JP3753600B2 - Image forming method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming method, and more particularly, to an electrophotographic image forming method for forming a halftone image using white toner.
[0002]
[Prior art]
Conventionally, in order to obtain a halftone of a desired image density, a ratio of black toner per total toner with respect to document density or development potential is set using a toner in which white toner and black toner are mixed (for example, In an electrophotographic image forming apparatus having a soft tone mode and a hard tone mode, when a soft tone mode is designated, a specified amount of white toner is supplied onto the developing sleeve and smooth There is known one that forms a halftone (see, for example, Japanese Patent Laid-Open No. 3-4259).
[0003]
[Problems to be solved by the invention]
However, in the former, the mixing ratio of the white toner is changed with respect to each image density, but it takes time until a stable mixing state is obtained, and it is not suitable for high speed or high resolution. Furthermore, the mixing process of white and black toner is extremely analog, and a quantified stable image quality cannot be expected.
[0004]
Also in the latter, only rough image quality switching between soft tone mode and hard tone mode can be performed, and white toner is also supplied to the developing sleeve according to the mode, so it is not suitable for fine gradation reproduction and high image quality. It is.
The present invention has been made in view of such circumstances, and provides an image forming method that enables fine gradation printing by dispersing white toner during transfer.
[0005]
[Means for Solving the Problems]
In this invention, an electrostatic latent image is formed by irradiating light on the surface of a charged electrostatic latent image carrier with light writing means, and colored toner and white toner are attached to the formed electrostatic latent image. And developing a color toner and a white toner from the latent electrostatic image bearing member to the transfer target member to form an image. In the transfer step, an area to be occupied by a predetermined number of adjacent colored toner pixels is defined. The present invention provides an image forming method characterized in that a unit region for gradation control is used, and white toner is dispersed and transferred in the center of the unit region .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
As the electrostatic latent image carrier in the present invention, a conventionally known one, for example, a drum-like or belt-like photoreceptor can be used.
The optical writing means is means for modulating and emitting a light beam from, for example, a laser light source or an LED light source with print data (binary signal), and a conventionally known one can be used for this.
[0007]
In the developing process of the present invention, developing devices for color toner development and white toner development are used, respectively, and conventional ones can be used for each developing device.
Further, the toner is charged by frictional charging by stirring in the developing device. In the transfer process, the white toner is dispersed from the electrostatic latent image carrier by preliminarily setting the white toner with a larger charge amount than the colored toner and setting the transfer current of the white toner larger than that of the colored toner. The development can be performed using white toner scattered on the member.
[0008]
The colored toner means a toner having a color other than white, and examples thereof include toners having colors such as cyan, magenta, yellow, and black.
The transfer member is temporarily transferred from the electrostatic latent image carrier by interposing between the recording medium on which an image is directly formed, such as transfer paper or an OHP film, or between the electrostatic latent image carrier and the recording medium. An intermediate transfer member for retransferring the toner image to the recording medium.
[0009]
When the transferred portion is a transfer paper, it is preferable that the white toner is transferred to the uppermost layer on the transfer paper in the transfer step.
By transferring the white toner to the uppermost layer, the colored toner is concealed and the gradation is improved.
[0010]
The white toner attached to the electrostatic latent image preferably has a larger charge amount than the colored toner.
By increasing the charge amount of the white toner, the repulsive force between the white toners at the time of transfer can be increased and the white toner can be easily scattered.
[0011]
The white toner preferably has a particle size of 3 μm or more and less than the color toner particle size. If the particle size is 3 μm or less, the particle size is too small, and the cohesive force works, making it difficult to disperse. On the other hand, when the particle diameter is larger than that of the colored toner, the presence of the white toner is conspicuous and the gradation reproducibility is not improved.
[0012]
The white toner includes at least a base material and a white material, and the base material may be a polyester resin or a polymethyl methacrylate resin.
As the white toner base material, it is desirable to select a highly transparent resin so as not to interfere with the color development of the white material.
[0013]
The white toner is preferably composed of at least a base material and a white material, and the content of the white material is preferably 10 wt% to 30 wt%.
By adding a white material of 10% by weight or more based on the weight of the toner, the white toner is sufficiently colored, a white toner layer can be formed with a thin layer, and the underlying colored toner is sufficiently concealed. On the other hand, if it exceeds 30 wt%, the charging characteristics and the fixing characteristics of the toner are deteriorated.
[0014]
In the transfer step, it is preferable that the transfer current at the time of transferring the white toner is set larger than the transfer current at the time of transferring the colored toner.
