Transmission-type screen for a projection television device

Abstract: A transmission-type video projection television system employs a transmission-type screen for displaying an image projected from a rear projector for visual observation by an observer in front of the screen. The transmission-type screen has Fresnel (1) and lenticular lenses (11), one of which has an electrically conductlve layer or a metal member on its surface to prevent the lens from being electrostatically charged, so that dust or dirt particles will not be attracted to the screen.

Description: The present invention relates to a transmission type screen according to the preamble of claim 1 and a video projecting television system using the same. The transmission-type video projection television system which employs such a transmission-type screen for displaying an image projected from a rear projector for visual observation by an observer in front of the screen, and more particularly to an uncharged transmission-type screen which has an electrically conductive surface to prevent the screen from being electrostatically charged for thereby preventing dust or dirt particles in the air from being attracted to the screen, and a video projection television system which employs such an uncharged transmission-type screen. One conventional transmission-type screen of plastic material for use in transmission-type video projection television system is of a double-lens structure comprising a Fresnel lens and a lenticular lens which are combined with each other. The transmission-type screen has black stripes on its surfaces for absorbing and blocking rays of light. The black stripes are typically printed with black ink or coated with black paint. The black stripes of blank ink or paint present an electric resistance of 1.4 × 10 11 Ω on the exit-side surface (a) of the lenticular lens, an electric resistance of 3.5 × 10 11 Ω on the entrance-side surface (b) of the lenticular lens, an electric resistance of 1.4 × 10 11 Ω on the exit-side surface (c) of the Fresnel lens, and an electric resistance of 1.4 × 10 11 Ω on the exit-side surface (d) of the lenticular lens, an electric resistance of 1.4 × 10 11 Ω on the entrance-side surface of the lenticular lens, as shown in FIG. 18 in the row indicated at α. Since these surface electric resistances are very high, the screen surfaces can easily be triboelectrically charged up to an extremely high electrostatic potential. For example, when the exit-side surface (a) of the lenticular lens is rubbed, it is electrostatically charged up to 10 KV, and when the entrance-side surface (d) of the Fresnel lens is rubbed, it is electrostatically charged up to 30 KV. The electrostatically charged screen surfaces easily attract dust or dirt particles in the ambient air, and can be smeared very quickly. When the dust or dirt deposit is wiped off the charged screen surfaces with a dust cloth, the other screen surfaces, which are opposite the charged screen surfaces, also become triboelectrically charged up to a high electrostatic potential. In order to prevent the screen surfaces from being triboelectrically charged, it has been customary to use a surface-active agent as an antistatic agent which does not erode the plastic material. However, surface-active agents have a short service life, and remain effective for only half through one year even when they are left unused. When dust or dirt deposits are wiped off surfaces that are coated with a surface-active agent, the surface-active agent is also gradually wiped away, and hence has a shorter service life. The surface-active agent which is applied to the entire surfaces of a transmission-type screen of plastic material is selected to be transparent and highly transmission of light. Since the surface-active agent is heat-resistant only at low temperatures ranging from 60 to 80°C, it must be treated at a low temperature and does not last for a long time. When deposited dust or dirt particles are wiped off the screen, the surface-active agent is also removed from the screen by the friction within a short period of time. Therefore, the screen tends to attract dust or dirt particles easily under electrostatic charges that are developed by triboelectricity. This in turn requires the screen to be wiped again to get rid of the attracted dust or dirt particles, resulting in more triboelectric attraction of dust or dirt particles. A generic transmission type screen or video projection television system is known from the EP-A-0 154 053 and comprises a lens for transmission of rays of light therethrough in