Hardened reflective material

Abstract

To provide a cured reflective material that exhibits excellent visible light reflection efficiency and superior discoloration suppression. [Solution] A cured reflective material obtained by curing a resin composition containing a resin component mainly composed of a curable resin and a white inorganic filler, wherein when the cross-section of the cured reflective material is imaged with a scanning electron microscope and the backscattered electron image obtained is observed and classified into a first phase consisting of the resin component and a second phase consisting of the white inorganic filler, the average diameter of the equivalent circle diameter of the second phase is within a predetermined range, the proportion of the second phase having an equivalent circle diameter of 150 nm or less is 30% or less of the entire second phase, and the equivalent circle diameter is obtained by extracting the second phase from the backscattered electron image, setting a rectangular measurement field of 4.5 μm × 6.0 μm in the image after binarization of the backscattered electron image, and calculating the diameter corresponding to the area of ​​the extracted second phase in the measurement field.

Description

[Technical Field]

[0001] This invention relates to a cured reflective material. [Background technology]

[0002] In recent years, optical semiconductor devices such as LEDs (light-emitting diodes) have demonstrated high efficiency in light emission and excellent driving characteristics and repetition rate. Therefore, optical semiconductor devices are widely used as indicators or light sources. In particular, white LEDs are widely used as backlights for display devices or camera flashes, and are also expected to be used in next-generation lighting devices. Such lighting devices are equipped with reflective materials that reflect the emitted visible light in order to improve the efficiency of extracting visible light in the direction of illumination. Furthermore, with the miniaturization and weight reduction of white LEDs, there is a demand for highly reflective thin films. Currently, compositions using photocurable resins or thermosetting resins such as acrylic resin or epoxy resin in combination with white inorganic fillers are widely used as reflective materials (see Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2006-140207 [Overview of the initiative] [Problems that the invention aims to solve]

[0004] However, in the reflective material described in Patent Document 1, it was necessary to use a large amount of white inorganic filler or to make the cured film thick in order to increase the visible light reflection efficiency. As a result, problems arose such as peeling of the coating, a decrease in mechanical strength, problems with the dimensional accuracy of microfabrication due to the thickness of the cured film, and problems with weight reduction or miniaturization, making it difficult to apply the reflective material described in Patent Document 1 to the high-power light-emitting elements of recent years.

[0005] The present invention aims to provide a cured reflective material that exhibits excellent visible light reflection efficiency and superior discoloration suppression. [Means for solving the problem]

