Patent Application
20130071148
This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application Nos. 2011-203827 filed on Sep. 16, 2011, and 2012-162027 filed on Jul. 20, 2012, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein.
The present invention generally relates to a development device and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine having at least two of these capabilities, that includes a development device.
Development devices that include a development roller (i.e., a developer bearer) having surface unevenness are known. For example, JP-2007-178901-A and JP-2007-121951-A propose forming projections having a substantially identical height and recesses having a substantially identical depth regularly in the surface of the development roller.
In development devices, the amount of developer (i.e., toner) carried on the development roller is typically adjusted by a developer regulator such as a doctor blade. However, it is possible that toner firmly adheres to the developer regulator over time, degrading the capability to adjust the amount of toner. If a given area of the surface of the development roller carrying an excessive amount of toner reaches a position outside a development casing as the development roller rotates, it is possible that toner scatters outside the development device.
In configurations in which the development roller has surface unevenness, even if toner firmly adheres to the developer regulator, projections formed on the surface of the development roller can scrape off toner from the developer regulator. Thus, degradation in the toner amount adjustment capability and toner scattering caused thereby can be inhibited.
The surface unevenness of the development roller may be formed by continuous spiral grooves, serving as recesses, formed in the surface of the development roller. Such surface unevenness can be formed easily in the development roller by pressing a cutting die against the surface of a cylindrical pipe while the pipe is rotated and moved in the axial direction relative to the cutting die.
Additionally, in development devices, toner moves on the development roller in the axial direction along the developer regulator when its circumferential movement is inhibited by the developer regulator. When toner reaches an axial end area where the developer regulator is not present, it is possible that toner passes through gaps between the development casing and the development roller and leaks through the opening. To prevent leakage of toner in the axial end areas, typically lateral end seals are provided in the development device. The lateral end seals contact the surface of the development roller adjacent to the axial ends, thereby inhibiting toner from moving to the axial ends.
In view of the foregoing, one embodiment of the present invention provides a development device that includes a developer bearer to carry by rotation developer to a development range facing a latent image bearer, a planar developer regulator disposed to contact a surface of the developer bearer to adjust an amount of developer carried to the development range, and a lateral end seal to contact an axial end portion of the developer bearer. The developer bearer includes an uneven surface range having projections and recesses and including an axial center of the developer bearer, and smooth surface ranges positioned outside the uneven surface range in an axial direction of the developer bearer. The lateral end seal is disposed astride the uneven surface range and the smooth surface range of the developer bearer.
Another embodiment provides an image forming apparatus that includes a latent image bearer, a charging member to charge a surface of the latent image bearer uniformly, a latent image forming device to form a latent image on the latent image bearer, and the above-described development device.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to
The image forming apparatus 500 includes a body or printer unit 100, a sheet-feeding table or sheet feeder 200, and a scanner 300 provided above the printer unit 100. The printer unit 100 includes four process cartridges 1Y, 1M, 1C, and 1K, an intermediate transfer belt 7 serving as an intermediate transfer member that rotates in the direction indicated by arrow A shown in
It is to be noted that the suffixes Y, M, C, and K attached to each reference numeral indicate only that components indicated thereby are used for forming yellow, magenta, cyan, and black images, respectively. The four process cartridges 1 have a similar configuration except the color of toner used therein, and hereinafter the suffixes Y, M, C, and K may be omitted when color discrimination is not necessary.
Each process cartridge 1 includes a photoreceptor 2, a charging member 3, a development device 4, and a drum cleaning unit 5, and these components are housed in a common unit casing, thus forming a modular unit. The process cartridge 1 can be installed in the body 100 of the image forming apparatus 500 and removed therefrom by releasing a stopper.
The photoreceptor 2 rotates clockwise in the drawing as indicated by arrow shown therein. The charging member 3 can be a charging roller. The charging member 3 is pressed against a surface of the photoreceptor 2 and rotates as the photoreceptor 2 rotates. In image formation, a high-voltage power source applies a predetermined bias voltage to the charging member 3 so that the charging member 3 can electrically charge the surface of the photoreceptor 2 uniformly. Although the process cartridge 1 according to the present embodiment includes the charging member 3 that contacts the surface of the photoreceptor 2, alternatively, contactless charging members such as corona charging members may be used instead.
The exposure unit 6 exposes the surface of the photoreceptor 2 according to image data read by the scanner 300 or acquired by external devices such as computers, thereby forming an electrostatic latent image thereon. Although the exposure unit 6 in the configuration shown in
The four process cartridges 1 form yellow, cyan, magenta, and black toner images on the respective photoreceptors 2. The four process cartridges 1 are arranged in parallel to the belt travel direction indicated by arrow A. The toner images formed on the respective photoreceptors 2 are transferred therefrom and superimposed sequentially one on another on the intermediate transfer belt 7 (primary-transfer process). Thus, a multicolor toner image is formed on the intermediate transfer belt 7.
In
Among the multiple tension rollers, a tension roller 9a is disposed downstream from the four process cartridges 1 in the belt travel direction indicated by arrow A and presses against a secondary-transfer roller 9 via the intermediate transfer belt 7, thus forming a secondary-transfer nip therebetween. The tension roller 9a is also referred to as a secondary-transfer facing roller 9a. A predetermined voltage is applied to the secondary-transfer roller 9 or the secondary-transfer facing roller 9a to generate a secondary-transfer electrical field therebetween. Sheets P fed by the sheet feeder 200 are transported in the direction indicated by arrow S shown in
The fixing device 12 is disposed downstream from the secondary-transfer nip in the sheet conveyance direction. The fixing device 12 fixes the multicolor toner image with heat and pressure on the sheet P that has passed through the secondary-transfer nip, after which the sheet P is discharged outside the image forming apparatus 500.
Meanwhile, a belt cleaning unit 11 removes toner remaining on the intermediate transfer belt 7 after the secondary-transfer process. Additionally, toner bottles 400Y, 400M, 400C, and 400K containing respective color toners are provided above the intermediate transfer belt 7. The toner bottles 400 are removably installed in the body 100. Toner is supplied from the toner bottle 400 by a toner supply device to the development device 4 for the corresponding color.
Referring to
Inside the intermediate case 412, the development roller 42, a supply roller 44, a doctor blade 45, a paddle 46, a supply screw 48, and a toner amount detector 49 (shown in
An interior of the development device 4 communicates with the outside through an opening 56 (shown in
It is to be noted that, in
While rotating clockwise in
In the supply nip β, the surface of the supply roller 44 moves upward, whereas the surface of the development roller 42 moves downward. It is to be noted that, in the present embodiment, the supply roller 44 is in contact with the development roller 42 in the supply nip β.
In the development range α, a development field is generated by differences in electrical potential between the latent image formed on the photoreceptor 2 and a development bias applied from the development bias power source 142 to the development roller 42. The development field moves toner carried on the development roller 42 toward the surface of the photoreceptor 2, thus developing the latent image into a toner image. The photoreceptor 2 is contactless with the development roller 42 and rotates in the direction indicated by arrow D shown in
The development bias power source 142 applies alternating voltage to the development roller 42. The alternating voltage includes a first voltage to direct toner from the development roller 42 to the photoreceptor 2 and a second voltage to direct toner from the photoreceptor 2 to the development roller 42 for developing the latent image with toner transported to the development range α.
Thus, the development bias power source 142 applies alternating voltage to the development roller 42 as a bias to move toner toward the photoreceptor 2 as if toner jumps, which is a type of image development called “contactless AC jumping development”. Contactless image development is advantageous in that the surface unevenness of the development roller 42 is less likely to make the image density uneven, and use of alternating voltage can enhance such effects. Thus, image quality can improve.
Referring to
Toner T that is not used in image development but has passed through the development range α is collected from the surface of the development roller 42 by the supply roller 44 on an upstream side of the supply nip β in the direction B (shown in
Generally, toner T held in the recesses 42b formed regularly in the surface of the development roller 42 is not easily removed therefrom. If toner T that has passed through the development range α remains on the development roller 42 and passes through the supply nip β, it is possible that the toner T firmly adheres to the development roller 42, forming a film covering the surface of the development roller 42, which is a phenomenon called “toner filming”. Toner filming can cause fluctuations in the charge amount of toner carried on the development roller 42 per unit amount, the amount of toner carried on the development roller 42 per unit area, or both, making image density uneven.
In view of the foregoing, in the development device 4 according to the first embodiment, the development roller 42 and the supply roller 44 rotate in the opposite directions in the supply nip β. This configuration can increase the difference in linear velocity between the surface of the development roller 42 and that of the supply roller 44 in the supply nip β, and accordingly collection of toner by the supply roller 44 in the supply nip β can be facilitated. Since toner can be prevented from being carried over on the development roller 42, adhesion of toner to the development roller 42 can be inhibited. Consequently, density unevenness in image development resulting from toner adhesion can be reduced.
Additionally, in this regard, it is preferable that the linear velocity of the development roller 42 is higher. For example, in the first embodiment, the ratio of linear velocity of the development roller 42 to that of the supply roller 44 can be 1:0.85, but the linear velocity ratio is not limited thereto.
Additionally, in the configuration shown in
As shown in
As shown in
The lateral end seals 59 have curved faces in conformity to the shape of the development roller 42, and a part of the lateral end seal 59 slides on the development roller 42. When the development roller 42 is mounted in the development casing 41, the development roller 41 is pressed against the lateral end seals 59. Thus, the lateral end seals 59 contact the development roller 42. Being contact with the development roller 42, the lateral end seals 59 can seal clearance between the development roller 42 and the development casing 41.
Further, a part of the lateral end seal 59 also contacts the doctor blade 45. When the development roller 42 is mounted in the development casing 41, the doctor blade 45 is pushed by the development roller 41 and is pressed against the lateral end seals 59. With this configuration, clearance between the doctor blade 45 and the development casing 41 can be prevented.
Next, the development roller 42 is described in further detail below with reference to
The development roller 42 includes a roller shaft 421, a development sleeve 420, and the pair of spacers 420 provided to both axial end portions of the roller shaft 421. The spacers 422 are positioned outside the development sleeve 420 in the axial direction of the development roller 42.
The development roller 42 is rotatable upon the roller shaft 421 and is disposed with the axial direction thereof parallel to the longitudinal direction of the development device 4 or Y-axis in the drawings. Both axial end portions of the roller shaft 421 are rotatably supported by the side walls 412s (shown in
Additionally, the spacers 422 provided to either axial end portion contact the surface of the photoreceptor 2, and the distance between the surface of the development sleeve 420 and the surface of the photoreceptor 2 (i.e., development gap) in the development range α can be kept constant.
