next, a detailed evaluation method (measurement method) of the microscopic minute surface roughness Rq will be described.

  With a laser microscope VK-8510 manufactured by KEYENCE, an objective lens of 100 times is attached to obtain an uneven profile on the surface of the developing sleeve.

ここで、Ｆｎは、カットオフフィルターで、断面曲線からトナー粒径ｄ以下の微少粗さを抽出するため、カットオフレベルｋ、カットオフ幅ｗとおき下式で定義される。

なお、他の係数は以下のとおりである。

Measurement pitch in the lengthwise direction X is 0.14565Myuemu, the resolution of the height Y direction is set to 0.01 [mu] m, to collect height data y _m of 1024 points in the X direction.
It becomes a roughness measurement object of length L = 1499.1456 μm.
The obtained cross-sectional shape waveform is subjected to Fourier transform, and the surface roughness profile u of a fine region from which a large waviness equivalent to or larger than the toner particle size is removed is obtained as follows. Note that y ′ is an inverse Fourier transform, and g is a swell component.

Here, Fn is a cut-off filter, and a fine roughness equal to or smaller than the toner particle diameter d is extracted from the cross-sectional curve. Therefore, the cut-off level k and the cut-off width w are defined as follows.

Other coefficients are as follows.

The mean square value Rq is obtained from the fine surface roughness profile u _m obtained as described above. However, for the convenience of the height detection method of the laser microscope, a surface with a sharp change in the fine surface unevenness is detected as an unevenness larger than the actual one. Therefore, since u _m contains a lot of noise, noise removal is performed according to the following procedure.
<1> | u _m | <calculates a standard deviation σ only 1μ becomes u _m.
<2> | u _m | <calculates the root mean only 2σ becomes u _m, put and Rq this.
The above is the method for measuring the minute surface roughness Rq.

  Next, the operation of the first embodiment will be described.

  In the developing device 14 of the first embodiment, the developer D supplied from the developer accommodating chamber 18 to the developing roll accommodating chamber 22 is held on the surface of the developing sleeve 30 by the magnetic force of the magnet roll 28, and the photosensitive drum. The developer D is transported to the development region facing the toner 12. The transported developer D is formed in a thin layer on the developing sleeve 30 by the layer forming blade 32, and the developer D transported to the developing region is generated by applying a developing bias to the developing roll 20. It flies to the photosensitive drum 12 by the action of the electric field. A series of development operations are performed as described above.

  In the first embodiment, since the minute surface roughness Rq of the surface of the developing sleeve 30 is 0.08 μm or less, even when the toner is slid easily on the developing sleeve 30 and the cohesiveness is strong at the time of layer formation, It is difficult for toner to adhere to the surface. For this reason, even in the portion of the developing sleeve 30 where the toner has not been continuously consumed, the toner is not easily fixed on the developing sleeve 30, and a difference in developability from the portion where the toner has been continuously consumed is unlikely to occur. The development ghost can be suppressed. In addition, this effect is more effectively exhibited when the surface roughness Rq of the developing sleeve 30 is 0.045 μm or more.

  When the surface roughness Rq of the developing sleeve 30 exceeds 0.08 μm, the surface is rough and the toner tends to be caught on the surface of the developing sleeve 30, so that it is easily fixed on the surface of the developing sleeve 30 and development ghost is generated. Becomes prominent.

  Further, since the arithmetic average roughness Ra of the surface of the developing sleeve 30 measured by a measuring method based on JIS 1994 is set to 1.3 μm or more, the transportability of the developer D of the developing sleeve 30 is ensured. Sufficient toner can be supplied to the drum 12, and the density of the image does not decrease. This effect is more effectively exhibited when the arithmetic average roughness Ra of the surface of the developing sleeve 30 is 1.5 μm or more.

  When the arithmetic average roughness Ra of the developing sleeve 30 measured by a measuring method based on JIS 1994 is less than 1.3 μm, the conveying force of the developer D of the developing sleeve 30 is reduced, and sufficient toner is supplied to the photosensitive drum 12. Can not.

(Test example)
A comparative test was performed to confirm the effect of the first embodiment.

  In the above-described configuration of the first embodiment, a toner prepared by a polymerization method and having a weight average particle diameter of 8 μm or less is used, the value of the minute surface roughness Rq on the surface of the developing sleeve 30 is changed, and other conditions are the same. A comparison test was conducted to determine whether or not development ghosts occurred.

