Claims
- 1. An image forming method comprising:
- (a) developing an electrostatic image formed on an electrostatic image-bearing member with a developer to form thereon a developed image, said developer comprising 100 wt. parts of a toner and 0.3 to 1.6 wt. parts of silica fine powder treated with a silicone material selected from the group consisting of an amino-modified silicone oil and an amino-modified silicone varnish; and
- (b) electrostatically transferring the developed image on the electrostatic image-bearing member to a transfer material while pressing a transfer means supplied with a bias voltage against the electrostatic image-bearing member with the transfer material disposed between the electrostatic image-bearing member and the transfer means under a line pressure of 3 g/m or higher, wherein the electrostatic image-bearing member has a curvature radius of no greater than 25 mm at the transfer position.
- 2. A method according to claim 1, wherein the developer comprises:
- (i) an insulating magnetic toner; and
- (ii) the silica fine powder treated with the silicone material.
- 3. A method according to claim 1, wherein the developer is carried on a developing sleeve and is triboelectrically charged by the contact thereof with the developing sleeve.
- 4. A method according to claim 1, wherein the transfer means comprises a device selected from the group consisting of a transfer roller and a transfer belt.
- 5. A method according to claim 4, wherein the transfer means comprises a transfer roller comprising a metal core and an electroconductive elastic layer disposed thereon.
- 6. A method according to claim 5, wherein the electroconductive elastic layer of the transfer roller has a volume resistivity of 10.sup.6 to 10.sup.8 ohm.cm.
- 7. A method according to claim 1, wherein the developed image is electrostatically transferred to the transfer material while the transfer means is pressed against the electrostatic image-bearing member under a line pressure of 20 g/cm or higher.
- 8. A method according to claim 1, wherein the developed image is electrostatically transferred to the transfer material by the transfer means to which a bias having a transfer current of 0.1-50 .mu.A, and a transfer voltage of 500-4000 V (absolute value) is applied.
- 9. A method according to claim 1, wherein 100 wt. parts of the fine powder has been treated with 1-35 wt. parts of the amino-modified silicone oil.
- 10. A method according to claim 1, wherein 100 parts of the fine powder has been treated with 2-30 wt. parts of the amino-modified silicone oil.
- 11. A method according to claim 1, wherein the silica fine powder is obtained by treating a silica fine powder having a particle size of 0.001-2 microns with said silicone material.
- 12. A method according to claim 1, wherein the silica fine powder has been treated with a silane coupling agent and the silicone material.
- 13. A method according to claim 1, wherein the insulating magnetic toner has a residual magnetization ar of 1-5 emu/g, a saturation magnetization .sigma..sub.s of 15-50 emu/g, and a coercive force of 20-100 Oe.
- 14. A method according to claim 1, wherein the toner comprises an insulating magnetic toner, and the insulating magnetic toner
- (1) contains 17-60% by number of magnetic toner particles having a particle size of 5 microns or smaller,
- (2) contains 5-50% by number of magnetic toner particles having a particle size of 6.35-10.08 microns, and
- (3) contains 2.0% by volume or less of magnetic toner having a particle size of 12.7 microns or larger; wherein
- (a) the magnetic toner has a volume-average particle size of 6-8 microns, and
- (b) the magnetic toner particles having a particle size of 5 microns or smaller have a particle size distribution satisfying the following formula:
- N/V=-0.05N+k
- wherein N is a positive number of 17 to 60 that denotes the percentage by number of magnetic toner particles having a particle size of 5 microns or smaller,
- V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, and
- k denotes a positive number of 4.6 to 6.7.
- 15. A method according to claim 1, wherein the silica fine powder has been treated with an amino-modified silicone oil represented by the following formula: ##STR8## wherein R.sub.1 and R.sub.6 are each a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, an alkyl group having an amino group, an aryl group having an amino group, an alkyl group having a halogen atom or an aryl group having a halogen atom;
- R.sub.2 is an optional group selected from the group consisting of an alkylene group, a phenylene group, an alkylene group having an amino group, a phenylene group having an amino group, an alkylene group having a halogen atom and a phenylene group having a halogen atom;
- R.sub.3 is a nitrogen-containing heterocycle or a group having a heterocyclic structure;
- R.sub.4 and R.sub.5 are each a hydrogen atom, an alkyl group or an aryl group;
- m is a number of 1 or larger;
- n and 1 are each 0 or a positive number; and
- the sum of (n+1) is a positive number of 1 or larger.