The development roller 42 (development sleeve 420) includes a base 42g (shown in
As shown in
The grooved range 420a is a portion including an axial center of the development roller 42, and the surface thereof is processed to have irregularities to carry toner thereon properly. Thus, the grooved range 420a can serve as a developer carrying range. In the first embodiment, surface unevenness can be formed through rolling, and the projections 42a are enclosed by first and second spiral grooves L1 and L2 winding in different directions. In the development roller 42 in the first embodiment, for example, the pitch width W1 of the projections 42a in the axial direction can be 80 μm, and the axial length W2 of the top face 42t (shown in
It is preferred that the surface layer 42f of the development roller 42 be constructed of a material capable of causing normal charging of toner. Even if low-charge toner particles are present due to filming, low-charge toner particles can be pushed out by jumping toner T and charged at positions free of filming among the projections 42a and the recesses 42b. Thus, the amount of low-charge toner particles can be reduced, and image density can become constant.
Additionally, the surface layer 42f of the development roller 42 is preferably constructed of a material harder than doctor blade 45 (or blade member 450). With this configuration, the projections 42a of the development roller 42 are not easily abraded by the doctor blade 45, and a capacity (volume) of the recess 42b enclosed by the projections 42a and the doctor blade 45 does not change easily. Thus, an amount of toner (hereinafter “toner amount M”) carried on a unit area (hereinafter “roller unit area A”) of the development roller 42 (M/A) can be stable.
Additionally, it is preferable that the height (or the depth W3 shown in
Next, the supply roller 44 is described in further detail below.
The supply roller 44 can rotate about the roller shaft 441 that is rotatably supported by the side walls 412s of the intermediate case 412. The supply roller 44 is disposed such that a part of the outer circumferential surface of the supply sleeve 440 contacts the outer circumferential surface of the development sleeve 420 of the development roller 42, thus forming the supply nip β. As shown in
Further, in the supply nip β, the supply roller 44 rotates in the direction opposite the direction in which the surface of the development roller 42 moves as described above. In the configuration shown in
The supply sleeve 440 of the supply roller 44 is constructed of a foamed material, and a number of minute pores are diffused in a surface layer (sponge surface layer) thereof that contacts the development roller 42. The sponge surface layer of the supply roller 44 can make it ease for the supply roller 44 to reach the bottom of the recess 42b, thus facilitating resetting toner on the development roller 42.
Additionally, the amount by which the supply roller 44 extends into the range of the development roller 42, which can be expressed as the radius of the development roller 42 plus the radius of the supply roller 44 minus the distance between the axes of the development roller 42 and the supply roller 44, is greater than the height of the projections 42a of the development roller 42. With this configuration, toner in the recesses 42b can be reset properly. It is to be noted that the above-described amount should not be too large because toner may be pushed in the recesses 42b and agglomerate or coagulate if the above-described amount is extremely large relative to the height of the projections 42a.
In the present embodiment, a foamed material having an electrical resistance within a range from about 103Ω to about 1014Ω can be used for the supply sleeve 440 of the supply roller 44.
The bias power source 144 applies a supply bias to the supply roller 44, and the supply roller 44 promotes effects of pushing preliminarily charged toner against the development roller 42 in the supply nip β. The supply roller 44 supplies toner carried thereon to the surface of the development roller 42 while rotating clockwise in
Although alternating voltage is applied to the development roller 42, the bias voltage applied from the bias power source 144 to the supply roller 44 is a direct current (DC) voltage in the polarity opposite the polarity of normal charge of toner. In the first embodiment, toner is charged to have negative (minus) polarity, and the supply bias is a DC voltage in positive (plus) polarity. Thus, the voltage applied to not the development roller 42 but the supply roller 44 has the polarity (positive polarity) opposite the polarity of normal charge of toner. With this configuration, an electrical field in the direction for attracting toner T toward the supply roller 44 can be formed in the supply nip β, thus facilitating resetting of toner on the development roller 42. It is to be noted that, depending on the specification of the development device 4, the bias power source 144, which requires a separate DC power source, may be omitted, thereby reducing the cost.
Next, the doctor blade 45 is described below with reference to
As shown in
The doctor blade 45 includes a blade 450 and a metal pedestal 452. The blade 450 can be a thin planar metal member, and an end (base end) portion of the blade 450 is fixed to the pedestal 452. The other end portion (distal end portion) of the blade 450 contacts the development roller 42. The contact between the blade 450 and the development roller 42 can be either “end contact or edge contact” meaning that an edge portion or corner portion of the blade 450 contacts the development roller 42, or “planar contact” meaning that a part of the face of the blade 450 at a position between the edge portion and the base end contacts the development roller 42. The end contact is advantageous in that the blade 450 can scrape toner off the top face 42t of the projections 42a, and that only toner contained in the recesses 42b can be transported to the development range α. Thus, the amount of toner conveyed to the development range α can be kept constant.
The blade 450 can be fixed to the pedestal 452 using multiple rivets 451. The pedestal 452 is constructed of a metal member thicker than the blade 450 and can serve as a base plate to fix the blade 450 to a body (a side face of the intermediate case 412) of the development device 4. A main positioning pin holes 454a that is substantially circular and a sub-positioning pin hole 454b shaped into an oval (hereinafter also collectively “pin holes 454”) are formed in longitudinal end portions of the pedestal 452. A long diameter of the sub-positioning pin hole 454b is oriented to the main positioning pin hole 454a. With a pin inserted into the main positioning pin hole 454a, the position of the pedestal 452 relative to the body of the development device 4 is determined, and the pedestal 452 can be supported with the sub-positioning pin hole 454b. When the pedestal 452 to which the blade 450 is fixed is fixed to the body of the development device 4 with a screw 455, the blade 450 can be fixed to the development device 4.
For example, the blade 450 can be a metal leaf spring constructed of SUS304CSP or SUS301CSP (JIS standard); or phosphor bronze. The distal end (free end) of the blade 450 can be in contact with the surface of the development roller 42 with a pressure of about 10 N/m to 100 N/m, forming a regulation nip. While adjusting the amount of toner passing through the regulation nip, the blade 450 applies electrical charge to toner through triboelectric charging. To promote triboelectric charging, a bias can be applied to the blade 450 from the bias power source 145 shown in
Additionally, it is preferred that the blade 450 of the doctor blade 45 be electroconductive. When the blade 450 is electroconductive, charge amount of toner T having a greater charge amount Q per unit volume M (Q/M) can be reduced, and the charge amount Q of toner T per unit volume M can become uniform. Accordingly, toner T can be prevented from firmly sticking to the development roller 42.
The bias power source 145 can be configured to apply to the blade 450 a DC voltage within a range of the alternating voltage applied to the development roller 42 ±200 V so that the voltage value can be adjusted in accordance with usage conditions. This configuration can reduce fluctuations in the toner amount M carried on the roller unit area A.
The paddle 46 is described below with reference to
The paddle 46 is provided in the toner containing chamber 43 for containing toner and is rotatable relative to the development casing 41.
The paddle 46 includes a paddle shaft 461 and thin paddle blades 460 constructed of elastic sheet members such as plastic sheet, Mylar (registered trademark of DuPont). The paddle shaft 461 includes two planar portions facing each other. The two paddle blades 460 are attached to the two planar portions, respectively, to project in the opposite directions beyond the paddle shaft 461.
Multiple holes, arranged in parallel to the paddle shaft 461, are formed in a base portion of the paddle blade 460, and multiple projections, arranged in parallel to the paddle shaft 461, are formed on the paddle shaft 461. The projections of the paddle shaft 461 are inserted into the holes formed in the paddle blade 460 and fixed thereto in thermal caulking. Thus, the paddle blades 460 are fixed to the paddle shaft 461.
The paddle 46 is disposed with the paddle shaft 461 parallel to the longitudinal direction of the development device 4 (Y-axis direction in the drawings). Both axial ends of the paddle shaft 461 are rotatably supported by the side walls 412s of the intermediate case 412.
A distal end of the paddle blade 460 extending from the paddle shaft 461 projects a length suitable for the distal end to contact an inner wall of the toner containing chamber 43. As shown in
The inner bottom face 43b is continuous with the side wall 43s standing vertically on the side of the development roller 42. A top face of the side wall 43s parallels X-axis and is horizontal toward the development roller 42. A height of the top face of the side wall 43s is similar to or slightly lower than a center of the paddle shaft 461, thus forming the step 50.
A distance between the side wall 43s and the paddle shaft 461 is shorter than a distance between the inner bottom face 43b and the paddle shaft 461. Therefore, the paddle blades 460, which slidingly contact the inner bottom face 43b, can deform more when the paddle blades 460 contact the side wall 43s. Then, the paddle blade 460 is released and flipped up when the distal end of the paddle blade 460 reaches the step 50. As the paddle blades 460 thus move, toner can be flipped up, agitated, and transported.
The step 50 has a horizontal face parallel to X-Y plane and extends in the longitudinal direction of the development device 4 (Y-axis direction in the drawings). It is to be noted that, although the step 50 is present over the entire width in the first embodiment, the step 50 may extend partly inside the development device 4 as long as the paddle blades 460 can be flipped up.
The supply screw 48 includes the screw shaft 481 and the spiral blade 480 provided to the screw shaft 48. The supply screw 48 is rotatable upon the screw shaft 481, and screw shaft 481 parallels the longitudinal direction of the development device 4 (Y-axis direction in the drawings). Both axial ends of the screw shaft 481 are rotatably supported by the side walls 412s of the intermediate case 412.
An axial end portion of the supply screw 48 is positioned beneath the toner supply inlet 55 (shown in
Next, movement of toner inside the development device 4 is described below.
Toner supplied to the development device 4 from the toner supply inlet 55 is transported by the supply screw 48 to the toner containing chamber 43 and agitated by the paddle 46. As the paddle 46 rotates, toner is flipped up toward the development roller 42 and the supply roller 44. The toner supplied to the supply roller 44 is forwarded to the development roller 42 in the supply nip β where the supply roller 44 contacts the development roller 42. Then, the doctor blade 45 removes excessive toner from the development roller 42, thus adjusting the amount of toner transported to the development range α.
Toner remaining on the surface of the development roller 42 that has passed by the doctor blade 45 is transported to the development range α facing the photoreceptor 2 as the development roller 42 rotates. Toner that is not used in image development but has passed through the development range α further passes by the position to contact the entrance seal 47 and is transported to the supply nip β. In the supply nip β, the supply roller 44 removes toner from the development roller 42 and transports the toner.
Next, toner usable in the present embodiment is described in further detail below.
In the prevent embodiment, toner having a higher degree of fluidity suitable for high-speed toner conveyance is preferred. For example, toner usable in the present embodiment has a degree of agglomeration of about 40% or greater under accelerated test conditions described below. The degree of agglomeration under accelerated test conditions means an index representing fluidity of toner.
