JP3665199B2 - Manufacturing method of transmission type screen - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a transmissive screen used in a rear projection television or the like.
[0002]
[Prior art]
Sheets on which optical elements such as Fresnel lenses, lenticular lenses, prisms, light diffusion layers, external light absorption layers, and antireflection layers are formed as transmissive screens used in rear projection televisions (hereinafter referred to as optical components such as Fresnel lenses) A sheet on which elements are formed is referred to as a “sheet member”), and a plurality of sheets are arranged between the light source and the observer to identify the range of the field of view and to obtain an image with high contrast and uniform brightness. Is used. In general, a Fresnel lens sheet having a function of narrowing image light from a CRT or image light transmitted through a liquid crystal within a certain angle range, and a lenticular having a function of spreading the image light to a suitable angle range on the observer side A transmissive screen combined with a lens sheet is used.
[0003]
In a transmission screen in which a plurality of sheet members are stacked, a light-transmitting thermoplastic resin is often used as a material for the sheet members. A sheet member made of thermoplastic resin has low rigidity, and a difference in expansion and contraction occurs between the front and back surfaces of the sheet member due to changes in the temperature and humidity of the environment where the transmissive screen is installed. The so-called “floating” phenomenon occurs. For this reason, not only the appearance of the transmissive screen is distorted but also the image resolution is deteriorated and coloring occurs.
[0004]
In order to solve this problem, a plurality of sheet members are warped so that their curvatures are different in the same direction or warped in the opposite direction, and the sheet members are fixed to each other by fixing the periphery of the sheet members. Transmission screens with improved adhesion have been studied (Japanese Patent Laid-Open Nos. 58-178342, 59-16938, 60-61738, 62-146129). Gazette, JP-A-2-72341). As a method of giving warpage to the sheet members constituting these conventional transmission type screens, a translucent resin sheet without warpage, which is provided with optical elements by extrusion molding or the like, is produced, and this sheet is cut into a predetermined size. After that, the sheet is placed on a curved mold and the sheet is molded into a curved shape by heating the sheet for a long time at a temperature equal to or lower than the thermal deformation temperature so that the residual stress at the time of molding does not appear as distortion. It was done.
[0005]
Japanese Patent Application Laid-Open No. 5-204048 proposes a method of forming a curved shape by providing a temperature difference between the front surface and the back surface of the sheet in the process of applying an optical element to the translucent resin sheet by extrusion molding. ing.
[0006]
[Problems to be solved by the invention]
The method of bending the sheet member by heating at a temperature equal to or lower than the heat distortion temperature has a problem that a long heating time is required to obtain a curved shape. In addition, when a sheet member produced by this method is set on a projection television and held in a flat state, the sheet member is forced to return to its original flat shape, and the amount of warpage of the sheet member is reduced. However, there is a problem that floating tends to occur due to changes in the temperature and humidity of the environment where the projection television is installed.
[0007]
The present invention has been made in view of the above problems, and provides a method for manufacturing a transmission screen in which a curved shape does not change with time and a plurality of sheet members can maintain a stable adhesion state. With the goal.
[0008]
[Means for Solving the Problems]
The manufacturing method of the transmission type screen of the present invention that solves the above-mentioned problem is the method of extruding a translucent thermoplastic resin at a molding temperature such that the extruded sheet-like molded product has a curved shape, and the bending The molded product having the shape formed is placed on a mold having a curved shape and heated at a temperature equal to or lower than the heat deformation temperature, thereby warping the sheet member constituting the transmission screen. To do. According to the present invention, a known type of transmissive screen having a two-lens combination of a lenticular lens sheet and a Fresnel lens sheet and other various configurations can be manufactured.
[0009]
The heat distortion temperature as used in the field of this invention means the temperature calculated | required by the test method prescribed | regulated to JISK7202 or ASTM D648.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In order to give a warp so that the molded product has a curved shape when extruding a translucent thermoplastic resin, the surface of the sheet and the surface of the translucent resin sheet are added in the process of extruding the translucent resin sheet. What is necessary is just to make a temperature difference with a back surface. In order to create a temperature difference between the front and back surfaces of the sheet, the temperature of the mold that molds both sides of the molded product is varied, cold air is blown to the front or back surface of the sheet, and the front or back surface of the sheet is heated with a heater. A method may be employed in which a temperature difference is provided on the front and back surfaces of the sheet by means of heating or the like, and then cooling is performed while performing a pulling operation with a sheet take-up roll or the like.
[0011]
When the sheet member is heated at a temperature equal to or lower than the thermal deformation temperature, the extruded molded product is placed on a curved mold with a desired amount of warpage, and hot air is blown onto the molded product, or infrared rays are irradiated onto the molded product. Just do it.