[0006] According to the present invention, the following reflective material cured product is provided. [1] A cured reflective material obtained by curing a resin composition containing a resin component mainly composed of a curable resin and a white inorganic filler, When the cross-section of the cured reflective material is imaged with a scanning electron microscope and the resulting backscattered electron image is observed, and the material is classified into a first phase consisting of the resin component and a second phase consisting of the white inorganic filler, The average diameter of the equivalent circular diameter of the second phase is 0.15 μm or more and 0.3 μm or less. The proportion of the second phase having an equivalent circular diameter of 150 nm or less is 30% or less of the entire second phase. The equivalent circle diameter is obtained by extracting the second phase in the backscattered electron image, setting a rectangular measurement field of 4.5 μm × 6.0 μm in the image after the binarization of the backscattered electron image, and calculating the diameter corresponding to the area of ​​the extracted second phase in the measurement field. Cured reflective material. [2] In the cured reflective material described in [1], The white inorganic filler contains at least one metal oxide selected from the group consisting of titania, zirconia, yttria-stabilized zirconia, alumina, and silica. Cured reflective material. [3] In the cured reflective material described in [1] or [2], The aforementioned white inorganic filler is a core-shell type filler comprising a core layer and a shell layer. The aforementioned core layer consists of titania, The shell layer is made of at least one metal oxide selected from the group consisting of zirconia, alumina, and silica. The titania content in the aforementioned metal oxide is 90% by mass or more. Cured reflective material. [4] In a cured reflective material described in any of [1] to [3], The aforementioned white inorganic filler is subjected to an organic surface treatment. Cured reflective material. [5] In a cured reflective material described in any of [1] to [4], The aforementioned resin component contains an epoxy compound. Cured reflective material. [6] In a cured reflective material described in any of [1] to [5], The area ratio of the second phase is between 10% and 50% of the total area of ​​the first and second phases combined, which is 100%. Cured reflective material. [7] In a cured reflective material according to any one of [1] to [6], The average absolute maximum length of the second phase is 0.55 μm or less. The aforementioned absolute maximum length is the absolute maximum length of each Voronoi region in the Voronoi diagram obtained by performing a Voronoi tessellation with the centroid of the second phase as the generating point. The Voronoi diagram is obtained by extracting the second phase from the backscattered electron image, setting a rectangular measurement field of 4.5 μm × 6.0 μm in the image after binarization of the backscattered electron image, performing Voronoi tessellation with the centroid of the extracted second phase as the generating point within the measurement field, and calculating the Voronoi region of all the generating points. Cured reflective material. [8] In a cured reflective material described in any of [1] to [7], The average value of the Voronoi area of ​​the second phase is 0.13 μm². 2 The following: The aforementioned Voronoi area is the area of ​​each Voronoi region in the Voronoi diagram obtained by performing a Voronoi partition with the centroid of the second phase as the generating point. The Voronoi diagram is obtained by extracting the second phase in the reflected electron image, setting a measurement field of view of a 4.5 μm × 6.0 μm rectangle in the image after the binarization process of the reflected electron image, and performing Voronoi division with the center of gravity of the extracted second phase as the mother point in the measurement field of view to calculate the Voronoi regions of all the mother points. Reflective material cured product. [9] In the reflective material cured product according to any one of [1] to [8], When the thickness of the reflective material cured product is 30 μm, the reflectance of the reflective material cured product at a wavelength of 450 nm is 91% or more in the SCI (Specular Component Include: including specularly reflected light) method, in a nitrogen atmosphere (oxygen concentration: 2000 ppm), after performing a reflow process under the conditions of a peak temperature of 260 °C or higher for 6 seconds and a melting temperature of 240 °C or higher for 60 seconds, the reflectance of the reflective material cured product at a wavelength of 450 nm is 90% or more in the SCI method. Reflective material cured product.

Advantages of the Invention

[0007] According to one aspect of the present invention, a reflective material cured product excellent in visible light reflection efficiency and excellent in discoloration suppression can be provided.

Brief Description of the Drawings

[0008] [Figure 1] It is a reflected electron image obtained by imaging the cross sections of the reflective material cured products obtained in Example 1 and Comparative Example 1 with a scanning electron microscope. [Figure 2] It is a Voronoi diagram (color-coded according to the absolute maximum length of the second phase) obtained by performing Voronoi division from the reflected electron images obtained by imaging the cross sections of the reflective material cured products obtained in Example 1 and Comparative Example 1 with a scanning electron microscope. [Figure 3] It is a graph showing the relationship between the absolute maximum length of the second phase and its content rate in the reflective material cured products obtained in Example 1 and Comparative Example 1. [Figure 4]This is a Voronoi diagram (color-coded according to the Voronoi area of ​​the second phase) obtained by performing Voronoi tessellation on backscattered electron images obtained by imaging the cross-sections of the reflective material cured products obtained in Example 1 and Comparative Example 1 with a scanning electron microscope. [Figure 5] This graph shows the relationship between the Voronoi area of ​​the second phase and its content in the cured reflective material obtained in Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0009] The cured reflective material according to this embodiment is a cured reflective material obtained by curing a resin composition containing a resin component mainly composed of a curable resin and a white inorganic filler. When the backscattered electron image obtained by imaging a cross-section of this cured reflective material with a scanning electron microscope is observed and classified into a first phase consisting of the resin component and a second phase consisting of the white inorganic filler, the average diameter of the second phase in terms of the equivalent circle diameter is 0.15 μm or more and 0.3 μm or less, and the proportion of the second phase with an equivalent circle diameter of 150 nm or less is 30% or less of the entire second phase. In this specification, the equivalent circle diameter is obtained by extracting the second phase in the backscattered electron image, setting a rectangular measurement field of 4.5 μm × 6.0 μm in the image after binarization of the backscattered electron image, and calculating the diameter corresponding to the area of ​​the extracted second phase within the measurement field.