Specifically, the degree of agglomeration under accelerated test conditions used in this specification can be measured as follows. In measurement, a power tester manufactured by Hosokawa Micron Corporation may be used.
(Measurement Method)
The sample is left in a thermostatic chamber (35±2° C.) for about 24±1 hours. The degree of agglomeration can be measured using the powder tester. Three sieves different in mesh size, for example, 75 μm, 44 μm, and 22 μm are used. The degree of agglomeration can be calculated based on the amount of toner remaining on the sieves using the following formulas, and the sum of the three values obtained using the following formulas is deemed the degree of agglomeration under accelerated test conditions.
[Weight of toner remaining on the upper sieve/amount of sample]×100,
[Weight of toner remaining on the middle sieve/amount of sample]×100×3/5,
[Weight of toner remaining on the lower sieve/amount of sample]×100×1/5
As described above, the degree of agglomeration under accelerated test conditions used here is an index obtained from the weight of toner remaining on the three sieves different in mesh size after the sieves are stacked in the order of mesh roughness (with the sieve of largest mesh at the lowest), toner particles are put in the sieve on the top, and constant vibration is applied thereto.
Additionally, the mean circularity of toner usable in the present embodiment can be 0.90 or greater (up to 1.00). In the present embodiment, the value obtained from the formula below is regarded as circularity a. The circularity herein means an index representing surface irregularity rate of toner particles. Toner particles are perfect spheres when the circularity thereof is 1.00. As the surface irregularity increases, the degree of circularity decreases. In the formula below, L0 represents a circumferential length of a circle having an area identical to that of projected image of a toner particle, and L represents a circumferential length of the projected image of the toner particle.
Circularity a=L0/L
When the mean circularity is within a range of from 0.90 to 1.00, toner particles have smooth surfaces, and contact areas among toner particles and those between toner particles and the photoreceptor 2 are small, attaining good transfer performance. When the mean circularity is within a range from 0.90 to 1.00, the toner particle does not have a sharp corner, and torque of agitation of toner inside the development device 4 can be smaller. Accordingly, driving of agitation can be reliable, preventing or reducing image failure.
Further, since toner particles forming dots do not include any angular toner particle, pressure can be applied to toner particles uniformly when toner particles are pressed against recording media in image transfer. This can inhibit toner particles failing to be transferred to the recording medium.
Moreover, since toner particles are not angular, grinding force of toner particles thereof can be smaller, scratches on the surfaces of the photoreceptor 2, the charging member 3, and the like can be reduced. Thus, damage or wear of those components can be alleviated.
A measurement method of circularity is described below.
Circularity can be measured by a flow-type particle image analyzer FPIA-1000 from SYSMEX CORPORATION. More specifically, as a dispersant, 0.1 ml to 0.5 ml of surfactant (preferably, alkylbenzene sulfonate) is put in 100 ml to 150 ml of water from which impure solid materials are previously removed, and 0.1 g to 0.5 g of the sample (toner) is added to the mixture. The mixture including the sample is dispersed by an ultrasonic disperser for 1 to 3 min to prepare a dispersion liquid having a concentration of from 3,000 to 10,000 pieces/μl, and the toner shape and distribution are measured using the above-mentioned instrument.
To attain fine dots of 600 dpi or greater, it is preferable that the toner particles have the weight average particle size (D4) within a range from 3 μm to 8 μm. Within this range, the particle diameter of toner particles is small sufficiently for attaining good microscopic dot reproducibility. When the weight average particle size (D4) is less than 3 μm, transfer efficiency and cleaning performance can drop.
By contrast, when the weight average particle size (D4) is greater than 8 it is difficult to prevent scattering of toner around letters or thin lines in output images. Additionally, the ratio of the weight average particle diameter (D4) to the number average particle diameter (D1) is within a range of from 1.00 to 1.40 (Dv/Dn). As the ratio (D4/D1) becomes closer to 1.00, the particle diameter distribution becomes sharper. In the case of toner having such a small diameter and a narrow particle diameter distribution, the distribution of electrical charge can be uniform, and thus high-quality image with scattering of toner in the backgrounds reduced can be produced. Further, in electrostatic transfer methods, the transfer ratio can be improved.
Measurement of particle diameter distribution is described below.
The particle diameter distribution of toner can be measured as follows using a Coulter counter TA-II or Coulter Multisizer II from Beckman Coulter, Inc.
Initially, 0.1 ml to 5 ml of surfactant, preferably alkylbenzene sulfonate, is added as dispersant to 100 ml to 150 ml of electrolyte. Usable electrolytes include ISOTON-II from Coulter Scientific Japan, Ltd., which is a NaCl aqueous solution including a primary sodium chloride of 1%. Then, 2 mg to 20 mg of the sample (toner) is added to the electrolyte solution. The sample suspended in the electrolyte solution is dispersed by an ultrasonic disperser for about 1 to 3 min to prepare a sample dispersion liquid. Weight and number of toner particles for each of the following channels are measured by the above-mentioned measurer using an aperture of 100 μm to determine a weight distribution and a number distribution. The weight average particle size (D4) and the number average particle diameter (D1) can be obtained from the distribution thus determined.
The number of channels used in the measurement is thirteen. The ranges of the channels are from 2.00 μm to less than 2.52 μm, from 2.52 μm to less than 3.17 μm, from 3.17 μm to less than 4.00 μm, from 4.00 μm to less than 5.04 μm, from 5.04 μm to less than 6.35 μm, from 6.35 μm to less than 8.00 μm, from 8.00 μm to less than 10.08 μm, from 10.08 μm to less than 12.70 μm, from 12.70 μm to less than 16.00 μm, from 16.00 μm to less than 20.20 μm, from 20.20 μm to less than 25.40 μm, from 25.40 μm to less than 32.00 μm, from 32.00 μm to less than 40.30 μm. The range to be measured is set from 2.00 μm to less than 40.30 μm.
The toner preferably used in the present embodiment is obtained by cross-linking reaction and/or an elongation reaction of a toner constituent liquid in an aqueous solvent. Here, the toner constituent liquid is prepared by dispersing a polyester prepolymer including a functional group having at least a nitrogen atom, polyester, a colorant, and a releasing agent in an organic solvent. Such toner is called polymerized toner. A description is now given of toner constituents and a method for manufacturing toner.
(Polyester)
The polyester is prepared by a polycondensation reaction between a polyalcohol compound and a polycarboxylic acid compound. Specific examples of the polyalcohol compound (PO) include a diol (DIO) and a polyol having 3 or more valances (TO). The DIO alone, and a mixture of the DIO and a smaller amount of the TO are preferably used as the PO. Specific examples of the diol (DIO) include alkylene glycols (e.g., ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, and 1,6-hexanediol), alkylene ether glycols (e.g., diethylene glycol, triethylene glycol, dipropyrene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol), alicyclic diols (e.g., 1,4-cyclohexane dimethanol, and hydrogenated bisphenol A), bisphenols (e.g., bisphenol A, bisphenol F, and bisphenol S), alkylene oxide adducts of the above-described alicyclic diols (e.g., ethylene oxide, propylene oxide, and butylene oxide), and alkylene oxide adducts of the above-described bisphenols (e.g., ethylene oxide, propylene oxide, and butylene oxide). Among the above-described examples, alkylene glycols having 2 to 12 carbon atoms and alkylene oxide adducts of bisphenols are preferably used. More preferably, the alkylene glycols having 2 to 12 carbon atoms and the alkylene oxide adducts of bisphenols are used together. Specific examples of the polyol having 3 or more valances (TO) include aliphatic polyols having 3 to 8 or more valances (e.g., glycerin, trimethylolethane, trimethylol propane, pentaerythritol, and sorbitol), phenols having 3 or more valances (e.g., trisphenol PA, phenol novolac, and cresol novolac), and alkylene oxide adducts of polyphenols having 3 or more valances.
Specific examples of the polycarboxylic acids (PC) include dicarboxylic acids (DIC) and polycarboxylic acids having 3 or more valances (TC). The DIC alone, and a mixture of the DIC and a smaller amount of the TC are preferably used as the PC. Specific examples of the dicarboxylic acids (DIC) include alkylene dicarboxylic acids (e.g., succinic acid, adipic acid, and sebacic acid), alkenylene dicarboxylic acids (e.g., maleic acid and fumaric acid), and aromatic dicarboxylic acids (e.g., phthalic acid, isophthalic acid, terephthalic acid, and naphthalene dicarboxylic acid). Among the above-described examples, alkenylene dicarboxylic acids having 4 to 20 carbon atoms and aromatic dicarboxylic acids having 8 to 20 carbon atoms are preferably used. Specific examples of the polycarboxylic acids having 3 or more valances (TC) include aromatic polycarboxylic acids having 9 to 20 carbon atoms (e.g., trimellitic acid and pyromellitic acid). The polycarboxylic acid (PC) may be reacted with the polyol (PO) using acid anhydrides or lower alkyl esters (e.g., methyl ester, ethyl ester, and isopropyl ester) of the above-described materials.
A ratio of the polyol (PO) and the polycarboxylic acid (PC) is normally set in a range between 2/1 and 1/1, preferably between 1.5/1 and 1/1, and more preferably between 1.3/1 and 1.02/1 as an equivalent ratio [OH]/[COOH] between a hydroxyl group [OH] and a carboxyl group [COOH].
The polycondensation reaction between the polyol (PO) and the polycarboxylic acid (PC) is carried out by heating the PO and the PC to from 150° C. to 280° C. in the presence of a known catalyst for esterification such as tetrabutoxy titanate and dibutyltin oxide and removing produced water under a reduced pressure as necessary to obtain a polyester having hydroxyl groups. The polyester preferably has a hydroxyl value not less than 5, and an acid value of from 1 to 30, and preferably from 5 to 20. When the polyester has the acid value within the range, the resultant toner tends to be negatively charged to have good affinity with a recording paper, and low-temperature fixability of the toner on the recording paper improves. However, when the acid value is too large, the resultant toner is not stably charged and the stability becomes worse by environmental variations.
The polyester preferably has a weight-average molecular weight of from 10,000 to 400,000, and more preferably from 20,000 to 200,000. When the weight-average molecular weight is too small, offset resistance of the resultant toner deteriorates. By contrast, when the weight-average molecular weight is too large, low-temperature fixability thereof deteriorates.
The polyester preferably includes urea-modified polyester as well as unmodified polyester obtained by the above-described polycondensation reaction. The urea-modified polyester is prepared by reacting a polyisocyanate compound (PIC) with a carboxyl group or a hydroxyl group at the end of the polyester obtained by the above-described polycondensation reaction to form a polyester prepolymer (A) having an isocyanate group, and reacting amine with the polyester prepolymer (A) to crosslink and/or elongate a molecular chain thereof.
