JP6001836B2 - Method for manufacturing Fresnel lens and method for manufacturing lighting apparatus - Google Patents

Description

The present invention relates to a method for manufacturing a Fresnel lens and a method for manufacturing a lighting fixture using the Fresnel lens manufactured by the manufacturing method .

Projector lenses that are convex lenses are used for headlamps (headlamps, fog lamps, etc.) of vehicles such as automobiles (see, for example, Patent Documents 1 and 2).
FIG. 15 is a cross-sectional view schematically showing the main part of the headlamp.
The headlamp conventionally includes a base portion 104 including a lens holding portion 101, a light source mounting portion 102, and a reflector holding portion 103, an aspherical lens 106 as a projector lens, a light source 107, and a reflector 108.
In this headlamp, the light from the light source 107 is reflected by the reflector 108, and the reflected light is incident on the aspherical lens 106 in a state of being diffused after being mainly focused in the vertical direction by the reflector 108. The light is emitted so that its direction is changed by the aspherical lens 106 and illuminates a predetermined light projection range.

  However, if the aspherical lens 106 is used as a projector lens, the center thickness of the lens becomes thick. Therefore, when the aspherical lens 106 is formed of resin by injection molding, the resin is hardened slowly and the molding time becomes long. There is a risk that deformation due to shrinkage during molding) will increase.

  Basically, in a lens for illumination including a lens for light projection such as the projector lens described above, for example, the diameter may be larger than the optical element for other applications, and the lens center thickness If the thickness is thicker, the volume becomes larger, resulting in problems such as the placement of each member of the lighting device, space efficiency is poor, the weight is increased, the amount of raw materials used is increased, and the cost is increased. There is a problem that a material whose light transmittance is not high increases or the amount of transmitted light is greatly attenuated by thickness.

  Therefore, it is conceivable to form the projector lens by injection molding with a resin using a Fresnel lens capable of reducing the thickness. By doing so, it is possible to shorten the molding time, reduce sink marks, reduce the weight of the lens, reduce the size (thinner), and improve the light transmittance.

JP 2007-207527 A JP 2008-47383 A

  However, since the Fresnel lens has a plurality of prisms (annular zones) whose cross-sectional shape is formed in a substantially triangular shape, a mold is used when the synthetic resin is used as a material by resin molding such as injection molding. In some cases, the molded product (Fresnel lens) tends to bite and the molded product is damaged and cannot be taken out. Even if it can be taken out, if there is a portion that is difficult to peel off locally from the mold, the molded product may be deformed by the taking out, and desired optical characteristics may not be obtained.

  In addition, the flow path of the resin becomes narrower toward the apex side of the prism having a substantially triangular cross section, and the prism apex portion is rounded because the resin is solidified in the middle without flowing into the apex, In some cases, so-called transfer is insufficient. In such a case, the roundness of the prism apex portion changes greatly even if there are minute fluctuations such as fluidity due to resin characteristic variations, mold temperature, molding machine injection pressure, etc. Optical characteristics vary greatly.

  Further, when manufacturing such a Fresnel lens molding die, if a concave portion having a substantially triangular cross section corresponding to the apex portion of the prism is to be in an acute angle state, a die processing tool having an acute angle tip portion However, when such a tool is used, the tip of the tool is likely to wear out, and it is necessary to change the tool frequently, the processing accuracy will deteriorate, and the surface roughness will deteriorate. Occurs.

  In solving the above problems, in the design stage, the cross-sectional shape of the apex portion of the prism of the Fresnel lens may be an arc shape, and the cross-sectional shape of the deepest portion of the concave portion of the mold may be arced accordingly. Although it is conceivable, if the shape of the apex portion of the prism changes as described above, the optical characteristics change, and there is a possibility that the emitted light quantity with respect to the incident light quantity decreases. In particular, the efficiency of the lens for illumination use may be reduced.

The present invention has been made in view of the above circumstances, and can easily produce a mold without reducing the injection efficiency as a ratio of the amount of emitted light to the amount of incident light. An object of the present invention is to provide a method of manufacturing a Fresnel lens for manufacturing a resin-made Fresnel lens with a high product yield rate, and a method for manufacturing a lighting fixture using the Fresnel lens manufactured by this manufacturing method.

  The present invention relates to a Fresnel lens formed by injection molding of a resin, the arrangement method of each prism, the effective diameter of the lens, the number of prisms, the aspect ratio obtained by dividing the height of each prism by the width of the base, and the cross section The effect of the radius of the arc at the apex of the prism on the arc on the quality and optical characteristics of the Fresnel lens was studied, and the ease of mold manufacture was examined. As a result, the height of the prism was set to h (mm) When the radius of the apex of the prism is r (mm), the effective lens diameter of the Fresnel lens is D (mm), and the number of prisms included in the range of the effective lens diameter D is N, the r is expressed by the following equation: When the value of k in Equation (1) is set to 0.04 to 0.38, the emission efficiency indicating the ratio of the emitted light to the incident light of the Fresnel lens is necessary and sufficient. thing And while, it is easy to manufacture mold and release the molded Fresnel lens becomes easy, and in which the quality of the molded Fresnel lenses found that it is possible to stabilize.

  Here, 2Nh / D represents the aspect ratio, and is obtained by dividing the prism height h by the average prism pitch (average prism width) indicated by D / 2N. Formula (1) basically defines the radius r of the arcuate apex by the aspect ratio. When the aspect ratio increases, the flow path of the resin is narrowed and the molded product of the mold is formed. Since transferability deteriorates, it is necessary to increase the radius r. By setting an appropriate radius r corresponding to the aspect ratio, it is possible to improve mold release and quality while maintaining the optical characteristics at a necessary and sufficient level.

  The height h of the prism indicates the height of all the prisms when the height of each prism is constant, but the height of each prism is the same as the average height of all the prisms. To do. In addition, when R is added to the apex of the prism, the height of the prism is reduced. The height here is the height when R is not added to the apex portion 7 of the prism 4, and R is It is the height of the prism at the time of design before attaching. In the case of a manufactured Fresnel lens, the cross section between the prism surface (optical function surface) of one prism and the split surface (the surface that divides the optical function surface of the original lens shape of Fresnel) is linear. (In the case of a curve, an approximate curve), the height of the portion where the prism surface and the extension surface to the apex side of the split surface intersect, or the above-mentioned extension surfaces of a plurality of prisms The average of the intersecting heights is the height h.

The manufacturing method of such a Fresnel lens of the present invention is as follows.
A first surface on which light is incident and a second surface from which light is emitted; a plurality of prisms are formed on the second surface; and the prism includes a prism surface, a split surface, A Fresnel lens manufacturing method for manufacturing a resin-made Fresnel lens whose cross section is formed in a substantially triangular shape from an arcuate apex portion connecting the prism surface and the dividing surface,
The radius of the arc at the apex is r (mm), the height of the prism is h (mm), the effective lens diameter is D (mm), and the number of prisms included in the effective lens diameter D (mm) is N. If
Said r (mm) shall be shown by the following formula | equation (1),
And the value of k (mm) in said Formula (1) shall be 0.04-0.38 mm.

