JP4928768B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus for forming an image on a display recording medium having a memory property.

  In recent years, a display recording medium (also referred to as electronic paper or digital paper) having both the advantages of an electronic display and paper has attracted attention as a display recording medium, in addition to a paper medium and an electronic display.

  Since this display recording medium has a memory property with respect to display, it is only necessary to give writing energy by the image forming apparatus only when information is rewritten, and it is not necessary to apply energy to maintain display. Therefore, after the information is written, only the display recording medium can be separated from the image forming apparatus and can be easily carried like a paper medium, stacked, arranged, or read by hand.

  As a display recording medium having the above memory properties, an optical writable display recording medium in which an image is memorized in a visible and erasable manner by light irradiation and voltage application, and image formation for writing an image on the display recording medium An apparatus is known (for example, refer to Patent Document 1).

  In the optical writable display recording medium described in Patent Document 1, a liquid crystal layer and a photoconductive layer whose resistance value is changed by light irradiation are laminated between a pair of transparent electrodes. An image forming apparatus for writing an image on the display recording medium receives light from a backlight arranged in a two-dimensional array and generates a two-dimensional light pattern from a transmissive LCD (liquid crystal display). Irradiating the photoconductive layer, generating a resistance distribution based on the optical pattern in the photoconductive layer, applying a voltage between the transparent electrodes, applying a partial pressure distribution based on the resistance distribution of the photoconductive layer to the liquid crystal layer, An image corresponding to the pressure distribution is recorded on the liquid crystal layer.

  FIG. 11 shows the configuration of the image forming apparatus. The image forming apparatus 50 irradiates the liquid crystal panel 53 with light 540 using the backlight 54 in which the LED lamps 54 a are arranged in a two-dimensional array, and an image is displayed on the display recording medium 2 by the image light 530 from the liquid crystal panel 53. Configured to write.

  According to this image forming apparatus, recording can be performed by exposing the image information in a planar shape while applying a voltage to a pair of electrodes, so that a large amount of image information can be obtained at a higher speed than line exposure or scanning exposure. It becomes possible to write.

On the other hand, in order to improve the viewing angle of the liquid crystal panel, an optical compensation film that optically compensates for the birefringence of the liquid crystal panel has been developed (for example, see Non-Patent Document 1).
JP 2001-301233 A (FIG. 4) FUJIFILM RESERCH & DEVELOPMENT (No. 46-2001) P51-55

  However, according to the conventional image forming apparatus, since a plurality of LED lamps 54a are used, the number of parts increases and the configuration becomes complicated. Further, in order to irradiate the liquid crystal panel 53 with parallel light as much as possible, the LED lamp 54a having a narrow directivity angle is used. In addition, since it is necessary to increase the distance from the liquid crystal panel 53, it is difficult to cope with downsizing (thinning).

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of simplifying the configuration and reducing the thickness and generating a recorded image having a stable contrast over the entire recording area of a display recording medium.

To achieve the above object, one embodiment of the present invention provides a display recording medium on which an image is written by light irradiation, a point light source that generates light, and the display recording medium that receives the light from the point light source. A liquid crystal panel for irradiating image light, and an optical compensation film for preventing light leakage of light obliquely incident on the liquid crystal panel from the point light source by optically compensating for the birefringence of the liquid crystal panel. An image forming apparatus is provided.

According to the image forming apparatus, since the birefringence of the liquid crystal panel is optically compensated by the optical compensation film, light leakage can be prevented even when light from the light source is incident on the liquid crystal panel obliquely. can be used a light source, it is possible to shorten the distance between the liquid crystal panel and the light source.

  The liquid crystal panel includes a liquid crystal layer, a first polarizing plate disposed on a light incident side of the liquid crystal layer, and a second polarizing plate disposed on a light emitting side of the liquid crystal layer, and the optical compensation The film may be arranged between the liquid crystal layer and the first polarizing plate, or between the liquid crystal layer and the first polarizing plate.

As the point light source, an LED (light emitting diode), a halogen lamp, or the like can be used.

  The display recording medium may have a configuration in which a photoconductive layer and a liquid crystal layer are laminated.

  According to the present invention, since the birefringence of the liquid crystal panel is optically compensated, the configuration can be simplified and thinned, and a recorded image with a stable contrast can be generated over the entire recording area of the display recording medium. It becomes possible.

