Light-transmissive resin member

Abstract

To provide a light-transmissive resin member that has a high droplet discharge effect and exhibits an excellent anti-fogging effect.SOLUTION: A light-transmissive resin member has a substrate, and a groove structure comprising a plurality of linear projections and a plurality of linear grooves and formed in a surface of the substrate. The plurality of linear projections and the plurality of linear grooves extend in directions parallel to each other. When the pitch between the linear grooves is defined as P, and the groove depth and the groove width of the linear grooves are defined as D and W2, respectively, the plurality of linear projections and the plurality of linear grooves satisfy D / P≥1.0 and W2 / P>0.5.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present invention relates to a translucent resin member, and more particularly to a translucent resin member having a fine groove structure formed on the surface of a substrate and exhibiting an anti-fogging effect. [Background technology]

[0002] Conventionally, in order to prevent the surfaces of optical components and the like from fogging up, it has been known to apply an anti-fogging coating to the surface of the component, or to form fine grooves on the surface of the component to turn water droplets into a water film.

[0003] For example, Patent Document 1 discloses a molded structure that exhibits hydrophilicity and antifogging properties by forming a fine uneven structure on the surface of a substrate made of resin or the like.

[0004] Furthermore, Patent Document 2 discloses a translucent resin member that can exhibit an anti-fogging effect while suppressing a decrease in light transmittance by forming a plurality of groove structures consisting of a plurality of linear recesses on the surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-193002 [Patent Document 2] Japanese Patent Publication No. 2022-122020 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors of the present application have conducted extensive research into the surface tension of water droplets on the top surface of a fine groove structure, as well as the solid-liquid interfacial tension and drainage performance of water droplets that have migrated into the grooves, and have discovered a groove shape that provides a high anti-fogging effect.

[0007] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a light-transmitting resin member that has a high liquid droplet discharge effect and exhibits an excellent anti-fogging effect. [Means for solving the problem]

[0008] A light-transmitting resin member according to one embodiment of the present invention comprises: A substrate; A light-transmitting resin member having a groove structure consisting of a plurality of linear convex portions and a plurality of linear grooves formed on a surface of the base material, the plurality of linear protrusions and the plurality of linear grooves extend in directions parallel to each other, When the pitch between the linear grooves is P, and the groove depth and groove width of the linear groove are D and W2, respectively, the plurality of linear convex portions and the plurality of linear grooves satisfy D / P≧1.0 and W2 / P>0.5. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view schematically showing a light-transmitting resin member according to an embodiment of the present invention. [Figure 2A] 3 is a cross-sectional view schematically showing a cross section of a light-transmitting resin member perpendicular to the extending direction of a groove. FIG. [Figure 2B] FIG. 10 is a diagram showing a case where the convex portion has a trapezoidal cross section. [Figure 3] FIG. 1 is a diagram showing the results of a fogging test and antifogging properties of the light-transmitting resin member of Example 1 (EX1) in comparison with the results of the light-transmitting resin member of Comparative Example 1 (CX1). [Figure 4] FIG. 1 is a graph showing the results of the anti-fogging properties of Example 1, Comparative Example 1, and Comparative Example 2 in comparison. [Figure 5] FIG. 1 is a diagram showing the state of water droplets on the surface of the groove structure and the results of anti-fogging properties for Example 1, Comparative Example 1, and Comparative Example 2, in comparison. [Figure 6] FIG. 1 shows cross-sectional SEM images and haze test photographs of samples of Example 2 (EX2), Comparative Example 3 (CX3), and Comparative Example 4 (CX4). [Figure 7A] 10 is a schematic diagram showing a water droplet dropped on a groove structure as viewed from above. [Figure 7B] 10 is a schematic diagram showing a water droplet dropped onto a groove structure with a wide groove width, as viewed from above. [Figure 7C] FIG. 2 is a cross-sectional view schematically showing a cross section of a groove structure. [Figure 8] 2 is a schematic cross-sectional view of a portion of a light-transmitting resin member. [Figure 9A] 10 is a cross-sectional view schematically showing a case where the corners of the top or bottom of the convex portion are rounded. FIG. [Figure 9B] FIG. 10 is a cross-sectional view schematically showing a case where the top surface of the convex portion has an upwardly convex curved shape. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the following, preferred embodiments of the present invention will be described, but these may be modified and combined as appropriate. In the following description and accompanying drawings, substantially the same or equivalent parts are designated by the same reference numerals.