the form of a sheet with ribs. The space between the ribs is filled with carbon black. A further transmission type screen is known from the EP-A-0 372 827. A rearmost part of the screen comprises a Fresnel lens sheet followed by an intermediate screen in the form of a lenticular lens and a foremost screen comprising parallel ridges. Furthermore, the EP-A-0 148 529 shows a transmission type screen comprising a combination of a Fresnel lens and a lenticular lens. It is an object of the present invention to provide a transmission type screen and a video projection television system using the same which is highly resistant to being electrically charged. According to the invention this object is achieved with respect to the transmission type screen by the features of claim 1 and with respect to the video projection television system by the features of claim 17. Advantageous further developments are set out in the dependent claims. According to the invention the lens for transmitting rays of light is composed of a Fresnel lens followed by a lenticular lens of by optical fibers. A plurality of electrically conductive layers are attached to steps of the Fresnel lens provided on the exit side surface thereof. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the lenticular lens having a plurality of black stripes on an exit-side surface thereof for absorbing and blocking rays of light, the black stripes being made of an electrically conductive material having a surface resistance of 1 × 10 9 Ω or less. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the lenticular lens having a plurality of parallel spaced grooves defined in an entrance-side surface thereof, and a plurality of electrically condutive layers disposed in the grooves, respectively, the electrically conductive layers being made of a material having a surface resistance of 1 × 10 9 Ω or less. The lens comprises a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the Fresnel lens having a plurality of axial steps on an exit-side surface thereof, and a plurality of electrically conductive layers attached to the axial steps, respectively, the electrically conductive layers being made of a material having a surface resistance of 1 × 10 9 Ω or less. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the Fresnel lens having a plurality of parallel spaced grooves defined in an entrance-side surface thereof for increasing a vertical field of view, and a plurality of electrically conductive layers or metal wires disposed respectively in the grooves, the electrically conductive layers being made of a material having a surface resistance of 1 × 10 9 Ω or less. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the Fresnel lens having electrically conductive layers disposed in a grid pattern on an entrance-side surface thereof, the electrically conductive layers being made of a material having a surface resistance of 1 × 10 9 Ω or less. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the Fresnel lens having a grid-like meshwork of metal wires disposed on an entrance-side surface thereof. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the lenticular lens having a plurality of parallel spaced black stripes disposed on an exit-side surface thereof and a plurality of parallel spaced grooves defined in an entrance-side surface thereof, the lenticular lens further including a plurality of metal wires disposed respectively in the black stripes or the grooves and having partly exposed surfaces. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the lenticular lens having a plurality of black, parallel spaced electrically conductive layers disposed on an exit-side surface thereof, and a plurality of black stripes disposed respectively on the electrically conductive layers. The lens may comprise a Fresnel lens and an array of parallel optical fibers which are positioned closely parallel to each other, the optical fibers being bonded by adhesive layers each comprising a mixture of an adhesive and an electrically conductive material which is added at a proportion such that the mixture has a surface resistance of 1 × 10 9 Ω or less. The lens may comprise a Fresnel lens and an array of parallel optical fibers which are positioned closely parallel to each other, the optical fibers being bonded by adhesive layers, and including electrically conductive layers disposed respectively on the adhesive layers, each of the electrically conductive layers being made of a material having a surface resistance of 1 × 10 9 Ω or less. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the lenticular lens having a plurality of parallel spaced black stripes disposed on an exit-side surface thereof and an electrically conductive layer interconnecting the black stripes and extending along outer peripheral edges of the lenticular lens, the electrically conductive layer being made of a material having a surface resistance of 1 × 10 9 Ω or less. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the lenticular lens having a plurality of parallel spaced black stripes disposed on an exit-side surface thereof and an electrically conductive layer interconnecting the black stripes and disposed over the exit-side surface, the electrically conductive layer being made of a material having a surface resistance of 1 × 10 9 Ω or less. The lens may comprise a Fresnel lens and a lenticular lens which are positioned closely parallel to each other, the lenticular lens having a plurality of parallel spaced black stripes disposed on an exit-side surface thereof, further comprising a frame of an electrically conductive material or a metal surrounding outer peripheral edges of the Fresnel lens and the lenticular lens, the electrically conductive material having a surface resistance of 1 × 10 9 Ω or less. The electrically conductive layer or the frame may be grounded by a ground wire. The electrically conductive layer may be made of a mixture of one of a printing paste, a paint, and an adhesive and carbon whose proportion is selected such that the mixture has a surface resistance of 1 × 10 9 Ω or less, or a mixture of carbon and another electrically conductive material at proportions selected such that the mixture has a surface resistance of 1 × 10 9 Ω or less. According to the present invention, there is also provided a video projection television system comprising a screen comprising a lens for transmitting rays of light therethrough, and an electrically conductive layer or a metal member mounted on a surface of the lens for preventing the surface from being electrostatically charged, and a projector for projecting an image onto the screen. The object, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. FIG. 1 is a fragmentary perspective view, partly cut away, of a transmission-type screen according to a first embodiment of the present invention; FIG. 2 is an enlarged fragmentary horizontal cross-sectional view of the transmission-type screen shown in FIG. 1; FIG. 3 is an enlarged fragmentary horizontal cross-sectional view of the transmission-type screen shown in FIG. 1; FIG. 4 is an enlarged fragmentary cross-sectional view of a transmission-type screen according to the first embodiment of the present invention; FIGS. 5A and 5B are fragmentary cross-sectional and rear elevational views, respectively, of a transmission-type screen according to a further embodiment of the present invention; FIGS. 6A and 6B are fragmentary cross-sectional and rear elevational views, respectively, of a modification of the transmission-type screen shown in FIGS. 5A and 5B; FIGS. 7A and 7B are fragmentary cross-sectional and rear elevational views, respectively, of another modification of the transmission-type screen shown in FIGS. 5A and 5B; FIG. 8 is a fragmentary perspective view, partly cut away, of a transmission-type screen according to a fourth embodiment of the present invention; FIG. 9 is an enlarged fragmentary horizontal cross-sectional view of the transmission-type screen shown in FIG. 8; FIG. 10 is a fragmentary perspective view of a transmission-type screen according to a fifth embodiment of the present invention; FIG. 11 is an enlarged fragmentary horizontal cross-sectional view of a transmission-type screen according to a sixth embodiment of the present invention; FIG. 12 is a fragmentary perspective view, partly cut away, of a transmission-type screen according to an seventh embodiment of the present invention; FIG. 13 is an enlarged fragmentary horizontal cross-sectional view of the transmission-type screen shown in FIG. 12; FIG. 14 is an enlarged fragmentary horizontal cross-sectional view of a transmission-type screen according to a eighth embodiment of the present invention; FIG. 15 is a fragmentary perspective view, partly cut away, of a transmission-type screen according to a ninth embodiment of the present invention; FIG. 16 is an enlarged fragmentary horizontal cross-sectional view of the transmission-type screen shown in FIG. 15; FIG. 17 is a schematic view of a transmission-type video projection television system; FIGS. 18A and 18B are tables of antistatic processes and electrostatic potentials of different screens; and FIG. 19 is a graph