JPH10177273A - Dry process toner for forming 1-dot binary image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily embody high resolution and high gradation characteristic by devising the conditions of the toners used in a basic 1-dot binary recording system in an electrophotographic method. SOLUTION: When the beam spot diameter at the time of optical writing to a photoreceptor is defined as DL[μm], the volume average grain size R[μm] of toner particles is specified to R>=DL/e. The volume content or weight content ρS of the toner particles having a toner grain size of <=5[μm] is specified to ρS<=10%. The number content ρ20 of the toner particles having the toner grain size of >=20[μm] is specified to ρ20 <=1%. The volume content or weight content ρSS of the toner particles having the toner grain size <=R/e<2> [μm] is specified to ρss <=5%. As a result, the optimum conditions with respect to the grain size of the toner particles may be obtd. in such a manner that the content of the fine powder toner is decreased in the dry process toner for forming the 1-dot binary images. In the equations, (e) denotes the base of a natural logarithm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-dot binary image forming dry toner used for development in an electrophotographic image forming apparatus such as a laser beam printer and an LED printer.

[0002]

2. Description of the Related Art In recent years, in the field of an electrophotographic image forming apparatus in which an electrostatic latent image is formed on a photoreceptor and this latent image is developed with toner to obtain a visible image, a higher resolution or higher order is required. There is a demand for adjustment, and various proposals have been made.

For example, as a method of realizing gradation in electrophotography, a method of replacing gradation information with a so-called area gradation, such as a dither method or an error diffusion method, is conventionally known. Such an area gradation is a one-dot binary recording method (a method in which one dot is recorded in binary of 0 or 1) when considered in units of one dot, and conventionally, the area gradation is a one-dot binary recording method. It is said that an attempt to express the gradation using the gradation requires a large area for the gradation expression, resulting in a coarse image. Regarding the toner particle size, since the toner particles are adhered faithfully in accordance with the exposure distribution, it is generally said that the exposure distribution which is about four times the toner particle size is the smallest dot that can be reproduced stably.

As a method for avoiding such inconvenience and achieving smooth high gradation, a one-dot multi-value recording method such as one-dot 64-value and one-dot 256-value is considered. Various proposals and announcements have been made.

[0005]

However, in order to maintain the relationship between the minimum dot and the toner particle size, which is generally referred to in the prior art as described above, a one-dot multi-value recording method is studied by focusing on toner. It can be seen that the toner particle diameter has been steadily reduced along with the trend toward higher resolution for higher gradation. For example, 400 dp corresponding to 256 values of one dot
In the case of the i level, the volume average particle diameter of the toner particles is about 7.5 [μm], and the content of fine powder having a toner particle diameter of 5 [μm] or less is about 10 to 30%. Furthermore, in the case of 1 dot 600 dpi level (1 dot = 42 [μm] × 42 [μm]) for achieving high resolution,
The volume average particle diameter of the toner particles is about 5.0 [μm], and the content of fine powder having a toner particle diameter of 5 [μm] or less is 10 to 5 μm.
It is about 0%.

That is, in the case of a dry toner for forming a one-dot multi-valued image, the toner particle size is 5
Since the content of the fine powder is extremely large, for example, [μm] or less, it is necessary to take measures for solving the problems of the fine powder toner. That is, in the case of the fine powder toner, in general, problems such as easy soiling of the background, easy scattering of the toner, easy deterioration of the developer (spent to the carrier of the toner), poor transfer, poor cleaning and poor fixing are likely to occur. In order to avoid this, it is necessary to take measures such as increasing the cut rate of the fine powder toner (the toner yield is deteriorated) and sharpening the toner particle size distribution by using an expensive polymerized toner.

Therefore, the present invention provides a one-dot binary image forming method which can easily realize high resolution and high gradation by devising toner conditions used in a basic one-dot binary recording method in electrophotography. It is intended to provide a dry toner for use.