In the present invention, the radius r of the apex of the arc-shaped prism is obtained in accordance with the above formula (1), that is, the aspect ratio. At this time, by setting the value of k as a coefficient multiplied by the aspect ratio in the above formula to 0.04 to 0.38, the molding problem is solved while ensuring necessary optical characteristics.
That is, by providing an upper limit of the radius r of the apex portion of the arcuate cross section of the prism, the optical characteristics of the Fresnel lens can be obtained by making the r dimension excessively large even though sufficient productivity can be secured in molding. Deterioration of the lens is prevented, and by setting a lower limit, damage or deformation of the lens due to insufficient transfer or mold release is prevented.

  When considering the phenomenon that the resin flows into the prism apex side in the mold cavity at the time of molding, the resin touching the mold is cooled to form a very thin cooling solidified layer, a so-called skin layer. As the resin moves toward the apex side of the prism, the flow path for the resin to flow becomes narrower, and near the apex, the skin layers formed on the prism surface and the divided surface meet to prevent the resin from flowing any further, resulting in insufficient transfer. Arise. The transferable region where the resin can flow must be considered by subtracting the thickness of the skin layer, and this region is related by the aspect ratio.

  When the prism arrangement method is changed as shown in FIG. 5 or when the lens diameter is increased proportionally even with the same shape, the prism height may be different even with the same aspect ratio. Compared to the low prism height, the higher the prism height, the more easily the heat of the resin is taken away, and the resin temperature drops and the fluidity becomes lower, and it goes to the apex side. The shortage area will increase. However, when the prism arrangement method is changed and the height of the prism is increased, the aspect ratio decreases, and when the lens diameter is increased proportionally with the same shape, the runner and gate are also increased proportionally, It works to offset the above effects. On the other hand, when the number of prisms divided from the lens before being converted to the Fresnel lens, that is, the number of prisms formed within the effective diameter of the lens is increased, the aspect ratio remains almost unchanged but the prism height decreases. Therefore, there is a tendency that transfer shortage hardly occurs.

  Various factors affect the transfer, but when capturing the macroscopic phenomenon from the viewpoint of the size of the area where transfer is insufficient, the aspect ratio is independent of the prism arrangement method and lens diameter if the number of divisions is the same. It is uniquely related by the ratio. On the other hand, when the number of divisions is different, the larger the number of divisions, the easier it is to transfer. Therefore, the prism apex R can be made smaller, so Equation 1 takes into account the influence of the number of divisions N.

  In this way, by making the prism apex part an arc having an appropriate radius r defined from Equation 1, it is possible to suppress the insufficient transfer and suppress the shape variation of the prism tip part, and to produce a stable quality Fresnel lens. .

In the above equation (1), the aspect ratio is defined by the average height h of the prisms, the effective lens diameter D, and the number N of prisms included in the range of the effective lens diameter D based on the above description. If the aspect ratio of each prism is obtained from the height and width of each prism and, for example, the average value of the individual aspect ratios is applied to the above equation (1), the aspect ratio changes when the prism arrangement method is changed. Thus, it does not fit the grounds of the above explanation.
Further, according to the above equation (1), the radius r of the apex portion of the prism having the arcuate cross section is not determined for each prism, but one r dimension is determined as being common to all apexes of the prism. For this reason, there is no need to change a processing tool or perform complicated processing in the middle of mold processing, and therefore it is possible to easily perform mold processing with high accuracy.

  When considering the release of the molded lens from the mold, the ease of release is related to the area of the part where the product bites into the mold. In a convex lens, the dividing surface is a portion that bites into the mold, but if the prism apex is not attached with an arc R in cross section, the area of this portion can be reduced even if the prism arrangement method and the number of divisions are changed. It does n’t change much. If the lens diameter increases proportionally, the area of the part that bites into the mold also increases proportionally, but the release mechanism provided on the mold such as the ejector pin can also be increased proportionally, so the lens It is possible to make the mold release as easy as when the diameter is small. When R is provided at the apex of the prism, the area of the portion that bites into the mold decreases in proportion to the size of the R dimension, so that release is facilitated. The reduction rate varies depending on the number of prism divisions. Even if the R dimension of the prism apex is the same, the greater the number of prism divisions, the greater the area reduction rate of the portion that bites into the mold. Therefore, as the number of prism divisions increases, it is possible to make the mold release easier even if the R dimension of the prism apex is reduced. Therefore, the expression 1 considers the influence of the division number N on the mold release. It is said.

As described above, the larger the R dimension of the prism apex, the less transfer is less likely to occur and the easier it is to release. When the R dimension of the prism apex is larger than a certain size, there is no molding problem and sufficient productivity is ensured. Increasing the R dimension beyond that does not change the productivity at all, but conversely causes problems such as a decrease in lens emission efficiency and a change in light distribution characteristics.
Considering the emission efficiency, which is the ratio of the emitted light quantity to the incident light quantity, if the number of divisions is increased, each prism is added to the optical functional surface of the original lens before Fresnelization even if the prism surface cross section is a straight line. Therefore, the optical characteristics of the lens should basically be improved, but each prism is basically smaller (higher). Therefore, when the apex portion of the prism is formed in an arc shape, if the radius r of the arc of the apex portion is the same regardless of the number of divisions, the ratio of the radius r to the prism height increases. This deteriorates the optical characteristics of each prism surface. In this case, there is a possibility that the demerit that the optical characteristics deteriorate due to the increase in the number of arcuate apex portions by increasing the number of divisions may be larger than the merit of increasing the number of divisions. Therefore, when the number of prisms is increased, it is preferable to reduce the radius r.

  In addition, because of the Fresnel lens, compared to conventional aspherical lenses, lighter, thinner, improved space efficiency by thinner, reduced costs by reducing raw materials, thinner molding time, The amount of deformation due to sink marks can be reduced due to the thinness.

In the above structure, it is preferable that the upper limit value of k is equal to or less than k = 0.5553e− ^0.02N (mm) .

  In the above configuration, each prism may be formed in a concentric circle shape or a concentric ellipse shape.

In the above configuration, a clearance angle is provided on the split surface of the prism,
The clearance angle of the dividing surface is
Of the light incident from the light source, set so that the split surface constituting the valley substantially follows the direction of the light reaching the deepest part of the valley formed by the prism surface and the split surface of the adjacent prisms. May be.

  The height h of each prism may be set within plus or minus 10% with respect to the average of the height h.

  Moreover, it is preferable that a lens diameter is 20 mm-80 mm.

  In the above configuration, the prism may be configured such that cross-sectional shapes of the prism surface and the dividing surface are straight lines or curved lines. Note that the curve is convex and is convex when assuming a line segment along the release direction from the base end portion of the dividing surface when it is a curve of the sectional shape of the dividing surface. It is necessary that the curve does not protrude from the line segment.