showing electrostatic potentials of the different screens as they decrease with time. Like or corresponding parts are denoted by like or corresponding reference characters throughout views. A transmission-type screen according to the present invention is designed for use in an integral transmission-type video projection television system as shown in FIG. 17. As shown in FIG. 17, the transmission-type video projection television system has a projector 5 for projecting an image onto a transmission-type screen mounted in a front opening in a projection television housing. A transmission-type screen according to a first embodiment of the present invention will be described below with reference to FIGS. 1 through 4. The transmission-type screen shown in FIGS. 1 through 3 is of a double-lens structure comprising a circular Fresnel lens 1 and a lenticular lens 11 which are positioned closely to each other in parallel relationship. The lenticular lens 11 has a plurality of spaced black stripes 14 (see FIGS. 2 and 3) printed on or otherwise applied to an exit-side surface 13 remote from the Fresnel lens 1. When rays 41 of light are incident perpendicularly to the lenticular lens 11 or rays 42 of light are incident obliquely to the lenticular lens 11, as shown in FIG. 3, they are focused by an entrance-side lens surface 12 onto the exit-side lens surface 13, and then are diverged by the exit-side lens surface 13 as they leave the lenticular lens 11. The black stripes 14 are positioned between the lens elements of the exit-side lens surface 13, and serve to absorb and block external light rays that are incident on the exit-side lens surface 13. The exit-side surface 13 and the entrance-side surface 12 of the lenticular lens 11 will also be referred to as the exit-side surface (a) and the entrance-side surface (b), respectively. The Fresnel lens 1 also has an exit-side surface (c) which faces the entrance-side surface (b) of the lenticular lens 11 and an entrance-side surface (d). When the transmission-type screen mounted in the transmission-type video projection television system is electrostaticalyly charged, dust or dirt particles would be attached to the exit-side surface (a) of the lenticular lens 11 and the entrance-side surface (d) of the Fresnel lens 1. Since the entrance-side surface (d) of the Fresnel lens 1 is located within the system, any dust or dirt deposits could not be wiped off. When the exit-side surface (a) of the lenticular lens 11 is rubbed to wipe off dust or dirt particles, it would be triboelectrically charged up to an electrostatic potential of up to 10 KV, and at the same time the entrance-side surface (d) of the Fresnel lens 1 would also be triboelectrically charged up to an electrostatic potential of up to 10 KV. Therefore, both the exit-side surface (a) and the entrance-side surface (d) would attract dust or dirt particles when the exit-side surface (a) is rubbed. According to the first embodiment of the present invention, the electric resistance of the exit-side surface (a) of the lenticular lens 11 is 1 × 10 9 Ω or less, so that the screen will not be electrostatically charged undesirably when rubbed to wipe off dust or dirt particles. More specifically, each of the black stripes 14 is formed as an electrically conductive layer A of a material having a surface resistance of 1 × 10 9 Ω or less by printing, coating, evaporation, adhesive bonding, or the like, as shown in FIG. 3. The surface resistances of the surfaces (a), (b), (c), (d) of the screen according to the first embodiment were measured in an experiment. The exit-side surface (a) was measured in both the directions indicated by the arrows X and Y (see FIG. 1). As shown in the row indicated by β in FIGS. 18A and 18B, the resistance of the exit-side surface (a) of the lenticular lens 11 was 0.8 × 10 11 Ω in the X direction and 2.2 × 10 4 Ω in the Y direction, the resistance of the entrance-side surface (b) of the lenticular lens 11 was 0.42 × 10 11 Ω, the resistance of the exit-side surface (c) of the Fresnel lens 1 was 1.2 × 10 11 Ω, and the resistance of the entrance-side surface (d) of the Fresnel lens 1 was 1.2 × 10 11 Ω. The resistance of the exit-side surface (a) of the lenticular lens 11 in the Y direction, in which electric conductivity appears, was much lower than the resistance thereof in the X direction. When the exit-side surface (a) of the lenticular lens 11 was rubbed, the exit-side surface (a) and the entrance-side surface (d) of the Fresnel lens were triboelectrically charged to an electrostatic potential of 0 V, i.e., they were not electrostatically