  FIG. 1 shows a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 includes a display recording medium 2 having a memory property, a backlight 4 that generates light 40, and optical compensation that receives the light 40 from the backlight 4 and irradiates the display recording medium 2 with image light 30. A voltage applying unit 5 for applying a voltage to the attached liquid crystal panel 3, the display recording medium 2, the liquid crystal panel 3 with optical compensation and the backlight 4, and a voltage applying unit 5 based on the image data stored in the image storage unit 7. And a control unit 6 for controlling the operation.

  The backlight 4 uses a single LED lamp 41 arranged within an allowable incident angle of the liquid crystal panel 3 with optical compensation. The LED lamp 41 has a structure in which the LED chip 41a is sealed with a sealing member 41b made of a transparent resin. The sealing member 41b has a lens function that gives wide directivity that can irradiate the entire light-emitting liquid crystal panel 3 with optical compensation to the light emitted from the LED chip 41a.

  The voltage application unit 5 includes a pair of power feeding units for applying a voltage to a pair of power receiving units connected to a pair of electrodes described later of the liquid crystal panel 3 with optical compensation, and a pair of electrodes described later of the display recording medium 2. And a pair of power feeding units for applying a voltage to the pair of connected power receiving units.

  The control unit 6 includes a CPU, a ROM that stores a program for writing an image on the display recording medium 2, a RAM that temporarily stores data, an interface circuit, and the like. In addition, an operation unit or a display that receives a user operation may be connected to the CPU via an interface circuit. Thereby, an image can be read out from the image storage unit 7 and displayed on the display, and an image to be written in the display recording medium 2 can be selected by operating the operation unit.

  The image storage unit 7 can be a DVD, a CD-RW, a hard disk, a semiconductor memory, or the like.

(Display recording medium)
2A and 2B show different types of display recording media. The display recording medium 2 shown in FIG. 2A includes transparent first and second substrates 200A and 200B made of PET (polyethylene terephthalate) films disposed opposite to each other, and first and second substrates 200A and 200B. The transparent first and second electrodes 201A and 201B made of ITO (indium tin oxide) formed on the inner side and the second electrode 201B are provided on the inner side, and reflectivity (depending on the applied voltage) (Transmissivity) is changed between the liquid crystal layer 202, the photoconductive layer 203 which is disposed inside the first electrode 201A and decreases in resistance by light irradiation, and is disposed between the liquid crystal layer 202 and the photoconductive layer 203. The light absorption layer 204 is provided.

  The liquid crystal layer 202 includes a microcapsule 202a in which cholesteric liquid crystal is sealed.

  The photoconductive layer 203 includes a charge transport layer and a pair of charge generation layers stacked on both sides of the charge transport layer. As a result, an AC voltage can be applied to the liquid crystal layer 202, so that the deterioration of the liquid crystal layer 202 can be suppressed, and the drive voltage can be lowered and the life of the display recording medium 2 can be increased. .

  The display recording medium 2 shown in FIG. 2 (b) is the same as the display recording medium 2 shown in FIG. 2 (a) except that the light absorption layer 204 is disposed inside the second electrode 201B, and the liquid crystal layer 202 is photoconductive. The isolation layer 205 is added between the layers 203, and other configurations are the same as those in FIG.

(LCD panel with optical compensation)
FIG. 3 shows a liquid crystal panel 3 with optical compensation. The liquid crystal panel 3 with optical compensation includes a liquid crystal layer 31 made of TN (twisted nematic) liquid crystal sandwiched between first and second alignment films 32A and 32B, and transparent first and second electrodes 33A and 33B. And the transparent first and second substrates 34A and 34B made of glass substrates and the like disposed so as to sandwich the liquid crystal layer 31 and the first and second substrates 34A and 34B, respectively. , Optical compensation films 35A and 35B for optically compensating the birefringence of the liquid crystal layer 31, and polarizing plates 36A and 36B that are arranged outside the optical compensation films 35A and 35B and whose polarization axis directions are orthogonal to each other.

  The liquid crystal layer 31 may use STN (super twisted nematic) liquid crystal in addition to the TN liquid crystal.