[0011] 1. Structure of the translucent resin material Fig. 1 is a perspective view schematically showing a light-transmitting resin member 10 according to one embodiment of the present invention. The light-transmitting resin member 10 is configured by forming a fine groove structure 15 on a surface 11S of a base material 11 made of resin. Fig. 1 shows a part of the light-transmitting resin member 10 on which the groove structure 15 is formed.

[0012] The groove structure 15 is composed of a plurality of linear convex portions 15F (hereinafter also simply referred to as convex portions 15F) and linear grooves 15G (hereinafter also simply referred to as grooves 15G), which are a plurality of linear concave portions formed between the convex portions 15F. Note that, although the light-transmitting resin member 10 has a flat plate shape as an example, the shape is not limited to this. The light-transmitting resin member 10 may have various shapes, such as a curved shape.

[0013] In the following, the groove structure 15 is described as being formed in a partial region of the substrate 11, but it may be formed over the entire substrate 11.

[0014] The substrate 11 is made of, for example, a thermoplastic resin such as acrylic resin (PMMA: polymethyl methacrylate resin) or polycarbonate (PC), or a thermosetting resin, but is preferably made of acrylic or polycarbonate.

[0015] The base material 11 may be made of a light-transmitting resin, and may be colored, for example, in red or amber.

[0016] The light-transmitting resin member 10 of the present embodiment is used, for example, in vehicle headlights, rear combination lamps, auxiliary lights, outer lenses of meters of motorcycles, sensor windows of LiDAR (Light Detection and Ranging), face shields of helmets, etc. However, the light-transmitting resin member 10 is not limited to these, and can be used in various products that require an anti-fogging structure.

[0017] 1, the plurality of protrusions 15F and the plurality of grooves 15G extend linearly in parallel directions. The plurality of protrusions 15F and the plurality of grooves 15G have constant widths W1 and W2 in the extension direction, respectively. The extension direction of the grooves 15G (also referred to as the groove direction) is indicated as the x-direction, and the direction perpendicular to the groove direction is indicated as the y-direction.

[0018] The plurality of convex portions 15F and the plurality of grooves 15G are not limited to being linear, but may be parallel curved.

[0019] 2A is a cross-sectional view schematically showing a cross section of the light-transmitting resin member 10 perpendicular to the extending direction of the grooves 15G. Note that FIG. 2A shows a part of the groove structure 15.

[0020] The convex portions 15F and the grooves 15G have rectangular cross sections, with the convex portions 15F having a width W1 (convex portion width) and the grooves 15G having a groove width W2. The groove pitch P (the pitch between the grooves 15G), which is one period of the convex portions 15F and the grooves 15G, is P = W1 + W2. The grooves 15G have a groove depth D. That is, in the groove structure 15, the grooves 15G are periodically formed at a constant groove pitch P and a constant groove depth D.

[0021] 2B shows a case where the protrusion 15F has a trapezoidal cross section. Specifically, both side walls of the protrusion 15F form an angle φ with the surface 11S of the substrate 11. In this case, the width W1 of the protrusion 15F and the groove width W2 of the groove 15G can be determined as the width at a position where the depth from the surface 11S is D / 2. Note that the edge of the top of the protrusion 15F may have a curved shape.

[0022] The groove pitch P of the groove structure 15 is, for example, 150 nm≦P≦390 nm. The groove pitch P is related to the transmittance of light that passes through the light-transmitting resin member 10. For example, if it is desired to transmit visible light with a wavelength of 380 nm or more, a decrease in transmittance can be suppressed by setting the groove pitch P to approximately 235 nm or less. In this case, it is preferable that the groove pitch P be 150 nm or more (150 nm≦P≦235 nm) so that part of ultraviolet light can be transmitted.