[0010] The average diameter of the equivalent circle diameter of the second phase must be between 0.15 μm and 0.3 μm. If this average diameter is outside the above range, the visible light reflectivity will be insufficient. From a similar viewpoint, the average diameter of the equivalent circle diameter of the second phase is preferably between 0.17 μm and 0.25 μm, and more preferably between 0.18 μm and 0.2 μm. The following methods can be used to adjust the average diameter of the equivalent circle diameter of the second phase to the aforementioned range. For example, the average diameter of the equivalent circle diameter of the second phase can be adjusted by changing the average particle size of the white inorganic filler.

[0011] The proportion of the second phase with an equivalent circular diameter of 150 nm or less must be 30% or less of the total second phase. If this average diameter falls outside the above range, the visible light reflection efficiency will be insufficient, or the discoloration suppression will be insufficient. The following methods can be used to adjust the proportion of the second phase with an equivalent circular diameter of 150 nm or less to within the aforementioned range. For example, the average diameter of the second phase can be adjusted by classifying the white inorganic filler.

[0012] The area ratio of the second phase is preferably 10% to 50% of the total area of ​​the first and second phases (100% total area). If the area ratio of the second phase is below the lower limit, the visible light reflection efficiency tends to be insufficient. On the other hand, if the area ratio of the second phase exceeds the upper limit, the cured reflective material tends to peel off easily. From a similar viewpoint, it is more preferable that the area ratio of the second phase is 20% to 40% of the total area of ​​the first and second phases (100% total area). The following methods can be used to adjust the area ratio of the second phase to the aforementioned range. For example, the area ratio of the second phase can be adjusted by changing the amount of white inorganic filler added.

[0013] The absolute maximum length of the second phase preferably has a peak between 0.3 μm and 0.5 μm. If the absolute maximum length of the second phase has a peak outside this range, the visible light reflection efficiency tends to be insufficient, or the discoloration suppression tends to be insufficient. From a similar viewpoint, it is more preferable that the absolute maximum length of the second phase has a peak between 0.35 μm and 0.45 μm. Furthermore, from the viewpoint of visible light reflectivity and discoloration suppression, the average value of the absolute maximum length of the second phase is preferably 0.55 μm or less, and more preferably 0.4 μm or more and 0.5 μm or less. The following are examples of methods for adjusting the absolute maximum length of the second phase to the aforementioned range. For example, the absolute maximum length of the second phase can be adjusted by changing the type of resin component, as well as the type of white inorganic filler, surface treatment, classification treatment, and dispersion method.

[0014] The Voronoi area of the second phase is 0.05 μm 2 or more and 0.13 μm 2 or less, and preferably has a peak. When the Voronoi area of the second phase has a peak outside the above range, the reflection efficiency of visible light tends to be insufficient, or the discoloration suppression tends to be insufficient. From the same perspective, the Voronoi area of the second phase is 0.09 μm 2 or more and 0.11 μm 2 or less, and more preferably has a peak. Also, from the perspective of the reflection efficiency of visible light and discoloration suppression, the average value of the Voronoi area of the second phase is preferably 0.13 μm 2 or less, and preferably 0.05 μm 2 or more and 0.12 μm 2 or less, and more preferably 0.08 μm 2 or more and 0.11 μm 2 or less, and particularly preferably. In addition, as a method for adjusting the Voronoi area of the second phase to the above range, the following methods can be mentioned. For example, the Voronoi area of the second phase can be adjusted by changing the type of resin component and the type, surface treatment, classification treatment, and dispersion method of the white inorganic filler.

