JPH0894808A - Linear fresnel lens - Google Patents

Abstract

PURPOSE: To decrease wrinkles due to curling which generates in a lens molded body when a UV-curing or radiation-curing resin is transferred from a roll-type mold to a transparent resin film and then the resin is irradiated with UV rays or radiation for curing. CONSTITUTION: This linear Fresnel lens consists of a base film 11 (transparent resin film) and a lens resin layer 2 comprising connection of prism unit lenses 1 formed by UV or radiation-curing method on the base film. This linear Fresnel lens is formed in such a manner that the height of the lens resin layer 2 in the center part is 1/2 of the height hmax of the lens resin layer 2 in the outermost circumference part and that the volume of each prism unit lens is made const. in any part in the lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear Fresnel lens used in a rear projection type projection television.

[0002]

2. Description of the Related Art At present, a projection screen using a circular Fresnel lens and a lenticular lens is the most common, but since the circular Fresnel lens has concentric prism-shaped unit lenses, it has to be produced in a single wafer. In comparison with a lenticular lens that can be produced by the extrusion method, the productivity is poor and it is difficult to reduce the production cost. Therefore, as shown in FIG. 5, a linear Fresnel lens 100A that can be continuously manufactured by an extrusion method or a UV curing method using a roll-shaped mold instead of the circular Fresnel lens described above.
And 100B are crossed and used in combination with the lenticular lens 110.

As a method of manufacturing such a linear Fresnel lens, an extrusion molding method in which a molten resin is poured into a roll-shaped mold, a photopolymer method in which a lens is formed on a transparent resin film by using an ultraviolet or radiation curable resin However, with the former method, the viscosity of the molten resin is high, and it is difficult to accurately transfer the shape of the linear Fresnel lens having a fine and acute angle shape. The latter photopolymer method is a method in which an ultraviolet or radiation curable resin is transferred from a roll-shaped mold to a transparent resin film and then cured by irradiation with ultraviolet rays or radiation. Although the mold reproducibility is excellent, there is a problem that the lens molded product is apt to curl due to the volume shrinkage during curing (polymerization) of the resin.

That is, according to the experience of the present inventor, in the above-mentioned curing process, the transparent resin film serving as the base film does not shrink, whereas only the ultraviolet or radiation curable resin shrinks, so that the curl occurs in the entire area. In addition to the above, for example, as shown in FIG. 6, in the linear Fresnel lens formed so that the bottom portions 4 of the prism type unit lenses 1 are aligned, the resin amount for each prism type unit lens 1 is Since the central part and the outer peripheral part of the lens are different from each other, both ends of the lens having a large amount of resin are largely curled at the time of curing, and the central part of the lens having a small amount of resin is curled smaller than the outer peripheral part of the lens. Similarly, even in the case of the linear Fresnel lens formed so that the tops 3 of the prism type unit lenses 1 are aligned, the resin amount of each prism type unit lens 1 is different between the central portion and the outer peripheral portion of the Fresnel lens, and the resin amount is different. There is much curl in the center of the lens, which curls more than at both ends.

This curl is corrected by the tension when the linear Fresnel lens is attached to the television set. However, when the curl has different curvatures as described above, the curl cannot be completely corrected and the peripheral portion of the linear Fresnel lens cannot be corrected. Or, wrinkles remained in the center, and when the image was projected, moire-like stripes were generated. Also, if the amount of curling differs depending on the part of the linear Fresnel lens,
There was also the problem of uneven winding when winding the linear Fresnel lens molded during lens production.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and after transferring an ultraviolet or radiation curable resin from a roll mold to a transparent resin film, An object of the present invention is to reduce wrinkles caused by curl generated in a lens molded article when a curing treatment is performed by irradiating ultraviolet rays or radiation.

[0007]

The present invention has been completed as a result of studies for solving the above problems, and it has been completed by using an ultraviolet or radiation curable resin on a base film having ultraviolet or radiation transparency. In the linear Fresnel lens in which the formed prism type unit lenses are arranged in a number of planes so that their ridge directions are parallel to each other, the volume of each pitch of the lens resin layer having the prism type unit lenses is The linear Fresnel lens is characterized in that it is constant at any part of the linear Fresnel lens.

[0008]

According to the present invention, the lens resin layer is formed on the base film having ultraviolet or radiation transparency so that the volume of the lens resin layer for each pitch is constant at any part of the linear Fresnel lens. The amount of volume shrinkage when the formed ultraviolet or radiation curable resin cures becomes constant at each part, and the linear Fresnel lens is curled so as to form a part of an arc having a constant curvature over the entire area. for that reason,
Curls can be easily corrected when installing a television set,
In addition, it is possible to prevent the occurrence of wrinkles due to the curl being corrected.

