Film-attached translucent substrate

Abstract

Provided is a film-attached translucent substrate exhibiting the properties of translucency, light diffusivity, and opacity. The film-attached translucent substrate comprises a translucent substrate and a film on the translucent substrate. The surface of the film has a surface roughness represented by an RSm of 12 μm or greater and an Rk of 1.2 μm or greater, the total light transmittance Tt is 70% or greater, and the clarity C is 40% or less. The clarity C is a percentage calculated by using the equation [(Tp - Tn) / (Tp + Tn) × 100%] in which narrow angle diffuse light transmittance measured within a range of emission angles of ±2.5° is defined as Tn, and parallel light transmittance is defined as Tp.

Description

Light-transmissive substrate with a film

[0001] The present invention relates to a light-transmissive substrate with a film, particularly a light-transmissive substrate with a film having both light-transmitting properties and opacity.

[0002] A technique for forming a film containing particles on a glass plate to impart light diffusion properties to the glass plate is known. Patent Document 1 discloses a glass plate with a film having light diffusion properties and opacity. In Patent Document 1, a film is formed by applying a coating liquid containing flaky silicon oxide fine particles onto a glass plate a plurality of times using an electrostatic coating device. According to Patent Document 1, the maximum height of the convex portions of the film, which are referred to as "first convex portions," is in the range of 8.0 μm to 30.0 μm (Claim 1).

[0003] Patent Document 1 provides a light-transmissive substrate with a film having high haze, that is, light diffusion properties, and low clarity, that is, opacity. Note that the clarity in Patent Document 1 has a different definition from the clarity C in this specification.

[0004] International Publication No. 2017 / 126230

[0005] The light-transmissive substrate with a film disclosed in Patent Document 1 is not aimed at achieving both light-transmitting properties and opacity. The purpose of the present invention is to provide a new light-transmissive substrate with a film having both light-transmitting properties and opacity.

[0006] The present invention provides a light-transmissive substrate with a film, comprising: a light-transmissive substrate; and a film on the light-transmissive substrate, wherein the surface of the film has a surface roughness represented by an RSm of 12 μm or more and an Rk of 1.2 μm or more, and a total light transmittance Tt of 70% or more and a clarity C of 40% or less. Here, the clarity C is a ratio calculated by [(Tp - Tn) / (Tp + Tn)] × 100 (%) using the angular scattering light transmittance Tn measured within a range of an emission angle of ±2.5° and the parallel light transmittance Tp.

[0007] According to the present invention, it is possible to provide a new light-transmissive substrate with a film having both light-transmitting properties and opacity.

[0008] This is a cross-sectional view showing an example of a film-coated translucent substrate according to the present invention. This is a cross-sectional view showing another example of a film-coated translucent substrate according to the present invention. This is a cross-sectional view showing yet another example of a film-coated translucent substrate according to the present invention. This is a schematic cross-sectional view for explaining Clarity C. This figure shows the film surface of the film-coated translucent substrate of Example 1 as observed by a scanning electron microscope (SEM).

[0009] Embodiments of the present invention will be described below with reference to the drawings. The following description is an example of the present invention, and the present invention is not limited to the following embodiments. In the following, the upper and lower limits of the numerical range can be combined arbitrarily.

[0010] As shown in Figure 1, the film-coated translucent substrate according to this embodiment comprises a translucent substrate 10 and a film 20 on the surface of the translucent substrate 10.

[0011] The surface of the film 20 has a surface roughness represented by an RSm of 12 μm or more and an Rk of 1.2 μm or more. The surface of the film 20 forms the interface between the film 20 and the air, and its surface roughness diffuses the incident light. RSm may be 13 μm or more, and in some cases 15 μm or more. Rk may be 1.3 μm or more, 1.4 μm or more, and even 1.6 μm or more. There is no particular upper limit to RSm, but for example, it is 30 μm or less, and even more specifically 25 μm or less. Similarly, there is no upper limit to Rk, but for example, it is 4 μm or less, 3 μm or less, 2.5 μm or less, and even more specifically 2.2 μm or less.

[0012] RSm is the average length Xs of the contour curve elements at the reference length. Rk is one of the plateau structure surface parameters and is a value that indicates the level difference of the core. RSm is specified in Japanese Industrial Standard (JIS) B0601-2001, and Rk is specified in JIS B0671-2002.