charged at all. This appears to be because when the exit-side surface (a) is rubbed, any electrostatic potential that is triboelectrically developed on the exit-side surface (a) is instantaneously removed by the electrically conductive black stripes 14. Therefore, no electrostatic charge is transferred to the entrance-side surface (d) of the Fresnel lens 1. When the entrance-side surface (d) of the Fresnel lens 1 was rubbed, it was charged to an electrostatic potential of 8 KV, but the exit-side surface (a) of the lenticular lens 11 was charged to an electrostatic potential of 0 V, i.e., was not electrostatically charged at all. The entrance-side surface (d) was charged onto to 8 KV because the originally developed electrostatic charge thereof was reduced by the electrically conductive black stripes 14 on the exit-side surface (a) of the lenticular lens 11. Unlike the conventional antistatic agents such as surface-active agents, the electrically conductive black stripes 14 are not worn away by rubbing, and can be used semipermanently. FIG. 4 fragmentarily shows the transmission-type screen according to the first embodiment of the present invention. While only a circular Fresnel lens 1 is shown in FIG. 4, the screen also has a lenticular lens as shown in FIG. 1. According to the first embodiment, an electrically conductive layer A is attached to each axial step 3 on its exit-end surface 2 or (c). When rays 43 of light are incident perpendicularly to the Fresnel lens 1 or rays 44 of light are incident obliquely to the Fresnel lens 1, they are bent by the Fresnel lens 1 and transmitted out of the exit-side surface (c) toward a focused point. An incident ray 45 of light is applied to an axial step 3 and divided thereby into rays 46 of light, one entering the step 3 and one reflected by the step 3. These rays 46 are not directed toward the focused point, and hence are not necessary. Therefore, each of the axial steps 3 may be utilized for other purpose, i.e., to support the electrically conductive layer A. The electrically conductive layers A are made of a material having a surface resistance of 1 × 10 9 Ω or less and is attached to each axial step 3 by printing, coating, evaporation, adhesive bonding, or the like. An experiment was conducted to measure the surface resistances of the surfaces (a), (b), (c), (d) of the screen according to the first embodiment. As shown in the row indicated by γ in FIGS. 18A and 18B, the resistance of the exit-side surface (c) of the Fresnel lens 1 was 1.8 × 10 8 Ω, the resistance of the entrance-side surface (d) of the Fresnel lens 1 was 1.4 × 10 11 Ω, the resistance of the exit-side surface (a) of the lenticular lens was 1.4 × 10 11 Ω, and the resistance of the entrance-side surface (b) of the lenticular lens was 3.5 × 10 11 Ω. When the exit-side surface (a) of the lenticular lens was rubbed, the exit-side surface (a) and the entrance-side surface (d) of the Fresnel lens were triboelectrically charged to electrostatic potentials of 500 V and 250 V, respectively. Although these electrostatic potentials were not nil, they were much lower than those of the corresponding surfaces of the conventional transmission-type screen as indicated in the row α in FIGS. 18A and 18B. The electrostatic potentials thus developed on the surfaces (a), (d) of the transmission-type screen as indicated in the row γ in FIGS. 18A and 18B disappear in a short period of time, as indicated by curves γ1, γ2 in FIG. 19, since they are much lower than those of the corresponding surfaces of the conventional transmission-type screen as indicated in the row α in FIGS. 18A and 18B and also by curves α1, α2 in FIG. 19. Therefore, less dust or dirt particles are attraced to these surfaces (a), (d) of the screen according to the first embodiment. When the exit-side surface (a) of the lenticular lens is rubbed, it may be charged up to an electrostatic potential of 10 KV as it has not antistatic or electrically conductive layer. However, since the resistance of the exit-side surface (c) of the Fresnel lens is 1.8 × 10 8 Ω, the electrostatic potential developed on the exit-side surface (a) is instantaneously reduced, in about several tens of munites, as indicated by the curve γ1 in FIG. 19. The electrostatic charge which was transferred to the entrance-side surface (d) of the Fresnel lens was 250 V, which was half 500 V of the exit-side surface (a), owing to the electrically conductive layers A on the axial steps 3 of the exit-side surface (c) of the Fresnel lens. When the entrance-side surface (d) of the Fresnel lens was rubbed, it was