Specific examples of the polyisocyanate compound (PIC) include aliphatic polyisocyanates (e.g., tetramethylene diisocyanate, hexamethylene diisocyanate, and 2,6-diisocyanate methylcaproate), alicyclic polyisocyanates (e.g., isophoron diisocyanate and cyclohexyl methane diisocyanate), aromatic diisocyanates (e.g., trilene diisocyanate and diphenylmethane diisocyanate), aromatic aliphatic diisocyanates (e.g., α,α,α′,α′-tetramethyl xylylene diisocyanate), isocyanurates, materials blocked against the polyisocyanate with phenol derivatives, oxime, caprolactam or the like, and combinations of two or more of the above-described materials.
The PIC is mixed with the polyester such that an equivalent ratio [NCO]/[OH] between an isocyanate group [NCO] in the PIC and a hydroxyl group [OH] in the polyester is typically in a range between 5/1 and 1/1, preferably between 4/1 and 1.2/1, and more preferably between 2.5/1 and 1.5/1. When [NCO]/[OH] is too large, for example, greater than 5, low-temperature fixability of the resultant toner deteriorates. When [NCO]/[OH] is too small, for example, less than 1, a urea content in ester of the modified polyester decreases and hot offset resistance of the resultant toner deteriorates.
The polyester prepolymer (A) typically includes a polyisocyanate group of from 0.5 to 40% by weight, preferably from 1 to 30% by weight, and more preferably from 2 to 20% by weight. When the content is too small, for example, less than 0.5% by weight, hot offset resistance of the resultant toner deteriorates, and in addition, the heat resistance and low-temperature fixability of the toner also deteriorate. By contrast, when the content is too large, low-temperature fixability of the resultant toner deteriorates.
The number of the isocyanate groups included in a molecule of the polyester prepolymer (A) is at least 1, preferably from 1.5 to 3 on average, and more preferably from 1.8 to 2.5 on average. When the number of the isocyanate group is too small per 1 molecule, the molecular weight of the urea-modified polyester decreases and hot offset resistance of the resultant toner deteriorates.
Specific examples of amines (B) reacted with the polyester prepolymer (A) include diamines (B1), polyamines (B2) having 3 or more amino groups, amino alcohols (B3), amino mercaptans (B4), amino acids (B5), and blocked amines (B6) in which the amines (B1 to B5) described above are blocked.
Specific examples of the diamines (B1) include aromatic diamines (e.g., phenylene diamine, diethyltoluene diamine, and 4,4″-diaminodiphenyl methane), alicyclic diamines (e.g., 4,4″-diamino-3,3″-dimethyldicyclohexylmethane, diamine cyclohexane, and isophoron diamine), and aliphatic diamines (e.g., ethylene diamine, tetramethylene diamine, and hexamethylene diamine).
Specific examples of the polyamines (B2) having three or more amino groups include diethylene triamine and triethylene tetramine. Specific examples of the amino alcohols (B3) include ethanol amine and hydroxyethyl aniline. Specific examples of the amino mercaptan (B4) include aminoethyl mercaptan and aminopropyl mercaptan.
Specific examples of the amino acids (B5) include amino propioic acid and amino caproic acid. Specific examples of the blocked amines (B6) include ketimine compounds prepared by reacting one of the amines B1 to B5 described above with a ketone such as acetone, methyl ethyl ketone and methyl isobutyl ketone; and oxazoline compounds. Among the above-described amines (B), diamines (B1) and a mixture of the B1 and a smaller amount of B2 are preferably used.
A mixing ratio [NCO]/[NHx] of the content of isocyanate groups in the prepolymer (A) to that of amino groups in the amine (B) is typically from 1/2 to 2/1, preferably from 1.5/1 to 1/1.5, and more preferably from 1.2/1 to 1/1.2.
When the mixing ratio is too large or small, molecular weight of the urea-modified polyester decreases, resulting in deterioration of hot offset resistance of the toner. The urea-modified polyester may include a urethane bonding as well as a urea bonding. The molar ratio (urea/urethane) of the urea bonding to the urethane bonding is typically from 100/0 to 10/90, preferably from 80/20 to 20/80, and more preferably from 60/40 to 30/70. When the content of the urea bonding is too small, for example, less than 10%, hot offset resistance of the resultant toner deteriorates.
The urea-modified polyester is prepared by a method such as a one-shot method. The PO and the PC are heated to from 150° C. to 280° C. in the presence of a known esterification catalyst such as tetrabutoxy titanate and dibutyltin oxide, and removing produced water while optionally depressurizing to prepare polyester having a hydroxyl group. Next, the polyisocyanate (PIC) is reacted with the polyester at from 40° C. to 140° C. to form a polyester prepolymer (A) having an isocyanate group. Further, the amines (B) are reacted with the polyester prepolymer (A) at from 0° C. to 140° C. to form a urea-modified polyester.
When the polyisocyanate (PIC), and the polyester prepolymer (A) and the amines (B) are reacted, a solvent may optionally be used. Suitable solvents include solvents which do not react with polyvalent polyisocyanate compound (PIC). Specific examples of such solvents include aromatic solvents such as toluene and xylene; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate; amides such as dimethylformamide and dimethylacetoaminde; ethers such as tetrahydrofuran.
A reaction terminator may optionally be used in the cross-linking and/or the elongation reaction between the polyester prepolymer (A) and the amines (B) to control a molecular weight of the resultant urea-modified polyester. Specific examples of the reaction terminators include monoamines (e.g., diethylamine, dibutylamine, butylamine and laurylamine), and their blocked compounds (e.g., ketimine compounds).
The weight-average molecular weight of the urea-modified polyester is not less than 10,000, preferably from 20,000 to 10,000,000, and more preferably from 30,000 to 1,000,000. When the weight-average molecular weight is too small, hot offset resistance of the resultant toner deteriorates. The number-average molecular weight of the urea-modified polyester is not particularly limited when the above-described unmodified polyester resin is used in combination. Specifically, the weight-average molecular weight of the urea-modified polyester resins has priority over the number-average molecular weight thereof. However, when the urea-modified polyester is used alone, the number-average molecular weight is from 2,000 to 15,000, preferably from 2,000 to 10,000, and more preferably from 2,000 to 8,000. When the number-average molecular weight is too large, low temperature fixability of the resultant toner and glossiness of full-color images deteriorate.
A combination of the urea-modified polyester and the unmodified polyester improves low temperature fixability of the resultant toner and glossiness of full-color images produced thereby, and is more preferably used than using the urea-modified polyester alone. Further, the unmodified polyester may include modified polyester other than the urea-modified polyester.
It is preferable that the urea-modified polyester at least partially mixes with the unmodified polyester to improve the low temperature fixability and hot offset resistance of the resultant toner. Therefore, the urea-modified polyester preferably has a composition similar to that of the unmodified polyester.
A mixing ratio between the unmodified polyester and the urea-modified polyester is from 20/80 to 95/5, preferably from 70/30 to 95/5, more preferably from 75/25 to 95/5, and even more preferably from 80/20 to 93/7. When the content of the urea-modified polyester is too small, the hot offset resistance deteriorates, and in addition, it is disadvantageous to have both high temperature preservability and low temperature fixability.
The binder resin including the unmodified polyester and urea-modified polyester preferably has a glass transition temperature (Tg) of from 45° C. to 65° C., and preferably from 45° C. to 60° C. When the glass transition temperature is too low, for example, lower than 45° C., the high temperature preservability of the toner deteriorates. By contrast, when the glass transition temperature is too high, for example, higher than 65° C., the low temperature fixability deteriorates.
Because the urea-modified polyester is likely to be present on a surface of the parent toner, the resultant toner has better heat resistance preservability than known polyester toners even though the glass transition temperature of the urea-modified polyester is low.
(Colorant)
Specific examples of colorants for toner usable in the present embodiment include any known dyes and pigments such as carbon black, Nigrosine dyes, black iron oxide, NAPHTHOL YELLOW S, HANSA YELLOW (10G, 5G and G), Cadmium Yellow, yellow iron oxide, loess, chrome yellow, Titan Yellow, polyazo yellow, Oil Yellow, HANSA YELLOW (GR, A, RN, and R), Pigment Yellow L, BENZIDINE YELLOW (G and GR), PERMANENT YELLOW (NCG), VULCAN FAST YELLOW (5G and R), Tartrazine Lake, Quinoline Yellow Lake, ANTHRAZANE YELLOW BGL, isoindolinone yellow, red iron oxide, red lead, orange lead, cadmium red, cadmium mercury red, antimony orange, Permanent Red 4R, Para Red, Fire Red, p-chloro-o-nitroaniline red, Lithol Fast Scarlet G, Brilliant Fast Scarlet, Brilliant Carmine BS, PERMANENT RED (F2R, F4R, FRL, FRLL, and F4RH), Fast Scarlet VD, VULCAN FAST RUBINE B, Brilliant Scarlet G, LITHOL RUBINE GX, Permanent Red F5R, Brilliant Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Toluidine Maroon, PERMANENT BORDEAUX F2K, HELIO BORDEAUX BL, Bordeaux 10B, BON MAROON LIGHT, BON MAROON MEDIUM, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarine Lake, Thioindigo Red B, Thioindigo Maroon, Oil Red, Quinacridone Red, Pyrazolone Red, polyazo red, Chrome Vermilion, Benzidine Orange, perynone orange, Oil Orange, cobalt blue, cerulean blue, Alkali Blue Lake, Peacock Blue Lake, Victoria Blue Lake, metal-free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, INDANTHRENE BLUE (RS and BC), Indigo, ultramarine, Prussian blue, Anthraquinone Blue, Fast Violet B, Methyl Violet Lake, cobalt violet, manganese violet, dioxane violet, Anthraquinone Violet, Chrome Green, zinc green, chromium oxide, viridian, emerald green, Pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake, Phthalocyanine Green, Anthraquinone Green, titanium oxide, zinc oxide, lithopone, etc. These materials can be used alone or in combination. The toner preferably includes a colorant in an amount of from 1 to 15% by weight, and more preferably from 3 to 10% by weight.
The colorant for usable in the present embodiment can be combined with a resin to be used as a master batch. Specific examples of the resin for use in the master batch include, but are not limited to, styrene polymers and substituted styrene polymers (e.g., polystyrenes, poly-p-chlorostyrenes, and polyvinyltoluenes), copolymers of vinyl compounds and the above-described styrene polymers or substituted styrene polymers, polymethyl methacrylates, polybutyl methacrylates, polyvinyl chlorides, polyvinyl acetates, polyethylenes, polypropylenes, polyesters, epoxy resins, epoxy polyol resins, polyurethanes, polyamides, polyvinyl butyrals, polyacrylic acids, rosins, modified rosins, terpene resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins, paraffin waxes, etc. These resins can be used alone or in combination.