[0013] The optical properties achievable with the film-coated translucent substrate of this embodiment are as follows: The film-coated translucent substrate has a total light transmittance Tt of 70% or more. The film-coated translucent substrate may have a total light transmittance Tt of 73% or more, and even more than 75% or more. The film-coated translucent substrate has a clarity of 40% or less. The film-coated translucent substrate may have a clarity C of 30% or less, 25% or less, 20% or less, 15% or less, 13% or less, 11% or less, and in some cases, 10% or less. The lower limit of clarity C is not particularly limited, but may be 3% or more. Furthermore, the film-coated translucent substrate may have a haze Hz of 75% or more. The film-coated translucent substrate may have a haze Hz of 78% or more, 80% or more, 85% or more, 88% or more, 90% or more, and even more than 91% or more.

[0014] As shown in Figure 4, the haze Hz is calculated by Td / Tt, and the clarity C is calculated by (Tp-Tn) / (Tp+Tn). Tt is the total light transmittance, Td is the total diffuse light transmittance, Tp is the parallel light transmittance, and Tn is the narrow-angle diffuse light transmittance. Tn is measured within a range of ±2.5° for the emission angle θ. The smaller the clarity C value, the higher the opacity of the sample S. The total light transmittance Tt, haze Hz, and clarity C can be measured, for example, using a haze-gard i manufactured by BYK. These characteristics are specified in ISO 13468, 14782, and ASTM D1003, D1004.

[0015] The inventors have found that a surface structure with RSm and Rk large to the extent described above makes it possible to achieve both high total light transmittance Tt and low clarity C. In other words, for the film surface to sufficiently influence light diffusion, or in other words for light to sufficiently perceive the surface irregularities of the film, it is desirable that Rk be above a predetermined value. In order to scatter light at a narrow emission angle, it is desirable that the change in the slope of the surface irregularities of the film be small, or in other words, that Rsm be above a predetermined value. Furthermore, surprisingly, although it is usually difficult to achieve both high total light transmittance Tt and high haze Hz, the inventors have also found that a surface structure with RSm and Rk large to the extent described above makes it possible to achieve high haze Hz simultaneously.

[0016] The maximum thickness Tmax of the film 20 (see Figure 1) may be less than 8 μm. Considering that the maximum height of the protrusions of the film disclosed in Patent Document 1 is 8.0 μm or more, it is considered that the maximum thickness Tmax will not be less than 8 μm. The maximum thickness Tmax may be between 2 μm and 7.5 μm. The maximum thickness Tmax may be 3 μm or more, 4 μm or more, 7 μm or less, or 6 μm or less. Achieving light diffusion and opacity with a film 20 that is not too thick offers advantages in mass production.

[0017] As can be seen from the Examples section, the film-coated translucent substrate of this embodiment can be manufactured without using equipment that could hinder mass production, such as electrostatic coating equipment, and is therefore advantageous in terms of mass production.

[0018] The translucent substrate 10 may be plate-shaped. In this case, the surface on which the film 20 is formed may be the main surface of the plate-shaped substrate. The plate-shaped substrate has two main surfaces 11 and 12, which are connected by their sides and are parallel to each other. In Figure 1, the film 20 is formed on the first main surface 11 of the translucent substrate 10. Incident light, for example, enters on the second main surface 12 side and exits from the first main surface 11 side.

[0019] The translucent substrate 10 may include a glass plate or a resin plate. There are no particular restrictions on the type of glass or resin. The glass plate may be, for example, float glass or patterned glass. The glass plate may also be tempered glass. The strengthening process may be either thermal strengthening or chemical strengthening. The thermal strengthening process may be carried out after the film 20 has been formed. As shown in Figure 2, the translucent substrate 10 may include a film 41 on the first main surface 11 side. The film 41 functions as an undercoat, and its surface becomes the first main surface 11. As shown in Figure 3, the translucent substrate 10 may include a film 42 on the second main surface 12 side opposite to the first main surface 11. Films 41 and 42 may be single-layer or multi-layer. Films 41 and 42 may be optically functional films that block ultraviolet rays, block infrared rays, control visible light reflectance, or perform other optical functions. Film 42 may have functions such as anti-fogging or water repellency.

[0020] One example of a method for setting the RSm and Rk of the film 20 to a desired range is to add oxide particles to the film, more specifically, to add two or more types of oxide particles with different average particle sizes to the film. The oxide particles are not particularly limited, but may be silicon oxide particles. However, the film-coated translucent substrate of this embodiment is not limited to having a film containing two or more types of oxide particles, as long as the film has a surface roughness in which the RSm and Rk are within a predetermined range.

