The present invention relates to a projection screen technology, and, more particularly, to a method of producing a transmissive screen used as a display screen of, for example, a projection television or a microfilm reader and to the transmissive screen produced by this method.
In recent years, a rear projector using a liquid crystal light valve or a CRT as a large screen display has been drawing attention. The display displays an image by forming an image on a transmissive screen using image light from an image projecting portion. This type of transmissive screen is bright when an observer observes the image and has predetermined very small lens members formed thereon so as to increase the viewing angle.
As shown in FIG. 11, with regard to light distribution property of such a bright screen having a wide viewing angle, a viewing angle 1101 which is wider in the horizontal direction than in the vertical direction is preferred. This is because the viewing angle of a human being is wider in the horizontal direction than in the vertical direction. When the light distribution is made equal in the vertical and horizontal directions, light is also distributed in the vertical direction which is not really necessary with regard to the viewing angle of a human being, so that the brightness as a whole is reduced.
Representative examples of the structures of the transmissive screen include the following:
{circle around (1)} A lenticular sheet including a lens portion formed by providing convex cylindrical lenses (semi-circular cylindrical convex lenses) side by side. As shown in FIG. 9(a), in general, the lenticular sheet has a structure formed by forming both surfaces of the sheet into convex cylindrical lens surfaces 901, forming protrusions at boundary portions between the respective cylindrical lenses at one of the surfaces of the sheet (the surface from which image light 201 exits), and forming a light-shielding layer (a black stripe having light-absorption property) 902 on the top portion of each of the protrusions.
The lenticular sheet is obtained by carrying out a press-molding operation on a transparent thermoplastic resin sheet or by molding both surfaces of the resin sheet at the same time that molten extrusion is carried out.
{circle around (2)} A planar lens having very small transparent balls arranged two dimensionally (disclosed in, for example, U.S. Pat. Nos. 2,378,252 and 3,552,822, and Japanese Utility Model Registration Gazette No. 2513508). As shown in FIG. 10(a), in the planar lens, each very small transparent ball 1002 has of the order of 50% of its diameter embedded in and held by a light-incident side transparent layer 1001 and the remaining 50% embedded in a light-exiting side light absorption layer 1003.
The planar lens is obtained by forming a sheet comprising a transparent layer, very small transparent balls, and a light-absorption layer, and, then, bonding it to a transparent substrate 1004.
However, such conventional transmissive screens have the following problems.
In the lenticular lens, it is difficult to achieve a fine pitch when each of the above-described molding methods is performed on thermoplastic resin, so that, when the lenticular lens is used as a screen of a rear projector, which, in recent years, has been providing increasingly higher definition, there is a problem in that deterioration of image quality occurs due to reduced resolution and production of moirxc3xa9. In addition, a very small light diffusing material is usually mixed in the inside portion of the lenticular lens in order to increase the viewing angle in the vertical direction (a direction parallel to the lenticular lens, which is represented by reference numeral 903 in FIG. 9(b)) in which the lenticular lens does not have optical power. This gives rise to the problem that image quality is deteriorated because speckles are produced due to the interference of image light caused by the light-diffusing material. Further, both of the molding methods performed on the thermoplastic resin require large molding machines or dies having diagonals equal to or greater than 50 inches, which are of the same size as the screen of the rear projector, giving rise to the problem that production costs become very high.
On the other hand, in the planar lens having very small transparent balls arranged two-dimensionally, as shown in FIG. 10(b) in which the planar lens is viewed from an image light incident side, dead spaces, which do not pass image light, are formed between the individual very small balls 1002, so that the image light incident thereupon is not transmitted to the observer side. In addition, it is very difficult to perform a minute filling operation completely with respect to the very small balls, so that the dead spaces increase in size. Further, since the thin light absorption layer 1003 remains at the observer-side surfaces of the very small transparent balls, light is absorbed. Due to these three reasons, the problem that light transmittance of the transmissive screen is low arises.
Since the increase in the viewing angle by the very small balls is completely isotropic, light is also diffused in the vertical direction, in which the viewing angle does not normally need to be increased very much, to the same extent as in the horizontal direction. This gives rise to the problem of insufficient brightness when the image is viewed from the front.
In general, the planar lens is produced by the step of forming a sheet comprising a transparent layer, very small transparent balls, and a light absorption layer, and bonding the sheet to a transparent substrate. However, in the step of bonding the sheet to the transparent substrate, unevenness in the bonding occurs, so that the display of the image becomes ununiform, and, by insufficient adhesiveness between the sheet and the transparent substrate, interfacial multiple reflection occurs, thereby giving rise to the problem of reduced resolution.
In order to overcome the above-described problems, it is an object of the present invention to realize a method of producing at a low cost a transmissive screen which is bright, which has high contrast and resolution, and which is capable of displaying a high-quality image without moirxc3xa9 and scintillation.
