JP4584746B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a fine laser beam technique used in an image forming apparatus, an optical disk recording apparatus, and the like.

As a technique for obtaining a high-definition image by narrowing the beam diameter of a writing light source in an image forming apparatus, etc. Some have realized a beam diameter that is less than or equal to the limit that could not be stopped by the wavelength, and as a result, can output a high-definition image (see, for example, Patent Document 1).
However, the wavelength of 400 nm to 500 nm is extremely fatal in that it causes fatal damage such as chemical bond breakage to OPC (organic photo semiconductor) used in image forming apparatuses utilizing most of the current electrophotographic principles. There is a big problem.
In addition, the current mainstream OPC has a characteristic that the sensitivity is drastically lowered in the wavelength range of 400 nm to 500 nm. Therefore, in addition to the problem of damage caused by using a short wavelength, there is a serious problem in terms of sensitivity. is there. Even if an amorphous silicon photoconductor that is free from damage due to the short wavelength is used, the optical band gap of amorphous silicon is about 1.75 eV. In this case, the sensitivity is drastically reduced, and this is a technology that is actually difficult to realize.

In an electrophotographic image forming apparatus, as a technique for providing a photonic crystal in the optical path of a writing unit, a wavelength tunable laser is made incident on a photonic crystal having wavelength dispersion so that the emission angle from the photonic crystal is continuous. (For example, refer to Patent Document 2). This technique is similar to the present invention, but the function exhibited by the photonic crystal is completely different from that of the present invention. In an image forming apparatus using a semiconductor laser as a light source of a writing unit, there are several techniques related to a configuration in which a photonic crystal is provided in the optical path of the laser beam. By using a combination to realize a large laser beam deflection with a slight change in wavelength, it is intended to provide a beam scanning system that does not use a polygon mirror that is generally used.
In an image forming apparatus using an electrophotographic system, a technique for realizing output of a high-definition image is not possible with a single technique, but for the first time with a combination of a plurality of techniques. For example, it is necessary to match various techniques such as the photosensitive layer thickness of the photoreceptor, the potential during development, and the toner particle size.
Further, when a semiconductor laser is used as the light source of the writing unit, the spot diameter of the laser beam finally incident on the surface of the photoconductor becomes very important. In other words, in order to output an image with a resolution of 600 dpi, the laser beam diameter needs to be reduced to 50 μm or less, and when aiming at 1200 dpi for higher resolution, the laser beam diameter is designed to be about 20 μm. It needs to be realized.

Here, paying attention to the relationship between the wavelength and the beam diameter that can be reduced, the following relational expression is established, and it can be seen that the shorter the wavelength, the more advantageous is the reduction of the beam diameter.
ω = (f · λ) / (π · ω0) (1)
Here, ω is the beam diameter at the exit of the optical system, f is the focal length of the lens, λ is the wavelength of the laser beam, and ω 0 is the diameter of the beam incident on the optical system.
Conventionally, a semiconductor laser having a wavelength of 780 nm, which is widely used for CD (Compact Disk) reading, has been widely used in image forming apparatuses such as copying machines and laser printers. For this reason, in the recent technology, a light source having a wavelength of 655 nm for DVD (Digital Versatile Disk) has appeared on the market as a light source having a shorter wavelength.
However, even if such a light source is used, it is inevitable that the beam diameter gradually widens after the beam is narrowed down at the exit of the writing unit. In order to output a high-definition image, the narrowed beam is used. It is essential to reach the surface of the photoreceptor without increasing the diameter. In that sense, changing from a semiconductor laser with a wavelength of 780 nm to a semiconductor laser with a wavelength of 655 nm is not sufficient as a solution to the problem, and there is an urgent need to develop a technology that can further reduce the beam diameter. In addition, there is a strong demand for the realization of a technology that can meet the demand for high-definition output of full-color images, which are currently in increasing demand.

