Ultraviolet-reflective resin composition and hardened substance of the same

Abstract

To provide an ultraviolet-reflective resin composition which includes aluminum oxide powder and enables the suppression of the precipitation of the aluminum oxide powder for a long period of time, while maintaining the moldability.SOLUTION: An addition-curing resin composition contains (A) organopolysiloxane, (B) organohydrogenpolysiloxane, (C) aluminum oxide powder having a volume average particle diameter of 0.1 to 10 μm, (D) silica powder having a volume average particle diameter of 1.0 μm or less, and (E) a curing catalyst. In the addition-curing resin composition, a content of the aluminum oxide powder is within the range of 10 to 200 pts.mass to 100 pts.mass of the total mass of (A) and (B), a content of the silica powder is within the range of 0.5 to 10 pts.mass to 100 pts.mass of the total mass of (A) and (B), and a ratio of viscosity of the resin composition at 23°C and a shear rate of 0.1 (1 / s) to viscosity of the resin composition at 23°C and a shear rate of 10 (1 / s) is within the range of 1.5 to 50.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ultraviolet reflective resin composition and a cured product thereof. [Background technology]

[0002] Ultraviolet irradiation devices equipped with light-emitting elements such as LEDs that emit deep ultraviolet light in the short wavelength range of 210 to 310 nm are used in various devices for disinfection, sterilization, and purification. In this case, the deep ultraviolet light emitted radially from the LEDs is sometimes controlled to a specific direction using a reflector or other device to increase the efficiency of use of the deep ultraviolet light.

[0003] Patent Document 1 describes an ultraviolet reflective composition that can be used as a material for reflectors, etc. The ultraviolet reflective composition described in Patent Document 1 has a matrix containing a silicone resin and an inorganic filler containing alumina (aluminum oxide) and silica. A cured product of this ultraviolet reflective composition reflects ultraviolet light emitted from a light-emitting element because the inorganic filler is dispersed in the matrix. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-248484 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the UV reflective composition described in Patent Document 1, alumina settles when left for a long period of time. In this case, the UV reflective composition must be mixed again when forming it into a reflector, etc., which may complicate the manufacturing process. In order to prevent the settling of alumina in the UV reflective composition, it is conceivable to use a high-viscosity silicone resin. In this case, it is thought that injection molding using the UV reflective composition and application of the UV reflective composition will become difficult. Another method for preventing the settling of alumina is to surface treat the alumina. In this case, it is thought that a lot of time will be spent selecting the optimal surface treatment agent and costs will increase.

[0006] A primary object of the present invention is to provide an ultraviolet reflective resin composition and a cured product thereof that can suppress the settling of aluminum oxide powder for a long period of time while maintaining moldability. [Means for solving the problem]

[0007] [1] An addition-curable ultraviolet reflective resin composition comprising: (A) an organopolysiloxane having at least two alkenyl groups per molecule; (B) an organohydrogenpolysiloxane having at least two hydrogen atoms bonded to silicon atoms per molecule; (C) aluminum oxide powder having a volume average particle size of 0.1 to 10 μm; (D) silica powder having a volume average particle size of 1.0 μm or less; and (E) a curing catalyst, wherein the content of the aluminum oxide powder is: an ultraviolet reflective resin composition in which the content of (A) and (B) is in the range of 10 to 200 parts by mass relative to 100 parts by mass of the total mass of (A) and (B); the content of the silica powder is in the range of 0.5 to 10 parts by mass relative to 100 parts by mass of the total mass of (A) and (B); and the ratio of the viscosity of the ultraviolet reflective resin composition at 23°C and a shear rate of 0.1 (1 / s) to the viscosity of the ultraviolet reflective resin composition at 23°C and a shear rate of 10 (1 / s) is in the range of 1.5 to 50. [2] The ultraviolet reflective resin composition according to [1], wherein the total content of Fe, Ga, Ti, and Zn in the ultraviolet reflective resin composition is 150 mass ppm or less. [3] A cured product obtained by curing the ultraviolet reflective resin composition according to [1] or [2]. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an ultraviolet reflective resin composition and a cured product thereof that can suppress the settling of aluminum oxide powder for a long period of time while maintaining moldability. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a graph showing the relationship between shear rate and viscosity of an ultraviolet reflective resin composition. [Figure 2] FIG. 2 is a graph showing the relationship between the wavelength of ultraviolet light and the diffuse reflectance of a cured product of an ultraviolet reflective resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Ultraviolet reflective resin composition) The addition-curable ultraviolet reflective resin composition of the present embodiment includes (A) an organopolysiloxane, (B) an organohydrogenpolysiloxane, (C) aluminum oxide powder, (D) silica powder, and (E) a curing catalyst.