[0008]

According to the first aspect of the present invention, there is provided:
When the beam spot diameter at the time of optical writing on the photoreceptor is D _L [μm], the volume average particle diameter R [μm] of the toner particles is expressed as R ≧
D _L / e. In the invention according to claim 2, the volume content or the weight content ρ ₅ of the toner particles having a toner particle diameter of 5 μm or less is ρ ₅ ≦ 10%. In the invention according to claim 3, the number content ρ ₂₀ of the toner particles having a toner particle diameter of 20 μm or more is ρ ₂₀ ≦ 1%. According to a fourth aspect of the present invention, the volume content or weight content ρ _ss of the toner particles having a toner particle size of R / e ² [μm] or less is ρ _ss ≦ 5.
%. For the volume content or weight content ρ _s of toner particles having a toner particle size of R / e [μm] or less, ρ _s > 5
% May satisfy ρ _ss ≦ 5%.

Therefore, in these inventions, the optimal condition is set for the particle size of the toner particles so that the content of the fine powder toner is reduced, so that the volume average particle size R of the toner particles is relatively large, and While the particle size distribution is wide,
It is possible to form a gradation image similar to a conventional one-dot multi-valued image by an area gradation method using one dot and two values.
It is also possible to form a high-resolution image such as a 0 dpi level. This is because, when the length of one side of at least one pixel is L [μm] as in the dry toner for forming a one-dot binary image according to the invention of claim 5, the volume average particle diameter of the toner particles is R [Μm], R ≧ L / e, 1200 dp
i is supported by L = 21 [μm].

In the dry toner for forming a one-dot binary image according to the invention, the volume average particle size of the toner particles is defined assuming that the beam spot diameter at the time of optical writing on the photosensitive member is D _L [μm]. diameter R [μm] _{is, D L / 2 ≧ R ≧} D L /
3. Therefore, in the present invention, since the optimal condition is set in relation to the particle diameter of the toner particles in relation to the beam spot diameter, the volume average particle diameter R of the toner particles is relatively large, and the particle diameter distribution is wide. It is possible to form an image of the minimum dot equivalent to the conventional one-dot multi-valued dot by the area gradation method using the dot binary. As described above, forming an image having the same minimum dot size as that of the related art can reduce the length of one side of a target minimum one pixel to 30 as in the case of the dry toner for forming a one-dot binary image according to the present invention. [Μm] or less.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. First, a schematic configuration of a laser printer is shown in FIG. 5 as an example of an image forming apparatus using the dry toner for forming a one-dot binary image according to the present embodiment. In this laser printer, a charging charger 2, a developing device 3, a transfer / separation charger 4, a cleaning unit 5, a static elimination lamp 6, and the like are arranged around a drum-shaped photoreceptor 1 which is driven to rotate in the direction of an arrow according to an electrophotographic process. Has been established. The surface of the photoreceptor 1 between the charging charger 2 and the developing device 3 is set as the irradiation position of the laser beam 7 by a laser writing unit (not shown).

Thus, when the surface of the photosensitive member 1 uniformly charged by the charger 2 is irradiated with the laser beam 7 modulated in accordance with image information, an electrostatic latent image is formed on the surface of the photosensitive member 1. You. The latent image is visualized by the toner attached by the action of the developing sleeve 8 of the developing device 3 or the like. The visualized toner image is transferred onto the transfer paper 9 by the action of the transfer / separation charger 4. The surface of the transferred photoreceptor 1 is cleaned by the cleaning unit 5 and is discharged by the discharge lamp 6 to prepare for the next image formation.

Here, the optical writing method by the laser writing unit is a one-dot binary recording method including gradation recording. Therefore, for example, the maximum resolution recordable by the laser printer of the present embodiment is set to 1200 dpi.
, The minimum one side L of one pixel is L ≒ 21 [μ
m].

In the present embodiment, conditions such as the particle size of the toner used in the developing device 3 (therefore, the dry toner for forming a one-dot binary image) in such a laser printer are optimized. Incidentally, 400 dpi (for forming a one-dot multi-valued image) is set to 600 dpi (for forming a one-dot multi-valued image) with respect to the method of the present embodiment.
Is referred to as Conventional Example 2.