As a technique for solving such a problem, by using a light source having a shorter wavelength of 400 nm to 500 nm as a light source of an exposure apparatus of an electrophotographic apparatus, writing light having a small beam diameter that could not be narrowed down by a conventional wavelength. And, as a result, a high-definition image can be output (see, for example, Patent Document 3).
However, the wavelength of 400 nm to 500 nm causes fatal damage such as causing chemical bond breakage to OPC (organic photo semiconductor) used in image forming apparatuses using most of the electrophotographic principles more than the above. Which has a significant impact on the life of the OPC and cannot be a realistic solution. A similar problem is involved in the sensitivity of the photoreceptor.

Japanese Patent Laid-Open No. 5-19598 JP 2001-13439 A Japanese Patent Laid-Open No. 5-19598

An object of the present invention is to provide an image forming apparatus using an electrophotographic method, which is increasingly demanding higher definition in recent years, without significantly changing the conventional writing unit and without requiring a large cost increase. An object of the present invention is to provide an image forming apparatus capable of outputting a fine image.
The present invention does not use such a short wavelength light source that damages the OPC, but uses a photonic crystal having a super prism effect, so that the beam diameter of the laser beam focused by the optical system is kept as it is. In this way, a high-definition image can be output by reaching the surface of the photoreceptor while maintaining the diameter.
That is, in an image forming apparatus using a laser light source, a photonic crystal having a super collimator effect is provided in order to reduce the laser beam diameter, which is an important factor for obtaining a high-definition image.
In order to efficiently use the super collimator effect of the photonic crystal, the photonic crystal is provided before the laser beam is incident on the surface of the photoreceptor through the beam scanning means, or the photonic crystal is provided after the beam scanning means.

In order to obtain a photonic crystal having a sufficient supercollimator effect with low energy and low cost, a photonic crystal using a close-packed structure of fine particles is used.
In order to form a high-quality photonic crystal, silica fine particles or polystyrene fine particles are used from the standpoints of good particle size distribution, availability, and safety.
In order to obtain a highly functional photonic crystal by a simple process, a reverse structure (inverse opal structure) using a material different from the material constituting the fine particle based on the close-packed packing structure of the fine particle is used. .
In order to safely and reliably form the inverted structure (inverse opal structure), a metal oxide or resin is used as a material different from the material constituting the fine particles.
In order to output a high-definition image at high speed, a plurality of exposure apparatuses each including a photonic crystal having a super collimator effect and a semiconductor laser light source are arranged.

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a semiconductor laser light source that emits a laser beam; a beam scanning unit that deflects and scans the laser beam; And wherein at least one photonic crystal having a super collimator effect is provided in the optical path of the laser beam.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the photonic crystal is disposed between the semiconductor laser light source and the beam scanning unit.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the photonic crystal is disposed between the beam scanning unit and the photoconductor.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the photonic crystal has a close-packed structure (opal crystal) of fine particles. And
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the fine particles are silica.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the fine particles are polystyrene.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the photonic crystal comprises the fine particles based on a close-packed structure of fine particles (opal crystal). It is characterized by having an inverse opal structure using a material different from the material to be used.
According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the inverse opal structure is formed of a metal oxide.
According to a ninth aspect of the invention, in the image forming apparatus according to the seventh aspect, the inverse opal structure is formed of a resin.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, the semiconductor laser light source, the beam scanning unit, the photoconductor, and the photonic crystal are included. A plurality of image forming means are arranged.

In order to realize an image forming apparatus using a wavelength different from that of a light source conventionally used for high definition, it is necessary to combine a photosensitive member having photosensitivity with the light source, and characteristics of optical components in the middle Need to be optimized for the wavelength used. However, in the present invention, the problem can be basically solved only by adding a relatively simple structure such as providing a photonic crystal in the optical path of a light source having a wavelength currently used. Thus, the conventional optical system reliably solves the problem of insufficient beam diameter reduction. Therefore, the light source, other optical systems, and the photoreceptor itself can be used as they are, and there is a great effect that the necessity for development of parts or design change can be reduced.
In addition, the photonic crystal used in the present invention is characterized by using a close-packed structure of fine particles or using an inverse opal structure based on it, and is easy to create. The problem can be solved at low cost.
In an exposure apparatus of an electrophotographic apparatus, since at least one photonic crystal having a super collimator effect is provided in an optical path of a laser beam, the beam diameter can be surely reduced, so that a laser light source and an optical system having a conventional wavelength can be used. Thus, it is possible to obtain an image forming apparatus capable of easily obtaining a high-definition image without making a major change to the above.