- 16. A method according to claim 1, wherein the silica fine powder has been treated with an amino-modified silicone varnish including a chemical structure represented by the following formula: ##STR9## wherein R.sup.31 is a methyl or phenyl group.
- 17. A method according to claim 1, wherein the toner comprises an insulating magnetic toner and the insulating magnetic toner contains:
- (1) 71-60% by number of magnetic toner particles having a particle size of 5 microns or smaller; and
- (2) 5-50% by number of magnetic toner particles having a particle size of 6.35-10.08 microns.
- 18. A method according to claim 1, wherein the toner comprises an insulating magnetic toner and the insulating magnetic toner contains:
- (1) 17-60% by number of magnetic toner particles having a particle size of 5 microns or smaller; and
- (2) 5-50% by number of magnetic toner particles having a particle size of 6.35-10.08 microns; wherein the magnetic toner particles having a particle size of 5 microns or smaller have a particle size distribution satisfying the following formula:
- N/V=-0.5N+k
- wherein N is a positive number of 17 to 60 that denotes the percentage by number of magnetic toner particles having a particle size of 5 microns or smaller,
- V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, and
- k denotes a positive number of 4.6 to 6.7.
- 19. A method according to claim 1, wherein the toner comprises an insulating magnetic toner and the insulating magnetic toner contains:
- (1) 17-60% by number of magnetic toner particles having a particle size of 5 microns or smaller; and
- (2) 5-50% by number of magnetic toner particles having a particle size of 6.35-10.08 microns; wherein
- (a) the magnetic toner has a volume-average particle size of 6-8 microns; and
- (b) the magnetic toner particles having a particle size of 5 microns or smaller have a particle size distribution satisfying the following formula:
- N/V=-0.5N+k,
- wherein N is a positive number of 17 to 60 that denotes the percentage by number of magnetic toner particles having a particle size of 5 microns or smaller,
- V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, and
- k denotes a positive number of 4.6 to 6.7.
- 20. A method according to claim 1, wherein the transfer means is pressed against the electrostatic image-bearing member under a line pressure of 3-80 g/cm.
Priority Claims (3)
| Number |
Date |
Country |
Kind |
| 1-111006 |
Apr 1989 |
JPX |
|
| 1-184421 |
Jul 1989 |
JPX |
|
| 1-184422 |
Jul 1989 |
JPX |
|
SUMMARY OF THE INVENTION
This application is a division of application Ser. No. 07/902,808, filed Jun. 25, 1992, now U.S. Pat. No. 5,270,770, which is a continuation of application Ser. No. 514,314, filed Apr. 25, 1990, now abandoned.
The present invention relates to an image forming method and an image forming apparatus, wherein a transfer device is caused to contact an electrostatic latent image-bearing member by the medium of a transfer material (or transfer-receiving material) and a magnetic toner image formed on the electrostatic latent image-bearing member is transferred to the transfer material.
As image forming apparatus wherein a toner image formed on a latent image-bearing member is electrostatically transferred to a transfer material in a sheet form such as paper, there have been proposed devices wherein a latent image-bearing member in the form of a rotary cylinder, an endless belt, etc., is used, a transfer device provided with a bias is caused to contact such a latent image-bearing member under pressure, and a transfer material is passed between these members, whereby the toner image on the latent image-bearing member is transferred to the transfer material, as disclosed in, e.g., Japanese Laid-Open Patent Application (JP-A, KOKAI) No. 46664/1984.