[0015] In this embodiment, the backscattered electron image, Voronoi diagram, absolute maximum length, and Voronoi area are obtained as follows. The backscattered electron image is obtained by imaging a cross-section of the cured product of the reflective material with a scanning electron microscope. As the scanning electron microscope, a publicly known one can be appropriately used. In addition, in order to calculate the average diameter, absolute maximum length, Voronoi area, and occupied area ratio of the equivalent circle diameter of the second phase, a binary process may be performed on the backscattered electron image. The binary process can be performed, for example, by an image analysis measurement system (product name "WinROOF2021", manufactured by Mitani Trading Co., Ltd.). A Voronoi diagram is obtained by extracting the second phase from a backscattered electron image, setting a 4.5 μm × 6.0 μm rectangular measurement field in the image after binarization of the backscattered electron image, and performing Voronoi tessellation within this measurement field, using the centroid of the extracted second phase as the generating point, to calculate the Voronoi region for all generating points. A Voronoi region is the area enclosed by a Voronoi boundary formed by dividing two adjacent generating points by a perpendicular bisector when multiple generating points are placed on the same plane. The absolute maximum length is the absolute maximum length of each Voronoi region in the Voronoi diagram obtained by performing a Voronoi tessellation with the centroid of the second phase as the generating point. The absolute maximum length of a Voronoi region is the distance between the furthest points within a single Voronoi region, measured by straight lines. Furthermore, the Voronoi area is the area of ​​each Voronoi region in the Voronoi diagram obtained by performing a Voronoi partition with the centroid of the second phase as the generating point.

[0016] (Resin composition) The resin composition used in this embodiment contains a resin component and a white inorganic filler. For example, a cured reflective material can be obtained by applying this resin composition, forming a coating film, and then curing it. The curing conditions can be appropriately set depending on the type of resin component.

[0017] (Resin components) The resin component (solid content) used in this embodiment mainly consists of a curable resin. The material can be cured using the curable resin, resulting in a cured reflective material. A curable resin is a resin that has at least one of the curability properties of photocuring and thermosetting. A curable resin may also be a resin that has both photocuring and thermosetting properties.

[0018] Examples of curable resins include epoxy resins, phenolic resins, urethane resins, and melamine resins. Furthermore, the curable resin may be, for example, a resin having carboxyl groups and photosensitive groups. The carboxyl groups react with epoxy compounds and become thermosetting. Examples of such curable resins include (i) a resin obtained by partially reacting an epoxy group-containing unsaturated compound with a copolymer of an unsaturated carboxylic acid and a compound having an unsaturated double bond other than an unsaturated carboxylic acid, and (ii) a resin obtained by adding a carboxyl group-containing compound to the epoxy group of a copolymer of an epoxy group-containing unsaturated compound and a compound having an unsaturated double bond other than an epoxy group-containing unsaturated compound, and then reacting the resulting hydroxyl group with a saturated or unsaturated polybasic acid anhydride.

[0019] The unsaturated carboxylic acid used in the synthesis of the curable resin in (i) above is acrylic acid, Examples include methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, and vinylacetic acid. Among these, acrylic acid or methacrylic acid is preferred, and methacrylic acid is particularly preferred. Other compounds having unsaturated double bonds besides unsaturated carboxylic acids include methyl methacrylate, methyl acrylate, ethyl methacrylate, cyclohexyl methacrylate, phenoxymethyl methacrylate, and 2-hydroxyethyl methacrylate. Examples of epoxy group-containing unsaturated compounds include glycidyl methacrylate, glycidyl acrylate, allyl glycidyl ether, and 4-hydroxybutyl acrylate glycidyl ether.

[0020] Examples of epoxy group-containing unsaturated compounds used in the synthesis of the curable resin described in (ii) above include glycidyl methacrylate, glycidyl acrylate, allyl glycidyl ether, and 4-hydroxybutyl acrylate glycidyl ether. Other unsaturated double bond compounds besides epoxy group-containing unsaturated compounds include methyl methacrylate, methyl acrylate, ethyl methacrylate, cyclohexyl methacrylate, phenoxymethyl methacrylate, and 2-hydroxyethyl methacrylate. Examples of carboxyl group-containing compounds include acrylic acid or methacrylic acid. Examples of saturated or unsaturated polybasic acid anhydrides include succinic acid, maleic acid, adipic acid, citric acid, phthalic acid, and tetrahydrophthalic acid.