  As a result, as shown in the table of FIG. 2, when the value of the minute surface roughness Rq exceeds 0.045 μm, a ghost is generated, and when the value of the minute surface roughness Rq is 0.045 μm or less. No ghost occurred. Further, when it exceeds 0.08 μm, a ghost outside the allowable range is generated, and when the value of the minute surface roughness Rq is 0.08 μm or less, a ghost within the allowable range is generated.

  In the above-described configuration of the first embodiment, the value of the arithmetic average roughness Ra of the surface of the developing sleeve 30 measured by a measuring method based on JIS 1994 using a toner prepared by a polymerization method and having a weight average particle diameter of 8 μm or less. The other conditions were adjusted to be the same, and the amount of developer that can be conveyed by the developing roll was measured.

As a result, as shown in the table of FIG. 4, when the arithmetic average roughness Ra measured by the measuring method based on JIS 1994 is set to 1.3 μm or more, the developer amount is such that the density does not decrease in the image. It was found that 7 mg / cm ² or more of developer D can be supported on the developer support.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the developing device according to the second embodiment, in addition to the configuration of the first embodiment, the resin layer on the surface of the developing sleeve 30 has a resistance value of 20Ω or less, preferably by dispersing a conductive substance in the resin material. It adjusted to 12 ohms or less. The resistance value was measured by a 4-probe method using a Mitsubishi Oily Corporation Loresta. As the resin material, for example, phenol resin (weight average molecular weight Mw = 4500, viscosity 150 mps, heating residue 43%) can be used, and as the conductive material, for example, carbon black (oil supply amount 169 cc / 100 g (ASTM Standard), heating residue ≦ 1% (ASTM standard), ash content ≦ 0.05% (ASTM standard), particle size 150-350 nm) can be used. For example, ethanol is used as the diluent.

  Adjust to 100 parts by weight of phenolic resin, 20 parts by weight of carbon black, and 250 parts by weight of diluent, and coat the surface of the # 60 glass bead-blasted aluminum sleeve with a thickness of about 6 μm. By setting the resistance value to 20Ω or less, preferably 12Ω or less, and the minute surface roughness Rq to 0.07 μm, the effect of suppressing development ghost was enhanced.

  Further, in the second embodiment, in addition to the above configuration, as shown in FIG. 4, the magnetic member is provided on the back side of the rubber member 36 of the layer forming blade 32 (the surface opposite to the surface contacting the surface of the developing sleeve 30). 40 may be provided. As the magnetic member 40, a SUM material can be used.

  With this configuration, by increasing the magnetic binding force between the toners on the developing sleeve 30, the binding force between the surface of the developing sleeve 30 and the toner can be weakened. As a result, the toner in the vicinity of the surface of the developing sleeve 30 (the toner in the lower layer) easily moves, acts to prevent toner retention and aggregation, and the effect of suppressing development ghost is enhanced.

  In the above configuration, the magnetic member 40 is attached to the back side of the rubber member 36, but a magnetic member may be used for the layer forming blade 32 itself.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. The developing apparatus of the third embodiment, in addition to the configuration of the first embodiment, adjusts the charging capacity Q / S of the developing sleeve 16, and 10 [mu] C / cm ² or more, preferably in the range of 10~22μC / cm ² More preferably, it was adjusted to 16 to 22 μC / cm ² . The charging ability Q / S is the toner charge amount per unit surface area of the developing carrier after the layer forming blade 32 forms a layer on the developing roll (developing carrier) 20 and is applied at the time of image printing. The same development bias as that described above was applied, and the black solid development was developed for 4 rotations of the development carrier, and then measured on the toner layer after idly rotating for 30 rotations without applying a bias. The measurement environment was 22 ° C. and 55% temperature and humidity.

  The rubber hardness of the rubber member 36 of the layer forming blade 32 (measurement method is JIS-K6301 spring type A type) is set to 40 degrees or less, preferably 35 degrees or less, and more preferably 30 degrees or less.

  The contact pressure with which the layer forming blade 32 contacts the surface of the developing sleeve 30 was adjusted to a linear pressure of 60 gf / cm or less, preferably 50 gf / cm or less, and more preferably 40 gf / cm or less.