  The first and second electrodes 33A and 33B may use a plurality of row electrodes and a plurality of column electrodes orthogonal to each other, and drive each pixel by passive matrix driving (simple matrix driving). The first and second electrodes 33A and 33B use full-surface electrodes and a plurality of pixel electrodes, and connect active elements such as TFTs to intersections of a plurality of data lines and a plurality of scanning lines orthogonal to each other. Each pixel may be driven by active matrix driving.

  As the optical compensation films 35A and 35B, for example, a trade name “WV-SA film” manufactured by FUJIFILM Corporation using a discotic liquid crystal can be used. In the present embodiment, the optical compensation film is arranged on both the light incident side and the light emitting side of the liquid crystal layer 31. However, the arrangement may be arranged on either one.

(Birefringence of liquid crystal layer)
FIG. 4A shows a refractive index ellipsoid model of liquid crystal molecules constituting the liquid crystal layer 31 of the liquid crystal panel 3 with optical compensation. 4A and 4B, n is a refractive index and the nz direction is an optical axis. The liquid crystal layer 31 using TN liquid crystal is an optically positive uniaxial substance, and is represented, for example, as a rugby ball type refractive index ellipsoid. Considering light 40a perpendicularly incident on the liquid crystal panel with optical compensation 3 and light obliquely incident light 40b and 40c, birefringence occurs in the obliquely incident light 40b and 40c.

  FIG. 4B shows a refractive index ellipsoid model of the material used for the optical compensation films 35A and 35B. The optical compensation films 35A and 35B have an optically negative uniaxial property. In FIG. 4B, the optically incident light 40a and the obliquely incident light 40b and 40c are incident on the liquid crystal panel 3 with optical compensation. Considering this, birefringence occurs in the obliquely incident light 40b and 40c.

  As is clear from FIG. 4B, the optical compensation films 35A and 35B having an optically negative uniaxial property have a property opposite to the positive uniaxial property of the TN liquid crystal, and therefore light incident obliquely. Since the direction of birefringence generated in 40b and 40c is opposite to the direction of birefringence generated in the liquid crystal layer 31 shown in FIG. 4A, the effect of birefringence inherent in the TN liquid crystal appears in the image. Can be countered.

(Operation of image forming apparatus)
Next, the operation of the image forming apparatus 1 according to the present embodiment will be described. Note that the case where the liquid crystal layer 31 of the liquid crystal panel 3 with optical compensation is normally white which displays white when no voltage is applied will be described. The control unit 6 controls the voltage application unit 5 based on the image data stored in the image storage unit 7. The voltage application unit 5 applies a voltage to the LED lamp 41 of the backlight 4 to light it, and in accordance with image data, a predetermined voltage is applied between the first and second electrodes 33A and 33B of the liquid crystal panel 3 with optical compensation. And a predetermined alternating voltage is applied between the first and second electrodes 201A and 201B of the display recording medium 2.

  Next, in the liquid crystal panel 3 with optical compensation, in the portion (pixel) of the liquid crystal layer 31 between the first and second electrodes 33A and 33B to which a voltage is applied, the liquid crystal molecules are in the vertical state, and the first and second In combination with the polarizing plates 36A and 36B, the passage of the light 40 from the LED lamp 41 is blocked. On the other hand, in the portion (pixel) of the liquid crystal layer 31 between the first and second electrodes 33A and 33B to which no voltage is applied, the liquid crystal molecules are twisted, and the light 40 from the LED lamp 41 is the first and second. Passes through the polarizing plates 36A and 36B. In this way, the image light 30 is generated and applied to the display recording medium 2. The birefringence of the liquid crystal layer 31 of the image light 30 is compensated by the first and second optical compensation films 35A and 35B.

(Display recording medium shown in FIG. 2A)
When the image light 30 is applied to the display recording medium 2, in the display recording medium 2 shown in FIG. 2A, the image light 30 passes through the first substrate 200A and the first electrode 201A and reaches the photoconductive layer 203. To reach.