  In the above configuration, the prisms may have substantially the same height, and the bottom surface may have a different width corresponding to the inclination angle of the prism surface.

  In the above configuration, the maximum thickness within the range of the effective lens diameter may be 0.5 to 4 mm.

An antireflection film may be formed on at least one of the first surface and the second surface.

Moreover, you may make it manufacture a lighting fixture using the Fresnel lens manufactured by the manufacturing method of the above Fresnel lenses.
Such lighting fixtures include, for example, vehicle headlamps (head lamps, hog lamps, etc.), traffic signal lights, spotlights, downlights, incandescent lamps, fluorescent lamps and the like.

  Moreover, you may make it the light source of the said lighting fixture be LED.

  According to the present invention, the mold can be easily manufactured while maintaining the necessary and sufficient optical properties of the Fresnel lens, the manufacture of the Fresnel lens can be facilitated by improving the releasability of the molded Fresnel lens, and the mold can be separated. It is possible to stabilize the quality of the Fresnel lens by suppressing deformation due to the mold and insufficient transfer.

(A) is a front view which shows the Fresnel lens which concerns on 1st Embodiment of this invention, (b) is sectional drawing which shows a Fresnel lens. It is a one part enlarged view of FIG.1 (b). FIG. 3 is an enlarged view of a part of FIG. 2. FIG. 3 is an enlarged view of a part of FIG. 2. FIG. 2 is a cross-sectional view showing a variation of a Fresnel lens, where (a) is a cross-sectional view showing a Fresnel lens having a substantially constant prism height, and (b) is a cross-section showing a Fresnel lens having a substantially constant prism width. FIG. 6C is a cross-sectional view showing a Fresnel lens in which the prism width is substantially constant and the apex positions of the prisms are matched. It is a figure for demonstrating the problem at the time of mold release of the Fresnel lens with a fixed prism width. It is a figure for demonstrating the problem by the solidification shrinkage at the time of mold release of a Fresnel lens. It is a figure for demonstrating the reduction | decrease of the prism surface which has an optical function by R of the circular-arc-shaped vertex of the prism of a Fresnel lens. It is a figure for demonstrating the setting of the clearance angle of a division surface. It is a figure for demonstrating the setting of the clearance angle of the division surface based on Formula (2). It is sectional drawing which shows the lighting fixture using a Fresnel lens. It is sectional drawing which shows the cavity part of the metal mold | die which shape | molds a Fresnel lens. It is a graph which shows the result of an Example. It is a graph which shows the result of an Example. It is a graph which shows the result of an Example. It is sectional drawing which shows the lighting fixture using the conventional aspherical lens.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1 to FIG. 4, the Fresnel lens 1 according to the embodiment of the present invention has a first surface 2 on which light is incident and a second surface 3 on which light is emitted. A plurality of prisms 4 are formed concentrically on the surface 3. 2 is an enlarged view from the center of the Fresnel lens 1 in FIG. 1B to the outer edge portion of the lens effective diameter D (the diameter of the range in which light enters and functions as a lens). FIG. 4 is an enlarged view of the inner diameter side of FIG. 2, and FIG. 4 is an enlarged view of the outer diameter side of FIG.

A plurality of prisms 4 are concentrically arranged on the second surface 3 of the disk-shaped base 10 with the center of the base 10 as the center. As shown in FIGS. 3 and 4, the prism 4 is formed in a substantially triangular cross section from a prism surface 5, a split surface 6, and a vertex 7 where the prism surface 5 and the split surface 6 are connected. ing. The central prism 4 has an isosceles triangular cross section, and both surfaces forming the left and right hypotenuses of the triangle are prism surfaces 5.
Further, a portion on the outside of the effective lens diameter D where the prism 4 of the base 10 is not formed is a flange portion 11 and is used for mounting the Fresnel lens 1 or the like.

  In the prism 4 of the Fresnel lens 1, a portion that becomes a side corresponding to the prism surface 5 portion and the dividing surface 6 having a cross-sectional shape is linear. In addition, since the prism 4 is formed in an annular shape, the prism surface 5 and the dividing surface 6 are curved surfaces of the outer peripheral surface of the truncated cone. In addition, the apex portion 7 where the prism surface 5 and the dividing surface 6 are connected has an arc-shaped cross section, and the radius of the arc is r. Further, between adjacent prisms 4, valleys (concave portions) having a substantially triangular cross section are formed, but the deepest portion of the valleys may be formed in an arc shape. The deepest part of the valley is the part where the resin first comes into contact during molding, so there is no shortage of transfer even if it is not arcuate, and the mold corresponding to this part is convex in the mold production. Therefore, even if the tip shape of the processing tool is not an acute angle, the mold can be easily formed into a square shape, so it is not necessarily an arc shape. However, in order to increase the strength of the lens itself, it is not a square shape but a minute shape. It is desirable to form a circular arc.

  Further, in this Fresnel lens 1, the prism height 5 and the dividing surface 6 are extended to the apex side from the base height of the prism 4 having a substantially triangular cross section before the R of each prism 4 is attached. The distance to the determined intersection point) is substantially constant. In addition, since the inclination angle of the prism surface 5 is set as a lens and is different for each prism 4, the width along the radial direction of the Fresnel lens 1 at the bottom of the prism 4 is It may be different for each prism 4. The larger the inclination angle of the prism surface, the narrower the width. In addition, it is not necessary to make the design height h before attaching R of each prism 4 highly accurate and constant, for example, the difference in the design height h before attaching R of each prism 4 is used as a reference. It is preferable to be within 10% of the height h.

  By making the heights of the respective prisms 4 substantially constant in this way, the prisms 4 that are considerably higher than the other prisms 4 are not provided, making it easy to manufacture the mold and releasing the molds easily. And an advantageous structure against sink marks. When the Fresnel lens 1 cools and shrinks, a difference in the degree of reduction between the thick part and the thin part causes deformation due to sink marks, and by making the height of each prism substantially constant, Deformation due to sink marks can also be suppressed. In addition, since there is no portion where the thickness varies greatly depending on the location of the Fresnel lens, and the thickness is averaged, the distance through which light is transmitted does not vary greatly based on the thickness, so the internal transmittance based on the light transmission distance It is possible to prevent light and dark due to the difference.

In such a Fresnel lens 1, the design height before attaching R of the prism 4 is h, the radius of the arc of the apex portion 7 is r, the lens effective diameter is D, and the lens effective diameter D is included in the range. When the number of prisms is N, the r is expressed by the following formula (1), and the value of k in the formula (1) is set to be 0.04 to 0.38. Yes.