[0021] The film 20 may contain first silicon oxide particles 21 and second silicon oxide particles 22. For example, the average particle size of the first silicon oxide particles 21 is greater than 2 μm, and the average particle size of the second silicon oxide particles 22 is 0.3 μm or more and 1.0 μm or less, and more specifically 0.3 μm or more and 0.8 μm or less. The film 20 may further contain third silicon oxide particles 23. The film 20 may further contain a binder 25.

[0022] The first main surface 11 may have a first region 31 in which first silicon oxide particles 21 are arranged in the film 20, and a second region 32 in which the first silicon oxide particles 21 are not present in the film 20. Second silicon oxide particles 22 are present in at least a part of the second region 32. On the surface of the film 20, protrusions 71 originating from the first silicon oxide particles 21 appear in the first region 31. The first region 31 and the second region 32 can be determined by observation from a direction perpendicular to the first main surface 11.

[0023] The average particle size of the first silicon oxide particles may be greater than 2 μm, and may be 2.2 μm or more, 2.4 μm or more, 2.5 μm or more, 2.7 μm or more, or 2.8 μm or more. The average particle size of the first silicon oxide particles may be 7 μm or less, 6 μm or less, 5 μm or less, or 4 μm or less.

[0024] The average particle size of the silicon dioxide particles may be 0.3 μm or more and 1.0 μm or less. The average particle size of the silicon dioxide particles may be 0.4 μm or more, 0.6 μm or more, or 0.8 μm or more. The average particle size of the silicon dioxide particles may be 0.95 μm or less, or 0.9 μm or less.

[0025] The average particle size of the silicon trioxide particles is 0.01 μm or more and 0.2 μm or less. The average particle size of the silicon trioxide particles may be 0.05 μm or more, 0.07 μm or more, or 0.1 μm or more. The average particle size of the silicon trioxide particles may be 0.18 μm or less, or 0.15 μm or less.

[0026] In this specification, "average particle size" may refer to the particle size corresponding to 50% of the volume cumulative distribution (d50) obtained from the particle size distribution measured on a volume basis by laser diffraction scattering. Note that the average particle size refers to the average particle size of the primary particles, i.e., the particle size measured when the particles are not aggregated.

[0027] The shape of the first silicon oxide particles, the second silicon oxide particles, and the third silicon oxide particles is not particularly limited and may be fibrous, flaky, spherical, or other. The first silicon oxide particles, the second silicon oxide particles, and the third silicon oxide particles may each be spherical. In this specification, "spherical" does not mean a perfect sphere, but rather means that when the particles are observed with a scanning electron microscope (SEM), the ratio of the maximum diameter to the minimum diameter (maximum diameter / minimum diameter) is 1.0 to 2.0, particularly 1.0 to 1.5. Spherical silicon oxide particles are mass-produced at low cost and are readily available in terms of quantity, quality, and cost.

[0028] Referring again to Figure 1, the desirable arrangement of each silicon oxide particle will be described. The surface of the translucent substrate 10 has a first region 31 in the film 20 where the first silicon oxide particles 21 are present, and a second region 32 in the film 20 where the first silicon oxide particles 21 are not present. Second silicon oxide particles 22 are present in at least a part of the second region 32. In the first region 31 and the second region 32, the first silicon oxide particles 21 and the second silicon oxide particles 22 exert effects such as scattering on incident light. As illustrated in Figure 1, a part of the second silicon oxide particles 22 may be present in the first region 31. Second silicon oxide particles 22 may not be present in a part of the second region 32. Third silicon oxide particles 23 may be present in the first region 31 or in the second region 32.

[0029] The number N1 of first silicon oxide particles 21 present on a line segment with a length of 50 μm set on the surface of the film-coated translucent substrate, specifically on the first main surface 11, may be 3 or more and 20 or less. The number N1 may be 5 or more, 7 or more, 18 or less, 15 or less, or even 12 or less.

[0030] On the surface of the translucent substrate with a film, specifically on the first main surface 11, along a line segment of length 50 μm, the ratio TL1 / (TL1+TL2) calculated from the total length TL1 of the first region 31 and the total length TL2 of the second region 32 may be 0.1 or more and 0.9 or less. The ratio TL1 / (TL1+TL2) may be 0.2 or more, 0.4 or more, 0.8 or less, or 0.6 or less.

[0031] The ratio TL1 / (TL1+TL2) and the number N1 can be determined by observing the surface of the translucent substrate 10 at at least 10 locations over a length of 50 μm and taking the simple average.

