JPH0372972B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rear projection screen for projection televisions in which a Fresnel lens and a lenticular lens are formed on a synthetic resin base material. It was an attempt to provide a screen. Rear projection screens mounted on projection televisions are known to have a Fresnel lens surface, a lenticular lens surface, or both. The Fresnel lens helps to maintain brightness especially at the periphery of the screen and achieves uniform brightness, and the lenticular lens has the effect of imparting directionality in the left and right directions, so it is best to combine both. is said to be advantageous. However, when the Fresnel lens surface and the lenticular lens surface are used in close proximity to each other in this way, a moiré phenomenon occurs, which adversely affects the image to be observed. This moiré phenomenon appears on the left and right sides of the center when a Fresnel lens and a lenticular lens intersect at a small angle. Even if they cannot be identified with a single lens, by combining the two, they can be identified with the naked eye. This moiré phenomenon is also related to the material that makes up the Fresnel lens or lenticular lens, the focal length of the Fresnel lens, the thickness of the lens, etc.
When a synthetic resin base material is used as in the present invention,
The refractive index is approximately 1.5 to 1.6, and the thickness is 0.8
~5mm, and the focal length of Fresnel lenses used for projection TVs is approximately
Considering that the distance is approximately 0.8 to 1.5 m, it has been confirmed that the dominant factor in the occurrence of moiré is the ratio of brightness and darkness due to the ratio of the lens widths between the Fresnel lens and the lenticular lens. One possible way to reduce the moiré phenomenon is to interpose an air layer between the Fresnel lens and the lenticular lens, or to form fine irregularities on the lenticular lens surface. Technically speaking, it is important to regulate the ratio of the widths of the lenses, and in addition to this, it is desirable to take measures to further reduce the moiré phenomenon. For this reason, the applicant has set the lens width ratio of the lenticular lens and Fresnel lens to 1:1.35~
1.43 (or 1/1.43 to 1/1.35) and a rear projection screen with a light diffusion means has already been proposed (Japanese Patent Application No. 77736/1983).
Further consideration revealed that 1: approx. 2.4, 1: approx. 3.4,
It has been found that there is a preferable region where the ratio is 1: about 2.4 or more, such as 1: about 4.4, and the present invention has been achieved. That is, the gist of the present invention is a rear projection screen for a projection television in which a Fresnel lens and a lenticular lens are formed on a synthetic resin base material, where the width of the Fresnel lens is 1. The ratio of the width of the lens in the lenticular lens is in the range of N + α or 1/N + α (where N is an integer of 2 to 12 and α is a value of 0.35 to 0.43),
A rear projection screen for projection is characterized in that the base material is provided with a light diffusing means. The present invention will be described below with reference to drawings of embodiments, and FIGS. 1 to 6 show a rear projection screen for a projection television with a single-screen structure, and a seventh
1 to 10 show a rear projection screen for a projection television having a plurality of screens. In the figure, reference numeral 1 denotes a Fresnel lens provided on one surface of a base material, and the Fresnel lens 1 in this case is formed with an array of concentric grooves on the base material. 2
is a lenticular lens provided on the other surface of the base material, and hemispherical semicylindrical lenses are continuously arranged in the vertical direction. Synthetic resins such as methacrylic resin, vinyl chloride resin, or polycarbonate resin are used as the base material for the rear projection screen for projection televisions of the present invention, but these are suitable as materials for the present invention because they have excellent moldability. These materials have excellent transparency and have a refractive index of approximately 1.49 to 1.6, so they can be treated similarly. The thickness of this base material is generally selected within the range of 0.8 to 5 mm. Further, in the figure, A, B, and C indicate light diffusing means, respectively, where A is the mixing of a diffusing agent into the base material, B is the formation of a fine uneven surface, and C is the formation of a layer mixed with the diffusing agent. The rear projection screen for projection television of the present invention is equipped with the Fresnel lens 1 and the lenticular lens as described above, and one of its features is that the ratio of the widths of both is set within a certain range. . That is, the lens width of Fresnel lens 1
When P ₁ is 1, the width of the lenticular lens 2 is set to the range of N+α or 1/N+α (where, in the formula, N is a natural number from 2 to 12, and α is a value from 0.35 to 0.43). This is what I did. If the ratio of the lens widths of the Fresnel lens 1 and the lenticular lens 2 is set to 1:1, a moiré phenomenon will occur severely. Furthermore, as shown in Japanese Patent Application Laid-Open No. 56-52985, Fresnel lenses and lenticular lenses in which the pitch ratio of one element is set to 1.5 or 1/1.5 have a lower moiré phenomenon than those with a pitch ratio of 1. Although it is improved to some extent, a fairly strong moiré phenomenon still occurs. On the other hand, it is possible to make the ratio 1:2.5, 1:3.5, 1:4.5, etc., but in most cases this ratio is 1:1.
In the end, the moire cannot be reduced.
Even if a light diffusing means is applied to a screen in which the moire phenomenon is not reduced, the moire phenomenon cannot be suppressed, or other drawbacks such as a decrease in the amount of transmitted light or a decrease in resolution occur. The present invention conducted many experiments on such phenomena, and based on the results, empirically determined the width ratio to be 1:N+α or 1/N+α (where N is a natural number between 2 and 12, and α is between 0.35 and 0.43. In addition to setting the ratio of the lens widths of the Fresnel lens 1 and the lenticular lens 2 in this way, it is also possible to apply the light diffusing means A to C to the base material. In this light diffusing means, the mixing of a diffusing agent A is an inorganic diffusing agent such as silicon oxide, barium sulfate, alumina oxide, calcium carbonate, etc. or an organic diffusing agent such as an opalizer for the base material. It is recommended to mix a relatively small amount of, for example, about 5 to 40 g/m ² .In order to form the finely uneven surface B, sandplast processing is performed on the lens surface or non-lens surface, or a finely uneven surface is formed on the mold surface. This can be obtained by forming a layer C and transferring it during manufacturing.
can be obtained by mixing the above-mentioned diffusing agent into various paints and applying the mixture. To explain the rear projection screen for projection television of the present invention in the order of the figures, FIG. 1 shows a structure in which a Fresnel lens 1 and a lenticular lens 2 of a predetermined ratio are formed on one synthetic resin base material. Fig. 2 shows an example in which a diffusing agent is mixed in A, Fig. 2 shows an example in which a fine uneven surface is formed on the surface of the lenticular lens 2, and Fig. 3 shows the example in Fig. 1 and Fig. 2. Further combined examples, FIG. 4 is an example in which a layer containing a diffusing agent is formed on the surface of the Fresnel lens 1, and FIG. 5 is an example in which this layer containing a diffusing agent is formed on the surface of the lenticular lens 2.
Figure 6 shows an example in which a diffusion agent-containing layer is formed in the base material C.
Examples are shown below. In addition, FIG. 7 and subsequent figures show examples of rear projection screens for projection televisions constructed using a plurality of synthetic resin base materials.
FIG. 7 shows an example in which a separate Fresnel lens 1 and a lenticular lens 2 are arranged opposite each other as shown in the figure, and a diffusion agent-containing layer C is formed on the surface of the lenticular lens 2. Arrange the lenticular lens 2 in the opposite direction and form a diffusion agent mixed layer on the back surface C
FIG. 9 shows an example in which a finely uneven surface is formed on the surface of the lenticular lens 2 using the same combination as shown in FIG. 7, and FIG. Examples are shown in which another diffuser plate 3 having a finely uneven surface B formed between it and the lens 2 is used in combination. In the above embodiments, the left side of each drawing is the projector side, and the right side is the viewer side. Note that when the ratio of the lens widths of the lenticular lens 1 and the Fresnel lens 2 is within the range of the present invention, the lens width of the Fresnel lens 1 or the lenticular lens 2 may be changed to another width in order to improve the resolution of the screen. It is effective when it is made smaller in comparison. This is because as the width of either one of them is made smaller, the ratio of the widths tends to increase, and it is preferable to increase the ratio of both widths. It should be noted that a range in which N exceeds 12 in terms of width ratio is impractical and also has restrictions in terms of mold production. In the embodiments shown in FIGS. 1 to 10 above, the width of the Fresnel lens 1 is reduced, but depending on the purpose, the width of the lens of the lenticular lens 2 may be reduced. good. More specific examples will be described below. Example 1 When manufacturing a methacrylic resin board, a resin board serving as a base material was manufactured by uniformly mixing silicon oxide as a light diffusing agent. Then, a mold with a Fresnel lens surface on one side of this resin plate and a mold with a lenticular lens surface on the other side are applied and heated (approximately
150 to 170° C.) and then pressurized (40 to 60 kg/cm ² ) to produce four types of one-piece rear projection screens for projection televisions as shown in FIG. The appearance of moiré on the sample was observed and the results were as shown in Table 1.