[0023] Furthermore, if it is desired to transmit red light with a wavelength of 630 nm or more, the decrease in transmittance can be suppressed by setting the groove pitch P to approximately 390 nm or less. Furthermore, if it is desired to transmit visible light (amber color) with a wavelength of 580 nm or more, the decrease in transmittance can be suppressed by setting the groove pitch P to approximately 360 nm or less.

[0024] (1) Evaluation of anti-fogging properties 3 shows the results of the fogging test and anti-fogging property of the light-transmitting resin member 10 of Example 1 (EX1) in comparison with the results of the light-transmitting resin member 10 of Comparative Example 1 (CX1). The sample of Example 1 was a resin molded product made using a metal mold, and the sample of Comparative Example 1 was made using a Si mold and by forming a groove structure by thermal imprinting of acrylic (PMMA).

[0025] More specifically, the translucent resin member 10 of Example 1 (EX1) has a substrate 11 which is an acrylic flat plate (60 mm square, 2 mm thick), and is provided with a groove structure 15 having a groove depth D=290 nm, a groove pitch P=290 nm, a width W1 of the convex portion 15F=60 nm, a groove width W2=230 nm, and an aspect ratio D / W2=1.26.

[0026] In addition, the translucent resin member 10 of Comparative Example 1 (CX1) has a groove structure 15 provided on a base material 11 made of the same material (acrylic) as the translucent resin member 10 of Example 1. The groove structure 15 of Comparative Example 1 is different from the groove structure 15 of the translucent resin member 10 of Example 1.

[0027] More specifically, in Example 1, the groove width W2 is larger than the width W1 of the convex portion 15F (W1 < W2), and the ratio W2 / P of the groove width W2 to the groove pitch P is W2 / P > 0.5. On the other hand, in Comparative Example 1, the groove width W2 is equal to the width W1 of the convex portion 15F (W1 = W2), and W2 / P = 0.5.

[0028] FIG. 3 shows water droplet images (microscopic images) in the fogging tests of Example 1 and Comparative Example 1. The water droplet images in the fogging test are images obtained by preparing warm water (40°C) in a thermostatic water bath where steam is generated, installing the groove structure 15 of the translucent resin member 10 above the thermostatic water bath so that it faces the thermostatic water bath, and observing with a microscope after 30 seconds. In the groove structure 15 of Example 1, it can be seen that a large number of minute water droplets on the groove structure 15 are elongated in the extending direction (groove direction) of the groove 15G, and high antifogging performance is exhibited.

[0029] In the groove structure 15 of Comparative Example 1, the elongation of the water droplets is clearly smaller than that in the case of Example 1, indicating that the antifogging property is inferior.

[0030] FIG. 4 shows a comparison of the antifogging results of Example 1 (EX1), Comparative Example 1 (CX1), and Comparative Example 2 (CX2).

[0031] Here, the translucent resin member 10 of Comparative Example 2 has a groove structure 15 provided on a base material 11 made of the same material (acrylic) as the translucent resin member 10 of Example 1. The groove structure 15 of Comparative Example 2 is different from the groove structure 15 of the translucent resin member 10 of Example 1. Specifically, in Comparative Example 2, the point that the groove width W2 is larger than the width W1 of the convex portion 15F (W2 / P > 0.5) is the same as in Example 1, but the ratio D / P of the groove depth D to the groove pitch P is D / P = 0.66, which is smaller than D / P = 1.0 of Example 1.

[0032] FIG. 5 shows a comparison of the water droplet images, water droplet states, and anti-fogging properties on the surface of the groove structure 15 for Example 1 (EX1), Comparative Example 1 (CX1), and Comparative Example 2 (CX2). The water droplet image was observed by the same method as the water droplet image shown in FIG. 3.

[0033] Referring to FIGS. 4 and 5, the ratio W2 / P of Example 1 (EX1) and Comparative Example 2 (CX2) exceeds 0.5, and the point that W1 < W2 is the same, but the anti-fogging property of Example 1 is superior to that of Comparative Example 2.