[0012]
During extrusion molding, if the sheet member is to be warped only by making a temperature difference between the front surface and the back surface, the range of molding temperatures that can be selected to obtain the desired amount of warpage is narrow, and the condition setting is difficult. Further, the amount of warpage applied to the sheet member by this method is limited to a certain range of size. Further, in this method, since the difference in residual stress amount remains between the front surface and the back surface, even if a desired warpage amount is obtained in the manufacturing stage of the sheet member, the warpage amount gradually increases thereafter. Subsequently, when the sheet member is combined with another sheet member, the adhesion between the sheet members becomes too strong, and a slight vibration is given to the sheet member when the projection television is transported. There are times when it is attached.
[0013]
In the present invention, when extruding a translucent thermoplastic resin, after giving a warp so that the molded product has a curved shape, the molded product is placed on a curved mold, Since the heating is performed at a temperature equal to or lower than the thermal deformation temperature, the stress remaining at the time of extrusion molding is removed by heating (so-called annealing) the sheet in a later step. That is, in the present invention, the difference in the amount of shrinkage between the front and back surfaces of the sheet member, which is generated by removing residual stresses of different sizes on the front and back surfaces, which are generated during the extrusion process, is utilized. Thus, warpage is given. Accordingly, since it is not necessary to secure a warping amount that is finally required at the time of extrusion molding, the degree of freedom in setting the conditions for extrusion molding is high. Further, since the warp is given in advance at the time of extrusion molding, the annealing time is short. Since the sheet member obtained by the method of the present invention is stable with the residual stress removed, the amount of warpage does not increase or decrease even after a long time.
[0014]
Examples of the translucent thermoplastic resin used in the present invention include polymethyl methacrylate, methyl methacrylate-styrene copolymer, polystyrene, polycarbonate, acrylonitrile-styrene copolymer, methyl methacrylate-butadiene-styrene copolymer, acrylonitrile-butadiene. -Although a styrene copolymer etc. are mentioned, it is not limited to these.
[0015]
【Example】
Hereinafter, the present invention will be described in detail by way of examples. FIG. 1 shows a side sectional view of an example of a sheet member constituting a transmission screen manufactured by the method of the present invention. The transmission screen 1 includes a lenticular lens sheet 2 and a Fresnel lens sheet 3. Light from the light source is projected onto the transmissive screen 1. A convex black stripe is generally formed in a portion of the surface on the light output side of the lenticular lens sheet 2 other than the portion from which the projection light is emitted. In FIG. 1, the lenticular lens sheet 2 and the Fresnel lens sheet 3 are shown separated from each other in order to clarify the shape when no stress is applied. In the state of use, the peripheral portions of both sheets are fixed so that they are in close contact with each other.
[0016]
The lenticular lens sheet 2 has a shape curved in the vertical direction so that the surface facing the Fresnel lens sheet 3 disposed on the light source side that projects the image light is convex. For example, when the amount of warpage (maximum depth of warpage) is measured while being supported while supporting the short side of a lenticular lens sheet cut to 1016 mm × 762 mm, the amount of warpage is 70 mm. The preferred range of warpage varies depending on the size of the lens sheet and usage conditions, but the warpage when measured by this method is preferably in the range of 30-100 mm for lens sheets having a screen size of 40-50 inches. The Fresnel lens sheet 3 is warped so that the same direction as the lenticular lens sheet 2 is convex. The amount of warping of the Fresnel lens sheet 3 is smaller than the amount of warping of the lenticular lens sheet 2.
[0017]
The transmissive screen manufactured by the method of the present invention has a peripheral portion fixed to the rear by a predetermined method such as sticking with an adhesive tape or sandwiching between frames so that the lenticular lens sheet 2 and the Fresnel lens sheet 3 are in close contact with each other. Mounted on projection TV.
[0018]
FIG. 2 shows a schematic configuration diagram of an example of an extrusion molding machine used in the present invention. An example of the extrusion molding method in the present invention will be described with reference to FIG. First, a light diffusion agent (for example, acrylic cross-linked beads) is dispersed in pellet-shaped polymethyl methacrylate (heat deformation temperature 92 ° C.) melted at a temperature of about 250 ° C., and a T die 5 connected to an extruder 4 is used. The polymethylmethacrylate containing the light diffusing agent is extruded into a sheet in a molten state. The melted sheet-like material has a shape in which the heated first roll 6 having a shape obtained by inverting the light incident side lenticular lens, and the light emitting side lenticular lens and the black stripe forming convex portion are reversed. Between the second roll 7 (for example, heated to a temperature 30 ° C. higher than that of the first roll 6) and the melted sheet-like material on the second roll 7 about a half turn. Further, the sheet-like material melted so as to be wound around the third roll 8 having a smooth surface heated to, for example, a temperature 20 ° C. higher than that of the second roll 7 is guided about a half turn. As a result, a lenticular lens sheet having a predetermined lenticular lens shape and black stripe forming convex portions on the light incident side surface and the light output side surface is obtained. In the extrusion molding machine having the configuration shown in FIG. 2, the temperature of the resin at the outlet of the third roll 8 is adjusted by adjusting the temperature of the third roll 8 so that the front surface and the back surface have a temperature difference of 5 ° C., for example. can do.