  The rubber member 36 of the layer forming blade 32 is configured such that the side surface facing the developing sleeve 30 has a straight shape or a curvature along the surface of the developing sleeve 30 except for the contact surface that contacts the developing sleeve 30. It is preferable.

  When the layer forming blade 32 has a curvature on the opposite side with respect to the developing sleeve 30, the contact width cannot be effectively achieved, and the rubber member 36 of the layer forming blade 32 is stretched to contact the surface of the developing sleeve 30. Therefore, the contact surface comes into contact with the developing sleeve 30 with a surface hardness substantially equal to or higher than the material hardness, and the contact pressure distribution becomes steep.

  On the other hand, when the opposite side surface of the developing sleeve 30 has a straight shape or a curvature along the developing sleeve 30, the contact width of the contact surface with the developing sleeve 30 can be effectively obtained, and the surface is equal to or higher than the material hardness. There is no contact with the developing sleeve 30 due to the hardness.

  Next, the operation of the third embodiment will be described while comparing with conventional problems.

  Although the toner charging mechanism has many complicated and unexplained phenomena, the frictional charging between the surface of the developing sleeve and the toner during the formation of the toner thin layer is mainly performed. In such a charging system, a difference in charge between the toner after black and the toner after white tends to occur. In the case of a conventional toner having low adhesion (cohesiveness) of a styrene acrylic type, this charge difference is regarded as a difference in developability. Appears and tends to appear as a density difference or ghost. Therefore, in the prior art, the developing property difference is made difficult to appear on the print by keeping the charging property low and reducing the absolute value of the charging difference.

In recent years, polyester-based toners have been used for securing fixing properties. Compared to styrene-acrylic, polyesters contain many ester bonds with strong polarization, and therefore, the polarization force due to polar groups and the so-called non-electrostatic adhesion due to hydrogen bonds act strongly between molecules. When such a material is powdered, there is a strong tendency for the particles to aggregate so as to reduce the surface energy. In addition, since the surface area per unit volume increases as the particle size is reduced, this agglomeration is relatively stronger than that of a large particle size toner. This effect occurs not only between the toner and the toner but also between the toner and the sleeve. For this reason, when the charging capability Q / S of the developing sleeve is less than 10 μC / cm ² , the charging level of the toner is low, the force in the electric development direction acting on the toner due to the developing electric field is weak, and non-electrostatic The adhesive force is in a condition that tends to hinder developability.

Therefore, as in the third embodiment, the charging capability Q / S of the developing sleeve 16 is indispensable to be 10 μC / cm ² or more. With this configuration, the electric developing direction acting on the toner due to the developing electric field is increased. Even if the toner has a strong force and a strong cohesiveness, sufficient toner is supplied to the photosensitive drum 12 and high developability can be obtained.

  However, if the toner is excessively charged, the toner can easily adhere to the sleeve due to electrostatic image force. Further, as the particle size is reduced, the surface area per unit volume increases, and the surface area of the toner that can be charged increases, so the charge amount increases. Taking a volume surrounded by the height of the sleeve unit surface area from the sleeve and considering a model in which the toner is filled, the fine powder toner stores more charge. Therefore, the electrostatic adhesion force acting on the toner layer in the volume means that fine powder toner is more strongly attached. In this way, overcharged toner easily adheres to the sleeve both electrostatically and non-electrostatically, and a sleeve with high chargeability alone hinders developability and causes a decrease in density after whitening, that is, ghosting. May end up.

Therefore, chargeability Q / S of the developing sleeve 16 is, more preferably preferably in the range of 10~22μC / cm ^2, in the range of 16~22μC / cm ^2, this arrangement, cohesive Even when a strong toner is used, density reduction after white does not occur and development ghosting is suppressed.

  Further, the rubber hardness of the rubber member of the layer forming blade (measurement method is JIS-K6301 spring type A) exceeds 40 degrees, and the contact pressure at which this layer forming blade contacts the surface of the developing sleeve is 60 gf in terms of linear pressure. In a configuration exceeding / cm, the charge-up phenomenon of toner appears remarkably, a difference in developability due to the charge difference between the toner after white and the toner after black appears, and a development ghost occurs.