Since the photonic crystal is provided after the semiconductor laser light source, even if the photonic crystal to be used is small, the photonic crystal is sufficiently functional and simple in configuration, and the diameter of the laser beam can be easily reduced.
Since the photonic crystal is provided after the beam scanning means, it is incident on the photosensitive member immediately after the beam diameter is reduced, and the effect of reducing the beam diameter can be utilized to the maximum.
Since the photonic crystal has a close-packed structure of fine particles, a large-area photonic crystal that can be easily formed and used as an optical component can be easily obtained.
Since the fine particles constituting the photonic crystal are silica or polystyrene, true spherical fine particles can be easily obtained, and as a result, a high-quality photonic crystal can be obtained.
Since the photonic crystal has an inverted structure (inverse opal structure) using a material different from the material constituting the fine particles based on the close-packed structure of the fine particles, a photonic crystal with a larger super prism effect can be obtained. can get.
Since the photonic crystal has an inverted structure (inverse opal structure) formed of a metal oxide or a resin, a photonic crystal having excellent safety and a large degree of freedom in refractive index design can be obtained.
Since a plurality of image forming means including a photonic crystal and a semiconductor laser light source are arranged, not only high definition of image formation but also speed improvement can be achieved at the same time.

FIG. 4 is a diagram schematically showing the super collimator effect by the photonic crystal.
In the figure, reference numeral 401 denotes incident light, 402 denotes a photonic crystal, and 403 denotes outgoing light.
Although the present invention appears to be similar to these conventional technologies in terms of the configuration using photonic crystals, it does not use photonic crystals having wavelength dispersion, but photonic crystals having a super prism effect. It is characterized by the use of crystals, and the issues and objectives to be solved are completely different.
Next, the photonic crystal will be briefly described. A photonic crystal is an artificial crystal in which materials with different dielectric constants are arranged alternately and periodically. Photons exhibit a phenomenon like Bragg diffraction due to their periodicity, and so-called complete photonic bands where light cannot propagate at all. This is a characteristic phenomenon called a gap. Besides the complete photonic band gap, the photonic crystal exhibits a characteristic phenomenon, and the super collimator effect used in the present invention is one of them. This is because the light incident on the photonic crystal is scattered coherently, so that the incident light beam propagates through the photonic crystal without spreading. In this figure, when incident light 401 is incident on a photonic crystal 402 having a super collimator effect, the incident light is collimated by the super collimator effect and propagates through the photonic crystal 402, and is output with the same beam diameter. The light 403 is emitted. This super collimator effect is insensitive to the incident angle of light on the photonic crystal, and thus is a very easy to use characteristic. FIG. 4 is a diagram schematically showing this state.

Several methods for forming photonic crystals, which are artificial crystals, have been proposed, but so-called opal crystals obtained by utilizing the self-organization phenomenon of microparticles are relatively easy to form, and even at a large area structure at low cost. Since it is obtained, it is optimal for realizing the present invention. Due to the self-organization phenomenon of the fine particles, the fine particle aggregate arranged in a close-packed structure can easily realize a periodic structure having a different dielectric constant depending on the fine particles and air, and functions as a photonic crystal.
As the fine particles to be used, silica fine particles and polystyrene fine particles are optimal from the viewpoints of good particle size distribution, easy availability, safety, etc., but of course not limited to these and silica depending on the application. Other fine particles such as metal oxides and compound semiconductors other than the above can be used.
Such a technique for regularly arranging the fine particles can be easily realized by using a known technique that has already been proposed. For example, a liquid dispersion medium of fine particles is spread on the substrate surface to form a liquid thin film, the liquid thickness is equal to or smaller than the particle size, and the fine particles are aggregated by the surface tension acting in the lateral direction when the liquid evaporates. A technique for performing the arrangement is disclosed.