[Table] As can be seen from the table in Table 1, the rear projection screen for projection TV of the present invention was excellent in that the occurrence of moiré was extremely slight and was hardly noticeable to the naked eye. The product had severe moiré, and in the case of sample No. 4, a considerable amount of diffusing agent had to be mixed, and there was concern that the amount of transmitted light would decrease. Example 2 Using the silicon oxide-containing methacrylic resin plate used in Example 1, 14 Fresnel lenses and 3 lenticular lenses having pitch ratios as shown in Table 2 were made, and these two types of lenses were Table 2 shows the results of determining the strength and weakness of moiré that appears on this screen by creating screens with varying ratios of the pitch width of the Fresnel lens and the pitch width of the lenticular lens. Table 3 shows the results in Table 2 organized by ratio. As shown in these tables, it can be seen that when the pitch ratio is N+α (where N is an integer from 2 to 12 and α is a value from 0.35 to 0.43), there is very little moire appearing on the screen.

【table】

【table】

[Table] The present invention has the configuration as detailed above, and the ratio of the lens width of the Fresnel lens to the lens width of the lenticular lens is set within a specific range, and then a light diffusing means is applied. This makes it possible to significantly reduce the occurrence of moiré phenomena, as well as to reduce the amount of light diffusing means used, i.e., to reduce the amount of diffuser mixed in and prevent the amount of transmitted light from decreasing, or to prevent the amount of transmitted light from decreasing. It has the advantage of being able to reduce the weight of forming an uneven surface to the extent that it does not significantly reduce the contrast of the screen, and can be obtained using the same equipment and methods as conventional methods. It is.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and FIGS. 1 to 6 are cross-sectional views showing examples of a rear projection screen for a projection television configured with one screen, and FIGS. FIG. 2 is a sectional view showing an example of a rear projection screen for a projection television. 1... Fresnel lens, 2... Lenticular lens, A, B, C... Light diffusion means.

Claims (1)

[Scope of Claims] 1. A rear projection screen for projection television in which a Fresnel lens and a lenticular lens are formed on a synthetic resin base material, where the width of the lens constituting the Fresnel lens is 1, The width ratio of the lenticular lens should be within the range of N+α or 1/N+α (where N is a natural number from 2 to 12 and α is a value from 0.35 to 0.43), and A rear projection screen for a projection television, characterized in that it is made of a material provided with a light diffusion means.