[0015] First, the beam spot diameter D _L when the optical writing by the laser beam 7 with respect to the photosensitive member 1, Fig. 3
When the exposure energy is Em as shown in FIG.
a diameter at the level of e ^2. Note that such an optical writing beam has a Gaussian distribution or a similar luminance distribution on the photoreceptor 1, and is substantially on the locus of E = Eme ＾ −2 (x / x ₀ ) ² . This beam spot diameter D _L is 1200d
In the case of pi is equivalent to one side L of 1 pixel, appropriate developing bias V _B to the developing sleeve 8 in the developing device 3 with respect to the surface potential when exposed to the surface of the photosensitive member 1 with a laser beam 7 Is reproduced as an image.

Further, as an element for conditioning, a volume average particle diameter R of toner particles [μm] Fine powder content: [%] a. Volume content (or weight content) of toner particles having a toner particle size of 5 [μm] or less ρ ₅ b. Toner particle size 4 [μm] volume content of less toner particles (or weight content) [rho ₄ meal content; number content of (%) Toner particle size 20 [μm] or more toner particles [rho ₂₀ R / e (and R / e ² ) D _L (ΔL) [μm] D _L / e Volume content (or weight content) of toner particles having a toner particle size of R / e [μm] or less ρ _s Toner particle size The volume content (or weight content) ρ _ss of toner particles of R / e ² [μm] or less was considered.

With respect to these elements, Table 1 summarizes the results of Conventional Examples 1 and 2 and numerical examples specified in the present embodiment.

[0018]

[Table 1]

The numerical example specified in the present embodiment is as follows: R = 11.5 ± 1.0 [μm] ≧ D _L /e=7.8
Meets ± 1 [μm] _{ρ 5 ≦ 10% ρ 20 ≦} 1% ρ s = 8> 5% ρ ss = 1.6 ≦ 5% following condition.

FIGS. 1 and 2 show graphs of the toner particle size distribution based on such numerical examples.
FIG. 1 shows the volume (or weight)% distribution at each particle size with respect to the toner particle size, and FIG. 2 shows the cumulative% distribution of the volume (or weight) at each particle size with respect to the toner particle size. Therefore, when looking at the distribution characteristics of Conventional Examples 1 and 2, as described above, the fine powder content is high, which causes inconvenience, so that the toner particle size distribution is sharpened. On the other hand, according to the toner particle size distribution of the present embodiment, the average particle size of the toner particles is relatively large, and the particle size distribution is wide, but the fine powder content and the coarse powder content are as low as possible. Have been. Therefore, a gradation image similar to a conventional one-dot multi-valued image can be formed by applying the method to the area gradation method using one-dot binary without accompanying the disadvantages caused by an extremely high fine powder content rate. In addition, a high-resolution image such as a 1200 dpi level can be formed.

When a minimum of one pixel (one dot) having a side length of L [μm] is more uniformly and densely packed in a square lattice with spherical toner having the same particle size, the volume average particle size of the toner particles If R [μm] is a fraction of L, the area coverage is uniformly 1 / 0.5 ² π, that is, 78.5 [%].
Namely, toner particles having a particle diameter R ₁ [μ in the conventional general example shown in FIG. 6
m] is L = 4R ₁ , whereas in the present embodiment, the toner particle size R ₂ [μm] is L = 4R _{1 as} shown in FIG.
3R ₂ , or L = 2R ₂ as shown in FIG. 4B, and both have an integral multiple relationship. In the case of the same degree of coloring, even if the area coverage is the same, the color toner has light transmittance because the color toner has a different particle diameter, so that the color reproducibility is different. Therefore, for a color toner having light transmittance, it is necessary to correct the degree of coloring in a form inversely proportional to the toner particle diameter (volume average). Further, by performing such a color degree correction, even if a toner having a larger particle diameter than the conventionally required small particle diameter toner such as in the present embodiment is used, visually the conventionally required small particle diameter is required. It is possible to obtain a dot image having the same shape and color reproduction as in the case of using the particle size toner, that is, an image having the same minimum dot size as the conventional one. Specifically, the volume average particle size R ₁ of the toner particles is 7.5 [μm] and the minimum is 1
The length L of one side of the pixel is L = 30 [μm] (= 7.5 ×
Assuming 4), this is supported by setting L ≦ 30 [μm].

In this embodiment, the laser beam 7
However, the present invention can be similarly applied to printers using an LED array as a writing light source. Further, the applicable model is not limited to a monochrome image, and can be similarly applied to a full-color recording type.