[0011] The ratio of the viscosity of the UV-reflecting resin composition at 23°C and a shear rate of 0.1 (1 / s) to the viscosity of the UV-reflecting resin composition at 23°C and a shear rate of 10 (1 / s) is within the range of 1.5 to 50. If this ratio is less than 1.5, sedimentation of the aluminum oxide powder cannot be suppressed. On the other hand, if this ratio exceeds 50, the UV-reflecting resin composition loses fluidity and its moldability becomes poor. The viscosity of the UV-reflecting resin composition at each shear rate can be measured using a rheometer (Discovery HR-2: TA Instruments) equipped with a 25 mm diameter cone plate and a sample temperature-controlled at 23°C using a Peltier plate. Because viscosity is time-dependent under constant temperature and shear rate conditions, the measured value was the viscosity at the time when the viscosity reached equilibrium.

[0012] The organopolysiloxane (A) is an organopolysiloxane having at least two alkenyl groups per molecule, and the average composition of the organopolysiloxane is represented by formula (1). Formula (1)R 1 a SiO (4-a) / 2

[0013] R in Equation (1) 1 is an alkenyl group, an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group having 1 to 6 carbon atoms, or a cycloalkyl group having 5 to 12 carbon atoms. 1 At least two of these R are alkenyl groups. 1 is a substituent that does not absorb deep ultraviolet (UVC) light in the range of 220 to 300 nm.

[0014] Examples of the alkenyl group include a vinyl group, an allyl group, a butenyl group, a pentenyl group, and a hexenyl group, and the vinyl group is preferred. The alkenyl group may be located at the end of the molecular chain or in a side chain.

[0015] Examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethylene, propyl, and butyl groups, and examples of fluorinated alkyl groups having 1 to 6 carbon atoms include groups in which a portion of these alkyl groups has been substituted with a fluorine atom. Examples of cycloalkyl groups having 5 to 12 carbon atoms include cyclohexyl and cyclohexenyl groups.

[0016] In formula (1), a is a positive number between 1.95 and 2.05.

[0017] The organopolysiloxane represented by formula (1) is preferably linear, but may contain a branched structure in part. That is, the organopolysiloxane represented by formula (1) preferably contains diorganosiloxane units (D units) as the main component. Specifically, the content of D units is preferably 90 mol% or more based on the total structural units (total siloxane units) of the organopolysiloxane. The type and amount of siloxane units can be determined by 29Si-NMR analysis.

[0018] The organopolysiloxane represented by formula (1) is preferably a linear organopolysiloxane whose main chain contains diorganosiloxane units (D units) as the main component and whose molecular chain is terminated at both ends with triorganosiloxane units (M units). 1 Among these, the groups other than the alkenyl group preferably contain a methyl group, and the alkenyl group is preferably a vinyl group.

[0019] The viscosity of the organopolysiloxane represented by formula (1) at 23°C is preferably 0.1 Pa s or more, and more preferably 1 Pa s or more, from the viewpoint of further reducing molding defects such as flash. From the viewpoints of easily dispersing the aluminum oxide powder, preventing filling defects, and ease of application and other operations, the viscosity at 23°C is preferably 200 Pa s or less, and more preferably 150 Pa s or less.

[0020] Two or more organopolysiloxanes represented by formula (1) with different viscosities may be used in combination, as long as the viscosity of the mixture is within the above range. The viscosity of the organopolysiloxane (A) can be measured at 23°C using a cone-and-plate rotational viscometer in accordance with JIS Z8803:2011.