Here, D / 2N is obtained by dividing the effective lens diameter D by twice the number of prisms, and indicates the pitch along the radial direction of the Fresnel lens 1 of the prism 4. Therefore, D / 2N indicates an average value of the width b of the base along the radial direction of the Fresnel lens 1 of each prism 4 described above.
In addition, when the height of each prism 4 is made substantially constant as described above, the height h is common to each prism 4, but when the height may be different for each prism 4, The height h may be an average value. Note that the height here is the design height before R is added to the apex of the prism, and when the cross section of the prism 4 is viewed, it becomes the extension line of the side that becomes the prism surface and the dividing surface. The intersection point where the extended line of the side intersects is the design virtual vertex of the prism 4, and the distance from the base to the design virtual vertex is the height h.

  Further, when the aspect ratio is obtained by dividing the height h by the width b, 2Nh / D is an average aspect ratio obtained by dividing the height (average) by the average width. In this case, as described later, as the aspect ratio increases, that is, the height h increases with respect to the width b of the prism 4 having a substantially triangular cross section, and the sharper (pointed) triangle becomes, Deformation is likely to occur near the apex of the prism 4, making it difficult to release the mold, and it becomes difficult for the resin to flow into the deepest part of the concave portion corresponding to the prism of the mold, thereby deteriorating transferability. Therefore, when the ease of molding is taken into consideration, a smaller aspect ratio is preferable.

In consideration of ease of mold release and good transferability, it is preferable that the radius r of the arc of the apex portion 7 of the prism 4 is large.
On the other hand, when the optical characteristics of the Fresnel lens, particularly when used for illumination, the radius r is preferably small in order to increase the emission efficiency, which is the ratio of the emitted light to the incident light.

  Therefore, it is preferable that the value of k is 0.04 or more in consideration of good transferability at the time of molding and ease of release. The value of k is preferably 0.38 or less in order to prevent the light emission efficiency from being lowered by setting a radius r larger than necessary even though the molding effect cannot be expected. . In this case, depending on the selected combination of the number of divisions and the k value, the emission efficiency may be lower than that of the original lens that is the basis for designing the Fresnel shape. When injection efficiency is given the highest priority, necessary and sufficient efficiency can be secured by selecting a small number of divisions or selecting a small k value.

Since the appearance of the lens is emphasized, there are cases where it is not desired to increase the number of divisions and make individual annular prisms stand out. In such a case, there is a possibility that the emission efficiency becomes worse than that of the original lens due to an increase in the number of divisions. In such a case, it is preferable to set the upper limit value of k to k = 0.5553e ^-0.02N or less, so that the emission efficiency is improved over the original lens regardless of the combination of the number of divisions and the k value. be able to.

  Here, the shape of the Fresnel lens 1 has been described in which the height of the prism 4 is substantially constant and the width of the prism bottom is variable when the optical functional surface of the original lens is divided. As shown, in addition to the Fresnel lens 1, the Fresnel lens 12 having a shape in which the bottom width of the prism 4 is substantially constant and the height of the prism 4 is variable, and the bottom width of the prism 4 is substantially constant. In addition, there is a Fresnel lens 13 in which the position of the bottom of the prism 4 is variable so that the apex position of the prism 4 is substantially constant, and the above formula (1) is also described including these Fresnel lenses 12 and 13. To do.

  In the shape of the Fresnel lens 1, the prism 4 has the same height from the center of the optical axis toward the outer periphery, but the bottom width of the prism 4 gradually decreases. In this case, the width of the bottom of the prism 4 is an inflow port of the resin that flows toward the apex of the prism 4, and if the width becomes narrow, the resin hardly flows into the apex of the prism 4. For this reason, the resin on the outer peripheral side of the prism 4 is less likely to be filled up to the apex of the prism 4, and the transfer to the mold is insufficient and the predetermined shape may not be obtained. In other words, the mold transfer becomes insufficient, and in this case, the minute variation in the molding temperature and the fluidity of the material itself also greatly affects the shape, resulting in a large variation. There is a risk that quality variations such as characteristics will increase.

  In the shape of the Fresnel lens 12, the bottom width of the prism 4 serving as the resin inlet is the same for any prism, but the height of the prism 4 increases from the center of the optical axis toward the outer periphery. Similarly, the resin tends to hardly flow into the prism 4 from the center of the optical axis toward the outer periphery.

  When comparing the shapes of the Fresnel lens 1 and the Fresnel lens 12 with the same number of divisions, for example, when the same outermost prisms 4 are compared, the ratio of the prism height to the bottom width of the prism 4 (aspect ratio) is The Fresnel lens 12 is smaller. This tendency is the same for the second prism 4 from the outer periphery, or the third, fourth, and Nth prisms 4, and the Fresnel lens 12 is more advantageous for transferring the mold shape. Conceivable. On the other hand, the height h of the prism of the Fresnel lens 12 is higher than the prism height of the Fresnel lens 1 by about 40% of the prisms on the outer peripheral side, and the heat of the resin is deprived and the fluidity is lowered accordingly. It can be said that it is difficult to transfer. As a result, it is considered that these effects are offset, so that the transfer is almost as easy.

  Comparing the number of divisions of the prism 4 (the number of prisms 4), the aspect ratio tends to become extremely small as the number of divisions increases in both cases of the Fresnel lens 1 and the Fresnel lens 12, but it is almost the same. It is thought to be about. However, since the height h of the prism decreases as the number of divisions increases, it is considered that the larger the number of divisions, the more advantageous for the transfer.

  Further, when considering a mold release process for taking out a molded product from the mold 40 (shown in FIG. 6), there is a problem of deformation near the apex of the prism 4. As shown in FIG. 6, in the case of the shape of the Fresnel lens 12, deformation near the vertex 7 of the prism 4 on the outer peripheral side is particularly likely to occur. In the process of gradually separating the molded product from the mold 40, first, the prism 4 near the center of the optical axis is completely separated from the mold 40, and the prism 4 at the outermost periphery is finally separated from the mold 40. Become. For this reason, the posture of the molded product at the time of mold release is not stable, and the external force is likely to be applied to the portion in contact with the mold 40 (the dividing surface 6 of the prism 4 on the outer peripheral side) due to the tilted posture.

In the case of the shape of the Fresnel lens 1, there is a final release portion from the center side to the outermost peripheral side prism 4, and all the prisms 4 are released almost simultaneously, and the posture of the molded product is easily stabilized. In addition, even if the posture is inclined, the external force is dispersed by all the prisms 4, so that deformation is hardly caused. Also, in the case of the Fresnel lens 13, all the prisms 4 are basically released at substantially the same time, and are hardly deformed as in the case of the Fresnel lens 1.
In any shape, the apex portion 7 of the prism 4 is thin, so that it is easily deformed by a slight external force. Further, the larger the aspect ratio, the thinner the tip (vertex portion 7) of the prism 4, and the more easily deformed with respect to external force. This deformation can be suppressed by reducing the thin portion by providing R at the apex portion.
In addition, in order to stabilize the posture of the molded product at the time of mold release and to prevent the deformation of the part where the mold release is delayed due to the shift of the mold release timing between the inner ring zone and the outer ring zone, each wheel after the R is formed in the ring zone It is preferable that the height of the belt is uniform. Relative to the minimum height of the valley portion on the inner peripheral side of the entire annular zone of the molded product, when h ′ is the average height of each annular zone provided with R, each annular zone provided with R The height is desirably within ± 10% of h ′.