If this technique is used, a high-quality photonic crystal with fine particles can be easily obtained without requiring a large-scale apparatus or large energy. In addition, there is also a great advantage that even a large part is relatively easy to form as compared with other photonic crystal forming methods using a microfabrication technique.
In the opal crystal, which is a structure in which fine particles are accumulated in a close-packed structure, there are slight voids between the fine particles, and these voids also have regular periodicity. Therefore, by filling this void with a certain substance and then removing only the first existing fine particles, the place where the first fine particles existed becomes a spherical void, and the inverted structure of the opal crystal, the so-called inverse opal structure can get. In general, it is known that such inverse opal structure also shows the characteristics of photonic crystals. By appropriately selecting the material that fills the gap, a photonic crystal with higher performance than the original opal crystal can be obtained. It is possible to obtain.

The process of forming an inverse opal structure using the present invention will be briefly described with an example. When silica fine particles are initially selected as the fine particles that form the opal crystals, only the silica fine particles can be selectively removed by filling the voids with, for example, an ultraviolet curable resin and immersing in hydrofluoric acid after curing. In particular, an inverse opal structure made of an ultraviolet curable resin can be obtained.
As another example, when polystyrene fine particles are initially selected as the fine particles that form the opal crystal, the metal oxide is obtained by filling the voids with, for example, a metal oxide alkoxide solution and sintering in an electric furnace or the like. Simultaneously with the sintering, polystyrene fine particles are decomposed and volatilized, and as a result, an inverse opal structure of a metal oxide can be obtained.
Thus, by using an opal crystal using fine particles, there is an advantage that it is relatively easy to change the structure and material, and a photonic crystal having desired characteristics can be obtained.

FIG. 1 is a diagram for explaining a first embodiment of the present invention.
In the figure, reference numeral 101 is a semiconductor laser, 102 is a collimator lens, 103 is a photonic crystal, 104 is a polygon mirror, 105 is a motor, 106 is a spherical lens, 107 is an fθ lens, 108 is a mirror, and 109 is a photoreceptor. Show.
The laser beam emitted from the semiconductor laser 101 enters the photonic crystal 103 through the collimator lens 102. At this time, the laser beam is reduced in diameter by the super collimator effect of the photonic crystal 103 and is scanned by the polygon mirror 104 that is rotated at high speed by the motor 105 with the beam diameter as it is. The scanned laser beam is deflected by passing through the spherical lens 106 and the fθ lens 107, reflected by the mirror 108, and reaches the photosensitive member 109. Naturally, the laser beam has information that has been converted into an image signal by an image processing circuit (not shown). With such a configuration, a problem that the beam diameter is widened by passing through the optical system of the writing unit does not occur, and a high-definition image can be obtained.

FIG. 2 is a diagram for explaining a second embodiment of the present invention.
In the figure, reference numeral 201 is a semiconductor laser, 202 is a collimator lens, 203 is a photonic crystal, 204 is a polygon mirror, 205 is a motor, 206 is a spherical lens, 207 is an fθ lens, 208 is a mirror, and 209 is a photoreceptor. Show.
This figure is different from the previous figure only in the position where the photonic crystal is provided, and the other optical systems are the same. That is, the photonic crystal 203 is provided immediately before entering the photoconductor, and the laser beam is collimated by the super collimator effect of the photonic crystal and is incident on the photoconductor 209 immediately after collimation. With such a configuration, it is possible to solve the problem that a high-definition image cannot be obtained due to an increase in the diameter of the laser beam.