[0021] The alkenyl group content of the organopolysiloxane represented by formula (1) is preferably 0.02 mmol / g or more, more preferably 0.05 mmol / g or more. When the alkenyl group content is 0.02 mmol / g or more, the crosslink density of the cured product becomes higher, making it easier to improve hardness properties. The upper limit of the alkenyl group content is preferably less than 1.0 mmol / g, more preferably less than 0.8 mmol / g. When the alkenyl group content is less than 1.0 mmol / g, the crosslink density of the cured product is unlikely to become excessively high, making it less likely that the breaking elongation of the cured product will be impaired and even less likely that the toughness will be impaired.

[0022] Two or more types of organopolysiloxanes represented by formula (1) with different alkenyl group contents may be used in combination, as long as the alkenyl group content of the mixture is within the above range.

[0023] (B) organohydrogenpolysiloxane is a curing agent for the ultraviolet reflective resin composition that functions as a crosslinking agent for (A) organopolysiloxane. (B) organohydrogenpolysiloxane is an organohydrogenpolysiloxane that has at least two hydrogen atoms bonded to silicon atoms (-SiH) per molecule.

[0024] (B) organohydrogenpolysiloxane may be linear or branched. The degree of polymerization of (B) organohydrogenpolysiloxane is not particularly limited, but is preferably in the range of 2 to 300, more preferably 4 to 200. The hydrogen atom bonded to the silicon atom may be at the end of the molecular chain or in a side chain.

[0025] The organic group bonded to the silicon atom is an alkyl group having 1 to 6 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms. The organic group bonded to the silicon atom is preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group.

[0026] The content of hydrogen atoms bonded to silicon atoms in (B) organohydrogenpolysiloxane is not particularly limited as long as it is sufficient to react with the alkenyl groups in component (A), but is preferably within the range of 0.1 to 20 mmol / g.

[0027] Examples of (B) organohydrogenpolysiloxane include diorganopolysiloxanes blocked with dimethylhydrogensilyl groups, copolymers containing dimethylsiloxane units, methylhydrogensiloxane units, and terminal trimethylsiloxy groups, copolymers containing dimethylhydrogensiloxane units and SiO 4 / 2 units (Q units), 1,3,5,7-tetrahydrogen-1,3,5,7-tetramethylcyclotetrasiloxane, 1-propyl-3,5,7-trihydrogen-1,3,5,7-tetramethylcyclotetrasiloxane, and 1,5-dihydrogen-3,7-dihexyl-1,3,5,7-tetramethylcyclotetrasiloxane.

[0028] The content of (B) organohydrogenpolysiloxane is not particularly limited as long as it is within a range that can sufficiently crosslink (A) organopolysiloxane, but the amount is preferably such that the number of moles of hydrosilyl groups in (B) organohydrogenpolysiloxane is within a range of 0.8 to 5 moles, and more preferably 1 to 3 moles, per mole of alkenyl groups in (A) organopolysiloxane.

[0029] (C) The aluminum oxide powder functions as a reflector of ultraviolet rays. The volume average particle diameter of the aluminum oxide powder is within the range of 0.1 to 10 μm, preferably within the range of 0.1 to 8.0 μm, and more preferably within the range of 0.1 to 3.0 μm. When the volume average particle diameter of the aluminum oxide powder is within the above range, ultraviolet rays can be suitably reflected. The volume average particle diameter of the aluminum oxide powder can be measured, for example, by a laser diffraction / scattering method.

[0030] The content of (C) aluminum oxide powder is within the range of 10 to 200 parts by mass, preferably 15 to 150 parts by mass, and more preferably 20 to 100 parts by mass, per 100 parts by mass of the total mass of (A) organopolysiloxane and (B) organohydrogenpolysiloxane. When the content of aluminum oxide powder is within the above range, ultraviolet rays can be suitably reflected. The (C) aluminum oxide powder may or may not be surface-treated.