In order overcome the above-described problems, according to the present invention, there is provided a first form of a method of producing a transmissive screen having a structure including light-absorption-material patterns formed at locations corresponding to locations of lens members, which are provided side by side on a light-transmissive substrate, and to locations of boundary portions between the corresponding lens members, the method comprising the step of forming the lens members or precursors thereof by causing very small drops of lens compositions to be discharged and to land near a light-transmission area on a surface of the light-transmissive substrate. Means for causing the very small drops of the lens compositions to be discharged and to land is an inkjet recording head. Preferably, the inkjet recording head is a piezo jet recording head.
According to this form, the individual lens members, formed on the surface of the transmissive screen, are formed by the discharging of lens compositions from an inkjet recording head, typified by, for example, a piezo jet recording head, having the excellent feature of forming a very fine form with high precision over a large area. Therefore, very fine lens members can be produced. Consequently, it is possible to provide a transmissive screen which provides excellent resolution and which does not have reduced image quality due to moirxc3xa9. In addition, this method can be used in producing a transmissive screen by a manufacturing device including a mechanism that scans the piezo jet recording head in the horizontal/vertical directions of the screen. Therefore, expensive manufacturing devices, such as large dies and molding devices, are not required, thereby making it possible to reduce production costs.
In a second form of a method of producing a transmissive screen in accordance with the present invention, the surface form of each of the lens members is restricted by adjusting the surface tension and viscosity of each of the lens compositions, and the wettability of each of the lens compositions and a surface which each of the lens compositions contacts.
According to this form, a processing operation using a die is not required, so that the forms of the lens members can be controlled by a simple step, thereby making it possible to reduce production costs.
A third form of a method of producing a transmissive screen in accordance with the present invention comprises the step of forming the light-absorption-material patterns into the shape of a bank on a surface of the light-transmissive substrate prior to forming the lens members and the precursors thereof by causing the very small drops of the lens compositions to be discharged and to land near a light-transmission portion of the bank-shaped light-absorption-material patterns.
According to this form, the lens resin compositions are discharged onto the vicinity of the light-transmission portions of the bank-shaped light-absorption-material patterns in order to form the lens members, so that the light-absorption-material patterns and the lens members are aligned with high precision, thereby increasing the light transmittance of the transmissive screen.
In a fourth form of a method of producing a transmissive screen in accordance with the present invention, the surface of the light-transmissive substrate on which the light-absorption-material patterns are formed is different from the surface where the lens members are formed.
According to this form, it no longer becomes necessary to consider the chemical reaction between the light-absorption-material-pattern compositions and the lens member compositions, thereby increasing the variety of materials from which selection can be made, so that it is possible to provide a low-cost transmissive screen using low-cost materials.
In a fifth form of a method of producing a transmissive screen in accordance with the present invention, the light-absorption-material patterns or precursors thereof are formed by causing very small drops of light-absorption-material pattern compositions to be discharged and to land. Means for causing the very small drops of the light-absorption-material pattern compositions to be discharged and to land is an inkjet recording head. Preferably, the inkjet recording head is a piezo jet recording head.
According to this form, since the light-absorption-material patterns and the lens members can be formed by the method of discharging very small drops and causing them to land, the production process is simplified, thereby making it possible to provide a low-cost transmissive screen.
In addition, since the light-absorption-material patterns are formed by discharging the light-absorption-material-pattern compositions from the inkjet recording head, typified by, for example, a piezo jet recording head, having the excellent feature of forming a very fine form with high precision over a large area, it is possible to form very fine light-absorption-material patterns. Therefore, it is possible to provide a transmissive screen which provides excellent resolution and which does not have reduced image quality due to moirxc3xa9. Further, this method can be used to produce a transmissive screen by a manufacturing device including a mechanism that scans the piezo jet recording head in the horizontal/vertical directions of the screen. Therefore, expensive manufacturing devices, such as large dies and molding devices, are not required, thereby making it possible to reduce production costs.
A sixth form of a method of producing a transmissive screen in accordance with the present invention comprises the step of restricting a planar form of each of the lens members on the surface of the light-transmissive substrate situated at the side where the lens members are formed prior to forming the lens members or the precursors thereof, with the restricting operation being a chemical operation or a restricted form formation operation, which restrict spreading of the lens member compositions on the transparent substrate.
According to this form, since the forms of the lens members can be controlled without using a die, it is possible to produce a transmissive screen having any viewing angle at a low cost.
In a seventh form of a method of producing a transmissive screen in accordance with the present invention, the step of restricting the planar form of each of the lens members is the same as the step of forming the light-absorption-material patterns.
According to this form, it is possible to omit additional steps of restricting the planar forms, so that the process can be simplified.
In an eighth form of a method of producing a transmissive screen in accordance with the present invention, adjacent lens members are formed of different lens member compositions. Preferably, the different lens member compositions are adjusted so as to hardly mix with each other.
According to this form, since the adjacent lens member compositions may be those that do not mix easily with each other, it is possible to reduce the distances between the adjacent lens members, so that dead spaces become smaller. Therefore, it is possible to realize a transmissive screen having high light transmittance.
A form of a transmissive screen is produced by any one of the methods of producing a transmissive screen.