[0032] It is desirable that the first silicon oxide particles 21 exist without overlapping in the thickness direction of the film 20. However, the second silicon oxide particles 22 and the third silicon oxide particles 23 may overlap with the first silicon oxide particles 21, or with each other, in the thickness direction of the film 20. As shown in Figure 1, the first silicon oxide particles 21 may be in contact with each other in the direction along the first main surface 11.

[0033] Furthermore, the maximum thickness Tmax of the film 20 may be less than twice the average particle size of the first silicon oxide particles 21, and even less than or equal to 1.5 times.

[0034] The binder 25 has the function of holding silicon oxide particles in the film. The binder 25 may contain an oxide, specifically at least one selected from the group consisting of silicon oxide, zirconium oxide, aluminum oxide, niobium oxide, and tantalum oxide, particularly silicon oxide. The binder 25 may also consist solely of silicon oxide. The binder 25 can be introduced into the film 20, for example, by the so-called sol-gel method.

[0035] Next, the ratios of each silicon oxide particle and the binder in the film 20 will be explained. The following numerical values ​​describing ratios and proportions are all based on mass. The ratio R1 of the first silicon oxide particle 21 to the second silicon oxide particle 22 is, for example, 0.1 or more and 4 or less. Ratio R1 may be 0.5 or more, 0.7 or more, 0.9 or more, 1 or more, or 3 or less, 2.5 or less, 2.3 or less, or 2.1 or less. The ratio R3 of the third silicon oxide particle 23 to the second silicon oxide particle 22 is, for example, 0.1 or more and less than 7. Ratio R3 may be 0.5 or more, 1 or more, 1.2 or more, or 5 or less, or 4 or less. The ratio RB of the binder 25 to the total amount of all silicon oxide particles 21, 22, and 23 and the binder 25 is, for example, 5% or more and 40% or less. The ratio RB may be 10% or more, 13% or more, 15% or more, or 35% or less, 30% or less, or 25% or less.

[0036] The film 20 may contain other components besides silicon oxide particles and the binder. An example of other components is oxide particles other than silicon oxide particles. Examples of oxide particles other than silicon oxide particles include titanium oxide particles and zirconium oxide particles. The oxide particles may be composite oxide particles or multilayer particles having a core-shell structure. The film 20 does not have to contain titanium oxide particles. The film 20 does not have to contain oxide particles other than silicon oxide particles.

[0037] As described above, this specification discloses the following technologies. The first technology is a translucent substrate and a film on the translucent substrate, wherein the surface of the film has a surface roughness represented by RSm of 12 μm or more and Rk of 1.2 μm or more, the total light transmittance Tt is 70% or more, and the clarity C is 40% or less, and the clarity C is a translucent substrate with a film. Here, the clarity C is a ratio calculated by [(Tp - Tn) / (Tp + Tn)] × 100 (%), where Tn is the narrow-angle diffuse light transmittance measured within a range of ±2.5° at the emission angle and Tp is the parallel light transmittance.

[0038] The second technology is a translucent substrate with a film of the first technology, where the haze Hz is 75% or higher.

[0039] The third technology is a translucent substrate with a film of the first or second technology, wherein the RSm is 13 μm or more, the Rk is 1.5 μm or more, and the clarity C is less than 12%.

[0040] The fourth technology is a translucent substrate with a film of the second technology, wherein the haze Hz is 90% or more and the clarity C is 10% or less.

[0041] The fifth technology is a translucent substrate with a film of any one of the first to fourth technologies, wherein the maximum film thickness Tmax of the film is 8 μm or less.

[0042] The sixth technology is a translucent substrate with a film of any one of the first to fifth technologies, wherein the film contains oxide particles.

[0043] The present invention will be described in more detail below with reference to examples. (Sample 1) Commercially available propylene glycol monomethyl ether, tetraethoxysilane, purified water, dispersion of silicon oxide particles (average particle size 3.2 μm), dispersion of silicon oxide particles (average particle size 0.8 μm), dispersion of silicon oxide particles (average particle size 0.075 μm), and a binder converted to SiO2 were weighed into a glass container so that the mass ratio of silicon oxide particles (average particle size 3.2 μm), silicon oxide particles (average particle size 0.8 μm), dispersion of silicon oxide particles (average particle size 0.075 μm), and a solid content concentration of 12% were obtained.