[0009]

EXAMPLES The present invention will be described in more detail below with reference to examples. FIG. 1 is a schematic side view illustrating an embodiment of the linear Fresnel lens according to the present invention.
2 is an enlarged view of a part of the right half (the portion indicated by the arrow from the dotted line in the figure) from the center of the linear Fresnel lens 100 shown in FIG. 1. FIG. The central part of 100, FIG. 2 (b) is a part where the lens angle φ of the prismatic unit lens 1 is less than 45 °,
2C shows a portion where the lens angle φ of the prismatic unit lens 1 is 45 ° or more, and FIG. 2D shows the outermost peripheral portion of the linear Fresnel lens 100.

As shown in the figure, the linear Fresnel lens 100 of this embodiment is composed of a lens resin layer 2 in which prism-shaped unit lenses 1 having the same lens pitch are formed and a base film 11, and a lens for each lens pitch is formed. The volume of the resin layer 2 is such that the lens pitch is pt, the height of the lens resin layer 2 at the outermost periphery of the linear Fresnel lens 100 (the height from the top 3 of the prism-shaped unit lens to the base film 11) is h _max , and the lens is Let L be the length in the ridge direction,
1/2 · pt · h _max · is formed to be L, the height h of the lens resin layer 2 in the center of the linear Fresnel lens 100, the lens of the resin layer 2 the height of the outermost peripheral portion h
It is 1/2 of _max .

A method and apparatus for manufacturing such a mold for a linear Fresnel lens is disclosed in Japanese Patent Laid-Open No. 56-1722.
Several inventions such as the invention of Japanese Patent No. 9 have been proposed, but as a roll-shaped mold for a linear Fresnel lens, a "double-cut Fresnel part" is cut from both the outer peripheral portion of the lens and the cutting blade is cut by one of the cutting blades. It is composed of a "single-sided Fresnel part" and a "equal-angle prism part" at the center, and is formed by cutting so as to form the height h of the lens resin layer 2 at each part as described below. When cutting with a cutting blade having a certain angle, for example, a cutting edge angle of 45 °, first, the height h _max of the lens resin layer 2 at the outermost peripheral portion is the lens angle at the outermost peripheral portion. Is φ _max and the lens pitch is pt, and is calculated by the following (Equation 1).

[0012]

[Equation 1] Then, the height h of the lens resin layer 2 at the center of the linear Fresnel lens 100 is _calculated by 1/2 · h _max .

Next, when the lens angle φ of the prismatic unit lens 1 is less than 45 °, the height h of the lens resin layer 2 is
As shown in the part of FIG. 2 (b), the top 3 and the bottom of the prismatic unit lens 1 are located from the position of 1/2 · h _max with reference to the height of the lens resin layer 2 at the center. By making the distances up to 4 equal, it can be obtained from the following (Equation 2).

[0014]

[Equation 2]

Further, when the lens angle φ of the prism-shaped unit lens 1 is 45 ° or more, the non-lens surface is also inclined, but the height of the lens resin layer 2 is the same as that of the linear Fresnel lens. By making the distances from the position of 1/2 · _max to the top 3 and the bottom 4 of the prismatic unit lens 1 with respect to the height of the lens resin layer 2 at the center of 100, respectively, As shown in the part of FIG. 2C, it can be obtained from the following (formula 3).

[0016]

[Equation 3]

The amount of cut formed as described above is gradually reduced from the outermost peripheral portion toward the central portion, and the central resin portion is shallowly cut by 1/2 of the height of the lens resin layer 2 at the outermost peripheral portion. Using the roll-shaped mold for forming the linear Fresnel lens, the original film (base film) was supplied from the original roll and wound so as to be sandwiched between the nip roll and the roll-shaped mold. In the state, supply an ultraviolet or radiation curable resin, irradiate an ultraviolet lamp or a radiation source to cure the ultraviolet or radiation curable resin, peel it from the roll-shaped mold, and form a molded article. The linear Fresnel lens of the present invention can be obtained by winding on a winding roll.

The base film 11 used in the present invention has good transparency to ultraviolet rays or radiation used to cure the ultraviolet or radiation curable resin, and
It is possible to use a material having high transparency in the visible region, for example, a thickness of 50 made of a resin such as polymethylmethacrylate, polyethylene terephthalate, or polycarbonate.
Films of about 300 μm can be used.
As the ultraviolet or radiation curable resin used to form the lens resin layer 2, urethane acrylate, epoxy, polyester, acrylic or the like can be used, but for the convenience of winding and processing the molded product, cracking during processing, etc. To prevent this, select one that is relatively flexible and flexible.

In the linear Fresnel lens of the present invention, in addition to the one described in the prior art, as shown in FIGS. 7A and 7B, the axis of the light beam incident on the projection screen 202 is the projection screen 202. In the method of making the depth of the rear projection type TV shallow by making the light obliquely incident with respect to the normal, it can be applied to the linear Fresnel lens 100 that changes the angle of the projection optical axis. In this case, the lens angle of the linear Fresnel lens 100 generally increases monotonically from the upper end to the lower end of the screen,
Also, since it is less than 45 °, with respect to the lens height described above, with respect to the lens height, h _max = pt · tan φ _max (Equation 4) The lens height, including the smallest part, can be calculated by h = 1/2 · (tan φ _max + tan φ) pt (Equation 5).