[0021] The resin component used in this embodiment preferably contains an epoxy compound. The epoxy compound is a compound having an epoxy group. This epoxy compound can increase the crosslinking density of the cured resin composition. Any known epoxy compound can be used as appropriate.

[0022] The resin component used in this embodiment may contain a photopolymerization initiator. This photopolymerization initiator can improve the photosensitivity of the resin composition. Any known photopolymerization initiator can be used as appropriate.

[0023] The resin component used in this embodiment may contain a reactive diluent. The reactive diluent is, for example, a photopolymerizable monomer, which is a compound having at least one polymerizable double bond per molecule. This reactive diluent can improve the photocurability of the resin composition. Any known reactive diluent can be used as appropriate.

[0024] (White inorganic filler) The white inorganic filler used in this embodiment is a white inorganic filler. This white inorganic filler can impart visible light reflectivity to the cured reflective material. Examples of white inorganic fillers include titania, zirconia, yttria-stabilized zirconia, alumina, and silica. These may be used individually or in mixtures of two or more.

[0025] From the viewpoint of dispersibility of the white inorganic filler in the resin component, the white inorganic filler is preferably a core-shell type filler comprising a core layer and a shell layer. Here, the core layer is preferably made of titania. Furthermore, the shell layer is preferably made of at least one metal oxide selected from the group consisting of zirconia, alumina, and silica. Furthermore, from the viewpoint of further improving the dispersibility of the white inorganic filler, it is preferable that the white inorganic filler is subjected to an organic surface treatment. Examples of organic surface treatments include surface treatments using silane coupling agents. Furthermore, from the viewpoint of reducing the proportion of the second phase with an equivalent circle diameter of 150 nm or less, the white inorganic filler may be classified. In addition, it is preferable to use an ultrafine air classifier for the classification process.

[0026] (Other ingredients) The resin composition used in this embodiment may contain, in addition to the resin component and the white inorganic filler, other components as needed. Other components include defoaming agents, thickeners, thixotropic agents, flame retardants, curing catalysts, and non-reactive diluents. These may be used individually or in combination of two or more.

[0027] (Method for manufacturing resin compositions) The method for producing the resin composition used in this embodiment is not limited to any particular method, as long as it can ensure the dispersibility of the white inorganic filler. For example, after blending each component in a predetermined proportion, the composition can be produced by kneading or mixing at room temperature using a kneading means such as a three-roll mill, ball mill, or sand mill, or by stirring means such as a super mixer or planetary mixer. Among these, the use of a three-roll mill is preferred. Furthermore, pre-kneading or pre-mixing may be performed before kneading or mixing as needed.

[0028] (Method for producing cured reflective materials) The cured reflective material according to this embodiment can be produced by forming the cured reflective material on a substrate using the resin composition used in this embodiment as described above. Examples of circuit boards include those used for LEDs and other electronic devices.

[0029] Specifically, first, the resin composition used in this embodiment is applied to the substrate, and then pre-dried to form a coating film. Here, examples of coating methods include screen printing, bar coating, applicator coating, blade coating, knife coating, roll coating, gravure coating, and spray coating. The pre-drying conditions vary depending on the type of resin composition and are not particularly limited, but for example, heating at a temperature in the range of 60°C to 80°C for a period of 15 minutes to 60 minutes is sufficient. Such pre-drying volatilizes solvents and other substances in the resin composition, allowing for the formation of a tack-free coating. The thickness of the coating film (DRY film thickness) is not particularly limited, but is usually between 5 μm and 200 μm, and preferably between 10 μm and 70 μm.

[0030] When using a photo-developable resin composition, a negative film having a pattern with areas other than the circuit pattern lands being translucent may be placed in close contact with the coating film, ultraviolet light may be irradiated from above, and then the unexposed areas may be removed with a dilute alkaline aqueous solution to develop the coating film after exposure. This makes it possible to create openings in the coating film corresponding to the circuit pattern.