By making the transfer current larger than that of the colored toner, an excessive transfer current is generated and the transfer is performed with a stronger electric field, so that it is possible to effectively scatter and transfer.
[0015]
It is preferable that the method further includes a step of neutralizing the electrostatic latent image carrier before transferring the white toner.
By performing static elimination before transfer, the adhesion force to the image carrier at the latent image edge portion is weakened, and scattering before transfer is likely to occur.
[0016]
In the electrostatic latent image forming process, when two types of electrostatic latent image carriers for white toner image formation and colored toner formation are used, the former has a thickness of the electrostatic latent image carrier more than the latter. Thin is preferred. If the thickness of the electrostatic latent image bearing member, the electric field strength of the latent image edge is steep, easily disturbed electric field in the transfer portion, scattering is likely to occur.
[0017]
In the development step, it is preferable to make the absolute value of the charging potential of the electrostatic latent image carrier when forming the white toner image higher than the charging potential when forming the colored toner image.
As the difference between the charged potential and the exposure potential of the electrostatic latent image carrier increases, the difference in the electric field strength at the edge portion of the latent image increases, and the electric field at the time of transfer is easily disturbed.
[0018]
(Example)
Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. This does not limit the invention.
[0019]
Monochrome printing method FIG. 1 is an explanatory diagram of a monochrome printing method of the present invention using white toner and colored toner. As shown in FIG. 1, a contact-type or discharge-type charger 2a is used to uniformly charge the surface of the drum-shaped photosensitive member 1a rotating in the direction of arrow R, and the light beam from the laser light source is binary. An electrostatic latent image is written on the photosensitive member 1a using a light beam 3a modulated by a signal, and a colored toner is supplied from the developing device 4a to the photosensitive member 1a to be attached to the electrostatic latent image and developed (visualized). . The toner image obtained here is transferred onto transfer paper P that moves in the direction of arrow A using transfer means 5a such as a non-contact charger or a roller transfer device.
[0020]
Thereafter, the surface of the drum-shaped photosensitive member 1b rotating in the direction of arrow R is uniformly charged using a contact-type or discharge-type charger 2b, and the light beam from the laser light source is modulated with a binary signal. An electrostatic latent image is written on the photosensitive member 1b using the light beam 3b, white toner is supplied from the developing device 4b to the photosensitive member 1b, and is attached to the electrostatic latent image and developed (visualized). Thereafter, the white toner image is transferred onto the transfer paper P on which the color toner has already been transferred using a transfer means 5b such as a non-contact charger or a roller transfer device.
[0021]
Further, the transfer toner is fixed onto the transfer paper P by passing through the fixing means 6. The fixing unit 6 may use either a non-contact fixing method or a contact fixing method. The cleaning members 7a and 7b collect the untransferred toner remaining on the photoreceptors 1a and 1b.
The neutralization member 10 neutralizes the charge on the photosensitive drum 1b as necessary, and a non-contact type charger can be used for this.
[0022]
Color printing method FIG. 2 is an explanatory diagram of the color printing method of the present invention using white toner and various colored toners. As shown in FIG. 2, the surface of a drum-shaped photosensitive member 1c rotating in the direction of arrow R is uniformly charged using a charger 2c, and a light beam 3c obtained by modulating a light beam from a laser light source with a binary signal is obtained. An electrostatic latent image is written on the photoreceptor 1c.
[0023]
Next, white toner is supplied from the developing unit W to the photosensitive member 1c to adhere to the electrostatic latent image to form a white toner image, which is supported by the roller 6 and moved in the arrow S direction (for example, a belt-like intermediate transfer member (for example, The film is transferred onto a PVDF film 9 having a thickness of 75 to 100 μm using a transfer means 5c. Next, the untransferred toner remaining on the photosensitive drum 1c is collected by the cleaning member 7c. In this way, first, the process of transferring the white toner image to the intermediate transfer member 9 is completed.
[0024]
Similarly, an electrostatic latent image for cyan, magenta, yellow, and black printing is written on the photosensitive member 1c with the light beam 3c, and cyan, magenta, yellow, and black are written by the developing units C, M, Y, and B. The process of developing with toner is repeated, and each color toner image is sequentially transferred to the intermediate transfer member 9 using the transfer means 5c.
[0025]
At this time, a color image is formed on the intermediate transfer member 9 with the white toner layer printed on the lowermost layer and the cyan, magenta, yellow and black toner layers printed thereon.