(Charge Controlling Agent)
The toner usable in the present embodiment may optionally include a charge controlling agent. Specific examples of the charge controlling agent include any known charge controlling agents such as Nigrosine dyes, triphenylmethane dyes, metal complex dyes including chromium, chelate compounds of molybdic acid, Rhodamine dyes, alkoxyamines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkylamides, phosphor and compounds including phosphor, tungsten and compounds including tungsten, fluorine-containing activators, metal salts of salicylic acid, and salicylic acid derivatives, but are not limited thereto. Specific examples of commercially available charge controlling agents include, but are not limited to, BONTRON® N-03 (Nigrosine dyes), BONTRON® P-51 (quaternary ammonium salt), BONTRON® S-34 (metal-containing azo dye), BONTRON® E-82 (metal complex of oxynaphthoic acid), BONTRON® E-84 (metal complex of salicylic acid), and BONTRON® E-89 (phenolic condensation product), which are manufactured by Orient Chemical Industries Co., Ltd.; TP-302 and TP-415 (molybdenum complex of quaternary ammonium salt), which are manufactured by Hodogaya Chemical Co., Ltd.; COPY CHARGE® PSY VP2038 (quaternary ammonium salt), COPY BLUE® PR (triphenyl methane derivative), COPY CHARGE® NEG VP2036 and COPY CHARGE® NX VP434 (quaternary ammonium salt), which are manufactured by Hoechst AG; LR1-901, and LR-147 (boron complex), which are manufactured by Japan Carlit Co., Ltd.; copper phthalocyanine, perylene, quinacridone, azo pigments and polymers having a functional group such as a sulfonate group, a carboxyl group, a quaternary ammonium group, etc. Among the above-described examples, materials negatively charging the toner are preferably used.
The content of the charge controlling agent is determined depending on the species of the binder resin used, and toner manufacturing method (such as dispersion method) used, and is not particularly limited. However, the content of the charge controlling agent is typically from 0.1 to 10 parts by weight, and preferably from 0.2 to 5 parts by weight, per 100 parts by weight of the binder resin included in the toner. When the content is too high, the toner has too large a charge quantity. Accordingly, the electrostatic attraction of the developing roller 42 attracting toner increases, thus degrading fluidity of toner and image density.
(Release Agent)
When wax having a low melting point of from 50° C. to 120° C. is use in toner as a release agent, the wax can be dispersed in the binder resin and serve as a release agent at an interface between the fixing roller of the fixing device 12 and toner particles. Accordingly, hot offset resistance can be improved without applying a release agent, such as oil, to the fixing roller. Specific examples of the release agent include natural waxes including vegetable waxes such as carnauba wax, cotton wax, Japan wax and rice wax; animal waxes such as bees wax and lanolin; mineral waxes such as ozokelite and ceresine; and petroleum waxes such as paraffin waxes, microcrystalline waxes, and petrolatum. In addition, synthesized waxes can also be used. Specific examples of the synthesized waxes include synthesized hydrocarbon waxes such as Fischer-Tropsch waxes and polyethylene waxes; and synthesized waxes such as ester waxes, ketone waxes, and ether waxes. Further, fatty acid amides such as 1,2-hydroxylstearic acid amide, stearic acid amide, and phthalic anhydride imide; and low molecular weight crystalline polymers such as acrylic homopolymer and copolymers having a long alkyl group in their side chain such as poly-n-stearyl methacrylate, poly-n-laurylmethacrylate, and n-stearyl acrylate-ethyl methacrylate copolymers can also be used.
The above-described charge control agents and release agents can be dissolved and dispersed after kneaded upon application of heat together with a master batch pigment and a binder resin, and can be added when directly dissolved or dispersed in an organic solvent.
(External Additives)
The toner particles are preferably mixed with an external additive to improve the fluidity, developing property and charging ability of the toner particles. Preferable external additives include inorganic fine particles. The inorganic fine particles preferably have a primary particle diameter of from 5×10−3 μm to 2 μm, and more preferably from 5×10−3 μm to 0.5 μm. In addition, the inorganic fine particles preferably has a specific surface area measured by a BET method of from 20 to 500 m2/g. The content of the external additive is preferably from 0.01 to 5% by weight, and more preferably from 0.01 to 2.0% by weight, based on total weight of the toner composition.
Specific examples of the inorganic fine particles include silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, tin oxide, quartz sand, clay, mica, sand-lime, diatom earth, chromium oxide, cerium oxide, red iron oxide, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, and silicon nitride. Among the above-described examples, a combination of a hydrophobic silica and a hydrophobic titanium oxide is preferably used. In particular, the hydrophobic silica and the hydrophobic titanium oxide each having an average particle diameter of not greater than 5×10−2 μm considerably improves an electrostatic force between the toner particles and van der Waals force. Accordingly, the resultant toner composition has a proper charge quantity. In addition, even when the toner composition is agitated in the developing devices 5, the external additive is hardly released from the toner particles. As a result, image defects such as white spots and image omissions are hardly produced. Further, the amount of residual toner after transfer can be reduced.
When titanium oxide fine particles are used as the external additive, the resultant toner can reliably form toner images having a proper image density even when environmental conditions are changed. However, the charge rising properties of the resultant toner tend to deteriorate. Therefore, an additive amount of the titanium oxide fine particles is preferably smaller than that of silica fine particles.
The amount in total of hydrophobic silica fine particles and hydrophobic titanium oxide fine particles added is preferably from 0.3 to 1.5% by weight based on weight of the toner particles to reliably form high-quality images without degrading charge rising properties even when images are repeatedly copied.
A method for manufacturing the toner is described in detail below, but is not limited thereto.
(Toner Manufacturing Method)
(1) The colorant, the unmodified polyester, the polyester prepolymer having an isocyanate group, and the release agent are dispersed in an organic solvent to obtain toner constituent liquid. Volatile organic solvents having a boiling point lower than 100° C. are preferable because such organic solvents can be removed easily after formation of parent toner particles. Specific examples of the organic solvent include toluene, xylene, benzene, carbon tetrachloride, methylene chloride, 1,2-dichloroethane, 1,1,2-trichloroethane, trichloroethylene, chloroform, monochlorobenzene, dichloroethylidene, methyl acetate, ethyl acetate, methylethylketone, and methylisobutylketone. The above-described materials can be used alone or in combination. In particular, aromatic solvent such as toluene and xylene, and chlorinated hydrocarbon such as methylene chloride, 1,2-dichloroethane, chloroform, and carbon tetrachloride are preferably used. The toner constituent liquid preferably includes the organic solvent in an amount of from 0 to 300 parts by weight, more preferably from 0 to 100 parts by weight, and even more preferably from 25 to 70 parts by weight based on 100 parts by weight of the prepolymer.
(2) The toner constituent liquid is emulsified in an aqueous medium under the presence of a surfactant and a particulate resin. The aqueous medium may include water alone or a mixture of water and an organic solvent. Specific examples of the organic solvent include alcohols such as methanol, isopropanol, and ethylene glycol; dimethylformamide; tetrahydrofuran; cellosolves such as methyl cellosolve; and lower ketones such as acetone and methyl ethyl ketone.
The toner constituent liquid includes the aqueous medium in an amount of from 50 to 2,000 parts by weight, and preferably from 100 to 1,000 parts by weight based on 100 parts by weight of the toner constituent liquid. When the amount of the aqueous medium is too small, the toner constituent liquid is not well dispersed and toner particles having a predetermined particle diameter cannot be formed. By contrast, when the amount of the aqueous medium is too large, production costs increase.
A dispersant such as a surfactant or an organic particulate resin is optionally included in the aqueous medium to improve the dispersion therein. Specific examples of the surfactants include anionic surfactants such as alkylbenzene sulfonic acid salts, et-olefin sulfonic acid salts, and phosphoric acid salts; cationic surfactants such as amine salts (e.g., alkyl amine salts, aminoalcohol fatty acid derivatives, polyamine fatty acid derivatives, and imidazoline) and quaternary ammonium salts (e.g., alkyldimethyl ammonium salts, dialkyldimethyl ammonium salts, alkyldimethyl benzyl ammonium salts, pyridinium salts, alkyl isoquinolinium salts, and benzethonium chloride); nonionic surfactants such as fatty acid amide derivatives and polyhydric alcohol derivatives; and ampholytic surfactants such as alanine, dodecyldi(aminoethyl)glycin, di(octylaminoethyle)glycin, and N-alkyl-N,N-dimethylammonium betaine.
A surfactant having a fluoroalkyl group can achieve a dispersion having high dispersibility even when a smaller amount of the surfactant is used. Specific examples of anionic surfactants having a fluoroalkyl group include fluoroalkyl carboxylic acids having from 2 to 10 carbon atoms and their metal salts, disodium perfluorooctanesulfonylglutamate, sodium 3-[ω-fluoroalkyl(C6-C11)oxy]-1-alkyl(C3-C4)sulfonate, sodium-[ω-fluoroalkanoyl(C6-C8)-N-ethylamino]-1-propane sulfonate, fluoroalkyl(C11-C20) carboxylic acids and their metal salts, perfluoroalkylcarboxylic acids (C7-C13) and their metal salts, perfluoroalkyl(C4-C12) sulfonate and their metal salts, perfluorooctanesulfonic acid diethanol amides, N-propyl-N-(2-hydroxyethyl)perfluorooctanesulfone amide, perfluoroalkyl(C6-C10)sulfoneamidepropyltrimethylammonium salts, salts of perfluoroalkyl(C6-C10)-N-ethylsulfonylglycin, and monoperfluoroalkyl(C6-C16)ethylphosphates.
Specific examples of commercially available surfactants include SURFLON® S-111, SURFLON® S-112, and SURFLON® S-113 manufactured by AGC Seimi Chemical Co., Ltd.; FRORARD FC-93, FC-95, FC-98, and FC-129 manufactured by Sumitomo 3M Ltd.; UNIDYNE DS-101 and DS-102 manufactured by Daikin Industries, Ltd.; MEGAFACE F-110, F-120, F-113, F-191, F-812, and F-833 manufactured by DIC Corporation; EFTOP EF-102, EF-103, EF-104, EF-105, EF-112, EF-123A, EF-123B, EF-306A, EF-501, EF-201, and EF-204 manufactured by JEMCO Inc.; and FUTARGENT F-100 and F-150 manufactured by Neos Co., Ltd.
Specific examples of cationic surfactants include primary and secondary aliphatic amines or secondary amino acid having a fluoroalkyl group, aliphatic quaternary ammonium salts such as perfluoroalkyl(C6-C10)sulfoneamidepropyltrimethylammonium salts, benzalkonium salts, benzetonium chloride, pyridinium salts, and imidazolinium salts. Specific examples of commercially available products thereof include SURFLON® S-121 manufactured by AGC Seimi Chemical Co., Ltd.; FRORARD FC-135 manufactured by Sumitomo 3M Ltd.; UNIDYNE DS-202 manufactured by Daikin Industries, Ltd.; MEGAFACE F-150 and F-824 manufactured by DIC Corporation; EFTOP EF-132 manufactured by JEMCO Inc.; and FUTARGENT F-300 manufactured by Neos Co., Ltd.