[0031] Next, the substrate is subjected to heat treatment (hereinafter sometimes referred to as post-curing). This allows a cured reflective material to be formed on the substrate. The heat treatment conditions vary depending on the type of resin composition and are not particularly limited. For example, a hot air circulation type dryer and a far-infrared furnace can be used as the heat treatment furnace. When using a hot air circulation type dryer, the heat treatment temperature is preferably 130°C to 170°C, and the heat treatment time is preferably 30 minutes to 120 minutes. Furthermore, when using a far-infrared furnace, the heat treatment temperature is preferably 200°C to 250°C, and the heat treatment time is preferably 3 minutes to 10 minutes.

[0032] (Physical properties of cured reflective materials) As described above, the cured reflective material according to this embodiment exhibits excellent visible light reflection efficiency and superior discoloration suppression. Furthermore, compared to conventional reflective materials, the cured reflective material according to this embodiment can maintain sufficient reflection efficiency even when the thickness of the cured reflective material is reduced. For this reason, while the thickness of conventional cured reflective materials is usually between 100 μm and 500 μm, the cured reflective material according to this embodiment can be made thinner than conventional materials. The cured reflective material according to this embodiment is preferably 5 μm to 200 μm thick, more preferably 10 μm to 100 μm thick, and particularly preferably 20 μm to 70 μm thick.

[0033] In this embodiment, the cured reflective material preferably satisfies the following conditions when the thickness of the cured reflective material is 30 μm. The reflectance of the cured reflective material at a wavelength of 450 nm is preferably 91% or higher, and more preferably 92% or higher, using the SCI (Specular Component Include) method. If this reflectance is above the aforementioned lower limit, it can be said that the visible light reflection efficiency is excellent. Furthermore, it is preferable that the reflectance of the cured reflective material at a wavelength of 450 nm after reflow treatment under the conditions of a nitrogen atmosphere (oxygen concentration: 2000 ppm), with a peak temperature of 260°C or higher for 6 seconds and a melting temperature of 240°C or higher for 60 seconds, is 90% or higher using the SCI method. If this reflectance is above the aforementioned lower limit, it can be determined that the decrease in reflectance efficiency due to heat treatment such as reflow treatment has been suppressed. [Examples]

[0034] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited in any way by these examples.

[0035] (Resin components) Curable resin: A mixture containing acrylic resin acrylate ("Cychromer P" manufactured by Daicel Ornex), an epoxy compound, and a reactive diluent. (White inorganic filler) White inorganic filler A: Prepared by classifying titanium oxide (silica-alumina treated, product name "CR-80", manufactured by Ishihara Sangyo Co., Ltd.) using a classifier. White inorganic filler B: Titanium oxide (silica-alumina treated, product name "CR-80", manufactured by Ishihara Sangyo Co., Ltd.) (Other ingredients) Thickening agent: Hydrophilic fumed silica, product name "LeoroSeal DM-20S", manufactured by Tokuyama Corporation. Antifoaming agent: Silicone-based antifoaming agent, product name "X-50-1095C", manufactured by Shin-Etsu Chemical Co., Ltd.

[0036] [Example 1] 56.75% by mass of curable resin, 39.71% by mass of white inorganic filler A, 1.65% by mass of thickener, and 1.89% by mass of defoaming agent were placed in a container, pre-mixed with a stirrer, and then mixed and dispersed at room temperature using a three-roll roller to obtain the resin composition. Next, a copper foil substrate (copper foil thickness: 35 μm, substrate thickness: 1.6 mm) was surface-treated by buff polishing, and then the obtained resin composition was applied by screen printing to a predetermined dry film thickness to obtain a coated substrate. After application, pre-drying was performed in a box oven at 80°C for 20 minutes. After pre-drying, post-curing was performed in a box oven at 150°C for 60 minutes to form a cured reflective material on the substrate, and evaluation substrates were prepared. Three evaluation substrates were prepared with different reflective material thicknesses of 20 μm, 45 μm, and 70 μm. In addition, a substrate with a reflective material thickness of 40 μm was prepared for color difference evaluation.