A specific manufacturing example will be described below. (Embodiment 1) First, with respect to a roll-shaped object to be cut having a surface length of 1200 mm, a lens pitch pt of 0.112 mm and a cutting edge angle of 45 at a distance (radius) of 0 to 500 mm from the center. The lens angle φ and the height h of the lens resin layer 2 were set as shown in Table 1 for each distance, and cutting was performed to obtain a roll-shaped mold 10.

[0021]

[Table 1]

The distance from the above-mentioned center portion (the moving radius of the roll-shaped die during cutting) [mm] and the height h of the lens resin layer 2 [m]
FIG. 3 is a graph showing the relationship with [m]. Figure 4
FIG. 3 is a diagram illustrating a concept of forming a linear Fresnel lens by using a roll-shaped mold 10. Thickness 0.1 mm
An original film (base film) 11 made of polyethylene terephthalate is supplied from an original roll 12,
It is guided so as to be sandwiched between the nipple roll 13 and the roll-shaped mold 10 and supplied with a urethane acrylate-based UV curable resin 14 and irradiated with a UV lamp 15 to cure the UV curable resin. The resin 14 was cured, and the resin 14 was peeled off from the roll-shaped mold 10 to form a molded product (linear Fresnel lens) 100, which was wound on a winding roll 16 to obtain a linear Fresnel lens of the present invention. . In the linear Fresnel lens formed in this way, the amount of the ultraviolet curable resin for each pitch of the lens resin layer is almost equal over the entire lens, and in the cross section perpendicular to the ridge direction of the prismatic unit lens of the linear Fresnel lens, Curl occurred so that it became part of an arc with a constant curvature. When the obtained linear Fresnel lens was fixed to a resin frame on all four sides with an adhesive and mounted on a projection TV, no wrinkles were observed and no moire fringes were observed in the entire area.

[0023]

According to the present invention, the height of the lens resin layer 2 is changed so that the volume (resin amount) of the lens resin for each one pitch of each prism-shaped unit lens of the linear Fresnel lens becomes constant. In addition, there is no difference in the amount of volume shrinkage when the ultraviolet or radiation curable resin shrinks, and it is possible to reduce the occurrence of wrinkles in the lens molded product. Further, when the linear Fresnel lens is mounted on the projection screen, it is only necessary to prevent the generation of wrinkles that are difficult to remove due to the nonuniform volume contraction and correct the simple curl due to the base film and the lens resin layer. In addition, it is possible to prevent uneven winding in the winding process after lens molding.

[Brief description of drawings]

FIG. 1 is a schematic side view illustrating an example of a linear Fresnel lens of the present invention.

2 is an enlarged view of a part of FIG. 1, and FIG.
Is at the center, FIG. 2 (b) is at a lens angle φ of less than 45 °, FIG. 2 (c) is at a lens angle φ of 45 ° or more, and FIG. Indicates a part.

FIG. 3 is a graph showing the relationship between the distance from the center of the linear Fresnel lens molded article of the embodiment of the present invention and the height of the lens resin layer 2.

FIG. 4 is a schematic view illustrating a situation in which a linear Fresnel lens molded product is formed from a roll-shaped mold according to an embodiment of the present invention.

FIG. 5 is a schematic perspective view showing a screen configuration of a rear projection type projection television in which a general linear Fresnel lens is crossed and a part of each lens is cut away.

FIG. 6 is a schematic side view illustrating a linear Fresnel lens molded product of a comparative example.

FIG. 7 is a conceptual diagram illustrating another lens system to which the linear Fresnel lens of the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Prism type unit lens 2 Lens resin layer 3 Top part of prism type unit lens 4 Bottom part of prism type unit lens 10 Roll-shaped die 11 Original film (base film) 12 Original film 13 Nip roll 14 UV Curable resin 15 Ultraviolet lamp 16 Winding roll 100 Molded product (linear Fresnel lens) 100A Linear Fresnel lens (for horizontal focusing) 100B Linear Fresnel lens (for vertical focusing) 110 Lenticular lens 201 Rear projection TV 202 Projection Screen 203 CRT 204 Virtual light source 207 Circular Fresnel lens

Claims (1)

[Claims] 1. A prism-shaped unit lens formed of an ultraviolet or radiation curable resin is arranged on a base film having ultraviolet or radiation transparency in a multiplicity of planes with their ridge lines parallel to each other. In the linear Fresnel lens, the volume of the lens resin layer having the prismatic unit lens for each pitch is made constant at any part of the linear Fresnel lens.