JP3726889B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus of a cleanerless system using a toner whose surface is coated with an external additive.
[0002]
[Prior art]
In color electrophotography, an intermediate transfer member is used in order to prevent the photoconductor from being worn and to facilitate superimposition of color images. Further, the resolution is improved by using a toner having a small particle diameter of 20 μm or less or 10 μm or less. However, the toner having a small particle diameter is poor in transferability as compared with the toner having a large particle diameter, and there is a problem that when the transfer electric field is increased in order to improve transferability, dielectric breakdown occurs and an image defect occurs. This transferability greatly depends on the adhesion force between the toner and the photoreceptor, and between the toner and the intermediate transfer member (Van der Worth force, mirror image force).
[0003]
Therefore, in order to improve transferability, the adhesion force between the intermediate transfer member and the toner is made larger than the adhesion force between the photosensitive member and the toner, and the toner and the transfer sheet are more adhered than the adhesion force between the intermediate transfer member and the toner. One that increases the adhesive force has been proposed (Japanese Patent Publication No. 5-50337).
[0004]
[Problems to be solved by the invention]
By the way, the toner is coated with an external additive in order to improve the chargeability, but there are several percent of free mother particles that are not sufficiently coated with the external additive. Further, in the one-component development method, the external additive is peeled off from the toner surface due to deterioration in use durability, or the amount of the external additive on the surface is reduced by being embedded in the resin mother particles. With such free mother particles and toner with deteriorated durability, the chargeability deteriorates. Therefore, when a charging failure occurs, the transferability from the photosensitive member to the intermediate transfer member or paper due to electric force is reduced, and transfer residue is generated. End up. In the conventional image forming apparatus, the untransferred toner is removed by a cleaner. However, in the cleanerless image forming apparatus, such a transfer remaining is not allowed to occur.
[0005]
[Means for Solving the Problems]
The present invention is for solving the above-mentioned problems, and prevents residual transfer due to charging defects due to free mother particles or deteriorated toner whose amount of external additive has decreased due to durability deterioration, and realizes cleanerless in an image forming apparatus. Aim to do.
For this reason, the present invention provides a cleanerless system image forming apparatus using a toner whose surface is coated with an external additive on the surface of the resin base particles, wherein the adhesive force between the resin base particles is greater than the adhesive force between the resin base particles and the image carrier. In addition, the transfer between the image carrier and the resin mother particles is reduced by transferring with a speed difference, and the toner on the image carrier including all the free mother particles is transferred. To do.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a configuration example of a monochrome image forming apparatus to which the present invention is applied.
Around the photoconductor (image carrier) 10, a charger 11, an exposure unit 12, a developing device 13, and a transfer roller 18 are arranged, and the electrostatic on the photoconductor 10 formed by the charger 11 and the exposure unit 12. The latent image is developed with toner by the developing device 13. In the developing device 13, a small particle size toner 15 of 10 μm or less whose surface is coated with an external additive on the surface of the resin mother particles is stirred by a stirrer (not shown) and supplied onto the surface of the developing roller 16 by a supply roller 14. The toner is charged by the friction between the rollers, and further regulated to a constant layer thickness by the regulating blade 17 and is also frictionally charged at this time, and is conveyed to the nip portion with the photoreceptor 10. In the nip portion, the charged toner is transferred from the developing roller to the photosensitive member by a developing electric field, and toner development is performed. At this time, the toner used for development is about several percent, and the remaining toner is collected in the developing device 13 and supplied again to the developing roller by the supply roller 14 for development. The toner image on the photosensitive member is transferred to an intermediate transfer member or paper 19 by a transfer electric field by the transfer roller 18 and fixed by a fixing device 20.
[0007]
FIG. 2 is a diagram schematically showing the toner used in the present invention.
The toner 40 is a toner having a small particle size of 10 μm or less for high resolution, and the surface of the resin mother particles 40a is coated with an external additive 40b for improving the charging property and weakening the adhesive force.
[0008]
FIG. 3 is a diagram for explaining an example of a developing device of a one-component non-magnetic developing system.
The toner 40 shown in FIG. 2 is stirred by the stirring rod 41, supplied to the developing roller 44 by the supply roller 42, rubbed against the surface thereof, and frictionally charged, and further regulated to a certain thickness by the regulating blade 43. Then, it is triboelectrically charged and conveyed to the nip portion with the photoreceptor. The toner that has not been developed is returned to the developing device, and the frictional charging by the stirring, the supply roller, and the regulating blade is repeated again. In development, selective development is performed in which new toner with favorable charging performance and uniform charge distribution is preferentially consumed. When the amount of toner consumed until the life of the developing device is compared with the number of printed sheets, about 95% of each development is not consumed and returned to the developing device. As a result of such use durability, the toner surface external additive is embedded in or peeled off from the mother particles, and the amount of the external additive on the toner surface decreases. Even in new toners, there are several percent of free mother particles that are not sufficiently coated with external additives. In toners that are sufficiently coated with external additives, the transfer efficiency is good because the charging performance is good and the adhesive force is weak. It increases and the charging performance also decreases.