[0031] The (D) silica powder suppresses the settling of the (C) aluminum oxide powder in the UV reflective resin composition. The (D) silica powder is added so as to satisfy the above-mentioned ratio. The (D) silica powder may be silica powder that has not been hydrophobized, or may be silica powder that has been hydrophobized. In this embodiment, the (D) silica powder is silica powder that has not been hydrophobized. Examples of hydrophobized silica powder include silica powder that has been surface-treated with a silane coupling agent, a silazane compound, or a low-molecular-weight siloxane compound having a hydrophobic group.

[0032] Examples of the silazane compound include hexamethyldisilazane and 1,3-divinyl-1,1,3,3-tetramethyldisilazane. Examples of the low molecular weight siloxane compound include octamethylcyclotetrasiloxane.

[0033] The silane coupling agent having a hydrophobic group has both a hydrolyzable group and a hydrophobic group. Examples of the hydrolyzable group include alkoxy groups such as methoxy and ethoxy groups, chloro groups, and silazane groups. Examples of the hydrophobic group include alkyl groups having 1 to 6 carbon atoms and alkenyl groups having 1 to 6 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms and alkenyl groups having 1 to 3 carbon atoms, and more preferably methyl and vinyl groups. The hydrolyzable group is hydrolyzed by water to form a hydroxyl group, which undergoes a dehydration condensation reaction with the hydroxyl groups on the surface of the (E) silica powder, thereby imparting a hydrophobic group to the surface of the (D) silica powder. This suppresses aggregation of the (D) silica powder and unintended effects on the (E) curing catalyst, improving the dispersibility of the (D) silica powder.

[0034] The volume average particle diameter of the (D) silica powder is 1.0 μm or less, and preferably 0.5 μm or less. If the volume average particle diameter of the (D) silica powder is 1.0 μm or less, it is likely to exhibit the function of suppressing the settling of the aluminum oxide powder. The volume average particle diameter of the (D) silica powder can be measured, for example, by a laser diffraction / scattering method.

[0035] The content of the (E) silica powder is within a range of 0.5 to 10 parts by mass, and more preferably within a range of 0.5 to 5.0 parts by mass, per 100 parts by mass of the total mass of the (A) organopolysiloxane and the (B) organohydrogenpolysiloxane. If the content of the (E) silica powder is within the above range, sedimentation of the (C) aluminum oxide powder in the ultraviolet reflective resin composition can be suppressed.

[0036] The (E) curing catalyst is a platinum-based catalyst for promoting the hydrosilylation reaction between the alkenyl groups of the (A) organopolysiloxane and the hydrogen atoms bonded to the silicon atoms of the (B) organohydrogenpolysiloxane. Known platinum-based catalysts can be used. The platinum-based catalyst may be a platinum catalyst such as chloroplatinic acid or a platinum complex catalyst. The platinum complex catalyst may be a Karstedt catalyst or a catalyst other than a Karstedt catalyst.

[0037] The Karstedt catalyst is, for example, a platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex.

[0038] The platinum complex catalyst other than the Karstedt catalyst is, for example, a complex represented by the following formula (2). Formula (2) L1→Pt←L2

[0039] L1 in formula (2) represents a ligand having a double bond, and the ligand having a double bond is preferably a compound having two double bonds (diolefin compound).

[0040] The content of the (E) curing catalyst is preferably 0.5 ppm by mass or more, more preferably 1 ppm by mass or more, and most preferably 2 ppm by mass or more, in terms of the amount of platinum atoms per 100 parts by mass of the total mass of the (A) organopolysiloxane and the (B) organohydrogenpolysiloxane, from the viewpoint of sufficiently promoting the hydrosilylation reaction of the (A) organopolysiloxane and the (B) organohydrogenpolysiloxane. Furthermore, from the viewpoint of increasing transmittance in the UVC wavelength region, the upper limit of the content of the (E) curing catalyst is preferably 300 ppm by mass or less, more preferably 200 ppm by mass or less, and particularly preferably 100 ppm by mass or less, in terms of the amount of platinum atoms per 100 parts by mass of the (A) organopolysiloxane and the (B) organohydrogenpolysiloxane.

[0041] The ultraviolet reflective resin composition of the present invention may further contain other components in addition to those described above, as necessary, as long as the viscosity ratio does not deviate from the range of 1.5 to 50. Examples of other components include (F) a reaction inhibitor and a silicone resin.

