Description of the Related Art The viewing screen of a projection television receiver (hereinafter "projection television screen") is usually wider than the viewing screen of a conventional television receiver and thus weighs much more than the viewing screen of the conventional television receiver. A projection screen should be mechanically strong but not too heavy. Since a projection television screen is an exposed component of the television receiver, it is vulnerable to impact damage when the receiver is handled, used or moved.

A conventional projection television screen is made from an extruded polymethylmetacrylate(PMMA) sheet, which may be either a plain sheet or a sheet with shapes formed upon it to facilitate its various functions. PMMA sheets are heavy and have low mechanical strength and especially low impact strength. When a conventional projection screen is broken by an external impact, the pieces are very dangerous because they have many sharp edges.

SUMMARY OF THE INVENTION An object of the present invention is to provide a projection television screen that it is safe, light, and mechanically strong.

Another object of the present invention is to provide a continuous-mode process for making a projection television screen that is safe, light, and mechanically strong.

In order to accomplish the above objects, the projection television screen of the present invention is made of a thin transparent film with high mechanical strength. Shapes may be formed on the surface of the film made of photo-curing resin in order to perform the necessary functions. After that, another type of film could be attached onto the shape formed on the substrate.

The resultant structure according to the present invention is used as a projection television screen.

Yet another object of the present invention is to provide a manufacturing process for providing a screen which is described above. While in prior art a screen has been manufactured in a non-continuous way because only a planar shaped die is available in the prior art, with the manufacturing process of the present invention, a roll-shaped die can be easily fabricated using an electroforming method. Thus, continuous manufacture of a screen can be accomplished.

BRIEF DESCRIPTION OF DRAWINGS These and other advantages and features of the present invention can be better understood with reference to the following description which will be described in conjunction with the accompanying drawings in which: FIG. 1 illustrates the use of a projection television screen.

FIG. 2 illustrates the structure of a projection television screen according to an embodiment of the present invention.

FIG. 3 illustrates the detailed structure of the projection television screen shown in Figure 2.

FIG. 4 illustrates a process of manufacturing a projection television screen according to an embodiment of the present invention.

FIG. 5 illustrates a conventional process of manufacturing an objective lens. mG. 6 illustrates a conventional process of manufacturing a Fresnel lens.

FIG. 7 illustrates a second conventional process of manufacturing a Fresnel lens.

FIG. 8 illustrates a process of fabricating an electroforming roll suitable for manufacturing the Fresnel lens and the objective lens of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in Figures 2 and 3, a projection television screen 1 of the present invention comprises: a Fresnel lens 4; an objective lens 5 adjacent to and optically aligned with the Fresnel lens 4; and a transparent protective sheet 6 adjacent to the surface of the objective lens 5 furthest from the fresnel lens 4.

The Fresnel lens 4 comprises: a first transparent substrate 8; and a phase grating 7 mounted on the surface of the first substrate 8 nearest the objective lens 5. The Fresnel lens 5 collimates light from an image protector 3 and uniformly projects the collimated light onto the surface of the objective lens nearest the Fresnel lens 4. The phase grating 7 is formed from a resin that is cured by exposure to ultraviolet light(hereinafter "ultra-violet resin") after the shape of the grating has been impressed upon the fluid resin.

The objective lens 5 comprises: a second transparent substrate 10; a plurality of lenticular structures 9 mounted on both surfaces of the second substrate 10; and an anti-reflective layer 11 mounted on the surface of the second substrate 10 furthest from the Fresnel lens 4. The objective lens 5 collects parallel red, green, and blue image beams from the Fresnel lens 4 at a predetermined position of each of the color cell. The anti-reflective layer 11 absorbs stray ambient light and thus brightens the images on the screen.

The ultra-violet resin used to make the grating 7 may also be employed to make the lenticular structures 9. The type of film used for the substrate 8 of the Fresnel lens may also be employed for the substrate 10 of the objective lens. A diffusion agent may be used, depending on the degree of light diffusion required, the ultra-violet resin used to make the grating 7. An ultra-violet curing black ink with extinction and adhesion characteristics is employed, for the anti-reflective layer 11.

The protective sheet 6 protects the Fresnel and objective lenses against damage from outside. The material of the protective sheet 6 may be the same as that of the substrate 8 of the Fresnel lens or the substrate 10 of the objective lens. If desired, various coatings such as an anti-reflection coating and a scratch-resistant coating may be applied to the protective sheet 6. The protective sheet may also be colored.

The viscosity of the ultra-violet resin used to make the grating 7 and the lenticular structures 9 ranges from 100 to 3000 cps at 25 °C. The resin transmits more than 75 % of the light incident on it. Preferably, the viscosity of the ultra-violet resin lies within the range 500 to 1500 cps at 25 "C, and the transmissivity of the resin is more than 85 %. Although the resin could be sufficiently spread on the surface of a shaping roller 12, when the viscosity is less than 100 cps, process control would not be easy and a significant amount of low-boiling point material would be lost. If the resin's viscosity were more than 3000 cps, spray coating process would be difficult and air bubbles could well be formed because the shaping roller 12 would not be sufficiently wet by the resin.

Materials which may be used for the ultra-violet resin of the grating 7 and the lenticular structures 9 include: urethane acrylate resin, epoxy acrylate resin, ester acrylate resin, ether acrylate resin, and mixtures thereof.

The transparent substrate 8 of the Fresnel lens 4, the transparent substrate 10 of the objective lens 5, and the protective sheet 6 preferably have thickness of 10-250 jim, light transmissivity of 75 % or more and a tensile strength of at least 600 kgicm2, and more preferably thickness of 50-150 jim, light transmissivity of 85 W0 or more and a tensile strength of at least 1000 kg'rn2. If the thickness were less than 10 jim or the tensile strength less than 600 kg/cm2, the screen 1 could be easily damaged and the film torn during the preparation of the screen.

