JPS63280220A - Liquid crystal printer head - Google Patents

Abstract

PURPOSE:To attain the expression of gradation by using a monochromatic light emitting light source and arranging plural liquid crystal arrays changing a gap, i.e. the layer thickness of liquid crystal. CONSTITUTION:A liquid crystal printer head is provided with the monochromatic light emitting light source lamp 14, two kinds of liquid crystal shutter arrays 11, 12 having different gaps and SELFOC lens arrays 15, 16. When liquid crystal is homogeneously orientated and held by polarizing plates whose polarizing axes are rectangular to each other in the liquid crystal shutter array, the transmitted light intensity I of monochromatic light is proportional to the following formula sin<2>(pidDELTAn/eta), where (d) is the layer thickness of liquid crystal, DELTAn is the double refraction of liquid crystal and lambda is the wavelength of incident light, and when monochromatic light is made incident, the transmitted light intensity depends upon the gap of the liquid crystal shutter array. The surface potential is reduced in accordance with the exposure of the photosensitive body. Consequently, the liquid crystal printer head capable of expressing gradation without forming a microshutter with a small area can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic liquid crystal printer head, and particularly to a printer head that expresses gradations.

[Conventional technology]

Liquid crystal elements have been actively researched and developed as direct-view display elements, and are now widely used. On the other hand, light modulation elements using liquid crystals are also used. For example, the intensity of the light irradiated onto the photoreceptor is modulated using a light modulation element,
An electrophotographic printer is known in which the resulting latent image on a photoreceptor is developed on plain paper using toner. In such a printer, a portion including a light source, a light modulation element, an imaging optical system, etc. of the printer is called a printer head. The liquid crystal light modulation element used in this printer head functions as a liquid crystal light shutter.

In addition, liquid crystal light modulation elements are widely applied to optical logic elements and the like, but all of them use a function of spatially modulating the intensity of incident light.

In recent years, demands for printers such as high speed, high resolution, low price, low noise, and compactness have been increasing, and in response to these demands, non-impact printers such as laser beam printers are becoming widely used.

Under these circumstances, large demand is expected for liquid crystal printers that use liquid crystal shutter arrays, especially due to their low cost, and active development is progressing, and liquid crystal printers that use dual-frequency drive liquid crystals have been developed. . Furthermore, in recent years, ferroelectric liquid crystals have been developed as liquid crystals with high response speeds, and efforts are being made to increase the speed.

Generally, a liquid crystal printer head has the following characteristics as shown in FIG.
Light source lamp 31. It consists of a liquid crystal light shutter array 32° and a SELFOC lens array 33.

Light from a light source lamp 31 is turned on and off by a liquid crystal light shutter array 32 to form an electrostatic latent image on a photoreceptor 34. However, with such a configuration, only binary values of on and off, that is, white and black, can be expressed in printing.

On the other hand, in order to reproduce shading or gradation in an electrophotographic printer, it is sufficient to apply density modulation or area modulation to the light modulation system, and for example, halftone dot method, which is a type of area modulation, is known.

[Problem that the invention seeks to solve]

Ferroelectric liquid crystal is used as a liquid crystal material for some liquid crystal shutters, and its high-speed response has expanded the range of applications of liquid crystal shutters, and they are now being used not only in printers but also, for example, in electrophotographic facsimiles. When considering facsimile applications, it is necessary to reproduce gradations, but if area modulation is to be used, a micro-shutter with a small area that corresponds to the required gradations must be formed.
Technically it will be very difficult.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a liquid crystal printer head using a liquid crystal shutter that can realize gradation without using a small-area micro shutter.

[Means for solving problems]

The present invention is a liquid crystal printer head used in an electrophotographic printing apparatus that exposes a photoreceptor to write an image, and includes a plurality of liquid crystal optical shutters sandwiched between two substrates and having different thicknesses of liquid crystal layers. It is characterized by having a liquid crystal light shutter array and changing the amount of light transmitted through each liquid crystal light shutter array.

[Effect]

In the electrophotographic process, a charged photoreceptor is exposed to light to form an electrostatic latent image, but the final print density can be adjusted by adjusting the surface potential of the photoreceptor, and the so-called gradation It will be possible to express. The height of the surface potential of the photoreceptor is determined by the amount of exposure of the photoreceptor, and this can be done by changing the intensity of light transmitted through the liquid crystal light shutter array.

The present invention makes it possible to express gradations by using a monochromatic light source lamp and providing a plurality of liquid crystal light shutter arrays with varying gaps, ie, liquid crystal layer thicknesses.

〔Example〕

The present invention will be explained in detail below.