chargded to an electrostatic potential of 3 KV, but the exit-side surface (a) of the lenticular lens was charged to only an electrostatic potential of 1 KV. This also proves the effectiveness of the electrically conductive layers A on the exit-side surface (c) of the Fresnel lens. According to a second embodiment of the present invention, as indicated by the imaginary lines in FIG. 3, an elecrically conductive layer A of a material having a surface resistance of 1 × 10 9 Ω or less is applied in each of parallel spaced grooves 15 between adjacent parallel ridges or lens elements on the entrance-side surface 12 of the lenticular lens 11 by printing, coating, evaporation, adhesive bonding, or the like. FIGS. 5A and 5B fragmentarily show a transmission-type screen according to a third embodiment of the present invention. In FIGS. 5A and 5B, the transmission-type screen includes a Fresnel lens 1 having a plurality of parallel spaced grooves 16 defined in its entrance-side surface (d) for increasing a vertical field of view. An electrically conductive layer A of a material having a surface resistance of 1 × 10 9 Ω or less is applied in each groove 16 by printing, coating, evaporation, adhesive bonding, or the like. The electrically conductive layers A are as effective to remove or reduce an electrostatic charge as those of the first and second embodiments described above. As an alternative, metal wires may be used in place of the electrically conductive layers A. FIGS. 6A and 6B fragmentarily show a modification of the third embodiment. According to this modication, electrically conductive layers A of a material having a surface resistance of 1 × 10 9 Ω or less are applied in a grid pattern to the entrance-side surface (d) of a Fresnel lens 1. According to another modification shown in FIGS. 7A and 7B, electrically conductive layers A of a material having a surface resistance of 1 × 10 9 Ω or less are applied in an oblique grid pattern to the entrance-side surface (d) of a Fresnel lens 1. When the entrance-side surface (d) of the Fresnel lens 1 in each of the above modifications was rubbed, it was charged to an electrostatic potential of about 0 V, i.e., was not electrostatically charged. In FIGS. 6A, 6B and 7A, 7B, a black grid-like meshwork of metal wires B may be used instead of the electrically conductive layer A, the metal wires B being partly embedded in the entrance-side surface (d). The grid pattern of electrically conductive layer A or the black grid-like meshwork of metal wires B absorbs and blocks incident rays of light, lowering the transmittance of light through the Fresnel lens 1. It is necessary that the width of the electrically conductive layer A or the metal wires B be selected such that the transmittance of light through the Fresnel lens of the modified screen will be 95 % or more of that which is achieved before the grid pattern or grid-like meshwork is applied. FIGS. and 9 show a transmission-type screen according to a fourth embodiment of the present invention. The transmission-type screen shown in FIGS. 8 and 9 comprises a Fresnel lens 1 and an array of parallel optical fibers 21, the Fresnel lens 1 and the optical fiber array being positioned closely parallel to each other. Grooves 22 defined between the optical fibers 21 are filled with adhesive layers C which bond the optical fibers 21 together. The adhesive layers or fillings C also serve as black stripes to absorb and block external light applied thereto. The adhesive material is mixed with an electrically conductive material such that the resulting adhesive layers C have a surface resistance of 1 × 10 9 Ω or less, and then the mixture is applied as the adhesive layers C to bond the optical fibers 21. Alternatively, after the optical fibers 21 are bonded together by the adhesive layers 21, an electrically conductive layer of a material having a surface resistance of 1 × 10 9 Ω or less is applied to the surface of each of the adhesive layers 21 by printing, coating, evaporation, adhesive bonding, or the like. The transmission-type screen shown in FIGS. 8 and 9 is effective to prevent an electrostatic charge buildup when the exit-side surface (a) of the optical fiber array is rubbed, as with the first and second embodiments of the present invention. As shown in FIG. 10, a transmission-type screen according to a fifth embodiment of the present invention has parallel spaced electrically conductive layers D in the form of black foils or plates of silver, copper, aluminum, or the like. The electrically conductive layers D are embedded in or attached to the respective