In such a device, when the contact pressure between a transfer roller and the latent image-bearing member is appropriately regulated, the region in which the transfer material contacts to the latent image-bearing member may be extended, as compared with a transfer means utilizing corona discharge which has heretofore been used widely. Further, since the transfer material is positively supported under pressure in the transfer position, the above-mentioned device is less liable to cause transfer deviation due to synchronism failure caused by a transfer material-conveying means, or due to loop or curl present in the transfer material. As a result, the above-mentioned device may easily meet the demand for shortening the conveying path for the transfer material and for miniaturizing the latent image-bearing member along with the miniaturization of an image forming apparatus.
On the other hand, in the device for effecting the transfer operation which is capable of causing a transfer means to contact a latent image-bearing member by the medium of a transfer material, since a transfer current is supplied to the transfer material in the contact position, it is necessary to apply a certain pressure to the transfer device. When such a contact pressure is applied to the transfer material, the pressure is also applied to the toner image formed on the latent image-bearing member, whereby the toner particles constituting the toner image tend to agglomerate.
Further, in a case where the surface portion of the latent image-bearing member comprises a resin, the above-mentioned toner agglomerates are liable to closely adhere to the latent image-bearing member and the transfer of the toner to the transfer material may be inhibited. In an extreme case, toner particles corresponding to a portion showing strong adhesion are not transferred at all, whereby the resultant toner image is liable to be lacking.
Such a phenomenon is particularly noticeable in a line image portion having a width of 0.1-2 mm. Since a so-called "edge phenomenon (or edge effect)" may occur in the line image portion, a larger amount of toner particles are attached thereto, whereby the agglomeration of toner particles due to pressure and image defects due to transfer operation are liable to occur. When such a phenomenon occurs, the resultant toner image becomes a copied image wherein toner particles are only attached to the contour portion thereof. Such a phenomenon is referred to as "partially white image (e.g., hollow character)". FIGS. 1B and 1D show examples of the partially white image.
The partially white images are particularly liable to occur in the case of thick paper of above 100 g/cm.sup.2, a film for OHP (overhead projector) having high smoothness, or second-side copying operation in double-side copying, etc. In the case of the thick paper or OHP film, it is considered that since the transfer material is thick, the effect of the transfer electric field is weakened and the pressure becomes strong, whereby the partially white images are liable to occur. In the case of the second copying in double-side copying, it is considered that a release agent for prevention of offset phenomenon is attached to a transfer material from a fixing device when the transfer material is passed between the fixing device at the time of the first-side copying, and the release agent prevents the close adhesion between the toner particles and transfer material at the time of the second-side transfer operation, whereby partially white images are liable to occur.
As described hereinabove, when a transfer device utilizing a contact member is used, it has many advantages such as miniaturization and small power consumption, but conditions for the transfer materials become severer.
Recently, as image forming apparatus such as electrophotographic copying machines have widely been used, their uses have also extended in various ways, and higher image quality has been demanded. For example, when original images such as general documents and books are copied, it is demanded that even minute letters are reproduced extremely finely and faithfully without thickening or deformation, or interruption. However, in ordinary image forming apparatus such as copying machines for plain paper, when the latent image formed on a photosensitive member thereof comprises thin-line images having a width of 100 microns or below, the reproducibility in thin lines is generally poor and the clearness of line images is still insufficient.
Particularly, in recent image forming apparatus such as electrophotographic printer using digital image signals, the resultant latent picture is formed by a gathering of dots with a constant potential, and the solid, half-tone and highlight portions of the picture can be expressed by varying densities of dots. However, in a state where the dots are not faithfully covered with toner paraticles and the toner particles protrude from the dots, there arises a problem that a gradational characteristic of a toner image corresponding to the dot density ratio of the black portion to the white portion in the digital latent image cannot be obtained. Further, when the resolution is intended to be enhanced by decreasing the dot size so as to enhance the image quality, the reproducibility becomes poorer with respect to the latent image comprising minute dots, whereby there tends to occur an image without sharpness having a low resolution and a poor gradational characteristic.
On the other hand, in image forming apparatus such as electrophotographic copying machine, there sometimes occurs a phenomenon such that good image quality is obtained in an initial stage but it deteriorates as the copying or print-out operation is successively conducted. The reason for such a phenomenon may be considered that only toner particles which are more contributable to the developing operation are consumed in advance as the copying or print-out operation is successively conducted, and toner particles having a poor developing characteristic accumulate and remain in the developing device of the image forming apparatus.