The resin particles are added to stabilize parent toner particles formed in the aqueous medium. Therefore, the resin particles are preferably added so as to have a coverage of from 10% to 90% over a surface of the parent toner particles. Specific examples of the resin particles include polymethylmethacrylate particles having a particle diameter of 1 μm and 3 μm, polystyrene particles having a particle diameter of 0.5 μm and 2 μm, and poly(styrene-acrylonitrile) particles having a particle diameter of 1 μm. Specific examples of commercially available products thereof include PB-200H manufactured by Kao Corporation, SGP manufactured by Soken Chemical & Engineering Co., Ltd., Technopolymer SB manufactured by Sekisui Plastics Co., Ltd., SGP-3G manufactured by Soken Chemical & Engineering Co., Ltd., and Micropearl manufactured by Sekisui Chemical Co., Ltd.
In addition, inorganic dispersants such as tricalcium phosphate, calcium carbonate, titanium oxide, colloidal silica, and hydroxy apatite can also be used.
As dispersants usable in combination with the above-described resin particles and inorganic dispersants, it is possible to stably disperse toner constituents in water using a polymeric protection colloid. Specific examples of such protection colloids include polymers and copolymers prepared using monomers such as acids (e.g., acrylic acid, methacrylic acid, α-cyanoacrylic acid, α-cyanomethacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid, and maleic anhydride), (meth)acrylic monomers having a hydroxyl group (e.g., β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, β-hydroxypropyl acrylate, β-hydroxypropyl methacrylate, γ-hydroxypropyl acrylate, γ-hydroxypropyl methacrylate, 3-chloro-2-hydroxypropyl acrylate, 3-chloro-2-hydroxypropyl methacrylate, diethyleneglycolmonoacrylic acid esters, diethyleneglycolmonomethacrylic acid esters, glycerinmonoacrylic acid esters, glycerinmonomethacrylic acid esters, N-methylolacrylamide, and N-methylolmethacrylamide), vinyl alcohol and its ethers (e.g., vinyl methyl ether, vinyl ethyl ether, and vinyl propyl ether), esters of vinyl alcohol with a compound having a carboxyl group (e.g., vinyl acetate, vinyl propionate, and vinyl butyrate), acrylic amides (e.g., acrylamide, methacrylamide, and diacetoneacrylamide) and their methylol compounds, acid chlorides (e.g., acrylic acid chloride and methacrylic acid chloride), nitrogen-containing compounds (e.g., vinyl pyridine, vinyl pyrrolidone, vinyl imidazole, and ethylene imine), and homopolymer or copolymer having heterocycles of the nigtroge-containing compounds. In addition, polymers such as polyoxyethylene compounds (e.g., polyoxyethylene, polyoxypropylene, polyoxyethylenealkyl amines, polyoxypropylenealkyl amines, polyoxyethylenealkyl amides, polyoxypropylenealkyl amides, polyoxyethylene nonylphenyl ethers, polyoxyethylene laurylphenyl ethers, polyoxyethylene stearylphenyl esters, and polyoxyethylene nonylphenyl esters), and cellulose compounds (e.g., methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose) can also be used as the polymeric protective colloid.
The dispersion method is not particularly limited, and well known methods such as low speed shearing methods, high-speed shearing methods, friction methods, high-pressure jet methods, and ultrasonic methods can be used. Among the above-described methods, the high-speed shearing methods are preferably used because particles having a particle diameter of from 2 to 20 μm can be easily prepared. When a high-speed shearing type dispersion machine is used, the rotation speed is not particularly limited, but the rotation speed is typically from 1,000 to 30,000 rpm, and preferably from 5,000 to 20,000 rpm. The dispersion time is not particularly limited, but is typically from 0.1 to 5 minutes for a batch method. The temperature in the dispersion process is typically from 0° C. to 150° C. (under pressure), and preferably from 40° C. to 98° C.
(3) While the emulsion is prepared, amines (B) are added thereto to react with the polyester prepolymer (A) having an isocyanate group. This reaction is accompanied by cross-linking and/or elongation of a molecular chain. The reaction time depends on reactivity of an isocyanate structure of the polyester prepolymer (A) and amines (B), but is typically from 10 minutes to 40 hours, and preferably from 2 to 24 hours. The reaction temperature is typically from 0° C. to 150° C., and preferably from 40° C. to 98° C. In addition, a known catalyst such as dibutyltinlaurate and dioctyltinlaurate can be used as needed.
(4) After completion of the reaction, the organic solvent is removed from the emulsified dispersion (a reactant), and subsequently, the resulting material is washed and dried to obtain a parent toner particle. The prepared emulsified dispersion is gradually heated while stirred in a laminar flow, and an organic solvent is removed from the dispersion after stirred strongly when the dispersion has a specific temperature to form a parent toner particle having the shape of a spindle. When an acid such as calcium phosphate or a material soluble in alkaline is used as a dispersant, the calcium phosphate is dissolved with an acid such as a hydrochloric acid, and washed with water to remove the calcium phosphate from the parent toner particle. Besides the above-described method, the organic solvent can also be removed by an enzymatic hydrolysis.
(5) A charge control agent is provided to the parent toner particle, and inorganic fine particles such as silica fine particles and titanium oxide fine particles are added thereto to obtain toner. Well known methods using a mixer or the like are used to provide the charge control agent and to add the inorganic fine particles. Accordingly, toner having a smaller particle diameter and a sharper particle diameter distribution can be easily obtained. Further, strong agitation in removal of the organic solvent can cause toner particles to have a shape between a spherical shape and a spindle shape, and surface morphology between a smooth surface and a rough surface.
Next, a distinctive feature of the development device 4 according to the present embodiment is described below.
As described above with reference to
Comparative examples in which the lateral end seal 59 contacts the surface of the development roller 42 differently from the present embodiment are described with reference to
Additionally, scattering of toner is also affected by adhesion of toner to the developer regulator. In development devices, toner can scatter if an excessive amount of toner is supplied to the development roller, and typically it is prevented by the developer regulator adjusting the amount of toner supplied thereto. However, if toner firmly adheres to the developer regulator over time, the capability to adjust the toner amount is degraded, increasing the possibility of scattering of toner. Regarding this inconvenience, the projections 42a formed on the surface of the development roller 42 can scrape off toner from the doctor blade 45. Thus, in the axial range where the projections 42a are present, degradation in the toner amount adjustment capability and toner scattering caused thereby can be inhibited.
However, in the configuration shown in
By contrast, in the development device 4 according to the present embodiment, as shown in
It is to be noted that, although felt is used as the lateral end seal 59 in the present embodiment, the material of the lateral end seal 59 is not limited thereto.
Additionally, the position of the smooth surface range 420b in the axial direction is outside an image formation area where toner is supplied from the development roller 42 to the photoreceptor 2 in the development range α. Although the amount of toner may differ between the grooved range 420a and the smooth surface range 420b, it does not make image density uneven because toner carried on the smooth surface range 420b does not contribute to image development.
Additionally, the surface unevenness of the development roller 42 is formed by the first and second spiral grooves L1 and L2 winding in the opposite directions. Such surface unevenness can help the development roller 42 to carry a desired amount of toner and the supply roller 44 to scrape off toner from the surface of the development roller 42, and useful life of toner can be extended. Additionally, only the grooved range 420a, which includes the axial center, may be plated. Plating of the grooved range 420a can enhance charging of toner and inhibit movement of toner to the smooth surface range 420b. Plating can help toner to roll on the development roller 42, thus facilitating charging of toner.
Additionally, it is preferable that the depth of the recess 42b, the height from the bottom face of the recess 42b to the top face 42t (shown in
(First Variation)
A first variation of the first embodiment is described below with reference to
The development roller 42-1 according to the first variation includes a grooved range 420a1 that is divided into areas different in the depth of the recesses 42b, namely, an axial center area 420c including an axial center of the development roller 42-1 and axial end areas 420d positioned outside the axial center area 420c in the axial direction. The recesses 42b in the axial end area 420d are shallower than those in the axial center area 420c.
In the first variation, the position of the axial end area 420d in the axial direction is outside the image formation area where toner is supplied from the development roller 42-1 to the photoreceptor 2 in the development range α. Although, with the shallower recesses 42b, the amount of toner carried in the axial end area 420d is reduced from that in the axial center area 420c, it does not invite image density unevenness because toner carried in the axial end area 420d does not contribute to image development. Since the recesses 42b in the axial end area 420d adjacent to the smooth surface range 420b are shallower, the amount of toner moving along the groove to the smooth surface range 420b can be reduced, thus securing prevention of leakage of toner in the axial end portion.
(Second Variation)
A second variation of the first embodiment is described below.
In the development roller 42-2 according to the second variation, the grooved range 420a2 is divided into areas different in inclination relative to the axial direction, of the spiral grooves (L1 and L2 shown in
In the second variation, in the axial direction, the axial end areas 420d′ are positioned outside the image formation area where toner is supplied from the development roller 42-2 to the photoreceptor 2 in the development range α. Although differences in the inclination of the spiral grooves between the axial center area 420c′ and the axial end area 420d′ can causes differences in the amount of toner carried between the axial center area 420c′ and the axial end area 420d′, it does not invite image density unevenness because toner carried in the axial end areas 420d′ does not contribute to image development.
As shown in
In the development roller 42-2 according to the second variation, since the angle of spiral is sharper in the axial end area 420d′, which is adjacent to the smooth surface range 420b, than in the axial center area 420c′, the action of toner moving along the spiral grooves to the smooth surface range 420b can be smaller. Accordingly, the amount of toner moving to the smooth surface range 420b can be reduced, thus securing prevention of scattering of toner in the axial end portions.
(Third Variation)
A third variation of the first embodiment is described below.
As shown in
The first spiral groove L1 is inclined a predetermined angle (for example, but not limited to, 45° in
The first and second spiral grooves L1 and L2 inclined in the respective directions are formed periodically at predetermined cyclic pitch widths W1 in the axial direction. It is to be noted that, alternatively, the first and second spiral grooves L1 and L2 can be different in inclination and cyclic width (pitch). Additionally, the top face 42t (shown in
The development roller 42-3 includes a base and a surface layer formed on the outer circumferential surface of the base. The base can be a metal sleeve constructed of aluminum alloy such as 5056 or 6063 (JIS standard); or iron alloy such as Carbon Steel Tubes for Machine Structural Purposes (STKM, JIS standard), for example.