FIG. 3 is a diagram for explaining a third embodiment of the present invention.
In the figure, reference numeral 301 is a semiconductor laser, 302 is a collimator lens, 303 is a photonic crystal, 304 is a polygon mirror, 305 is a motor, 306 is a spherical lens, 307 is an fθ lens, 308 is a mirror, and 309 is a photoreceptor. Show.
In order to respond to the speeding up of color image output, which has been increasingly demanded in recent years, the so-called tandem engine system that uses multiple photoconductors is the mainstream, since the image forming method uses a conventional single photoconductor. This is expected to improve business efficiency in the office. The present invention is a technology that can meet such needs, and can also be applied to a tandem engine that is completed by combining a plurality of image forming means. This is schematically shown in FIG. This figure shows a state in which two image forming units described so far are combined. In the figure, a configuration using two image forming units is shown for ease of explanation, but naturally two or more combinations are possible. Therefore, if a configuration using four sets of image forming means for full color support is used, high-definition full color images can be output at high speed. As described above, since the present invention does not require a large change to the conventional image forming system, it can be easily mounted on a tandem engine.

In this example, a photonic crystal was formed using silica fine particles. The forming method is as follows. Silica fine particles having an average particle size of 250 nm and a CV value of 4% representing the degree of particle size distribution are adjusted to 5% by weight concentration in pure water on a quartz glass of 2 cm × 2 cm and a thickness of 0.5 mm. 200 μl of the dispersed liquid was dropped and dried slowly to form a close-packed structure of silica fine particles, which was used as a photonic crystal.
Next, a part of a general digital copying machine using a semiconductor laser having a wavelength of 780 nm as an exposure light source is modified so that the laser beam emitted from the semiconductor laser is immediately after the lens installed. The photonic crystal prepared in the above was provided.
When the test chart was copied with the digital copier thus modified and the output image was observed with a microscope, it was confirmed that a test pattern corresponding to a resolution of 800 dpi was reproduced.

In this example, unlike Example 1, a photonic crystal was formed using polystyrene fine particles. The forming method is as follows. A polystyrene particle having an average particle size of 210 nm and a CV value of 2% indicating the degree of particle size distribution is adjusted to 3% by weight concentration in pure water on a quartz glass of 4 cm × 25 cm and a thickness of 0.5 mm. 200 μl of the dispersed liquid was dropped and dried slowly to form a close-packed structure aggregate of polystyrene fine particles, which was used as a photonic crystal.
Next, a part of a general digital copying machine using a semiconductor laser having a wavelength of 650 nm as an exposure light source was remodeled to provide the photonic crystal prepared earlier immediately after the mirror 208 shown in FIG. .
When the test chart was copied with the digital copier thus modified and the output image was observed with a microscope, it was confirmed that a test pattern corresponding to a resolution of 1200 dpi was reproduced.

In this example, an inverse opal made of an ultraviolet curable resin was formed based on an opal crystal formed using silica fine particles, and this was used as a photonic crystal. The forming method is as follows. Disperse silica fine particles with an average particle size of 250 nm and a CV value of 4% representing the degree of particle size distribution in pure water adjusted to a weight concentration of 5% by weight concentration in sapphire of 2 cm × 2 cm and a thickness of 0.5 mm. 200 μl of the liquid was dropped and dried slowly to form a close-packed structure aggregate of silica fine particles. The voids of the silica opal were gently filled with an ultraviolet curable resin having a viscosity of 20 mPa · s, and cured by irradiating with ultraviolet rays having an energy of 6500 mJ.
Thereafter, the silica particles were immersed in 5% hydrofluoric acid for 1 hour, and the silica particles accumulated first were removed by etching. The inverse opal by the resin thus obtained was used as a photonic crystal.
A part of a general digital copying machine that uses a semiconductor laser with a wavelength of 780 nm as an exposure light source was modified, and was created immediately after the lens installed to focus the laser beam emitted from the semiconductor laser. A photonic crystal was provided.
When the test chart was copied with the digital copier thus modified and the output image was observed with a microscope, it was confirmed that a test pattern corresponding to a resolution of 1000 dpi was reproduced.