If the thickness were more than 250 jim, the total thickness and weight of the screen 1 would be too great and the advantages of employing a film in the present invention would be lost. If the transmissivity were less than 75 %, the transmissivity the screen 1 would be too low.

Materials which may be used for the transparent film of the substrate 8 of the Fresnel lens, the substrate 10 of the objective lens, and the protective sheet 6 include: polyester, polyestersulfon, polyamide 6, polyamide 66, polycarbonate, polyestersulfon, polyester ketone, polyesterimide, polyacrylate, and mixtures thereof.

Fig. 4 illustrates an apparatus for making shapes on one surface or both surfaces of the substrate of the Fresnel lens 4 and the objective lens 5 according to the present invention, the apparatus comprising a shaping roller 12; a device 13 for applying liquid resin to the substrate; an ultra-violet irradiating device 14; and a roller 15 for supplying the substrate film. The shaping roller 12 is easily replaceable in order to impress one surface or both surfaces of the substrate with various shapes.

Fig. 5 illustrates a conventional apparatus used for manufacturing an objective lens. In Fig. 5, a film extruded by an extruder 17 is shaped by a shaping roller 12 and thereafter cooled by a cooling roller 18 and drawn by a drawing roller 19. Such an apparatus cannot be used for manufacturing a thin-film objective lens.

FIG. 6 illustrates a conventional process of manufacturing a Fresnel lens.

In the process shown in Fig. 6, a liquid ultraviolet resin 21 is poured into a flat mold 20 to shape a Fresnel lens. The flat mold 20 is then covered with a panel 22 which forms the substrate of the Fresnel lens.

The resin 21 is passed through a roller 23 and is exposed to an ultra-violet irradiating device 14. The conventional method of Fig. 6 is not applicable to mass production and the process can be operated only in a batch mode. A thin-film type substrate could not easily be used in the method illustrated by Figure 6.

FIG. 7 illustrates a conventional process of manufacturing a Fresnel lens using a press. In the process shown in Fig. 7, a Fresnel substrate 25 is inserted between the flat mold 20 and a planar upper die 24. The Fresnel substrate 25 is then heated, pressed, rolled and released. However, this press process has the disadvantages of long manufacturing time, and short duration of the die, and consequent low productivity.

FIG. 8 illustrates a process of manufacturing a shaping roller for forming a Fresnel lens and an objective lens according to an embodiment of the present invention. According to the present invention, the Fresnel lens 4 and the objective lens 5 can be manufactured in continuous mode due to the use of a roll shaped die rather than the planar die of the prior art.

The electroforming method illustrated in Fig. 8 may be used, for manufacturing a shaping roller. In Fig. 8, a silicone rubber die mold 26 is patterned using a planar die 20. The patterned silicone rubber die mold 26 is made into a tube-type die by a reinforcing steel tube 27. After a metal electroforming die 28, made, for example, of nickel chromium has been fabricated at the inner side of the tube-type silicone rubber die mold 26 by means of an electroforming method, the reinforcing steel tube 27 is removed, which leaves only the electroformed metal die 28. Finally the shaping roller is completed by inserting and fixing a cylindrical steel tube roller with shaft into the electroformed metal die 28.

The invention described above will be more fully understood with reference to the following Example and Comparative Example.

Example Urethane acrylate resin is used as the ultra-violet resin of the grating 7 and the lenticular structures 9. Polyester film is used for the substrate 8 of the Fresnel lens, the substrate 10 of the objective lens, and the protective sheet 6. The properties of urethane acrylate resin and polyester film used in the present example are summarized in tables 1 and 2, respectively.

The process conditions are as follows: - surface temperature: 35+5°C; and - manufacturing speed: 4 to 7 m/min.

Comparative Example A comparative product is manufactured as a prior art product.

Polymethylmetacrylate is used for the substrate 8 of the Fresnel lens and the substrate 10 of the objective lens. Urethane acrylate is used for the grating 7.

Table 1 . Properties of Urethane Acrylate Resin used in Fresnel lens and lenticular lens Item | Properties Remarks Composition Urethaneacrylate Sunkyung-UCB Co., Ltd. Viscosity(cps) 950t50 25 °C Transmission rate of 91+1 total amount of light(%) Index of Reflection 1.52#0.02 Specific Gravity 1.1 Table 2 : Properties of Polyester Film used in Protective Sheet Item Properties Remarks Composition Polyester SKC Co., Ltd. 200 protective sheet 100 Fresnel lens Thickness(µm) 50 lenticular lens Index of Reflection 1.64t0.01 Transmission rate of 91 total amount of light(%) Specific Gravity 1.4 Tensile Strength 2,500#50 (Kg/cm2) Table 3 : Properties of the Screens Item | Example Comparative 1 Example 1 protective sheet(6) j 160 1260 Weight Fresnel lens(4) 140 504 (gr) objective lens(5) 191 1250 total 491 3014 Thickness of Screen (mm) 0.85 5.00 Tensile protective sheet(6) 2500/2500 550/550 * P Strength Fresnel lens(4) 2200/2200 480/480 film (Kg/cm') ! objective lens(5) 2100/2050 500/120 0 direction (90° direction) Transmission rate of total 89 1 85 amount of light (%) Particulars | - Screen (1) diagonal length: 43 inch - Aspect ratio = 4:3 As can be seen from Table 3, the projection tv screen 1 according to an embodiment of the present invention weights of 84 % less and has tensile strength 4.5 times greater than conventional television screen.