  As in the third embodiment, the rubber hardness of the rubber member 36 of the layer forming blade 32 (measurement method is JIS-K6301 spring type A) is 40 degrees or less, preferably 35 degrees or less, more preferably 30 degrees. The contact pressure at which the layer forming blade 32 contacts the surface of the developing sleeve 30 is 60 gf / cm or less, preferably 50 gf / cm or less, more preferably 40 gf / cm or less. Thus, the charge distribution of the toner layer after white and black can be made substantially the same, and the charge amount of the toner layer from the middle layer to the upper layer can be increased without excessively increasing the charge amount of the lower layer of the toner layer. By increasing the amount of toner that can contribute to toner and making the charging property after white and black equal, it becomes possible to make the developing property the same, and the generation of the development ghost can be suppressed.

  In order to effectively obtain this characteristic, a developing sleeve having a minute surface roughness Rq of 0.08 μm or less is required. This is presumably due to the good migration of the toner at the thin layer forming contact portion. The developing sleeve surface is slidable, the contact hardness is wide with a low-hardness layer forming blade, the contact pressure is gentle, and the triboelectric charging property of the developing sleeve 30 is effective in a trinity.

(Test example)
In order to confirm the effect of the third embodiment, a comparative test was performed as follows.

  The developing device 14 uses a developing roller 20 comprising a cylindrical developing sleeve 30 having an outer diameter of 16 mm and a magnet roll 28 provided with a developing pole having a magnetic force of 900 gauss on the developing sleeve surface in the developing region. The separation distance L from the photosensitive drum 12 in the development area was set to 250 μm. As a developing bias, a DC component having a voltage of −400 V and an AC component composed of a rectangular wave having a frequency of 3.3 kHz, a peak-to-peak voltage Vpp of 1.8 kVpp, and a duty of 50% was applied.

  As the photosensitive drum 12, a photosensitive drum having a diameter of 30 mm was used. The photosensitive drum 12 was charged by a charger so that a charging potential (non-image portion potential) was −500 V, and then an electrostatic latent image having a latent image potential of −150 V was written. In this test, development and image formation were performed by operating the developing device 14 and the photosensitive drum 12 so that the process speed was 204 mm / sec. The peripheral speed ratio between the photosensitive drum 12 and the developing roll 20 is in the range of 1: 1 to 1: 1.2.

  A toner containing a polyester-based resin as a binder resin and having a volume average particle size of 7 μm or less and a particle size distribution in which the number percentage of 4 μunder is 15% or more was used.

  Each of the developing device 14 and the single component magnetic toner having the above-described configuration was used to test whether or not development ghosts occurred in a test environment of 22 ° C. and 55% RH.

  The layer forming blade used was a conventional blade (2 pieces) with a hardness of 65 (K6301 JIS-A), a tensile strength of 25 Mpa, and a urethane resin t = 1.3 mm pressed against the doctor. . The contact pressure of the blade was 60 gf / cm in terms of linear pressure.

  As a blade (3 pieces) of the third embodiment, a strip blade with a tensile strength of 6.2 Mpa and silicone rubber t = 1.0 is pressed against a spring material of phosphor bronze t = 0.08 so as to be pressed against the spring material, and the rubber hardness is 30, 35. , 40 (K6301 JIS-A). The contact pressure of the blade was set to 60 gf / cm as a linear pressure (see FIG. 5A).

  Further, as a blade (three pieces) of the third embodiment, a strip blade having a hardness of 30 (K6301 JIS-A) tensile strength of 6.2 Mpa and silicone rubber t = 1.0 is bonded to a spring material of phosphor bronze t = 0.08. The blade contact pressure was changed to a linear pressure of 40 gf / cm, 50 gf / cm, and 60 gf / cm (see FIG. 5B). Further, as this comparative example, a blade contact pressure of 70 gf / cm in linear pressure was used (see FIG. 5B).

  As a result, as shown in the tables of FIGS. 5A and 5B, it has been found that the configuration of the third embodiment does not cause a density difference in the print density or the density difference is small and can suppress development ghost. .

[Reference example]
Next, a technique related to the present invention will be described as a reference example.

  First, the background to which this technique was proposed will be described. In a conventional developing device, a layer forming blade that forms a thin layer of developer on the developing roll is pressed against the developing roll. Therefore, when the toner passes through the pressed portion, the toner is pressed onto the developing roll, and the toner Is agglomerated on the developing roll, it is known that the chargeability, adhesion, etc. of the toner change and development ghost is generated.

  As a means for solving this problem, there is a configuration in which, when a layer is formed, the toner is once peeled off from the developing roll, and new toner is supplied to eliminate aggregation of the toner and suppress development ghost.