[0009]
When toner having deteriorated chargeability is developed as described above, the amount of charged electric charge is small, so that when the transfer electric field is applied by the transfer roller 18, the transferability is not sufficient, and transfer residue occurs. Conventionally, the transfer residual toner is removed by a cleaner. However, in the present invention, since a cleaner-less system is employed, a transfer efficiency of almost 100% is achieved. This point will be described with reference to FIGS.
[0010]
FIG. 4 is a diagram schematically showing transfer from the photosensitive member to the intermediate transfer member or paper.
Normally, the toner development is performed with the peripheral surface speed of the developing roller larger than the peripheral surface speed of the photosensitive member. Therefore, the toner on the surface of the photoreceptor is developed with one or more layers. For example, as shown in FIG. 4, when the toner is developed in two layers, the adhesion force (Van der Worth force, mirror image force) between the resin base particles 30 and the photoreceptor 10 is F1, and the resin base particles When the adhesive force is F2, and the adhesive force between the resin mother particles and the intermediate transfer member or paper is F3,
F1 <F2 (1)
Is established. When equation (1) holds,
F1 <F3 (2)
Is applied between the resin base particles and the intermediate transfer member or paper by the transfer electric field, the toner is transferred without causing interlayer separation.
[0011]
FIG. 5 is a diagram schematically showing a state in which a toner that is not sufficiently charged and a toner that is normally charged are transferred without mutual separation due to mutual adhesion.
Assuming that the toner 31 is a toner whose durability has been deteriorated or is a free mother particle with a small amount of external additives, the chargeability has deteriorated and is not sufficiently charged, and the toner 32 is a normally charged toner. When the toner is attracted to the intermediate transfer member or the sheet by the adhesion force F3 between the resin mother particle and the intermediate transfer member or the sheet, the adhesion force F2 between the resin mother particles is an adhesion force between the resin mother particle and the photosensitive member. Since it is larger than F1, both the toners 31 and 32 are transferred.
[0012]
FIG. 6 is a diagram schematically illustrating a state in which a toner that is not sufficiently charged and a toner that is normally charged are transferred as a lump by mutual adhesion.
When the toner 31 with poor chargeability and the normally charged toner 32 are in a lump, the toner is attracted to the intermediate transfer member or paper by the adhesive force F3 between the resin mother particles and the intermediate transfer member or paper. In this case, since the adhesion force F2 between the resin mother particles is larger than the adhesion force F1 between the resin mother particles and the photoconductor, both the toners 31 and 32 are transferred as a lump.
[0013]
As described above, by making the adhesive force between the resin mother particles larger than the adhesive force between the photosensitive member and the resin mother particles, it is possible to prevent the transfer residue caused by the poorly charged toner. Of course, toner that is sufficiently coated with the external additive and sufficiently charged is transferred by the transfer electric field, so that no transfer residue occurs.
[0014]
A configuration example of the photoconductor for making the adhesive force between the resin base particles and the photoconductor smaller than the adhesive force between the resin base particles will be described.
Examples of photoreceptors for satisfying the above conditions include the following.
(1) Select a material having a small surface energy as the outermost surface resin of the photoreceptor.
(2) A surfactant that imparts water repellency and lipophilicity is added to the outermost surface layer of the photoreceptor.
(3) A material having high releasability is dispersed in the outermost layer of the photoreceptor.
[0015]
As an example of the above (1), a fluorine-containing group and a silicon-containing group are introduced into the resin structure.
[0016]
As an example of the above (2), ex polyoxyalkene alkyl ether, polyoxyalkene alkylphenyl ether, polyoxyalkene sorbitan fatty acid ester, fatty acid monoglyceride polyethylene glycol fatty acid ester and the like are added. Calcium stearate, potassium stearate, zinc stearate, iron stearate, barium stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, cadmium stearate, magnesium stearate, cobalt oleate, zinc oleate , Manganese oleate, iron oleate, zinc palmitate, cobalt palmitate, copper palmitate, magnesium palmitate, aluminum palmitate, calcium palmitate, lead caprylate, copper caprylate, zinc linolenate, cobalt linolenate, linolenic acid Apply calcium acid or the like (JP 2000-267303 A, JP 6-332324 A).