[0034] That is, the aspect ratio R of the stretched water droplet (FIG. 5) is larger in the case of Example 1 than in the case of Comparative Example 2. Specifically, in the case of Comparative Example 2, the aspect ratio R, which is the ratio of the length in the longitudinal direction (groove direction) to the width in the lateral direction (direction perpendicular to the groove direction) of the water droplet, is about 3, whereas in the case of Example 1, it is as large as about 7 to 9, indicating that the water droplet is greatly stretched in the groove direction and high anti-fogging property is exhibited. Here, the aspect ratio R is calculated as the average value of the ratios of the longitudinal and lateral lengths of a plurality of water droplets appearing in the water droplet image.

[0035] FIG. 5 shows the observed images and contact angles of water droplets dropped on the groove structures of the samples of Example 1, Comparative Example 1, and Comparative Example 2. In the sample of Comparative Example 2, as in Example 1 and Comparative Example 1, a Si mold was used, and the groove structure was formed by thermal imprinting of acrylic (PMMA).

[0036] The contact angle of a water droplet on each sample was observed using a contact angle meter (PCA-11 manufactured by Kyowa Interface Science). In each case, a 2 μl droplet was dropped from the nozzle NZ of the contact angle meter, and the contact angle and observation image from above the droplet 30 seconds after dropping are shown. The contact angles θp and θn in the groove direction (x direction) and the direction perpendicular to the groove direction (y direction), as well as the observation image, are shown.

[0037] The equilibrium contact angle θeq of water dropped onto the substrate 11 without grooves was 76°. This was measured by dropping water onto the substrate 11 without grooves and measuring the contact angle of the droplet after 30 seconds using the θ / 2 method.

[0038] In Comparative Example 1 (CX1) and Comparative Example 2 (CX2), the contact angle θp in the groove direction was 50.4° and 49.4°, respectively, but in Example 1 (EX1), it was reduced to 35.8°, and it was confirmed that the water droplets moved significantly in the groove direction.

[0039] Furthermore, in the direction perpendicular to the groove direction, the contact angle θn was 80.8° and 87.9° in Comparative Examples 1 and 2, respectively, but was reduced to 70.0° in Example 1. It is understood that in Example 1, the movement of water droplets into the grooves was promoted, reducing the contact angle θn in the direction perpendicular to the groove direction.

[0040] Furthermore, the degree of surface haze was quantitatively calculated for Example 1, Comparative Example 1, and Comparative Example 2 (hereinafter referred to as haze). Here, "haze" was calculated by grayscaling the RGB values ​​of each water droplet image shown in FIG. 5 using 255 gradations. More specifically, a histogram was obtained for the grayscale value of each pixel, and the ratio of the number of pixels whose grayscale value was equal to or greater than a predetermined threshold value TH to the total number of pixels was defined as haze. In other words, water droplets reflect white, and the brighter the pixel, the more light is scattered by the water droplets. Therefore, the ratio of the number of bright pixels to the total number of pixels was defined as haze.

[0041] In the case of Example 1 (EX1), the haze was 0.10, which was lower than the 0.12 in the case of Comparative Example 1 (CX1), and better anti-fogging properties were obtained. Moreover, in Example 1, the haze was significantly lower than the 0.89 in the case of Comparative Example 2 (CX2), and it is clear that excellent anti-fogging properties were obtained.

[0042] As explained above, the results shown in Figures 4 and 5 show that excellent anti-fogging properties can be obtained when the groove width W2 is larger than the width W1 of the convex portion 15F (W2 / P>0.5) and D / P≧1.0.

[0043] (2) Fogging test FIG. 6 shows cross-sectional SEM images and haze test photographs of samples of Example 2 (EX2), Comparative Example 3 (CX3), and Comparative Example 4 (CX4). It also shows structural values ​​such as groove depth D, groove pitch P, width W1 of convex portion 15F, and groove width W2 of each sample. Note that the structural values ​​of these groove structures of Example 2, Comparative Example 3, and Comparative Example 4 differ from those of Example 1 described above. Note that a printed matter with the letters ("STANLEY") printed in amber is placed behind the groove structure. The other configurations are the same as those of Example 1.