According to this form, the individual lens members, formed on the surface of the transmissive screen, are formed by the discharging of lens compositions from an inkjet recording head, typified by, for example, a piezo jet recording head, having the excellent feature of forming a very fine form with high precision over a large area. Therefore, very fine lens members can be produced. Consequently, it is possible to provide a transmissive screen which provides excellent resolution and which does not have reduced image quality due to moirxc3xa9. In addition, in this form, this method can be used in producing a transmissive screen by a manufacturing device including a mechanism that scans the piezo jet recording head in the horizontal/vertical directions of the screen. Therefore, expensive manufacturing devices, such as large dies and molding devices, are not required, thereby making it possible to reduce production cost, and, thus, to provide a low-cost transmissive screen.
In a second form of a transmissive screen of the present invention, spectral characteristics of the light-transmissive substrate, each of the lens members, and, each of the light-absorption-material patterns, are substantially uniform or smooth in light transmission or light absorption properties n the visible region.
According to this form, since the color of the display image can be faithfully reproduced, it is possible to realize a transmissive screen which can display a high-quality image.
In a third form of a transmissive screen of the present invention, the form of the bottom side of each of the lens members to be formed is substantially rectangular.
According to this form, since the bottom side forms of the individual lens members are substantially rectangular, when the individual lens members are subjected to a filling operation carried out with close attention, dead spaces between the individual lens members are not generated. Therefore, it is possible to realize a bright transmissive screen having high light transmittance.
In a fourth form of the transmissive screen of the present invention, when the radius of curvature of each of the lens members, which is to be formed, in a horizontal direction of the transmissive screen is RH and the radius of curvature of each of the lens members, which is to be formed, in a vertical direction of the transmissive screen is RV, RH less than RV.
According to this form, since the optical power of each lens member in the horizontal direction is greater than the optical power of each lens member in the vertical direction, the viewing angle of the transmissive screen in the horizontal direction can be made larger than the viewing angle of the transmissive screen in the vertical direction. Therefore, it is possible to adequately diffuse image light which has passed through the transmissive screen in the proper direction in accordance with the viewing angle characteristic of a human being. Consequently, a bright transmissive screen can be realized.
In a fifth form of a transmissive screen of the present invention, when the width of each of the lens members, which is to be formed, in a horizontal direction thereof is WH, and the width of each of the lens members, which is to be formed, in a vertical direction thereof is WV, WH less than WV.
According to this form, when the form of the surface of each lens member is restricted by adjusting the surface tension and viscosity of each of the lens compositions and the wettability of each of the lens compositions and a surface which each of the lens compositions contacts, the radius of curvature of the larger-width portion of each lens member becomes large and that of the smaller-width portion of each lens member becomes small. When this is seen from the point of view of optical power, the smaller radius of curvature corresponds to the larger optical power. Therefore, by causing the horizontal-direction width of each lens member to be smaller than the vertical-direction width thereof as in this form, the optical power in the horizontal direction becomes larger than that in the vertical direction, so that the viewing angle of the transmissive screen in the horizontal direction can be made larger than that of the transmissive screen in the vertical direction. Therefore, it is possible to adequately diffuse image light which has passed through the transmissive screen in the proper direction in accordance with the viewing angle characteristic of a human being. Consequently, a bright transmissive screen can be realized.
In a sixth form of a transmissive screen of the present invention, the distances between adjacent landing target locations of the lens compositions are not uniform in a plane of the transmissive screen.
According to this form, since the lens members are not disposed at the transmissive screen in a regular manner, it is possible to improve the quality of a projected image with reduced moirxc3xa9.
In a seventh form of a transmissive screen of the present invention, the distances between the adjacent landing target locations of the lens compositions in a horizontal direction and those in a vertical direction are different. Preferably, when the distances in the horizontal direction are PH and those in the vertical direction are PV, PH greater than PV. More preferably, when the diameter of a single lens member is SP, the distances between the adjacent landing target locations of the lens compositions are such that PH greater than SP greater than PV.
According to this form, it is possible to fuse adjacent lens members in the vertical direction. The resulting compound lens member obtained is such that its vertical-direction radius of curvature is larger than the horizontal-direction radius of curvature, so that it is possible for the horizontal-direction viewing angle of the transmissive screen to be greater than the vertical-direction viewing angle of the transmissive screen.
There is provided a ninth form of a method of producing a transmissive screen having a structure including light-absorption-material patterns formed on locations corresponding to locations of lens members, which are provided side by side on a light-transmissive substrate, and to locations of boundary portions between the corresponding lens members. The method comprises the step of forming volume-type phase devices or precursors thereof by causing very small drops of volume-type phase device compositions to be discharged and to land, with the volume-type phase devices having random phase distributions being provided side by side on a surface of the light-transmissive substrate where the lens members are formed or the back side of the surface. Means for causing the very small drops of the volume-type phase device compositions to be discharged and to land is an inkjet recording head. Preferably, the inkjet recording head is a piezo jet recording head.
According to this form, volume-type phase devices having random phase distribution are provided side by side on the back side of a lens-formation surface of the light-transmissive substrate. Since interference is reduced by randomly disturbing a wave surface of image light, speckles can be considerably reduced. In addition, since the volume-type phase devices are formed by using an inkjet recording head, typified by a piezo jet recording head, production costs can be reduced.