printed black stripes on the lenticular lens 11. FIG. 11 fragmentarily illustrates a lenticular lens 11 of a transmission-type screen according to a sixth embodiment of the present invention. The lenticular lens 11 includes metal wires E partly embedded in the respective printed black stripes of the lenticular lens 11 and thinner metal wires E placed in the respective grooves 15 in the entrance-side surface 12 of the lenticular lens 11. These metal wires E have partly exposed surfaces. FIGS. 12 and 13 show a transmission-type screen according to an seventh embodiment of the present invention. The transmission-type screen includes a lenticular lens 11 having a plurality of spaced parallel black stripes 14 each formed as an electrically conductive layer A of a material having a surface resistance of 1 × 10 9 Ω or less and attached to the exit-side surface by printing, coating, evaporation, adhesive bonding, or the like. The black stripes 14 are interconnected by a metal tape 31 extending along the outer peripheral edge of the lenticular lens 11. When the entrance-side surface (d) of the Fresnel lens 1 was rubbed, the surfaces (a), (b), (c) were not electrostatically charged, but the entrance-side surface (d) was electrostatically charged to 3 KV at its central region and 1 KV at its outer peripheral region, as shown in the row indicated by ε in FIGS. 18A and 18B. These electrostatic potentials are much lower than the electrostatic potential of 8 KV developed on the entrance-side surface (d) of the screen as indicated by β, where the black stripes are not interconnected by any metal tape. FIG. 14 fragmentarily shows a transmission-type screen according to a eighth embodiment of the present invention. In FIG. 14, the black stripes 14 are interconnected by an electrically conductive layer A of a material having a surface resistance of 1 × 10 9 Ω or less and attached to the exit-side surface of the lenticular lens 11 by printing, coating, evaporation, adhesive bonding, or the like. According to a ninth embodiment shown in FIGS. 15 and 16, the entire peripheral edges of a transmission-type screen composed of a Fresnel lens 1 and a lenticular lens 11 are surrounded and held by a frame 32 of an electrically conductive material or metal which is kept in contact with the entire peripheral edges of the screen. The frame 32 has a portion contacting the black stripes 14 on the exit-side surface of the lenticular lens 11. In the seventh through ninth embodiments, the electrically conductive layer A, the metal tape 31, and the frame 32 are grounded by a ground wire for better prevention of an electrostatic charge buildup and reduction of electrostatic potentials that are developed. The material of the electrically conductive layer used in each of the above embodiments may be either a mixture of a printing paste, a paint, or an adhesive and carbon whose proportion is selected such that the mixture has a surface resistance of 1 × 10 9 Ω or less, or a mixture of carbon and another electrically conductive material such as copper, silver, or other metal at proportions selected such that the mixture has a surface resistance of 1 × 10 9 Ω or less. In each of the above embodiments, the transmission-type screen is of a double-lens structure. However, the principles of the present invention are also applicable to a single-lens transmission-type screen comprising a single lens which has a Fresnel lens surface on an entrance side and a lenticular lens surface on an exit side. In such a single-lens transmission-type screen, one or both of the Fresnel and lenticular lens surfaces may be processed for antistatic treatment. Similarly, the transmission-type screen according to the present invention may be composed of a combination of three or more lenses. Furthermore, the antistatic treatment according to the present invention may be applied to a screen of a two-component reflection-type video projection television system which comprises a front projector for projecting an image onto the screen spaced from the projector so that the image reflected by the screen can be viewed by observers. A transmission-type video projection television system employs a transmission-type screen for displaying an image projected from a rear projector for visual observation by an observer in front of the screen. The transmission-type screen has Fresnel and lenticular lenses, one of which has an electrically conductive layer or a metal member on its surface to prevent the lens from being electrostatically charged, so that dust or dirt particles will not be attracted to the screen.