  As an example of this, a scraper method has been proposed in which the toner is mechanically removed from the developing roll. However, in this method, scratches on the contact portion between the scraper and the developing roll, processing of the toner after peeling, an increase in parts cost, etc. There is a problem.

  A configuration that gives a similar effect without adding parts such as a scraper is to increase the internal pressure of the toner in the wedge area formed by the contact surface on the free end side of the layer forming blade and the surface of the developing roll, thereby It is considered effective to form a static toner area.

  In order to increase the internal pressure of the toner, it is desirable to reduce the angle of the wedge region. However, in a general configuration, the contact surface of the layer forming blade is formed as a straight surface. The roll diameter is almost determined by the roll diameter. There is a configuration in which the roll angle of the developing roll is not increased and the wedge angle is reduced, and there is a configuration in which the shape of the layer forming blade is changed in advance, but in this configuration, a uniform layer cannot be obtained if the mounting position is shifted. It was necessary to attach with high accuracy.

  In consideration of the above facts, the present proposal controls the shape of the wedge region with a simple configuration, strengthens the static toner generated in the region, enhances the effect of removing the toner from the developing roll, and suppresses the development ghost. It was made for the purpose.

  Next, the structure of this proposal is demonstrated. Note that the overall configuration of the developing device is the same as that of the first embodiment, and is omitted, and a layer forming blade (layer forming member) that is a different part will be described.

  The layer forming blade in this proposal includes a rubber member having a rubber hardness of 50 degrees or less in contact with the developing roll (measurement method is JIS-K6301 spring type A), and a resin or metal thin film sheet covering the contact surface of the rubber member And a pressing member that is provided on the back surface (opposite surface to the contact surface) of the rubber member and presses the rubber member against the developing roll, and the pressing member is a contact portion where the developing roll and the rubber member are in contact with each other The rubber member is fixedly adhered to the back surface corresponding to the downstream portion in the rotation direction of the developing roll when viewed from the contact portion, and the rubber member is The upstream portion in the rotational direction is free (free state).

  Specifically, in the proposed layer forming blade 50, as shown in FIG. 6, a rubber member 54 having a thickness of 1 mm and a width of 8 mm is provided on a leaf spring 52 made of stainless steel (SUS304) having a thickness of 0.1 mm as a pressing member. (For example, silicon rubber) was pasted. At that time, the rubber member is bonded so as to protrude 3 mm from the tip of the leaf spring. The rubber member used has a rubber hardness of 50 degrees or less, preferably 30 degrees or less when measured with a JIS-K6301 spring type A type.

  In FIG. 6, the position of the developing roll 20 when the layer forming blade 50 is mounted is indicated by an imaginary line. A portion that contacts the developing roll 20 and a back surface of the leaf spring 52 corresponding to the downstream side of the developing roll 20 in the rotation direction (direction A in FIG. 6) are covered. On the other hand, there is no leaf spring 52 on the free end side (the upstream portion in the rotation direction) from the contact portion, and the rubber member 54 is free (free state). A 50 micron PET film 56 as a thin film sheet is attached to the contact surface of the rubber member 54 with the developing roll 20. The thin film sheet is not limited to a PET film, and other resin materials may be used, or a metal sheet may be used.

  The layer forming blade 50 is pressed against a developing roll coated with a mixture of phenol resin and carbon having a diameter of 16 mm at a linear pressure of 50 g / cm.

  Using the developing device 14 having the above configuration using the layer forming blade 50 (the hardness of the rubber member is 30 degrees (measurement method is JIS-K6301 spring type A type, with a PET film on the contact surface)) When the cycle characteristics of the toner amount were measured, the toner amount was stable at the first rotation and the eighth rotation.

  As shown in FIG. 7, as a comparative example, a layer forming blade 60 (the hardness of the rubber member 64 is 50 degrees (measurement method is JIS-K6301 spring type A), no PET film on the contact surface) is used. When the cycle characteristics of the amount of toner on the developing roll were measured by sticking to the leaf spring 62 over the entire back surface and adjusting other conditions to be the same, there was an approximately double increase in the first and eighth rotations. An increase in the amount of toner on the developing roll 20 with the rotation cycle of the developing roll 20 indicates that the adhesion force of the toner has increased. In this proposal, an increase in the adhesion force of the toner can be suppressed. It is thought that. Actually, as a result of collecting an image for confirming the development ghost in this state, a development ghost was seen in the comparative example, but the ghost was suppressed in the proposed developing device 14.