FIG. 1 is a diagram showing an embodiment of a liquid crystal printer head, which includes a monochromatic light source lamp 14, two types of liquid crystal light shutter arrays 11.12 with different gaps, and a SELFOC lens array 15.16. We are prepared.

Note that in the figure, 13 is a photoreceptor.

In the liquid crystal light shutter array, when the liquid crystal is homogeneously aligned and the liquid crystal is sandwiched between polarizing plates whose polarization axes are perpendicular to each other, the transmitted light intensity l of monochromatic light is proportional to the following equation.

sin" (1 history sushi) λ Here, d is the liquid crystal layer thickness, Δn is the birefringence of the liquid crystal, and λ is the wavelength of the incident light. Therefore, when monochromatic light is incident,
The transmitted light intensity depends on the thickness of the liquid crystal, that is, the gap of the liquid crystal light shutter array.

Further, the relationship between the exposure amount and the surface potential of the photoreceptor can be represented by a graph as shown in FIG. That is, as the exposure amount increases, the surface potential decreases. The amount of toner adhering to the photoreceptor varies depending on the value of the surface potential of the photoreceptor, resulting in printing with shading or gradation.

If we change the gap between the liquid crystal light shutter arrays 11 and 12 in FIG. 1 and adjust the amount of transmitted light of each as shown in FIG.
The exposure amount indicated by a3 can be obtained by a combination of liquid crystal light shutter arrays as shown in Table 1.

Table 1 With the combinations shown in Table 1, you can select four types of surface potential of the photoreceptor, for example, exposure in the printed state! a.

is black and the exposure amount is al, a2. It is possible to express four gradations, such as whitening in the order of ``a'' and ``white''.

FIG. 4 is a diagram showing an example of the configuration of a liquid crystal optical shutter array, and a specific example will be further explained. In this liquid crystal optical shutter array, a substrate 22 on which a signal electrode 21 is formed and a substrate 24 on which a scanning electrode 23 is formed are arranged to face each other with a spacer interposed therebetween. Filled with dielectric liquid crystal C3-1014. Furthermore, polarizing plates 26.27 are bonded to each substrate 22.24. Sixteen scanning electrodes 23 are formed per 1 mm and driven by time-division driving with a 1/4 duty, so that one signal electrode 21 faces four scanning electrodes 23. The signal electrode 21 is connected to a signal electrode drive circuit 28, and the scan electrode 23 is connected to a scan electrode drive circuit 29.
It is connected to the.

Two types of liquid crystal light shutter arrays with such a structure are prepared, one in which the distance between the substrates 22 and 24 is 2 μm and 2.5 μm, and these liquid crystal light shutter arrays are used to construct the structure shown in FIG. A printer head was created.

Turn on the two liquid crystal light shutter arrays so that the combinations shown in Table 1 are obtained.

When the surface potential of the photoreceptor was measured with the combination of OFF and OFF, the results were 400V, 300V, 200V, and 100V, and if these were used for printing, four gradations could be expressed.

Here, a liquid crystal printer head is constructed with two liquid crystal optical shutter arrays, but by providing a transparent thin film such as Sin on one substrate, two shutter arrays with different gaps are formed. It's okay. Further, although ferroelectric liquid crystal is used in this embodiment, the printer head may be manufactured with a liquid crystal optical shutter array using TN liquid crystal.

In the above embodiment, the case where two liquid crystal light shutter arrays are used has been described, but in general, 2'' gradation can be expressed by using n liquid crystal light shutter arrays.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a liquid crystal printer head that can express gradations without forming a small-area micro-shutter.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of the liquid crystal printer head of the present invention, Fig. 2 is a graph showing the relationship between the exposure amount and surface potential of the photoreceptor, and Fig. 3 is a diagram showing the configuration of two liquid crystal light shutter arrays. . FIG. 4 is a graph showing the amount of transmitted light in the off state. FIG. 4 is a diagram showing an example of the configuration of a liquid crystal optical shutter array. FIG. 5 is a diagram showing the configuration of a printer head. 11, 12...Liquid crystal light shutter array 13...
Photoreceptor 14...Light source lamps 15, 16...Selfoc lens array 21...
...Signal electrodes 22, 24...Substrate 23...Scanning electrode 25...Liquid crystal material 26, 27...Polarizing plate

Claims (1)

[Claims] (1) A liquid crystal printer head used in an electrophotographic printing device that exposes a photoreceptor to write an image, and includes a plurality of liquid crystal optical shutter arrays with varying layer thicknesses of liquid crystal sandwiched between two substrates. A liquid crystal printer head characterized in that the amount of light transmitted through each liquid crystal light shutter array is changed.