Claims: A transmission type screen comprising: a lens (1, 11) for transmitting rays of light therethrough ,and a plurality of electrically conductive layers (14, 31, 32, A, C, D) or a metal member (B, E) mounted on a surface (12, 13, a, b, c, d) of said lens (1, 11) for preventing said surface (12, 13, a, b, c, d) from being electrostatically charged characterized in that said lens comprises a Fresnel lens (1) and either a lenticular lens (11) or an array of optical fibers (21) which are positioned closely parallel to each other, wherein said Fresnel lens (1) has a plurality of axial steps (3) on the exit-side surface (2, c) thereof, and said plurality of electrically conductive layers (A) are attached to said steps (3). A transmission type screen according to claim 1, characterized in that said electrically conductive layers (14, 31, 32, A, C, D) are made of an electrically conductive material having a surface resistance of 1 x 10 9 Ω or less. A transmission type screen according to claim 1 or 2, characterized in that said lenticular lens (11) has a plurality of black stripes (14) on the exit-side surface (a) thereof for absorbing and blocking rays of light, said black stripes (14) being made of an electrically conductive material having a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to any of claims 1 to 3, characterized in that said lenticular lens (11) has a plurality of parallel spaced grooves (15) defined in the entrance-side surface (12) thereof, and said plurality of electrically conductive layers (A) are disposed in said grooves (15), respectively, said electrically conductive layers (A) being made of a material having a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to any of claims 1 to 4, characterized in that said Fresnel lens (1) has a plurality of parallel spaced grooves (16) defined in an entrance-side surface (d) thereof for increasing a vertical field of view, and said plurality of electrically conductive layers (A) or metal wires (B) are disposed respectively in said grooves (16), said electrically conductive layers (A) being made of a material having a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to any of claims 1 to 5, characterized in that said Fresnel lens (1) has said electrically conductive layers (A) disposed in a grid pattern on the entrance-side surface (d) thereof, said electrically conductive layers (A) being made of a material having a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to any of claims 1 to 5, characterized in that said Fresnel lens (1) has a grid-like meshwork of metal wires (B) disposed on the entrance-side surface (d) thereof. A transmission-type screen according to claim 3 or 4, characterized in that said lenticular lens (11) further includes a plurality of metal wires (E) disposed respectively in said black stripes (14) or said grooves (15) as has partly exposed surfaces. A transmission-type screen according to any of claims 1 to 7, characterized in that said lenticular lens (11) has a plurality of black, parallel spaced electrically conductive layers (A) disposed on the exit-side surface (a) thereof, and a plurality of black stripes (14) disposed respectively on said electrically conductive layers (A). A transmission-type screen according to claim 1, characterized in that said optical fibers (21) are bonded by adhesive layers (C) each comprising a mixture of an adhesive and an electrically conductive material which is added at a proportion such that said mixture has a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to claim 1 or 10, characterized in that said optical fibers (21) are bonded by adhesive layers (e), and include electrically conductive layers disposed respectively on said adhesive layers (C), each of said electrically conductive layers being made of a material having a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to claim 1, characterized in that said lenticular lens (11) has a plurality of parallel spaced black stripes (14) disposed on the exit-side surface (a) thereof and an electrically conductive layer (31) interconnecting said black stripes (14) and extending along outer peripheral edges of said lenticular lens (11), said electrically conductive layer (31) being made of a material having a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to claim 1 or 12, characterized in that said lenticular lens (11) has a plurality of parallel spaced black stripes (14) disposed on the exit-side surface (a) thereof and an electrically conductive layer (A) interconnects said black stripes (14) and is disposed over said exit-side surface (a), said electrically conductive layer (A) being made of a material having a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to claim 1 , 12 or 13, characterized in that said lenticular lens (11) has a plurality of parallel spaced black stripes (14) disposed on the exit-side surface (a) thereof, wherein a frame (32) of an electrically conductive material or a metal surrounds outer peripheral edges of said Fresnel lens (1) and said lenticular lens (11), said electrically conductive material having a surface resistance of 1 x 10 9 Ω or less. A transmission-type screen according to claim 12, 13, or 14, characterized by a ground wire by which said electrically conductive layer or said frame is grounded. A transmission-type screen according to any of the preceding claims, characterized in that electrically conductive layer (14, 31, 32, A, C, D) is made of a mixture of one of a printing paste, a paint, and an adhesive and carbon whose proportion is selected such that said mixture has a surface resistance of 1 x 10 9 Ω or less, or a mixture of carbon and another electrically conductive material at proportions selected such that said mixture has a surface resistance of 1 x 10 9 Ω or less. A video projection television system comprising a transmission-type screen according to any of the preceding claims.

Inventors: MATSUMURA TOSHIAKI, MITANI KATSUAKI, YASUMATSUYA NOBORU, MATSUMURA, TOSHIAKI, MITANI, KATSUAKI, YASUMATSUYA, NOBORU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: G03B21
IPC codes: G02B3, G03B21