Hitherto, there have been proposed some developers for the purpose of enhancing the image quality. For example, Japanese Laid-Open Patent Application (JP-A, KOKAI) No. 3244/1976 (corresponding to U.S. Pat. Nos. 3,942,979, 3,969,251 and 4,112,024) has proposed a non-magnetic toner wherein the particle size distribution is regulated so as to improve the image quality. This toner comprises relatively coarse particles and predominantly comprises toner particles having a particle size of 8-12 microns. However, according to our investigation, it is difficult for such particle size to provide uniform and dense cover-up of the toner particles to a latent image. Further, the above-mentioned toner has a characteristic such that it contains 30% by number or less of particles of 5 microns or smaller and 5% by number or less of particles of 20 microns or larger, and therefore it has a broad particle size distribution which tends to decrease the uniformity in the resultant image. In order to form a clear image by using such relatively coarse toner particles having a broad particle size distribution, it is necessary that the gaps between the toner particles are filled by thickly superposing the toner particles thereby to enhance the apparent image density. As a result, there arises a problem that the toner consumption increases in order-to obtain a prescribed image density.
Japanese Laid-Open Patent Application No. 72054/1979 (corresponding to U.S. Pat. No. 4,284,701) has proposed a non-magnetic toner having a sharper particle size distribution than the above-mentioned toner. In this toner, particles having an intermediate weight has a relatively large particle size of 8.5-11.0 microns, and there is still room for improvement as a toner for a high resolution.
Japanese Laid-Open Patent Application No. 129437/1983 (corresponding to British Patent No. 2114310) has proposed a non-magnetic toner wherein the average particle size is 6-10 microns and the mode particle size is 5-8 microns. However, this toner only contains particles of 5 microns or less in a small amount of 15% by number or below, and it tends to form an image without sharpness.
Further, U.S. Pat. No. 4,299,900 has proposed a jumping developing method using a developer containing 10-50 wt. % of magnetic toner particles of 20-35 microns. In this method, the particle size distribution of the toner is improved in order to triboelectrically charge the magnetic toner, to form a uniform and thin toner layer on a sleeve (developer-carrying member), and to enhance the environmental resistance of the toner. However, at present, further improvements in developing and transfer steps have been demanded.
An object of the present invention is to provide an image forming method and apparatus which have solved the above-mentioned problems encountered in the prior art.
Another object of the present invention is to provide an image forming method and apparatus utilizing an electrostatic pressure transfer method such as contact transfer method, which has a transfer step capable of providing high-quality images faithful to a latent image regardless of transfer conditions and transfer materials.
A further object of the present invention is to provide an image forming method and apparatus wherein the above-mentioned partially white images are obviated or suppressed.
A further object of the present invention is to provide an image forming method and apparatus capable of providing high-quality images without a partially white image, even when a transfer material such as thick paper is used.
A further object of the present invention is to provide an image forming method capable of constantly exhibiting good performances stably, even under environmental change such as high temperature--high humidity and low temperature--low humidity conditions.
According to the present invention, there is provided an image forming method, comprising:
The present invention also provides an image forming apparatus comprising:
The present invention further provides a facsimile comprising an image forming apparatus and receiving means for receiving image information from a remote terminal; the image forming apparatus comprising:
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
US Referenced Citations (20)
Foreign Referenced Citations (5)
| Number |
Date |
Country |
| 0318078 |
May 1989 |
EPX |
| 0081681 |
Apr 1987 |
JPX |
| 0242978 |
Oct 1987 |
JPX |
| 0286879 |
Nov 1989 |
JPX |
| 2114310 |
Oct 1987 |
GBX |
Non-Patent Literature Citations (1)
| Entry |
| Xerox Disclosure Journal, "High Frequency Pulse Bias Roller Transfer", Fletcher. |
Divisions (1)
|
Number |
Date |
Country |
| Parent |
902808 |
Jun 1992 |
|
Continuations (1)
|
Number |
Date |
Country |
| Parent |
514314 |
Apr 1990 |
|
Patent Grant
5392103