In this example, an inverse opal made of titanium oxide was formed on the basis of an opal crystal formed using polystyrene fine particles, and this was used as a photonic crystal. The forming method is as follows. Disperse polystyrene particles with an average particle size of 210 nm and a CV value of 2% representing the degree of particle size distribution in pure water adjusted to a weight concentration of 3% by weight concentration in quartz of 2 cm × 2 cm and a thickness of 0.5 mm. 200 μl of the solution was dropped and dried slowly to form a close-packed aggregate of polystyrene particles. Titanium oxide alkoxide solution is gently filled into the voids of polystyrene opal, and heat treatment is performed at 120 ° C. for 1 hour and then at 600 ° C. for 5 hours to sinter to obtain titanium oxide, and polystyrene fine particles are burned off to oxidize. Inverse opal with titanium was obtained.
A part of a general digital copying machine using a semiconductor laser with a wavelength of 650 nm as an exposure light source was modified, and was created immediately after the lens installed to narrow down the laser beam emitted from the semiconductor laser. A photonic crystal was provided.
When the test chart was copied with the digital copier thus modified and the output image was observed with a microscope, it was confirmed that a test pattern corresponding to a resolution of 1200 dpi was reproduced.

In this embodiment, unlike the previous embodiments, two sets of image forming systems including an exposure optical system are arranged. A photonic crystal is formed using polystyrene fine particles, and the forming method is as follows. A polystyrene particle having an average particle size of 210 nm and a CV value of 2% indicating the degree of particle size distribution is adjusted to 3% by weight concentration in pure water on a quartz glass of 4 cm × 25 cm and a thickness of 0.5 mm. 200 μl of the dispersed liquid was dropped and dried slowly to form a close-packed structure aggregate of polystyrene fine particles, which was used as a photonic crystal.
A part of a general tandem color digital copying machine that uses a semiconductor laser with a wavelength of 650 nm as an exposure light source is modified, and immediately after the lens installed to narrow down the laser beam emitted from the semiconductor laser. The photonic crystal prepared in the above was provided.
The color image output by copying the test chart with the digital copier thus modified was observed with a microscope, and it was confirmed that a test pattern corresponding to a resolution of 1200 dpi was reproduced.

It is a figure for demonstrating the 1st Embodiment of this invention. It is a figure for demonstrating the 2nd Embodiment of this invention. It is a figure for demonstrating the 3rd Embodiment of this invention. It is the figure which showed typically the super collimator effect by a photonic crystal.

Explanation of symbols

101, 201, 203 Semiconductor laser 103, 203, 303 Photonic crystal 104, 204, 304 Polygon mirror 109, 209, 309 Photoconductor

Claims (10)

  In an image forming apparatus, comprising: a semiconductor laser light source that emits a laser beam; beam scanning means that deflects and scans the laser beam; and a photosensitive member that is irradiated with the laser beam that has been deflected and scanned. An image forming apparatus comprising at least one photonic crystal having a super collimator effect.   2. The image forming apparatus according to claim 1, wherein the photonic crystal is disposed between the semiconductor laser light source and the beam scanning unit.   2. The image forming apparatus according to claim 1, wherein the photonic crystal is disposed between the beam scanning unit and the photoconductor.   4. The image forming apparatus according to claim 1, wherein the photonic crystal has a close-packed structure of fine particles (opal crystal). 5.   The image forming apparatus according to claim 4, wherein the fine particles are silica.   The image forming apparatus according to claim 4, wherein the fine particles are polystyrene.   4. The image forming apparatus according to claim 1, wherein the photonic crystal is made of a material different from a material constituting the fine particles based on a close-packed structure of fine particles (opal crystal). An image forming apparatus having an inverse opal structure.   8. The image forming apparatus according to claim 7, wherein the inverse opal structure is formed of a metal oxide.   8. The image forming apparatus according to claim 7, wherein the inverse opal structure is formed of a resin.   10. The image forming apparatus according to claim 1, wherein a plurality of image forming units including the semiconductor laser light source, the beam scanning unit, the photosensitive member, and the photonic crystal are arranged. An image forming apparatus.

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