  In the photoconductive layer 203, the resistance value of the portion irradiated with light is reduced, whereby the partial pressure of the liquid crystal layer 202 determined by the impedance ratio with the photoconductive layer 203 is increased, and the voltage in the liquid crystal layer 202 after voltage application is increased. The light reflectance increases. Accordingly, when the surface 2a of the display recording medium 2 is irradiated with the illumination light after the image writing is completed, the region irradiated with the image light 30 of the liquid crystal layer 202 has a high reflectance, and thus the illumination light. Is reflected and appears white, and the area where the image light 30 is not irradiated appears black because the illumination light passes through the liquid crystal layer 202 and is absorbed by the light absorption layer 204. This can be viewed as an image from the direction of the line of sight E. This image is held for a long time even after voltage application to the first and second electrodes 201A and 201B disappears.

(Display recording medium shown in FIG. 2B)
In the case of the display recording medium 2 shown in FIG. 2B, the image light 30 sequentially passes through the first substrate 200A, the first electrode 201A, the liquid crystal layer 202, and the isolation layer 205, and reaches the photoconductive layer 203. To do.

  In the photoconductive layer 203, the resistance value of the portion irradiated with light is reduced, whereby the partial pressure of the liquid crystal layer 202 determined by the impedance ratio with the photoconductive layer 203 is increased, and the voltage in the liquid crystal layer 202 after voltage application is increased. The light reflectance increases. Accordingly, when the back surface 2b of the display recording medium 2 is irradiated with illumination light, the region irradiated with light is reflected by the liquid crystal layer 202 and appears white, and the region not irradiated with light passes through the liquid crystal layer 202. Since it is absorbed by the light absorption layer 204, it looks black. This can be viewed as an image from the direction of the line of sight E. This image is held for a long time even after voltage application to the first and second electrodes 201A and 201B disappears.

  According to the present embodiment, since the liquid crystal panel 3 with optical compensation is used as the liquid crystal panel, the allowable incident angle of the liquid crystal panel can be enlarged, and even if a point light source is used as the backlight 4, the black display portion , Leakage of oblique light components is reduced, and a reduction in contrast occurring in the peripheral portion can be reduced. This makes it possible to write a good image over the entire recording area of the display recording medium 2. Moreover, since a point light source can be used as the backlight 4, the structure of the backlight 4 can be simplified. Furthermore, since the distance between the liquid crystal panel 3 and the backlight 4 can be shortened, the apparatus 1 can be thinned.

  After describing a comparative example, Example 1 of the present invention will be described.

<Comparative example>
FIG. 5 shows an image forming apparatus of a comparative example. This image forming apparatus 1 uses a single LED lamp 41 as a backlight 54 and a normal 2.2 inch liquid crystal panel 13 having no optical compensation film in the conventional configuration shown in FIG. Is. Further, the distance between the liquid crystal panel 13 and the lower end of the backlight (the sum of the distance h ₁ between the liquid crystal panel 13 and the backlight 4 and the height h ₂ of the backlight 4) is 30 mm, and the peripheral portion (diagonal) of the liquid crystal panel 13 A 2.2 inch area) was illuminated.

FIG. 6 shows the display characteristics of the display recording medium 2 in the comparative example. The integrated reflectance on the vertical axis means the ratio of the integrated value of the intensity of light reflected in all directions to the light incident from a predetermined direction. In a normal liquid crystal panel 13 having no optical compensation film, birefringence does not occur in the central portion where light perpendicular to the liquid crystal panel 13 is incident, so that sufficient contrast (light quantity difference 190 μW / cm ² ) is obtained. It is done. However, since light enters obliquely from the periphery, birefringence occurs, linearly polarized light becomes elliptically polarized light, and light that passes through the polarizing plate is generated, thereby reducing the contrast (light quantity difference 170 μW / cm ² ). , A dark light amount floating (an increase in black reflectance) occurs.

  FIG. 7 shows the contrast when a monochrome stripe image is written on the display recording medium 2 by the apparatus of the comparative example. In the figure, the solid line indicates the reflectance at the central portion, and the broken line indicates the reflectance at the peripheral portion. As can be seen from the figure, the contrast in the peripheral portion (reflectance difference 24) is lower than the contrast in the central portion (reflectance difference 38).

  FIG. 8 shows a luminance distribution on the display recording medium 2 when the liquid crystal panel 13 is in a dark state in the comparative example. In addition, AA line and BB line show the measurement position of the amount of leakage light. As can be seen from the figure, a large light leak (up to 3.8) occurs in the peripheral portion.