  Another problem at the time of mold release is the overall distortion, cracks and breakage of the molded product. In injection molding, two molds, a movable mold and a fixed mold, are used, and when releasing, two molds are opened and a molded product is taken out. As shown in FIG. 2, one surface is in a state of being in one mold 40, and the opposite surface is first separated from the mold and is in contact with air without being constrained by the mold.

  The surface in contact with the mold 40 is at the same high temperature as the mold 40, while the surface not restrained by the mold is cooled by air. The internal stress of compression always works, and it becomes the force which bites into the metal mold | die 40, and makes it difficult to release.

The degree of shrinkage varies depending on the type of resin material, the temperature of the mold 40, and the like, but from the viewpoint of shape, the more the area that bites into the mold 40, the more difficult it is to release.
As shown in FIG. 7, a biting force is generated on the divided surface 6 which is a vertical surface obtained by dividing the original lens shape, which makes it difficult to release the mold. Compared with the case of the Fresnel lens 1 and the Fresnel lens 12, the area of the dividing surface 6 is hardly changed. When compared in terms of the number of divisions, the area of the dividing surface 6 tends to increase slightly as the number of divisions increases, but there is no significant difference. When R is provided at the apex of the prism, the area of the portion that bites into the mold decreases in proportion to the size of the R dimension, so that mold release is facilitated, but the reduction rate varies depending on the number of prism divisions. If the R dimension of the prism apex is the same, the area reduction rate of the portion that bites into the mold increases as the number of prism divisions increases. Therefore, the larger the number of prism divisions, the easier the mold can be released even if the R dimension of the prism apex is reduced.

  The dividing surface 6 is provided with a draft as described later, so that the angle is slightly different from the vertical surface along the releasing direction, and the dividing surface 6 is released from the case where the dividing surface 6 is a vertical surface. Easy shape. Since stress is generated in the mold release direction due to shrinkage of the molded product, mold release is further facilitated.

  In general, the molded product is released from the mold by ejector pins arranged around the molded product. However, if the above-mentioned biting force is too large, the molded product is not pushed out of the mold and the ejector pin is embedded in the molded product. If it is severe, deformation / distortion occurs in the vicinity of the ejector pin and in a region away from the ejector pin, or in a severe case, the molded product is cracked or damaged. In the case of lenses having the same diameter, the thicker the original design lens before dividing into Fresnel lenses, the larger the area of the dividing surface 6, so that the force to bite into the mold increases and it becomes difficult to release. . On the other hand, even if the thickness is the same, when the lens diameter is large, for example, the number of ejector pins can be increased or the diameter of the ejector pins can be increased, so that release is facilitated.

  As described above, in the molding of the Fresnel lens, there are problems such as “insufficient transfer”, “deformation near the apex 7 of the prism 4 due to mold release”, and “total distortion and breakage due to mold release”.

Regarding “insufficient transfer”, the larger the aspect ratio, the harder it is to transfer. Although it does not change greatly depending on the difference in lens shape, there is a tendency that transfer becomes easier as the number of divisions increases.
As for “deformation near the apex 7 of the prism 4 due to mold release”, the larger the aspect ratio, the easier the deformation because the tip becomes thinner. Regarding the shape of the Fresnel lens, the shape of the Fresnel lens 12 is likely to be deformed.
As for “overall distortion and breakage due to mold release”, adding an R to the prism apex reduces the area that bites into the mold and facilitates mold release. There is almost no difference in the area that bites into the mold depending on the lens shape, but as the number of divisions increases, the effect of adding R increases.

  In order to solve such molding problems, it is desirable to provide r as large as possible at the apex portion 7 of the prism 4. However, increasing the radius r reduces the prism surface 5 as an optical function surface in the first place as shown in FIG. 8, and the desired light distribution characteristics and emission efficiency may not be obtained. . Also, changing the r shape of each prism individually is not desirable from the viewpoint of mold fabrication.

For example, when trying to change the r shape individually, mold processing is performed over a plurality of processes using a tool for die processing suitable for each r shape, or die processing is performed according to the smallest r shape. A cutting tool is selected and a large R shape is machined by contour control of the cutting tool.
According to the former method, since the step spans a plurality of steps (or byte replacement) for each difference in the concave portion r of the mold 40 corresponding to the prism 4, there is a possibility that the position between the annular zones cannot be maintained with high accuracy.

  In the case of the latter method, the machining machine control becomes complicated, and the machining time becomes long to ensure sufficient surface roughness. The tool shape is caused by misalignment due to temperature changes in the machining environment and tool wear. There is a possibility that the positional accuracy and the shape accuracy cannot be kept sufficiently high.

  In consideration of the above-mentioned problems in optical properties and problems in mold fabrication, the relationship between the molding failure generation mechanism and the Fresnel shape was examined. As a result, in order to realize a Fresnel lens with excellent productivity and good optical characteristics, it has been found that the radius r of R provided at the apex portion 7 of the prism 4 is an appropriate value. As described above, the range of k is assumed to be 0.04 to 0.38.

The basic idea of this embodiment is to calculate an appropriate R dimension by multiplying the aspect ratio by a factor (to calculate the radius r of the cross-section arcuate vertex 7 of the prism 4).
Further, in consideration of the above-described problem of manufacturing the mold 40, the aspect ratio is set so that all the prisms 4 have a uniform R instead of changing the R shape (radius r) individually. The average aspect ratio is adopted as the representative value.

Even if the height h is different even if the aspect ratio is the same, the amount of decrease in the apparent aspect ratio due to the addition of R is different. The height h varies depending on the number of divisions.
Therefore, the number of divisions N is taken into the equation as the correction. As a result of the study, it is realistic to set (1 / √N).

  Here, h is the height of the designed prism 4 not including r, and when the height of the designed shape is obtained from the molded Fresnel lens, 2 of the prism surface 5 and the divided surface 6 as described above. It is calculated from the intersection (line) of the extended surfaces of each surface.

  This equation (1) is not applied only to the Fresnel shape with a constant height of the prism 4 shown in the shape of the Fresnel lens 1 as described above. When the height is variable like the Fresnel lens 12, the average height of all the prisms 4 can be applied as the height h. Similarly, the formula (1) can also be applied to the Fresnel lens 13.

The average height of all the prisms 4 is the same regardless of the shape of the Fresnel lens 1 or the shape of the Fresnel lens 12. Basically, the average height of all the prisms 4 in the Fresnel lens 13 is substantially the same as that of the Fresnel lens 1.
The circular arc provided at the apex portion 7 of the prism 4 in terms of the cross-sectional shape is not limited to a perfect circular arc. For example, the cross-sectional shape includes an approximate polygon with respect to the circle, and the same effect can be expected.