[0037] [Comparative Example 1] A resin composition and an evaluation substrate were obtained in the same manner as in Example 1, except that each material was blended according to the composition shown in Table 1.

[0038] [Evaluation of hardened reflective materials] The cured reflective material was evaluated using the following methods (observation of backscattered electron images, reflectance, reflectance after reflow treatment, and color difference). The results are shown in Table 1. (1) Observation of backscattered electron images Using an evaluation substrate with a reflective coating cured to a thickness of 20 μm as a sample, the cross-section of the coating was imaged at 20,000x magnification using a scanning electron microscope. The resulting 4.5 μm × 6.0 μm backscattered electron image was extracted using an image analysis and measurement system (product name "WinROOF2021", manufactured by Mitani Corporation) to extract the second phase. After binarization, a Voronoi tessellation was performed using the centroid of the extracted second phase as the generation point to create a Voronoi diagram. The obtained backscattered electron image is shown in Figure 1. In addition, from the obtained backscattered electron image, the average diameter of the second phase in terms of the equivalent circle diameter, the proportion of the second phase with an equivalent circle diameter of 150 nm or less, and the area ratio of the second phase were calculated. Furthermore, the obtained Voronoi diagram (color-coded according to the absolute maximum length of the second phase) is shown in Figure 2. The absolute maximum length of each Voronoi region and the average absolute maximum length were also calculated from the obtained Voronoi diagram. Furthermore, Figure 3 shows the relationship between the absolute maximum length of each Voronoi region and its content. Furthermore, the obtained Voronoi diagram (color-coded according to the Voronoi area of ​​the second phase) is shown in Figure 4. The Voronoi area and the average Voronoi area were also calculated from the obtained Voronoi diagram. Finally, Figure 5 shows the relationship between the Voronoi area and its content. (2)Reflectance For three evaluation substrates with different thicknesses of reflective material curing, the SCI at 450 nm was measured using a spectrophotometer (product name "CM-700d," manufactured by Konica Minolta). The obtained reflectances were plotted, and the reflectance converted to a thickness of 30 μm was calculated from the approximation curve. (3) Reflectance after reflow treatment Three evaluation substrates with different thicknesses of reflective material curing were reflow-treated under nitrogen atmosphere (oxygen concentration: 2000 ppm) with a peak temperature of 260°C or higher for 6 seconds and a melting temperature of 240°C or higher for 60 seconds. The SCI at 450 nm was measured for each of these reflow-treated evaluation substrates using a spectrophotometer (product name "CM-700d", Konica Minolta). The obtained reflectances were plotted, and the reflectance converted to a thickness of 30 μm was calculated from the approximation curve. (4) Color difference For a color difference evaluation substrate with a reflective material curing thickness of 40 μm, the L*a*b* value was measured using a spectrophotometer (product name "CM-700d", manufactured by Konica Minolta Corporation) in accordance with JIS Z 8781-4 "Colorimetry - Part IV: CIE1976 L*a*b* color space". Next, a 40 μm color difference evaluation substrate made of cured reflective material was reflowed three times under nitrogen atmosphere (oxygen concentration: 2000 ppm) with a peak temperature of 260°C or higher for 6 seconds and a melting temperature of 240°C or higher for 60 seconds. The L*a*b* values ​​were measured for these reflow-treated color difference evaluation substrates in the same manner as described above. Then, the color difference △E was calculated using the following formula, and the color difference was evaluated according to the following criteria. Color difference △E = [(L value after reflow - initial L value)] 2 +(a value after reflow - initial a value) 2 +(b value after reflow - initial b value) 2 ]1 / 2 ○: The color difference △E is less than 0.7. △: The color difference △E is 0.7 or greater and less than 0.8. ×: The color difference △E is 0.8 or greater.