[0044] 6.25 g of the aforementioned high-concentration solution, 3.23 g of propylene glycol monomethyl ether, 6.25 g of propylene glycol, 0.12 g of a zirconium compound (concentration 25 wt% as ZrO₂), and 0.02 g of a surfactant (manufactured by Shin-Etsu Silicone Co., Ltd., KP-341, diluted to 10 wt% with propylene glycol monomethyl ether) were stirred and mixed to obtain a coating solution. The solid content concentration in the coating solution was 7.8%. The concentration of the solid content with respect to the entire coating solution according to Example 1 was 7.8% by mass. In the solid content of the coating solution according to Example 1, 23.1% by mass of silicon oxide fine particles of the first type were contained, 23.1% by mass of silicon oxide fine particles of the second type were contained, 30.8% by mass of silicon oxide fine particles of the third type were contained, 19.2% by mass of tetraethoxysilane converted to SiO₂ was contained, and 3.8% by mass of the zirconium compound converted to ZrO₂ was contained. The mass of the solid content in the coating solution is defined as the sum of the mass of tetraethoxysilane (the source of silicon oxide in the binder) converted to SiO₂, the mass of the solid content of the first silicon oxide fine particle dispersion, the mass of the solid content of the second silicon oxide fine particle dispersion, the mass of the solid content of the third silicon oxide fine particle dispersion, and the mass of the optionally added zirconium compound converted to ZrO₂.

[0045] The coating solution was applied onto the surface of a washed glass plate (100 × 100 mm; thickness 3 mm; float plate glass) at 200 rpm by the spin coating method. The coating solution was continuously stirred until immediately before application. The glass plate coated with the coating solution was dried in an oven set at 200 °C to obtain a light-transmissive substrate with a film according to Example 1. The results of observing the film by SEM are shown in Fig. 5.

[0046] For the light-transmissive substrate with a film thus obtained, the surface shape of the film was measured using a hybrid laser microscope OPTELICS manufactured by Lasertec Corporation to obtain the values of RSm and Rk. Also, the optical properties (total light transmittance Tt, haze Hz, and clarity C) of the glass plate with a film were measured using the above-mentioned haze - gard - i manufactured by BYK Co., Ltd. The optical properties were measured with the surface of the light-transmissive substrate without forming a film as the light incident surface. The results are shown in Table 2.

[0047] (Samples 2 to 7) As shown in Table 1, a glass plate with a film was produced in the same manner as Sample 1, except that the mixing ratio, coating method, and drying method of each silicon oxide particle were appropriately changed, and the surface shape and optical properties were measured. In addition, the speed in the "Coating" column for Samples 2 to 5 in Table 1 is the conveyance speed of the glass plate.

[0048]

[0049]

[0050] For Samples 1 to 5 where RSm was 12 μm or more and Rk was 1.2 μm or more, high total light transmittance Tt and haze Hz and low clarity C were measured. In addition, for Samples 2 to 4 where RSm was 13 μm or more and Rk was 1.5 μm or more, even lower clarity C was obtained. Since Sample 5 was heated by infrared rays for drying, it took time to dry the film. As a result of the arrangement of the binder and the second and third silicon oxide particles moving toward the substrate side, Rk became a slightly small value and clarity C increased slightly.

[0051] When the above-mentioned number N1 and ratio TL1 / (TL1 + TL2) were measured using a field emission scanning electron microscope SU8220 manufactured by Hitachi High-Tech Corporation, the number N1 was in the range of 3 or more and 11 or less. The ratio TL1 / (TL1 + TL2) was in the range of 0.1 or more and 0.7 or less. In addition, the maximum film thickness Tmax of the film in each example was in the range of 2 μm or more and 7.5 μm or less.

Claims

1. A translucent substrate with a film, comprising a translucent substrate and a film on the translucent substrate, wherein the surface of the film has a surface roughness represented by RSm of 12 μm or more and Rk of 1.2 μm or more, the total light transmittance Tt is 70% or more, and the clarity C is 40% or less. Here, the clarity C is a ratio calculated by (Tp - Tn) / (Tp + Tn) × 100%, where Tn is the narrow-angle diffuse light transmittance measured within a range of ±2.5° of the emission angle and Tp is the parallel light transmittance.

2. A translucent substrate with a film according to claim 1, wherein the haze Hz is 75% or higher.

3. The film-coated translucent substrate according to claim 1, wherein the RSm is 13 μm or more, the Rk is 1.5 μm or more, and the clarity C is less than 12%.

4. The film-coated translucent substrate according to claim 2, wherein the haze Hz is 90% or more and the clarity C is 10% or less.

5. The translucent substrate with a film according to claim 1, wherein the maximum film thickness Tmax of the film is less than 8 μm.

6. The translucent substrate with a film according to claim 1, wherein the film contains oxide particles.

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