  Further, it is not necessary that the radius r of the vertexes 7 of all the prisms 4 provided within the effective diameter of the lens is set to a value satisfying the above range of k, and the optical characteristics of the Fresnel lens 13 are allowed. As long as it falls within the range, the value of the radius r at the apex portion 7 of some of the prisms 4 may be a value out of the range of k described above. For example, the radius r of the apex portion 7 of the prism 4 is set to a predetermined r corresponding to a predetermined k within the range of k described above except for one to several prisms 4. The radius r of the apex portion 7 of several prisms 4 may be a value corresponding to the value of k that is out of the range of k described above.

In the Fresnel lenses 1, 12, and 13 in which the radius r of the apex portion 7 of the prism 4 is set by such an expression (1), by defining the minimum r, damage, cracks, and distortion of the molded product due to biting can be prevented. Can be suppressed.
Further, by defining the range of r as the product of k and the average aspect ratio, it is possible to obtain a yield that can be sufficiently produced. By defining the maximum r as the product of k and the average aspect ratio, there is no uselessly large r that does not contribute to yield improvement, and the injection efficiency can be ensured.

Further, in the Fresnel lenses 1, 12, and 13, for example, when the diffused light of the point light source 16 is incident, the Fresnel lens is obtained when the divided surface is substantially along the optical axis direction of the original lens that is the Fresnel lens 1. A part of the light emitted from 1, 12, and 13 hits the split surface 6 of the prism 4 and is subjected to multiple reflections between adjacent prisms 4, which causes a reduction in emission efficiency.
Further, when releasing the Fresnel lenses 1, 12, and 13 as molded products, the movable mold moves with respect to the fixed mold as described above. At this time, as shown in FIG. 7, the mold release direction of the Fresnel lenses 1, 12, 13 as the molded product that is separated from the other mold and is held by the one mold 40 and the movement of the movable mold described above. The direction is the same and is along the optical axis direction. If the split surface 6 is along the mold release direction of the Fresnel lenses 1, 12, and 13 with respect to the mold 40, the mold will be released with the split surface 6 and the inner surface of the mold being in contact with each other at the time of mold release. This causes deformation of the tip portion of the prism 4. In addition, the above-mentioned biting makes it difficult to release the mold and causes damage to the Fresnel lenses 1, 12, and 13.

  Here, it is conceivable to set the above-mentioned clearance angle by inclining the dividing surface 6 of the prism 4 in order to facilitate mold release. However, depending on the setting of the clearance angle, the prism surface as an optical function surface decreases. In addition, the optical characteristics may be deteriorated. Therefore, as shown in FIG. 9, when a point light source (light source) 20 is provided at a predetermined position of the Fresnel lens 1, the prism surface 5 and the dividing surface 7 of the adjacent prism 4 out of the light incident from the point light source 20. The dividing plane 7 constituting the valley 8 is set substantially along the direction of light (L) reaching the deepest portion 9 of the valley 8 constituted by The clearance angle is an angle with respect to the mold release direction of the Fresnel lens 1 with respect to the mold 40 described above.

  Thereby, it can suppress that the light which passed the Fresnel lens 1 hits the division surface 6, and can suppress multiple reflection. By providing the clearance angle on the dividing surface 6 as described above, there is a possibility that the light emission efficiency may be reduced. However, by setting the clearance angle as described above, the emission efficiency is reduced due to multiple reflection at the prism 4. Can be prevented. Accordingly, providing the clearance angle facilitates mold release and suppresses deterioration of optical characteristics such as injection efficiency. That is, the deterioration of the optical characteristics due to the inclination of the dividing surface 6 by the clearance angle can be suppressed by preventing the multiple reflection and improving the optical characteristics.

  The light reaching the deepest portion 9 of the valley 8 is refracted when entering the Fresnel lens 1 and then reaches the deepest portion 9, and is determined based on the refractive index of the Fresnel lens 1. In this example, for example, since it is used for a headlight of an automobile, for example, a white LED having a wavelength spread in the visible light region is used. Therefore, a wide range of wavelengths is used, and the refractive index at the center wavelength is adopted as the refractive index.

  The clearance angle of the dividing surface 6 does not need to follow the light L with high accuracy, and may be within a range of plus or minus 3 degrees with respect to the angle of the light passing through the deepest portion 9 of the valley 8. The clearance angle is required to be at least 0.5 degrees from the viewpoint of mold release.

Here, of the light incident from the point light source 20, the valley 8 is set in the direction of the light (L) reaching the deepest portion 9 of the valley 8 constituted by the prism surface 5 and the dividing surface 7 of the adjacent prism 4. For example, as shown in FIG. 10, the distance from the central axis of the Fresnel lens to the apex of the prism 4 is set as X ₁ , and the lens rear end surface is set as an example of a method for setting the dividing surface 7 to be configured to be substantially along. X _{0 is} the distance from the intersection of the split surface set to the clearance angle and the extended surface of the split surface to the center axis of the Fresnel lens, H is the height from the lens rear end surface of the apex of the prism, and When the distance to the light source 20 is B and the refractive index of the lens is n, the clearance angle defined by the following equation (2) can be adopted.
X ₁ = X ₀ + (h × tan (sin ⁻¹ (sin (tan ⁻¹ (X ₀ / B)) / n))) (2)

    Moreover, Formula (2) is calculated | required from below-mentioned Formula (3), Formula (4), and Formula (5).

The angle theta ₀ in equation obtained by substituting equation (3) in equation (4) can be obtained formula (2) by substituting the angle theta ₁ of the formula (5).

The lens diameter is preferably 20 mm to 80 mm. When the lens diameter of the Fresnel lenses 1, 12, and 13 is made shorter than 20 mm, it is difficult to release the Fresnel lenses 1, 12, and 13 by the ejector pins due to the biting on the mold. When the molded product is pressed, there is a risk of deformation, cracking, breakage, and the like.
On the other hand, if the lens diameter is larger than 80 mm, the ejector pin distance from the center of the lens becomes too long, and bending deformation tends to occur.

  The Fresnel lens 1 preferably has a maximum thickness within the range of the lens effective diameter D of 0.5 mm to 4 mm. If the maximum thickness is less than 0.5 mm, the thickness of the Fresnel lens 1 is reduced accordingly, and it becomes difficult to maintain the shape of the Fresnel lens 1. Moreover, it can prevent that shaping | molding time becomes long by making maximum thickness into 4 mm or less.

  It is also possible to apply an AR coat (antireflection film) to at least one of the first surface 2 on which light from the Fresnel lens 1 enters and the second surface 3 from which light exits.