[0019]
The sheet-like material coming out of the third roll 8 is cooled to the heat deformation temperature or lower while being pulled by the take-up rolls 9a and 9b. Thereafter, the sheet is cut into a desired size by the cutting machine 10. Since the surface of the sheet-like material is at a lower temperature than the back surface at the third roll 8 outlet, a stress stress larger than that on the back surface is generated on the front surface by the pulling operation by the take-up rolls 9a and 9b.
[0020]
The cut sheet-like material 11 is set on a warp die 12 as shown in FIG. 3 after a light-shielding layer is formed on the surface of the black stripe-forming projection by applying a light-shielding substance. . The sheet-like material 11 is heated and warped by blowing hot air having a temperature lower than the thermal deformation temperature of polymethyl methacrylate (for example, hot air at 80 ° C. for 5 minutes). A lenticular lens sheet is obtained. If a warp amount of 70 mm is obtained for a 1016 mm × 762 mm lenticular lens sheet, the warp depth of the mold 12 shown in FIG. 3 may be 70 mm.
[0021]
Warpage of the lenticular lens sheet when the lenticular lens sheet manufactured by the method of the present invention is combined with the Fresnel lens sheet and set in a cabinet of a rear projection TV at normal room temperature and humidity (25 ° C., 50% RH). The amount of change over time was measured. Also, a lenticular lens sheet made of the same material and flat on the whole is later warped at a temperature lower than the heat deformation temperature (70 ° C., 18 hours) (prior art 1) and by an extrusion molding method. Changes in warpage over time when a conventional lenticular lens sheet (conventional technology 2) curved with a temperature difference between the front and back surfaces in the process of imparting a lens shape to a transparent resin sheet is left in a room with the same temperature and humidity. It was measured. The measurement results are shown in FIG. Here, the warpage amount is a value obtained by measuring the maximum depth of warpage in a state where the lenticular lens sheet is removed from the frame of the cabinet and suspended while supporting the short side at two points. Immediately after measuring the amount of warpage, the lenticular lens sheet was reset on the frame of the cabinet.
[0022]
As is apparent from FIG. 4, in the lenticular lens sheet manufactured by the conventional method, the amount of warpage increases (conventional technology 2) or decreases (conventional technology 1), whereas it is manufactured by the method of the present invention. The warped amount of the lenticular lens sheet is stable, and the warped amount does not increase or decrease.
[0023]
【The invention's effect】
If a transmissive screen is manufactured by the method of the present invention, the amount of warpage does not change with time, and even when a plurality of lens sheets are used in combination for a long time, gaps are generated between the sheet members and floated. There is no possibility that the image quality is deteriorated, or the close contact between the lens sheets becomes too strong to cause rubbing and scratches.
[Brief description of the drawings]
FIG. 1 is a side sectional view of an example of a sheet member constituting a transmission screen manufactured according to the present invention.
FIG. 2 is a schematic configuration diagram of an example of an extrusion molding machine used in the present invention.
FIG. 3 is a diagram showing a state in which a sheet-like molded product is placed on a curved mold.
FIG. 4 is a diagram showing a change over time in the amount of warpage between a lenticular lens sheet manufactured according to the present invention and a lenticular lens sheet manufactured by a conventional method.
[Explanation of symbols]
1: transmission screen 2: lenticular lens sheet 3: Fresnel lens sheet 4: extruder 5: T die 6: first roll 7: second roll 8: third roll 9a, 9b: take-up roll 10: cutting machine 11 : Sheet material 12: Warpage imparting type

Claims (1)

The light-transmitting thermoplastic resin is extruded at a molding temperature such that the extruded sheet-like molded product has a curved shape, and the curved shaped molded product is placed on a mold having a curved shape. A method of manufacturing a transmissive screen, characterized in that the sheet-shaped member constituting the transmissive screen is warped by heating at a temperature equal to or lower than the heat distortion temperature.

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