[0026]
Next, the formed color image is transferred onto the transfer paper P moving in the direction of arrow A at once using the transfer means 5d. Then, the transfer toner is fixed on the transfer paper P by passing the fixing means 6.
The neutralizing member 10 is for neutralizing the charge on the surface of the photosensitive drum 1c as necessary, and a non-contact charger is used for this purpose, for example.
Further, a contact type or non-contact type transfer device is used for the transfer means 5d.
[0027]
In the case of a grayscale binary image using white toner , if color toner is used alone, for example, four adjacent pixels as shown in FIG. 3 are taken as one unit, and printing is performed as shown in FIGS. Gradation, 2/4 gradation, 3/4 gradation, and 4/4 gradation can be represented. In the present invention, as shown in FIGS. 8 to 11, white toner is further dispersed in substantially the center of the four pixels.
[0028]
Thereby, intermediate gradations can be obtained for each of FIGS.
In other words, in the concentration comparison,
3 <FIG. 8 <FIG. 4 <FIG. 9 <FIG. 5 <FIG. 10 <FIG. 6 <FIG. 11 <FIG.
Is obtained.
Since the gradation control of the present invention is performed by dispersing the white toner in this way, a smooth image without graininess can be obtained.
[0029]
Printing order of white toner FIG. 12 shows the printing order of the white toner and the colored toner of the present invention. After the color toner layer Tc is printed on the transfer paper P, the white toner layer Tw is printed. Accordingly, the colored toner layer Tc can be reliably hidden with the white toner layer Tw, and multi-value gradation expression with high reproducibility can be realized.
[0030]
Charge amount of white toner Generally, the charge amount of toner is a negatively charged toner in order to maintain good development transfer characteristics, so that the toner does not scatter and has stable electrical characteristics during development transfer. In this case, a charge amount of around −20 μq / g is maintained.
[0031]
With respect to the white toner used in this embodiment, since it is a condition that scattering (dispersion) occurs at the time of transfer, the charge amount of the white toner is set to about −40 to −50 μq / g. Thereby, scattering can be effectively generated by the repulsive force between the toners without deteriorating the transfer performance.
[0032]
In order to increase the charge amount of the white toner, it is necessary to increase the amount of CCA (charge control agent) added to the toner. The general toner is about 0.5 to 4% (a charge amount of about -20 μq / g is obtained in the case of a negatively charged toner), but in the case of a white toner, about 5 to 10% is preferably added.
[0033]
Examples of the CCA material include negatively charged azo metal-containing complexes, salicylic acid metal complexes, tetraphenols, borates, and the like. In the case of positive charging, nigrosine dyes, triphenylmethane, ammonium salts, organic phosphorus, phosphate compounds, and the like can be given.
[0034]
Method for generating scattering during transfer FIG. 13 shows the state of toner T before transfer, and FIG. 14 shows the state of toner T after transfer. In the case of colored toner, if the toner flies before transfer, it will lead to deterioration of the image. Therefore, a transfer current that causes transfer at the transfer portion is set. However, in the case of transferring the white toner, as shown in FIG. 14, the transfer current is colored in order to scatter the white toner toward the transfer paper P (or the intermediate transfer body 9) in the minute gap before the transfer. A value higher than the toner transfer current is set.
[0035]
As a result, a sufficient electric field E is applied to the white toner in the minute gap before the transfer, and the white toner starts to fly before the transfer and moves onto the transfer paper P (or the intermediate transfer member 9). At this time, since the white toner moves in the space and scatters, when the toner arrives at the transfer paper P or the intermediate transfer body 9, bounce or disturbance occurs, and the scatter occurs. For example, when a charger is used as the transfer means 5a, 5b, 5c, when the transfer current of the colored toner to the transfer paper P is 20 μA, the transfer current of the white toner is 40 μA.
[0036]
The transfer current when a charger is used as the transfer means 5a, 5b, 5c is defined as follows.
As shown in FIG. 16, it is assumed that the current obtained by applying the voltage E between the case C and the wire W is It, and the current flowing into the case C due to the discharge generated between the wire W and the case C is Ig, Assuming that the current flowing into the transfer paper P is I, It = Ig + I. Since the transfer current is a current that contributes to toner transfer, I is the transfer current. As the transfer current I, a value obtained by measuring the current It flowing from the power source E and subtracting the current Ig flowing into the case C from that value is used. That is, I = It−Ig.
[0037]
Further, in order to make it easy for the toner to fly to the transfer material before the transfer, in addition to increasing the transfer current, the neutralizing member 10 removes the white toner on the photoreceptors 1b and 1c in the region after the development and before the transfer. It is preferable that the electrostatic charge is weakened and the electrostatic adhesion force to the photoreceptors 1b and 1c is weakened to facilitate scattering.