[0023]

According to the dry toner for forming a one-dot binary image according to the first aspect of the present invention, when the beam spot diameter at the time of optically writing on the photosensitive member is D _L [μm],
The volume average particle diameter R [μm] of the toner particles is set to R ≧ D _L / e.
The volume content or the weight content ρ ₅ of the toner particles having a particle size of [μm] or less is set to ρ ₅ ≦ 10%. The ratio ρ _{20 is set} to ρ ₂₀ ≦ 1%. According to the invention of claim 4, the volume content or weight content ρ _ss of the toner particles having a toner particle size R / e ² [μm] or less is set to ρ _ss ≦ 5%
By doing so, the optimal conditions regarding the particle size of the toner particles so as to reduce the content of fine powder toner,
While the volume average particle size R of the toner particles is relatively large and the particle size distribution is wide, it is possible to form a conventional 1-dot multi-level gradation image by the area gradation method using one dot binary, In addition, a high-resolution image such as a 1200 dpi level can be formed. In particular, when the length of one side of at least one pixel is L [μm] as in the dry toner for forming a one-dot binary image according to the invention of claim 5, the volume average particle size of the toner particles R [μm Is set to R ≧ L / e, image formation at a 1200 dpi level can be realized without any trouble.

According to the dry toner for forming a one-dot binary image according to the present invention, when the beam spot diameter at the time of optical writing on the photosensitive member is D _L [μm], the volume of the toner particles is the average particle diameter R [μm] is, D _L / 2 ≧ R ≧
By setting D _L / 3, optimal conditions were set in relation to the particle diameter of the toner particles in relation to the beam spot diameter, so that the volume average particle diameter R of the toner particles was relatively large and the particle size distribution was wide. The image of the minimum dot which is comparable to the conventional one-dot multi-value can be formed by the area gradation method using one dot binary. In particular, one dot 2 of the invention according to claim 7
By setting the length of one side of at least one target pixel to 30 [μm] or less like a dry toner for forming a value image,
It is possible to reliably form an image having the same minimum dot as the conventional one.

[Brief description of the drawings]

FIG. 1 is a distribution characteristic diagram of toner particle diameter-volume% of each particle diameter, including characteristics of a conventional example, according to an embodiment of the present invention.

FIG. 2 is a distribution characteristic diagram of toner particle diameter-cumulative% of volume of each particle diameter, including characteristics of a conventional example.

FIG. 3 is an explanatory diagram for explaining a beam spot diameter and the like.

FIG. 4 is an explanatory diagram showing a case where L = 3R ₂ and L = 2R ₂ respectively.

FIG. 5 is a schematic configuration diagram illustrating an example of a laser printer.

FIG. 6 is an explanatory diagram showing a conventional case where L = 4R ₁ .

Claims (7)

[Claims] When a beam spot diameter at the time of optical writing on a photoreceptor is D _L [μm], a volume average particle diameter R [μm] of toner particles is R ≧ D _L / e (where, e = 2.71828...). 2. The one-dot binary image according to claim 1, wherein the volume content or weight content ρ ₅ of the toner particles having a toner particle size of 5 μm or less is ρ ₅ ≦ 10%. Dry toner for forming. 3. The one-dot binary image forming apparatus according to claim 1, wherein the number content ratio ρ ₂₀ of the toner particles having a toner particle diameter of 20 μm or more is ρ ₂₀ ≦ 1%. Dry toner. 4. The toner according to claim 1, wherein the volume content or weight content ρ _ss of the toner particles having a toner particle size of R / e ² [μm] or less is ρ _ss ≦ 5%. The dry toner for forming a one-dot binary image according to the above. 5. When the length of one side of at least one pixel is L [μm], the volume average particle diameter R [μm] of the toner particles is R ≧ L / e (where e = 2.771828...) A dry toner for forming a one-dot binary image, characterized in that: 6. When the beam spot diameter at the time of optical writing on a photoreceptor is D _L [μm], the volume average particle diameter R [μm] of the toner particles is: D _L / 2 ≧ R ≧ D _L / 1 dry toner for forming a one-dot binary image. 7. The length of one side of a target minimum one pixel is 3
7. The dry toner for forming a one-dot binary image according to claim 6, wherein the thickness is 0 [μm] or less.