[0044] More specifically, in Example 2, the ratio W2 / P of the groove width W2 to the groove pitch P is 0.57. That is, W2 / P>0.5, and the groove width W2 is greater than 50% of the groove pitch P. On the other hand, in Comparative Examples 3 and 4, the ratios W2 / P are 0.50 and 0.29, respectively, which are smaller than that in Example 2 and are W2 / P≦0.5.

[0045] Furthermore, the ratios D / P of the groove depth D to the groove pitch P are approximately the same, 1.07, 1.09, and 1.09, in Example 2, Comparative Example 3, and Comparative Example 4. That is, in Example 2, Comparative Example 3, and Comparative Example 4, the ratios D / P exceed 1.0 (D / P>1.0).

[0046] Referring to the photographs of the fogging test, it can be seen that in Example 2, the printed characters are clearly visible and excellent anti-fogging properties are obtained (double circle in the figure). In Comparative Example 3, W2 / P=0.50 and D / P=1.09, and it can be seen that the anti-fogging properties are inferior to those of Example 2 (circle in the figure). In Comparative Example 4, W2 / P=0.29, which is far outside the range of the above formula (1), and the anti-fogging properties are significantly inferior to those of Example 2 (x in the figure).

[0047] (3) Anti-fogging properties Based on the above results regarding the antifogging property, the following consideration was made regarding the manifestation of the antifogging property depending on the configuration of the groove structure 15.

[0048] 7A and 7B are schematic diagrams showing water droplets AQ, which are droplets dropped onto groove structure 15, as viewed from above groove structure 15 (i.e., as viewed from above). Fig. 7B shows a case where groove 15G has a wider groove width than groove 15G in Fig. 7A. Fig. 7C is a cross-sectional diagram showing a schematic cross section of groove structure 15.

[0049] As shown in Figure 7A, the edge of the water droplet AQ is subjected to the water droplet surface tension (solid-liquid interfacial tension) Fs and the capillary force Fc, and the elongation of the water droplet AQ is determined by the balance between the water droplet surface tension Fs and the capillary force Fc. As shown in Figure 7B, widening the groove width (W2) of the groove 15G increases the groove volume, which increases the total volume of water droplets that enter the groove relative to the total volume of the water droplet AQ on the groove, and the surface energy of the water droplet itself decreases. Furthermore, because the capillary force Fc increases, the water droplet AQ elongates more than when the groove width is narrower.

[0050] 7C, the resistance to the extension of the water droplet AQ on the groove structure 15 is the top of the protrusion 15F, and the extension of the water droplet AQ is determined by the area S. Therefore, the smaller the area S of the top of the protrusion 15F (the narrower the width W1), the smaller the resistance caused by the protrusion 15F, that is, the smaller the solid-liquid interfacial tension Fs, and therefore the wider the groove width W2 of the groove 15G, the easier it is for the water droplet AQ to extend.

[0051] As described with respect to the anti-fogging properties of Example 1 and Comparative Example 1 (see FIG. 3), by satisfying the ratio W2 / P of the groove width W2 to the groove pitch P with the following formula (1), a high droplet discharge effect can be obtained and excellent anti-fogging properties can be exhibited.

[0052] W2 / P > 0.5 ··· Formula (1) Note that Formula (1) can be rewritten as W1 < W2 using the width W1 of the convex portion 15F and the groove width W2.

[0053] Also, as described with reference to FIG. 4, good anti-fogging properties were obtained when the ratio D / P of the groove depth D to the groove pitch P was D / P ≥ 1.0. This is understood to be due to the increase in capillary force due to the increase in the groove depth D. Therefore, by satisfying the ratio D / P of the groove depth D to the groove pitch P with the following formula (2), a high droplet discharge effect can be obtained and excellent anti-fogging properties can be exhibited.

[0054] D / P ≥ 1.0 ··· Formula (2) Next, the upper limit value of W2 / P will be described. FIG. 8 schematically shows a cross section of a part of the translucent resin member 10.