[0038]
Further, as shown in FIG. 15, electric lines of force F are generated in the toner T that is developed on the photosensitive members 1a, 1b, and 1c and electrostatically adhered thereto, and the electric force lines F are generated in the region before transfer or before transfer. The toner flies along the force line F. At this time, it is good if the lines of electric force are directed toward the transfer paper P (or the intermediate transfer member 9), but the edge effect is strong, and the toner near the electric field that wraps around the photosensitive member is unstable. Due to the strong electric field, a phenomenon of scattering during transfer can be seen.
[0039]
As described above, in order to disperse the toner before transfer, it is preferable that the adhesion force of the toner to the image carrier is small, but conversely, it can be dispersed even if it is too strong. That is, it can be seen that a strong edge effect should work on the toner on the photoreceptor before transfer or transfer. By transferring this, white toner is scattered.
[0040]
In general, the electric field Eopc generated in the vicinity of the photoconductor is
Eopc ≒ (Vopc-Vtoner) / dopc
(Vopc: photoreceptor potential Vtoner: toner layer potential dopc: photoreceptor layer thickness)
Thus, it can be seen that the edge effect due to the electric field generated between the photoconductor and the toner works more strongly as the photoconductor layer is thinner and the potential difference between the toner layer and the photoconductor is larger. That is, it is preferable to set the photosensitive layer for the white toner to be thinner than the photosensitive member for the colored toner. Alternatively, the absolute value of Vopc-Vtoner can be set higher by setting the initial potential Vopc of the photoconductor when developing white toner to be higher than the initial potential of colored toner, and white toner is more scattered than colored toner. It becomes possible to make it easier.
[0041]
White toner base material Examples of the toner base material (base material) include styrene acrylic and polyester. In general, polyester is used when aiming for image quality with high color reproducibility such as a color image because the transparency of the resin is high. On the other hand, since styrene acrylic is milky white, its permeability is lowered, but it is used for achromatic toner such as black toner.
[0042]
Since the purpose of the white toner is to conceal the colored toner, it is preferable that the white toner has an effect of preventing the transmission of the background color and not affecting the color reproduction of the colored toner. That is, it is considered that colorless and transparent is suitable as a base material, and it is suitable to perform concealment using only a white material. Therefore, a polyester material that is a highly transparent resin is suitable as a base material for white toner. Polymethylmethacrylate having the same effect as polyester can also be used as a base material.
[0043]
White toner material The content of the white toner material is suitably 10% or more and less than 30%. In the case of 10% or less, since the transparency of the base material resin is high, the colored toner in the lower layer cannot be concealed. On the other hand, if it exceeds 30%, the characteristics as a toner cannot be maintained, and uneven charging and poor fixing are caused, so that the image quality and the development characteristics are greatly lowered. Therefore, the optimal white toner content is 10 wt% or more and 30 wt% or less with respect to the toner weight. As the white material, titanium oxide having high whiteness can be suitably used.
[0044]
Particle diameter of white toner Generally, the smaller the particle diameter is, the more cohesive force is exerted, so that scattering during transfer is less likely to occur. If the white toner that scatters during transfer is larger than other colored toners, the scattered white toner is noticeable and the graininess becomes rough. Therefore, the particle size of the white toner is suitably 3 μm or more where the cohesive force does not work and less than the particle size of the colored toner.
[0045]
【The invention's effect】
According to the present invention, since the white toner is dispersed and transferred onto the colored toner image, a smooth halftone image without graininess can be easily obtained.
[Brief description of the drawings]
FIG. 1 is a configuration explanatory view showing an example of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a configuration explanatory view showing another example of the image forming apparatus according to the embodiment of the present invention.
FIG. 3 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 4 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 5 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 6 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 7 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 8 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 9 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 10 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 11 is an explanatory diagram illustrating pixels of a halftone image according to an embodiment of the present invention.
FIG. 12 is an explanatory diagram showing the transfer order of toner onto transfer paper in an embodiment of the present invention.
FIG. 13 is an explanatory diagram showing a toner transfer operation in the embodiment of the invention.
FIG. 14 is an explanatory diagram showing a toner transfer operation in the embodiment of the invention.
FIG. 15 is an explanatory diagram showing an electric field at the time of transfer in an embodiment of the present invention.