The first and second spiral grooves L1 and L2 can be formed in the surface of the base metal sleeve of the development roller 42-3 through rolling processing. In rolling processing, while a pair of dies rolling in the same direction is pressed against the surface of the base metal sleeve of the development roller 42-3, the base metal sleeve is moved in a predetermined direction.
Although felt is used as the lateral end seals 59 in the first embodiment, the lateral end seals 59 in the third variation are constructed of pile fabric having a pile length or pile depth of 1.5 mm or longer. If the pile depth is smaller than 1.5 mm, rigidity of pile yarn (strands) is insufficient and pile fabric may fail to confirm to the surface unevenness.
It is to be noted that arrow E on the lateral end seals 59 in
Additionally, lubricant such as fluorine grease or contact improving agent may be applied to the surface of the development roller 42-3 that slidingly contacts the lateral end seals 59 to fill in the recesses 42b, thereby enhancing contact between the lateral end seals 59 and the surface of the development roller 42-3. It is preferable that the lubricant or contact improving agent is viscous to be buried in the recesses 42b in the surface of the development roller 42-3. When the recesses 42b within the range that contacts the lateral end seals 59 are filled in, the amount of toner moving along the spiral grooves L1 and L2 to the smooth surface range 420b can be reduced, thus securing prevention of scattering of toner.
It is to be noted that, other than the differences described above, the configurations of the first through third variations are similar to those of the first embodiment, and descriptions thereof are omitted.
Next, the development roller 42 and the doctor blade 45 according to the first embodiment are described in further detail below.
Development rollers for use in one-component development devices may have a surface abraded by sandblasting or the like to improve capability to carry toner on the development roller and transport thereby. However, surface unevenness formed by sandblasting or the like is typically irregular, creating projections and recesses different in height and depth and arranged unevenly, and it is possible that such irregular surface unevenness causes the amount of toner carried on the development roller to fluctuate, resulting in unevenness in image density.
By contrast, in the development device 4 according to the first embodiment, the development roller 42 has regular surface unevenness as described above. That is, the multiple projections 42a having a substantially identical height and the recesses 42b having a substantially identical depth (W3) are formed in the surface of the development roller 42 regularly. Accordingly, the amount of toner carried thereon can be constant, inhibiting image density unevenness. The term “regular surface unevenness” used in this specification means projections and recesses formed in succession to an extent that the amount of toner adhering thereto is substantially uniform to inhibit image density unevenness.
Alternatively, applicable surface irregularity arrangements can be described as follows, focusing on the latent image formed on the photoreceptor 2. For example, the latent image consists of multiple dot-like latent images formed in respective regions separated by a grid that can be formed at multiple different pitches in the axial direction, and, on the back side in the axial direction (back side of the apparatus), the grid is formed at pitches shorter than the longest pitch among the multiple different pitches.
It is to be noted that effects of the first embodiment, described in detail later, can be attained also in configurations in which the surface unevenness of the development roller 42 is not in regular arrangement. However, regular arrangement of surface unevenness is preferable in light of image quality.
In the development device 4 according to the first embodiment, as shown in
In this case, a downward force Fg acts on toner under weight of toner itself, and it can reduce compression force due to a stress Fb of the doctor blade 45. This configuration can inhibit aggregation of toner in the downstream portion 42c in
Additionally, use of toner whose degree of agglomeration under the above-described accelerated test conditions is 40% or lower can alleviate coagulation of toner in the downstream portion 42c of the projection 42a formed in the surface of the development roller 42. It is to be noted that, in
As shown in
By contrast, in the first embodiment, as shown in
In the comparative configuration shown in
By contrast, in the first embodiment, among the angles γ formed by the projections 42a and the recesses 42b, at least the downstream angles γ1 are obtuse as shown in
It is to be noted that, in the enlarged cross-sectional view shown in
By contrast, in the first embodiment, the top face 42t of the projection 42a has two pairs of parallel sides both oblique to the direction B in which the development roller 42 rotates as shown in (b) of
In the development device 4 according to the first embodiment, a metal blade is used as the doctor blade 45 (blade 450).
Resin or rubber blades are often used as the developer regulator disposed to contact the development roller having regular surface unevenness, that is, regularly arranged projections and recesses. However, in the case of rubber blades, it is possible that the amount by which the developer regulator projects from the fixed portion of the developer regulator (e.g., the portion held by the blade holder 45c), which is hereinafter referred to as “projecting amount of the developer regulator (or doctor blade), fluctuates due to tolerance in manufacturing or assembling, or abrasion of the developer regulator over repeated use. As a result, the amount of toner carried on the development roller fluctuates. Specifically, it is possible that the amount of toner carried on the development roller may be extremely small, making image density too light, or that the mount of toner is excessive and causes defective toner charging, resulting in scattering of toner on the background of output images.
By contrast, when a metal blade is used as the doctor blade 45 as in the first embodiment, the amount of toner carried on the development roller 42 can be kept substantially constant even if the projecting amount of the doctor blade 45 fluctuates in a certain range.
For the development roller 42, general purpose materials such as, but not limited to, carbon steel (such as STKM, JIS standard), aluminum, or SUS steel can be used. Examples of materials usable for the doctor blade 45 include, but not limited to, phosphor bronze such as C5210, copper such as C1202, beryllium copper such as C1720, and stainless steel such as SUS301 and SUS304.
(Experiment 1)
Descriptions are given below of experiment 1 performed to examine changes in the amount of toner carried on the development roller 42 depending on the projecting amount of the doctor blade 45 in cases of the metal doctor blade 45 and a rubber doctor blade as a comparative example.
Referring to
Initially, the doctor blade 45 is disposed in the edge contact state with the development roller 42 such that the doctor blade 45 extends in the vertical direction in
More specifically, the edge portion 45e is a corner portion (sharp, curved, or chamfered) on the free side of the planar doctor blade 45 and on the side facing the development roller 42, and the edge contact state means a state in which the edge portion 45e can contact the projections 42a of the development roller 42.
Additionally, regarding the direction of edge contact, as shown in
It is to be noted that, although a planer doctor blade may be bent into an L-shape so that the bent portion (i.e., a corner) contacts the development roller 42, the above-described edge contact state is preferred because toner can be scraped off better. Thus, the doctor blade 45 projects from the downstream side to the upstream side in the direction B to be in the edge contact state.
Referring back to the manner to change the projecting amount of the doctor blade 45, from the state shown in
When the blade holder 45c is moved from the position shown in
In the graph shown in
In
Referring to
As can be known form the results of experiment 1 shown in
The toner amount can be stable when the projecting amount is a given amount within the range (in minus direction) shown in
(Experiment 2)
In experiment 2, a positional range of the metal doctor blade 45 in which the edge contact state is secured was examined while changing the shift distance X1 (shown in
In the graph shown in
As can be known from
(Experiment 3)
Experiment 3 was executed to examine creation of substandard images having streaky unevenness in image density in cases of the doctor blades 45 constructed of phosphor bronze and SUS stainless steel, respectively. In experiment 3, the development roller 42 having a Vickers hardness greater than that of phosphor bronze and smaller than that of stainless steel was used. More specifically, the development roller 42 having an aluminum surface layer was used. It is to be noted that Vickers hardness can be measured according to JIS Z2244 standard.
The Vickers hardness of phosphor bronze used in experiment 3 was 80 Hv. It can be assumed that the doctor blade 45 constructed of a metal blade having a Vickers hardness lower than 80 Hv can inhibit adhesion of toner similarly to the phosphor bronze doctor blade 45 used in experiment 3. Although Vickers hardness was adopted in experiment 3, Brinell hardness or Rockwell number may be used depending on the material or shape of components.
In experiment 3, the metal blades 45 constructed of the respective materials were disposed in the state shown in
When the two doctor blades 45 were checked, adhesion of toner was found on the SUS doctor blade 45. By contrast, adhesion of toner was rarely found on the phosphor bronze doctor blade 45.
The amount of abrasion of the two doctor blades 45 used in experiment 3 was measured relative to the time during which the development roller 42 was rotated (rotation time of the development roller 42), and
It can be known from
When the surface layer 42f of the development roller 42 is harder than the contact portion of the doctor blade 45, the development roller 42 can abrade the doctor blade 45, thus inhibiting adhesion of toner.
To increase the hardness of the surface layer 42f of the development roller 42, the development roller 42 may be plated with nickel or the like. Also in configurations in which the surface layer of the development roller 42 is thus hardened, phosphor bronze is preferred as the material of the doctor blade 45 to prevent toner adhesion because phosphor bronze can be abraded more easily than stainless steel. Similarly, metals having a hardness lower than that (such as Vickers hardness of 80 Hv) of phosphor bronze can be effective to prevent adhesion of toner.
As can be known form the results of experiment 3, in the first embodiment, the doctor blade 45 itself is abraded to remove toner adhering thereto while the degree of toner adhesion is lower to inhibit streaky unevenness in image density. Therefore, it is preferred that the doctor blade 45 be abraded entirely in the width direction.
In the development roller 42 according to the first embodiment, in the circumferential direction of the development roller 42, at least one top face 42t, which is the highest surface of the projection 42a, is present at any position in the width direction (perpendicular to the direction B in which the development roller 42 rotates) in the grooved range 420a for carrying toner supplied to the photoreceptor 2.
To satisfy the above-described requirement of the surface unevenness of the development roller 42, the projections 42a and the recesses 42b are cyclically arranged in the width direction at a given circumferential position (such as line L11 shown in
With this configuration, when the line L11 of the development roller 42 is at the contact position with the doctor blade 45, there are portions of the doctor blade 45 that do not contact the top faces 42t, and such portions contact the top faces 42t when the line L12 of the development roller 42 contacts the doctor blade 45. Accordingly, while the development roller 42 makes one rotation, any axial position over the axial length of the doctor blade 45 can contact the top face 42t of the development roller 42 at least once. In other words, any axial position of the doctor blade 45 can be efficiently abraded by the top face 42 while the development roller 42 makes one rotation. Thus, streaky image density unevenness resulting from toner adhesion can be prevented securely.
In direct contact development methods in which the surface of the development roller 42 contacts the photoreceptor 2, it is possible that the development roller 42 fails to contact the photoreceptor 2 in some portions depending on manufacturing precision because the development roller 42 and the photoreceptor 2 both have little elasticity. In such portions, toner is not supplied to the photoreceptor 2, resulting in absence of toner in output images. In view of the foregoing, in the first embodiment, the development roller 42 is disposed contactless with, that is, across a gap from, the photoreceptor 2, and the development bias power source 142 applies to the development roller 42 the development bias in which an AC bias is superimposed on a DC bias. Such a development bias can move toner T from the development roller 42 to the photoreceptor 2 as if toner T jumps, thereby developing the latent image formed thereon. Thus, regardless of accuracy in the relative positions of the development roller 42 and the photoreceptor 2, absence of toner in output images can be prevented.