As the AR coat, for example, a four-layer structure made of silicon dioxide and zirconium dioxide can be applied. For example, the AR coat has a structure of ZrO ₂ —SiO ₂ —ZrO ₂ —SiO ₂ .
When the AR coating is provided on the first surface, it is possible to prevent the incident light from being reflected on the first surface and to improve the light emission efficiency.
Further, when the AR coating is applied to the second surface side, the multiple reflection described above can be prevented, and the light emission efficiency can be improved.
When the above-described four-layer AR coating is used, for example, when the reflectance without the AR coating is about 4%, the reflectance is reduced to about 1% by improving about 3%. It becomes possible. As a result, for example, when it is desired to increase the number of divisions, the injection efficiency decreases if an attempt is made to secure a sufficient manufacturing margin, but the injection efficiency can be improved by using the AR coating.
In addition, there is an AR coat for a single wavelength, but here, since the white light is used instead of the single wavelength as described above, the AR coat corresponding to the visible light region is used. become.

  In the above example, the plurality of annular prisms 4 having different diameters are concentrically arranged. However, the prism 4 may not be annular, but may be elliptical, or elliptical prisms may be concentrically arranged. Good. In this case, although the cross-sectional shapes are different between the long diameter side and the short diameter side, the effective diameter D is set as the respective diameter in the formula (1), and each k is determined so that r is the same on the long diameter side and the short diameter side. . However, k needs to be in the range of 0.04 to 0.38.

  Further, in the cross-sectional shape of the prism 4, the side to be the prism surface 5 and the side to be the divided surface 6 are formed in a straight line except for the arcuate apex portion 7, but either or both of these pieces are curved. It is good also as a shape.

The prism 4 of the Fresnel lens 1 needs to have a shape that can be released, and when each side is curved, for example, it becomes a convex curved shape. Also in this case, it is necessary that the curve protrudes to the extent that it does not interfere with mold release. In this case, the releasability may be improved.
Further, when the prism surface 5 is curved, for example, by making it a curve corresponding to an aspherical shape or the like, the light emission efficiency can be improved.

  In such a Fresnel lens 1, for example, by using a thick lens such as an aspheric lens as the Fresnel lens 1, it is possible to achieve a significant reduction in weight and thickness. Thereby, since it cools quickly at the time of shaping | molding, shaping | molding time can be shortened significantly. In addition, the arrangement of the lens can be facilitated due to the thinness. Further, the cost can be reduced by reducing the raw material by shortening the molding time and reducing the thickness.

  Further, by setting the value of k as described above, it is possible to make the structure easy to release while suppressing the decrease in injection efficiency, to facilitate the manufacture of the mold, and to the stable quality Fresnel lens 1. Can be provided.

  Next, a lighting fixture using this Fresnel lens will be described. The luminaire is, for example, a headlight of an automobile, and as a main part thereof, as shown in FIG. 11, a base part 34 including a lens holding part 31, a light source mounting part 32, and a reflector holding part 33, and a projector lens The Fresnel lens 1, the light source 37, and the reflector 38 are provided. The light source 37 is an LED.

  The light from the light source 37 attached to the light source attachment portion 32 of the base portion 34 is condensed mainly in the vertical direction by the reflector 38 and is incident on the Fresnel lens 1. The Fresnel lens 1 changes the direction of light so as to project incident light into a predetermined light projection range.

  In this luminaire, since the Fresnel lens 1 is used as a light projection lens in place of the conventional aspheric lens, the effects of weight reduction and thickness reduction can be obtained as described above. In particular, the space efficiency at the installation position of the headlamp can be improved by reducing the thickness. Moreover, a high-performance lighting fixture can be manufactured at low cost by using the Fresnel lens 1 that is highly efficient, easy to manufacture, and stable in quality as described above.

  In this luminaire, since an LED is used as the light source 37, the amount of heat generated is small compared to other light sources other than the LED, and the Fresnel lens 1 is not affected by a large amount of heat. Even if it is made of resin, it is not deformed by heat.

  In addition, since the wavelength of light emitted from the LED is limited, the function of the lens can be improved by using a refractive index corresponding to the wavelength in the design of the Fresnel lens 1. In particular, by making the refractive index when determining the clearance angle correspond to the wavelength as described above, multiple reflection can be prevented more reliably and the light emission efficiency can be improved. The lighting fixture is not limited to a headlamp and can be applied to various lighting fixtures. In particular, the Fresnel lens is suitable for a lighting fixture that projects light in a predetermined range using the Fresnel lens 1. 1 can be used.

Next, the metal mold | die used for manufacture of a Fresnel lens is demonstrated.
In the injection molding, the Fresnel lens 1 is molded by two molds. One of the two molds is a fixed mold and the other is a movable mold. At the time of mold release, the movable mold is moved away from the fixed mold.

  A cavity 41 shown in FIG. 12 for molding the second surface 3 of the Fresnel lens 1 is provided on the mold surface of the movable mold. A plurality of grooves 42 are formed in the cavity 41 corresponding to the plurality of prisms 4 on the second surface 3 of the Fresnel lens 1. The inner space of the groove 42 has a shape corresponding to the shape of the prism 4, and surfaces corresponding to the outer surfaces of the prism surface 5, the dividing surface 6, and the apex portion 7 are formed.

Basically, the shape of each groove 42 corresponds to each prism 4 of the Fresnel lens 1, but the prism 4 which is a molded product contracts slightly with respect to the groove 42 of the mold. . The cavity size of the mold is set to be larger than the final product at a ratio determined from the molding shrinkage rate of the resin in consideration of shrinkage of the resin used for molding.
By making the inner surface of the cavity 41 into a shape corresponding to the prism 4 of the Fresnel lens 1 described above, the groove 42 has a curved surface corresponding to the arc of the apex portion 7 of the prism 4, not the sharpest shape of the groove 42. Thus, the mold can be easily manufactured. Further, by making the mold shape corresponding to the Fresnel lens 1 as described above, the Fresnel lens 1 can be easily released and the quality of the Fresnel lens 1 can be stabilized in a highly efficient state. .

Next, an injection molding method for the Fresnel lens 1 will be described.
The injection molding of the Fresnel lens 1 is performed using a movable mold provided with the above-described cavity 41 and a fixed mold corresponding thereto.
With the fixed mold and the movable mold closed, the resin injected from the injection nozzle is injected into the cavity 41 through the sprue, runner and gate.

When the temperature of the cavity 41 is lowered to a predetermined temperature in this state, the molded Fresnel lens 1 is taken out by moving the movable mold with respect to the fixed mold.
At this time, since the Fresnel lens 1 is thinner than, for example, an aspherical lens or the like, the temperature is rapidly reduced, and the time required for release can be shortened.

  Further, at the time of molding, the shape of the deepest portion of the groove 42 of the cavity 41 of the mold is determined corresponding to the apex portion 7 of each prism 4 of the Fresnel lens 1. At this time, since the deepest portion of the groove 42 is formed in an arc shape corresponding to the apex portion 7 of the prism 4 within the range of the above-described value k, it is easy to release and stabilize the quality. Can do.