FIG. 16 is an explanatory diagram showing a transfer current at the time of transfer in an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1a Photoconductor drum 1b Photoconductor drum 1c Photoconductor drum 2a Charger 2b Charger 2c Charger 3a Light beam 3b Light beam 3c Light beam 4a Developer 4b Developer 5a Transfer means 5b Transfer means 5c Transfer means 5d Transfer means 7a Cleaning Member 7b Cleaning member 7c Cleaning member 9 Intermediate transfer member 10 Static elimination member P Transfer paper T Toner

Claims (16)

An electrostatic latent image is formed by irradiating light on the surface of the charged electrostatic latent image carrier with light writing means, and a colored toner and a white toner are attached to the formed electrostatic latent image and developed. A step of forming an image by transferring colored toner and white toner from a latent electrostatic image bearing member to a transfer member, and in the transfer step, an area to be occupied by a predetermined number of adjacent colored toner pixels is used for gradation control. An image forming method, wherein white toner is dispersed and transferred in the center of the unit area .   2. The image forming method according to claim 1, wherein when the member to be transferred is transfer paper, white toner is transferred to the uppermost layer on the transfer paper in the transfer step. White toner, image forming method according to claim 1, wherein the charge amount is equal to or larger than the color toner adhering to the electrostatic latent image.   The image forming method according to claim 1, wherein the white toner has a particle size of 3 μm or more and less than the color toner particle size.   2. The image forming method according to claim 1, wherein the white toner comprises a base material and a white material, and the base material is a polyester resin.   2. The image forming method according to claim 1, wherein the white toner comprises a base material and a white material, and the base material is a polymethyl methacrylate resin.   2. The image forming method according to claim 1, wherein the white toner comprises a base material and a white material, and the content of the white material is 10 wt% to 30 wt%.   2. The image forming method according to claim 1, wherein in the transfer step, the transfer current at the time of transferring the white toner is set larger than the transfer current at the time of transferring the colored toner.   The image forming method according to claim 1, further comprising a step of discharging the electrostatic latent image carrier before transferring the white toner. In an electrostatic latent image forming step, using the two kinds of electrostatic latent image bearing member for the color toner for forming a white toner image formation, the former that is thin in the electrostatic latent image bearing member than the latter The image forming method according to claim 1.   2. The image formation according to claim 1, wherein in the development step, the charging potential of the electrostatic latent image carrier when forming the white toner image is made higher than the charging potential when forming the colored toner image. Method. An electrostatic latent image is formed by irradiating light on the surface of the charged electrostatic latent image carrier with light writing means, and a colored toner and a white toner are attached to the formed electrostatic latent image and developed. A process of forming an image by transferring colored toner and white toner from a latent electrostatic image bearing member to a transfer member, wherein the white toner comprises a base material and a white material, and the content of the white material is Ten wt% ~ 30 An image forming method characterized by being wt%. An electrostatic latent image is formed by irradiating light on the surface of the charged electrostatic latent image carrier with light writing means, and a colored toner and a white toner are attached to the formed electrostatic latent image and developed. A process for forming an image by transferring colored toner and white toner from a latent electrostatic image bearing member to a transfer member, wherein the transfer current during white toner transfer is greater than the transfer current during color toner transfer in the transfer process; An image forming method characterized by being set. An electrostatic latent image is formed by irradiating light on the surface of the charged electrostatic latent image carrier with light writing means, and a colored toner and a white toner are attached to the formed electrostatic latent image and developed. A step of forming an image by transferring the colored toner and the white toner from the electrostatic latent image carrier to the transfer member, and further comprising a step of discharging the electrostatic latent image carrier before transferring the white toner. An image forming method. An electrostatic latent image is formed by irradiating light on the surface of the charged electrostatic latent image carrier with light writing means, and a colored toner and a white toner are attached to the formed electrostatic latent image and developed. It includes a step of forming an image by transferring colored toner and white toner from a latent electrostatic image bearing member to a transfer member. In the latent electrostatic image forming step, two types are used for forming a white toner image and for forming a colored toner. An electrostatic latent image carrier is used, and the former has a thinner electrostatic latent image carrier than the latter. An electrostatic latent image is formed by irradiating light on the surface of the charged electrostatic latent image carrier with light writing means, and a colored toner and a white toner are attached to the formed electrostatic latent image and developed. It includes a step of forming an image by transferring colored toner and white toner from a latent electrostatic image bearing member to a transfer member, and a charging potential of the latent electrostatic image bearing member when a white toner image is formed in the developing step. An image forming method characterized in that an absolute value is made higher than a charging potential when a colored toner image is formed.

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