Additionally, the image forming apparatus 500 according to the present embodiment may include an alert system to alert the user when it is time to replace the development device 4, or that the development device 4 is approaching to the end of operational life preliminarily set in accordance with operation conditions.
Referring to
As shown in
As described above, the development device 4 according to the first embodiment includes the development roller 42, serving as a developer bearer, that carries by rotation magnetic or nonmagnetic toner as one-component developer and supplies toner to the latent image formed on the photoreceptor 2, serving as the latent image bearer, in the development range α facing the photoreceptor 2. The development device 4 further includes the doctor blade 45 that can be a planar member serving as the developer regulator and having the base end supported by the blade holder 45c and the free end portion disposed in contact with the development roller 42 to adjust the amount of toner supplied to the development range α. Further, the projections 42a and the recesses 42b are formed in the surface of the development roller 42. The doctor blade 45 is constructed of metal, and the edge portion 45e thereof contacts the surface of the development roller 42.
It is preferable that the portion of the metal doctor blade 45 that contacts the development roller 42 has a degree of hardness lower than that of the development roller 42.
An image forming apparatus 600 according to a second embodiment is described below. For example, the image forming apparatus in the present embodiment is an electrophotographic printer.
As shown in
The four process cartridges 1 form yellow, cyan, magenta, and black toner images on the respective photoreceptors 2. The four process cartridges 1 are arranged in parallel to the belt travel direction indicated by arrow shown in
As one of multiple tension rollers around which the intermediate transfer belt 7 is looped is rotated by a driving roller, the intermediate transfer belt 7 rotates in the belt travel direction indicated by arrow shown in
Referring to
The development device 4A includes a partition 110 that separates an interior of the development device 4A into a toner containing chamber 101 for containing toner T serving as developer and a supply compartment 102 disposed beneath the toner containing chamber 101. As shown in
The development roller 42 serving as a developer bearer is provided beneath the supply compartment 102. The supply roller 44 provided in the supply compartment 102 serves as a developer supply member to supply toner T to the surface of the development roller 42. The supply roller 44 is disposed in contact with the surface of the development roller 42. Additionally, a doctor blade 45 serving as a developer regulator is provided in the supply compartment 102 to adjust the amount of toner supplied by the development roller 42 to the development range where the development roller 42 faces the photoreceptor 2. The doctor blade 45 is disposed in contact with the surface of the development roller 42.
The development roller 42 is contactless with the photoreceptor 2, and a high pressure power source applies a predetermined bias to the development roller 42. The conveyance member 106 serving as a toner conveyance member is provided in the toner containing chamber 101 to transport toner T in parallel to the axial direction of the photoreceptor 2, which is perpendicular to the surface of the paper on which
In the present embodiment, toner T contained in the toner containing chamber 101 can be produced through a polymerization method. For example, toner T has an average particle diameter of 6.5 μm, a circularity of 0.98, and an angle of rest of 33°, and strontium titanate is externally added to toner T as an external additive. It is to be noted that toner usable in the image forming apparatus 600 according to the second embodiment is not limited thereto.
As shown in
Additionally, in the second embodiment, toner is transported from the toner containing chamber 101 toward the supply roller 44 in a direction perpendicular to the axial direction of the conveyance member 106 and substantially vertically. Alternatively, toner may be transported in a direction perpendicular to the axial direction of the conveyance member 106 and substantially horizontally.
The toner agitator 108 is disposed in the supply compartment 102 under the partition 110. As shown in
As shown in
A surface of the supply roller 44 is covered with a foamed material in which pores or cells are formed so that toner T transported to the supply compartment 102 and then agitated by the toner agitator 108 can be efficiently attracted to the surface of the supply roller 44. Further, the foamed material can alleviate the pressure in the portion in contact with the development roller 42, thus preventing or reducing deterioration of the developer T. It is to be noted that the electrical resistance value of the foamed material can be within a range from about 103Ω to about 1014Ω. A supply bias is applied to the supply roller 44, and the supply roller 44 promotes effects of pushing preliminarily charged toner against the development roller 42 in the supply nip β. The supply roller 44 supplies toner carried thereon to the surface of the development roller 42 while rotating counterclockwise in
The doctor blade 45 is disposed to contact the surface of the development roller 42 at the position downstream from the supply nip β in the direction in which the development roller 42 rotates. As the development roller 42 rotates, the toner carried thereon is transported to the position where the doctor blade 45 contacts.
For example, the doctor blade 45 can be a metal leaf spring constructed of SUS304CSP or SUS301CSP (JIS standard); or phosphor bronze. The distal end (free end) of the doctor blade 45 can be in contact with the surface of the development roller 42 with a pressure of about 10 N/m to 100 N/m. While adjusting the amount of toner passing through the regulation nip, the doctor blade 45 applies electrical charge to toner through triboelectric charging. To promote triboelectric charging, a bias may be applied to the doctor blade 45.
The photoreceptor 2 is contactless with the development roller 42 and rotates clockwise in
As the development roller 42 rotates, the toner thereon is transported to the development range α, where a development field is generated by differences in electrical potential between the latent image formed on the photoreceptor 2 and the development bias applied to the development roller 42. The development field moves toner from the development roller 42 toward the photoreceptor 2, thus developing the latent image into a toner image.
A discharge seal 109 (shown in
To generate the development field, an AC bias that alternates between a voltage to move toner toward the photoreceptor 2 and a voltage to return toner to the development roller 42 is used. In the second embodiment, for example, a rectangular wave having a frequency (f) from 500 Hz to 10000, a peak-to-peak voltage (Vpp) from 500 V to 3000 V, a duty from 50% to 90% is usable. Toner that is not used in image development is returned to the supply compartment 102 and repeatedly used as the development roller 42 rotates.
The features of the development roller 42 and the doctor blade 45 according to the first embodiment can adapt to the development device 4A according to the second embodiment.
The various configurations according to the present inventions can attain specific effects as follows.
Configuration A:
A development device includes a developer bearer, such as a development roller 42, to carry by rotation magnetic or nonmagnetic one-component developer to a development range facing a latent image bearer, such as the photoreceptor 2, and to supply the developer to a latent image formed on the latent image bearer, a planar developer regulator, such as the doctor blade 45, that contacts a surface of the developer bearer to adjust an amount of developer carried to the development range α, and a lateral end seal (59) that contacts the surface of the developer bearer adjacent to the axial end. The developer bearer includes the grooved range (420a) having surface unevenness, such as the projections and the recesses formed by the spiral grooves (L1 and L2), and the smooth surface ranges (420b). The grooved range is a range including an axial center of the developer bearer, and the smooth surface ranges are positioned outside the grooved range in the axial direction. Each lateral end seal is provided astride the grooved range and the smooth surface range.
In this configuration, developer moving along the spiral grooves formed in the grooved range does not pass through the range inside the smooth surface range in contact with the lateral end seal. Accordingly, leakage of developer at the axial end can be prevented. Additionally, the axial area inside the contact ranges with the lateral end seals means the grooved range, and developer is not carried on the smooth surface ranges. Accordingly, developer does not firmly adhere to the axial end portions of the developer regulator that contact the smooth surface ranges. Thus, scattering of developer caused by adhesion of developer can be prevented. Thus, in the development device using the developer bearer having surface unevenness in regular arrangement, leakage of developer can be prevented.
Configuration B:
In configuration A, the grooved range (420a1) includes two different types of areas arranged in the axial direction, an axial center area (420c) and axial end areas (420d), which are different in depth of the recesses (grooves). The recesses in the axial center area of the grooved range are deeper than those in the axial ends. In this configuration, since the recesses in the axial end area of the grooved range adjacent to the smooth surface range (420b) is shallower, the amount of toner moving along the spiral grooves to the smooth surface range can be reduced, thus securing prevention of leakage of toner.
Configuration C:
In configuration A, the grooved range (420a2) includes two different types of areas arranged in the axial direction, an axial center area (420c′) and axial end areas (420d′), which are different in inclination of spiral grooves relative to the axial direction of the developer bearer. The inclination of spiral grooves in the axial end areas is greater than that in the axial center area. In this configuration, since the inclination of spiral grooves in the axial end area of the grooved range adjacent to the smooth surface range is sharper, the action of developer moving along the spiral grooves to the smooth surface range can be reduced. Accordingly, the amount of developer moving to the smooth surface range can be reduced, thus securing prevention of leakage of toner.
Configuration D:
In any of configurations A through C, in the axial direction of the developer bearer, the smooth surface range (420b) and the axial end area (420d or 420d′) are positioned outside the image formation area in which developer is supplied to the latent image bearer in the development range α. Although the amount of developer carried on the developer bearer may differ among the axial center grooved range, the outer grooved range, and the smooth surface range, it does not cause image density unevenness in the axial direction because toner carried on the smooth surface range and outer grooved range does not contribute to image development.
Configuration E:
In any of configurations A through D, the surface unevenness is formed by first and second spiral grooves L1 and L2 winding in the opposite directions and crossing each other at multiple positions on the developer bearer. With this configuration, the surface unevenness in regular arrangement can be formed easily in the surface of the developer bearer.
Configuration F:
In any of configurations A through E, the grooved range is plated, whereas the smooth surface range is not plated. Plating can help developer particles to roll on the development roller 42, thus facilitating charging of developer. Simultaneously, movement of developer to the smooth surface range can be inhibited.
Configuration G:
In any of configurations A through F, the depth of the recesses (42b), which is the height from the bottom face of the recess to the top face (42t) of the projections (42a), is equal to or smaller than twice the volume average particle size of developer particles. With this configuration, developer particles contained inside the recesses can contact at least one of the developer regulator or the developer bearer, attaining proper charging properties of developer.
Configuration H:
In any of configurations A through G, the lateral end seal (59) conforms to the surface unevenness of the grooved range. This configuration can inhibit developer from moving along the spiral grooves (L1 and L2) formed in the range of the grooved range that contacts the lateral end seal. Accordingly, the amount of toner moving along the spiral grooves to the smooth surface range can be reduced, thus securing prevention of leakage of toner.
Configuration I:
In configuration I, the lateral end seal is constructed of pile fabric whose strands lean in the direction of the spiral grooves forming the recesses in the surface of the developer bearer. This configuration can inhibit developer from moving along the spiral grooves in the range of the grooved range that contacts the lateral end seal. Accordingly, the amount of toner moving along the spiral grooves to the smooth surface range can be reduced, thus securing prevention of leakage of toner.
The above-described development device according to any of the configurations A through I is incorporated in an image forming apparatus that includes at least the latent image bearer, a charging member, and a latent image forming device such as the exposure unit 6.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-203827 | Sep 2011 | JP | national |
| 2012-162027 | Jul 2012 | JP | national |