[0039] [Table 1]

[0040] As is clear from the results shown in Table 1, the cured reflective material of the present invention (Example 1) was confirmed to have good results in all aspects, including reflectance, reflectance after reflow treatment, and color difference. Therefore, it was confirmed that the cured reflective material of the present invention has excellent visible light reflection efficiency and excellent discoloration suppression. [Industrial applicability]

[0041] The cured reflective material of the present invention is useful as a light-reflecting material, for example, as a reflective material for light-emitting devices, particularly for white LEDs.

Claims

1. A cured reflective material obtained by curing a resin composition containing a resin component mainly composed of a curable resin and a white inorganic filler, When the cross-section of the cured reflective material is imaged with a scanning electron microscope and the resulting backscattered electron image is observed, and the material is classified into a first phase consisting of the resin component and a second phase consisting of the white inorganic filler, The average diameter of the equivalent circular diameter of the second phase is 0.15 μm or more and 0.3 μm or less. The proportion of the second phase having an equivalent circular diameter of 150 nm or less is 30% or less of the entire second phase. The equivalent circle diameter is obtained by extracting the second phase in the backscattered electron image, setting a rectangular measurement field of 4.5 μm × 6.0 μm in the image after the binarization of the backscattered electron image, and calculating the diameter corresponding to the area of ​​the extracted second phase in the measurement field. Cured reflective material.

2. In the cured reflective material according to claim 1, The white inorganic filler contains at least one metal oxide selected from the group consisting of titania, zirconia, yttria-stabilized zirconia, alumina, and silica. Cured reflective material.

3. In the cured reflective material according to claim 1 or claim 2, The aforementioned white inorganic filler is a core-shell type filler comprising a core layer and a shell layer. The aforementioned core layer consists of titania, The shell layer is made of at least one metal oxide selected from the group consisting of zirconia, alumina, and silica. The titania content in the aforementioned metal oxide is 90% by mass or more. Cured reflective material.

4. In the cured reflective material according to claim 1 or claim 2, The aforementioned white inorganic filler is subjected to an organic surface treatment. Cured reflective material.

5. In the cured reflective material according to claim 1 or claim 2, The aforementioned resin component contains an epoxy compound. Cured reflective material.

6. In the cured reflective material according to claim 1 or claim 2, The area ratio of the second phase is 10% to 50% of the total area of ​​the first and second phases, Cured reflective material.

7. In the cured reflective material according to claim 1 or claim 2, The average absolute maximum length of the second phase is 0.55 μm or less. The aforementioned absolute maximum length is the absolute maximum length of each Voronoi region in the Voronoi diagram obtained by performing a Voronoi tessellation with the centroid of the second phase as the generating point. The Voronoi diagram is obtained by extracting the second phase from the backscattered electron image, setting a rectangular measurement field of 4.5 μm × 6.0 μm in the image after binarization of the backscattered electron image, performing Voronoi tessellation with the centroid of the extracted second phase as the generating point within the measurement field, and calculating the Voronoi region of all the generating points. Cured reflective material.

8. In the cured reflective material according to claim 1 or claim 2, The average value of the Voronoi area of ​​the second phase is 0.13 μm. ２ The following: The aforementioned Voronoi area is the area of ​​each Voronoi region in the Voronoi diagram obtained by performing a Voronoi partition with the centroid of the second phase as the generating point. The Voronoi diagram is obtained by extracting the second phase from the backscattered electron image, setting a rectangular measurement field of 4.5 μm × 6.0 μm in the image after binarization of the backscattered electron image, performing Voronoi tessellation with the centroid of the extracted second phase as the generating point within the measurement field, and calculating the Voronoi region of all the generating points. Cured reflective material.

9. In the cured reflective material according to claim 1 or claim 2, When the thickness of the cured reflective material is 30 μm, The reflectance of the cured reflective material at a wavelength of 450 nm is 91% or more using the SCI (Specular Component Include) method. The reflectance of the cured reflective material at a wavelength of 450 nm after reflow treatment under the conditions of a nitrogen atmosphere (oxygen concentration: 2000 ppm), with a peak temperature of 260°C or higher for 6 seconds and a melting temperature of 240°C or higher for 60 seconds, is 90% or higher using the SCI method. Cured reflective material.

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