[0055] When the refractive index n0 of air is 1.0 and the refractive index n1 of the base material 11 is 1.5, the effective refractive index n2 of the groove structure 15 changes according to W1:W2. Assuming that the lower limit value of the effective refractive index n2 of the groove structure 15 for the total reflection suppression effect to occur in the groove structure 15 is 1.05, then W1:W2 = 1:9. Therefore, 0.5 < W2 / P ≤ 0.9 ··· Formula (3) if this is the case, a translucent resin member 10 having a total reflection suppression effect and excellent anti-fogging properties can be obtained.

[0056] Furthermore, from the results of Example 2 (EX2) and Comparative Example 3 (CX3) shown in FIG. 6, W2 / P > 0.57 is preferable for obtaining excellent anti-fogging properties, and it is more preferable that W2 / P satisfies the following formula (4).

[0057] 0.57 ≤ W2 / P ≤ 0.9 ··· Formula (4) As described above in detail, according to the present invention, it is possible to provide a light-transmitting resin member that has a high droplet discharge effect and exhibits an excellent anti-fogging effect.

[0058] The cross-sectional shape of groove structure 15 is not limited to the above. For example, as shown in Fig. 9A, the corners of the top or bottom of convex portion 15F may be rounded, or as shown in Fig. 9B, the top surface of convex portion 15F may have an upwardly convex curved shape. Furthermore, by having a trapezoidal shape as shown in Fig. 2B, the abundance ratio of resin in the cross section as shown in Fig. 8 gradually decreases toward the upper surface of groove structure 15, thereby eliminating the steep change in refractive index between the refractive index n0 of air and the refractive index n1 of substrate 11, and improving the total reflection suppression effect.

[0059] In the above description, the plurality of protrusions 15F and the plurality of grooves 15G have constant widths W1 and W2 in the extension direction, respectively. However, this is not limiting. For example, the ratio of widths W1 to W2 (i.e., W2 / P) may be different for each region of the surface 11S of the base material 11.

[0060] Furthermore, the light-transmitting resin member according to the present invention can be suitably used particularly for the interior and exterior surfaces of vehicle lamps or windows, but is not limited thereto.

[0061] Furthermore, the base material 11 is not limited to a transparent material, and may be colored. Alternatively, a reflective layer such as a mirror may be formed on the back surface. [Explanation of symbols]

[0062] 10: Translucent resin member 11: Base material 11S:Substrate surface 15:Groove structure 15F: Linear convex part 15G: Linear groove D: Groove depth P: Groove pitch W1: Convex width W2: Groove width

Claims

1. A substrate; A light-transmitting resin member having a groove structure consisting of a plurality of linear convex portions and a plurality of linear grooves formed on a surface of the base material, the plurality of linear protrusions and the plurality of linear grooves extend in directions parallel to each other, A translucent resin member, wherein when the pitch between the linear grooves is P, and the groove depth and groove width of the linear grooves are D and W2, respectively, the plurality of linear convex portions and the plurality of linear grooves satisfy D / P≧1.0 and W2 / P>0.

5.

2. 2. The light-transmitting resin member according to claim 1, wherein the plurality of linear convex portions and the plurality of linear grooves satisfy D / P≧1.0 and 0.5<W2 / P≦0.

9.

3. 2. The light-transmitting resin member according to claim 1, wherein the plurality of linear convex portions and the plurality of linear grooves satisfy D / P≧1.0 and 0.57<W2 / P≦0.

9.

4. 2. The light-transmitting resin member according to claim 1, wherein the pitch is in the range of 150 nm≦P≦390 nm.

5. 2. The light-transmitting resin member according to claim 1, wherein the base material is made of acrylic or polycarbonate.

6. 2. The light-transmitting resin member according to claim 1, wherein the top surface of the linear convex portion has a convex curved shape.

7. The light-transmitting resin member according to claim 1 , wherein the base material has a curved shape.

8. 7. The light-transmitting resin member according to claim 1, wherein the linear convex portion has a rectangular or trapezoidal cross section.

Images