  This effect is thought to be because the angle of the wedge region was set small and a strong static toner was formed, but for confirmation, observation was performed from the axial direction of the developing roll 20.

  As shown in FIG. 8, it was confirmed that the rubber member 54 was bent and the angle of the wedge region θ1 was reduced. This is because, when the rubber member 54 is pressed against the developing roll 20 and deformed, a tensile stress is applied to the upper PET sheet 56 and the rubber member 54 is bent to relax the force. Since there is no leaf spring 52 on the back of the portion, it can be bent easily.

  On the other hand, the same observation was performed with the layer forming blade shown in FIG. 7 as a comparative example. As shown in FIG. 9, the rubber member 64 is not bent, and the angle θ2 of the wedge region remains large. This is because the leaf spring 62 is on the back side of the rubber member 64, so that it is difficult to bend, and the tensile load utilizing the deformation of the rubber member 64 is difficult to work on the blade surface because there is no PET sheet, and the rubber hardness is high and difficult to deform. This is the reason.

  In this proposal, the angle of the wedge region can be reduced without using the means for changing the roll diameter and the shape of the layer forming blade. Accordingly, the effect of scraping off the toner layer is enhanced even at a low linear pressure, and an increase in adhesion force is suppressed, and as a result, a ghost can be suppressed.

FIG. 1 is a schematic diagram illustrating an image forming apparatus including a developing device according to the first embodiment of the present invention. FIG. 2 is a table showing the relationship between the development ghost occurrence and the minute surface roughness in the developing device according to the first embodiment. FIG. 3 is a table showing the relationship between the arithmetic average roughness Ra of the developing sleeve surface measured by a measuring method based on JIS 1994 and the amount of developer that can be conveyed by the developing sleeve in the developing device according to the first embodiment. . FIG. 4 is a view showing a layer forming blade provided with a magnetic member according to the second embodiment. FIG. 5 is a table comparing print densities when the layer forming blade according to the third embodiment is used and when the layer forming blade of the comparative example is used. FIG. 6 is a diagram illustrating an example of a layer forming blade according to a reference example. FIG. 7 is a diagram illustrating an example of a conventional technology layer forming blade. FIG. 8 is an enlarged view showing the developing roll and the contact portion when the layer forming blade according to the reference example is applied. FIG. 9 is an enlarged view showing the developing roll and the contact portion when the layer forming blade according to the conventional example is applied.

Explanation of symbols

10 Image forming apparatus 12 Photosensitive drum (image carrier)
14 Developing Device 20 Developing Roll (Developer Carrier)
32 Layer forming blade (layer forming member)
40 Magnetic members

Claims (6)

In a magnetic one-component developing type developing device that carries and conveys toner on a developer carrying member, supplies the toner to an image carrier and develops it,
As for the surface roughness of the developer carrier, the arithmetic average roughness Ra measured by a measuring method according to JIS 1994 is 1.3 μm or more, and the measurement pitch of the surface roughness is 0.15 μm, Measure the surface shape under the condition of resolution of 0.01μm, Fourier transform the obtained cross-sectional shape waveform, cut the long frequency component over the toner particle size, and square the waveform with the weighted average of each point at 5 points A developing device having an average value Rq of 0.08 μm or less.   The developing device according to claim 1, wherein a layer forming member for forming a thin layer of toner is provided on the developer carrying member, and the layer forming member includes a magnetic material.   3. The developing device according to claim 1, wherein the developer carrying member includes a resin layer in which a resistance value is adjusted to 20Ω or less by dispersing a conductive substance in a resin material. . A layer forming member that contacts the developer carrier and forms a thin layer of toner on the developer carrier;
The developer carrying member has a charging ability Q / S of 10 μC / cm ² or more,
2. The layer forming member according to claim 1, wherein the layer forming member has a hardness of 40 degrees or less when measured with a JIS-K6301 spring type A type, and a contact pressure of 60 gf / cm or less in terms of linear pressure. Development device.   The developing device according to claim 4, wherein a surface of the layer forming member facing the developer carrying member is curved in a straight shape or along the developer carrying member.   An image forming apparatus comprising the developing device according to claim 1.

Images