<Example 1>
The first embodiment of the present invention uses a 2.2-inch liquid crystal panel 3 with optical compensation, and the distance between the liquid crystal panel 3 and the lower end of the backlight is 30 mm (the distance h ₁ between the liquid crystal panel 3 and the backlight 4 and the backlight). 4) (the sum of the height h ₂ of 4), and the peripheral portion of the liquid crystal panel 3 (region of 2.2 inches diagonal) was illuminated.

  FIG. 9 shows the contrast when a monochrome stripe image is written on the display recording medium 2 by the apparatus of the first embodiment. In the figure, the solid line indicates the reflectance at the central portion, and the broken line indicates the reflectance at the peripheral portion. The incident light to the peripheral portion reduces the light that passes through the polarizing plate because the birefringence generated in the light passing through the liquid crystal layer is compensated by the optical compensation films 35A and 35B. Therefore, as can be seen from the figure, there is no difference in reflectance change between the central portion and the peripheral portion, and a decrease in contrast in the peripheral portion can be prevented.

  FIG. 10 shows a luminance distribution on the display recording medium 2 when the liquid crystal panel 3 with optical compensation is in a dark state in the first embodiment. Lines AA and BB indicate measurement positions of the amount of leakage light. As can be seen from the figure, no large light leakage (maximum 1.3) occurred with the compensation film.

  In addition, this invention is not limited to the said embodiment and said Example, A various deformation | transformation is possible within the range which does not deviate from the meaning of the invention. For example, an optical system such as a mirror may be disposed between the optically compensated liquid crystal panel and the light source. Thereby, the thickness can be further reduced.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. (A), (b) is sectional drawing of the display recording medium from which a type differs, respectively. It is sectional drawing of a liquid crystal panel with optical compensation. (A) is a figure which shows the refractive index ellipsoid model of the liquid crystal molecule which comprises the liquid crystal layer of the liquid crystal panel with optical compensation, (b) is a figure which shows the refractive index ellipsoid model of the material used for an optical compensation film. is there. It is a figure which shows the structure of the image forming apparatus of a comparative example. It is a figure which shows the display characteristic of the display recording medium in a comparative example. It is a figure which shows the contrast at the time of writing the image of a monochrome stripe on the display recording medium with the apparatus of the comparative example. In a comparative example, it is a figure which shows the luminance distribution on the display recording medium when a liquid crystal panel is made into a dark state. FIG. 3 is a diagram showing contrast when a monochrome stripe image is written on a display recording medium by the apparatus of Example 1. In Example 1, it is a figure which shows the luminance distribution on the display recording medium at the time of making the liquid crystal panel 3 with optical compensation into a dark state. It is a figure which shows the structure of the conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Display recording medium 2a Front surface 2b Back surface 3 Optical compensation liquid crystal panel 4 Backlight 5 Voltage application part 6 Control part 7 Image memory | storage part 13 Liquid crystal panel 30 Image light 31 Liquid crystal layer 32A, 32B Orientation film 33A, 33B Electrode 34A, 34B Substrate 35A, 35B Optical compensation film 36A, 36B Polarizing plate 40, 40a-40c Light 41 LED lamp 41a LED chip 41b Sealing member 50 Image forming device 53 Liquid crystal panel 54 Backlight 54a LED lamp 200A, 200B Substrate 201A, 201B Electrode 202 Liquid crystal layer 202a Microcapsule 203 Photoconductive layer 204 Light absorption layer 205 Isolation layer E Line of sight h ₁ Distance h ₂ Height

Claims (3)

A display recording medium on which an image is written by light irradiation;
A point light source that generates light;
A liquid crystal panel that receives the light from the point light source and irradiates the display recording medium with image light;
An image forming apparatus comprising: an optical compensation film that optically compensates for the birefringence of the liquid crystal panel to prevent light leakage of light obliquely incident on the liquid crystal panel from the point light source . The liquid crystal panel includes a liquid crystal layer, a first polarizing plate disposed on the light incident side of the liquid crystal layer, and a second polarizing plate disposed on the light exit side of the liquid crystal layer,
The image according to claim 1, wherein the optical compensation film is disposed between the liquid crystal layer and the first polarizing plate, or between the liquid crystal layer and the second polarizing plate. Forming equipment.   The image forming apparatus according to claim 1, wherein the display recording medium has a configuration in which a photoconductive layer and a liquid crystal layer are stacked.