[0017]
As an example of the above (3), fluorine fine particles are dispersed. Polytetrafluoroethylene powder (particle size 0.1 to 0.3 μm) was dissolved in a polycarbonate resin in which a hole-transporting triphenylamine compound was dissolved at a weight ratio of 10: 8. Disperse ~ 50 parts by weight. ex tetrafluoroethylene resin, trifluoroethylene chloride resin, hexafluoroethylene propylene resin, vinyl fluoride resin, vinylidene fluoride resin, ethylene difluoride dichloride resin, and copolymers thereof Alternatively, two or more kinds are appropriately selected.
[0018]
Any one of the above (1), (2), and (3) is used as the photosensitive member, and the belt material of the intermediate transfer member is urethane, polyester, polycarbonate, PET, or the like (including PET containing fluorine or silicon-containing groups) For each of the new toner and the toner after use endurance, compress the toner into a tablet by compressing the toner, pressing it against the photosensitive material or a sheet of the same material, and pressing the tablets together An example in which the coefficient of friction when sliding is measured will be described.
[0019]
〔Example〕
Compressing the toner X in 1000~5000kgf / cm ² (Effect of the mother particle becomes dominant with respect to adhesion by compressing at a high pressure of the toner), a material obtained by tableting at 20gf / cm ² ~400gf / cm ² The friction coefficient when a toner tablet is slid on a sheet (fixed) when pressed against the same sheet as the image carrier and the surface material is based on the friction coefficient when one of the toner tablets is fixed and slid similarly. When the transfer efficiency was measured using a small toner, 99.6 to 100% at the initial stage and 99.3 to 99.7% after the endurance could be secured.
[0020]
When the initial toner was measured by a particle analyzer method using PT-1000 (manufactured by Yokogawa Electric Corporation), toner surface layer data of 5% free mother particles (number ratio) was obtained.
[0021]
In the above example, a monochrome image forming apparatus has been described as an example. However, the present invention can also be used when a tandem image forming apparatus having a plurality of image forming units each having a photoconductor is used as a monocolor. Applicable.
[0022]
In order to reduce the adhesion between the photosensitive member and the toner base particles, it is preferable to perform transfer with a speed difference so that a shearing force is applied to the toner.
[0023]
【The invention's effect】
In general, a toner is composed of mother particles mainly composed of a resin such as polyester, styrene, and acryl, and an external additive that covers the surface of the mother particle. The external additive serves to reduce adhesion between the toner and a member that contacts the toner. There is also a function to charge. In order to achieve an image forming apparatus having a configuration in which the transfer efficiency is close to 100% and the cleaner mechanism is omitted, the adhesion force with the contacting member is large and the charging ability is small (the charge amount is almost 0). The transfer efficiency of free mother particles whose particles are exposed on the surface and toner whose durability has deteriorated must also be considered.
[0024]
Therefore, in the present invention, the adhesion force between the resin mother particles constituting the toner is made larger than the adhesion force between the image carrier and the resin mother particles, so that the toner that is difficult to be transferred by an electric force is surrounded by the adhesion force. Therefore, it is possible to achieve stable transfer characteristics with high transfer efficiency and irrespective of the usage history (durability) of the apparatus.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration example of a monochrome image forming apparatus to which the present invention is applied.
FIG. 2 is a diagram schematically illustrating a toner used in the present invention.
FIG. 3 is a diagram illustrating an example of a developing unit of a one-component non-magnetic developing system.
FIG. 4 is a diagram schematically showing transfer from a photosensitive member to an intermediate transfer member or paper.
FIG. 5 is a diagram schematically illustrating a state in which a toner that is not sufficiently charged and a toner that is normally charged are transferred without mutual separation due to mutual adhesion.
FIG. 6 is a diagram schematically illustrating a state in which a toner that is not sufficiently charged and a normally charged toner are transferred as a lump by mutual adhesion.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Photoconductor, 11 ... Charging device, 12 ... Exposure unit, 13 ... Developer 1,14 ... Supply roller, 15 ... Toner, 16 ... Developing roller, 17 ... Regulator blade, 18 ... Transfer roller, 19 ... Intermediate transfer member Or paper, 20 ... fixer.

Claims (1)

In an image forming apparatus of a cleanerless system using a toner whose surface is coated with an external additive, the adhesion force between the resin mother particles is larger than the adhesion force between the resin mother particles and the image carrier, and the speed difference is reduced. An image forming apparatus characterized in that the adhesion force between the image carrier and the resin mother particles is reduced by providing and transferring the toner on the image carrier including the free mother particles .

Images