Below, the Fresnel lens 1 was manufactured as an Example, and the molding cycle, lens weight, and sink amount at that time were confirmed. Moreover, the emission efficiency (%), which is the ratio of the amount of emitted light to the amount of incident light of the manufactured Fresnel lens 1, and the non-defective product rate (%) were determined.
As the Fresnel lens 1, as shown in Table 1, lenses having the number N of prisms (annular zones) of 21, 42, and 63 were manufactured.
The effective lens diameter D on which the prism is formed is 30 mm, and the entire diameter of the lens including the mounting flange is 37 mm.
The thickness of the base excluding the prism-shaped portion was 2 mm. The prism is a type in which the designed prism height h is constant, as shown in the Fresnel lens 1 shown in FIG. The height of the designed prism was 0.4 mm for a lens with 21 prisms N, 0.2 mm for a 42 N lens, and 0.134 mm for a 63 N lens. The maximum thickness including the prism is the sum of the thickness of the base and the height h of the prism, which is 2.4 mm to 2.134 mm. Further, the clearance angle was set on the splitting surface of the prism so as to be along the direction of the light beam reaching the deepest portion 9 of the valley as described above.
Methacrylic resin (PMMA, also commonly called acrylic resin) was used as the lens material.
As shown in Tables 4 to 6 with respect to the number N of each prism, Fresnel lenses having different k values in four stages were manufactured. (In practice, for the convenience of mold manufacture, the radius r of the prism apex was set to 0 mm, 0.01 mm, 0.03 mm, and 0.05 mm.)
Note that the data of the Fresnel lens 1 having a k value of 0 and the aspherical lens are comparative examples. The product non-defective rate is obtained by dividing the number of non-defective products after looking into defective products from the manufactured Fresnel lens 1 by the total number of manufactured Fresnel lenses 1.

Tables 1 to 3 show the measurement results of the molding cycle, lens weight, and sink amount. In the case of a Fresnel lens with a prism number N of 21, 42 and 63, the data is when the radius r of the prism apex is 0.01 mm, but the values are substantially the same at 0.03 mm and 0.05 mm. However, when the r dimension was 0 mm, the molded product could not be released from the mold, and a complete sample could not be produced.
The results of injection efficiency and product yield rate are shown in Tables 4 to 6 and the graphs of FIGS.
13 to 15, P21 in FIG. 13 shows the emission efficiency of the Fresnel lens 1 with 21 prism numbers N, P42 in FIG. 14 shows the emission efficiency of the Fresnel lens 1 with 42 prism numbers N, and FIG. P63 indicates the emission efficiency of the Fresnel lens 1 having a prism number N of 63. In each figure, U indicates the product non-defective rate.
Incidentally, the injection efficiency when the apex r size in Tables 4 to 6 and FIGS. 13 to 15 is 0 mm is described as a result of simulation because the molded product could not be released and measured as described above. . When the apex r dimension is 0.01 mm, 0.03 mm, and 0.05 mm, the simulation result and the measurement result coincide with each other, and the measurement value is described.

  Further, the border line of the injection efficiency was 77% of the case of the aspherical lens as a comparative example. In addition, the border line of the non-defective product rate was set to 85% in consideration of costs and the like. As shown in FIG. 13, the non-defective product rate exceeds 85% of the border line when the value of k becomes 0.04 or more. The borderline 85% of the product non-defective rate means that when 100 pieces are molded, there are 85 pieces that are formed as a product without any deformation or insufficient transfer zone.

  The emission efficiency of the Fresnel lens 1 with 21 prisms N exceeds 77%, which is the borderline when the value of k is 0.38 or less. When the number of prisms N is 42 and 63, the value of k that exceeds 77%, which is the borderline, is even smaller. Therefore, in order to obtain sufficient emission efficiency when the value of k is in the range of 0.04 to 0.38, it is necessary to reduce the number N of prisms within the lens effective diameter D.

  However, even if the number N of prisms is large, the value of k exceeds the borderline by reducing the value of k, and these can be effectively used by narrowing the range of k. Also, depending on the purpose and application, it is difficult to understand the effects obtained by increasing the number of prisms, especially the effect of light intensity due to each prism (ring zone) 4, even if it is below the borderline of the emission efficiency. Since the lens 1 is difficult to understand, a Fresnel lens having a large number of prisms may be used.

DESCRIPTION OF SYMBOLS 1 Fresnel lens 2 1st surface 3 2nd surface 4 Prism 5 Prism surface 6 Dividing surface 7 Apex part 8 Valley 9 Deepest part 12 Fresnel lens 13 Fresnel lens 20 Point light source (light source)
h Prism height L Direction of light reaching the deepest part of the valley

Claims (12)

A first surface on which light is incident and a second surface from which light is emitted; a plurality of prisms are formed on the second surface; and the prism includes a prism surface, a split surface, A Fresnel lens manufacturing method for manufacturing a resin-made Fresnel lens whose cross section is formed in a substantially triangular shape from an arcuate apex portion connecting the prism surface and the dividing surface,
The radius of the arc at the apex is r (mm), the height of the prism is h (mm), the effective lens diameter is D (mm), and the number of prisms included in the effective lens diameter D (mm) is N. If
Said r (mm) shall be shown by the following formula | equation (1),
And the value of k (mm) in said Formula (1) is 0.04-0.38 mm, The manufacturing method of the Fresnel lens characterized by the above-mentioned.

The method for producing a Fresnel lens according to claim 1, wherein an upper limit value of k is k = 0.5553e −0.02 ^N (mm) or less. The method for manufacturing a Fresnel lens according to claim 1, wherein each of the prisms is formed in a concentric circle shape or a concentric ellipse shape. The split surface of the prism is provided with a clearance angle,
The clearance angle of the dividing surface is
Of the light incident from the light source, set so that the split surface constituting the valley substantially follows the direction of the light reaching the deepest part of the valley formed by the prism surface and the split surface of the adjacent prisms. The method for manufacturing a Fresnel lens according to any one of claims 1 to 3, wherein the Fresnel lens is manufactured . 5. The Fresnel lens according to claim 1, wherein a height h of each prism is set within plus or minus 10% with respect to an average of the height h. Manufacturing method . The method for manufacturing a Fresnel lens according to any one of claims 1 to 5, wherein the lens diameter is 20 mm to 80 mm. The method for manufacturing a Fresnel lens according to any one of claims 1 to 6, wherein the prism has a cross-sectional shape of the prism surface and the dividing surface that is a straight line or a curved line. 8. The Fresnel lens according to claim 1, wherein the prisms have substantially the same height and have different bottom surface widths corresponding to the inclination angles of the prism surfaces. 9. Manufacturing method . The method for producing a Fresnel lens according to any one of claims 1 to 8, wherein the maximum thickness of the effective lens diameter is 0.5 to 4 mm. 10. The manufacture of a Fresnel lens according to claim 1, further comprising a step of forming an antireflection film on at least one of the first surface and the second surface. 11. Way . Method for producing a lighting fixture, characterized in that to produce a lighting fixture using the Fresnel lens manufactured by the manufacturing method of the Fresnel lens as claimed in any one of claims 10. The method of manufacturing a lighting fixture according to claim 11, wherein the light source is an LED .

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