[0042] The reaction inhibitor (F) is preferably a hydrosilylation reaction inhibitor from the viewpoint of ensuring pot life, etc. Examples of hydrosilylation reaction inhibitors include polyfunctional alkenyl compounds of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, and acetylene alcohol derivatives of 2-methyl-3-butyn-2-ol, 3-methyl-1-butyn-3-ol, and 3-methyl-1-pentyn-3-ol.

[0043] The content of the reaction inhibitor (F) is preferably within a range from 0.001 to 0.05 parts by mass, and more preferably within a range from 0.001 to 0.02 parts by mass, per 100 parts by mass of the organopolysiloxane (A).

[0044] The ultraviolet reflective resin composition is preferably prepared by mixing a first material and a second material. The components of the first material and the second material can be appropriately selected from (A) organopolysiloxane, (B) organohydrogenpolysiloxane, (C) aluminum oxide powder, (D) silica powder, and (E) curing catalyst, respectively. Note that (A) organopolysiloxane, (B) organohydrogenpolysiloxane, and (E) curing catalyst are not mixed at the same time. The components of the first material and the second material are designed so that they are efficiently and uniformly mixed.

[0045] The total content of Fe, Ga, Ti, and Zn in the ultraviolet reflective resin composition is preferably 150 mass ppm or less. Fe, Ga, Ti, and Zn are impurities derived from the raw materials of the aluminum oxide powder. If the impurity content is low, the ultraviolet reflectance can be increased.

[0046] (Cured product of ultraviolet reflective resin composition) The cured product of the ultraviolet reflective resin composition can be produced, for example, by the following method. The shape of the cured product of the ultraviolet reflective resin composition is appropriately set depending on the intended use. The shape of the cured product of the ultraviolet reflective resin composition may be a plate shape or a shape having a curved surface.

[0047] When the ultraviolet reflective resin composition is molded into a member (cured product) having a thickness of 1 mm, the reflectance when ultraviolet light having a wavelength of 280 nm is incident in the thickness direction of the member is preferably 75% or more, and more preferably 80% or more.

[0048] The ultraviolet reflectance of the ultraviolet reflective resin composition can be measured, for example, by the following method. The above-mentioned ultraviolet reflective resin composition is molded into a plate-like member with a thickness of 1 mm, and measurement can be performed using an ultraviolet-visible spectrophotometer equipped with an integrating sphere. First, a reference sample (PTFE standard white plate) is set at a position where the measurement light entering the integrating sphere from the entrance opening reaches, and baseline correction is performed. Then, a plate-like member serving as the measurement sample is set in place of the reference sample, and measurement is performed, and the reflectance relative to the reference sample is taken as the ultraviolet reflectance of the ultraviolet reflective resin composition.

[0049] The light source is not particularly limited as long as it emits light with a wavelength of 280 nm. Examples of light sources include light-emitting diodes (LEDs), mercury lamps, metal halide lamps, xenon lamps, and laser diodes (LDs). The central wavelength of the ultraviolet light emitted from the light source is preferably 200 to 350 nm, and more preferably 240 to 300 nm from the viewpoint of particularly high sterilization efficiency. In other words, the ultraviolet light is more preferably deep ultraviolet (UVC).

[0050] (Method for producing a cured product of an ultraviolet reflective resin composition) The method for producing a molded article of an ultraviolet reflective resin composition includes a step of preparing an ultraviolet reflective resin composition and a step of curing the ultraviolet reflective resin composition.

[0051] In the step of preparing an ultraviolet reflective resin composition, a first material and a second material are mixed to prepare a resin composition of uniform concentration. In this embodiment, the first material contains (A) an organopolysiloxane, (C) aluminum oxide powder, (D) silica powder, and (E) a curing catalyst, and the second material contains (A) an organopolysiloxane, (B) an organohydrogenpolysiloxane, (C) aluminum oxide powder, and (D) silica powder.

[0052] In the curing step, for example, the ultraviolet reflective resin composition is poured into a heated mold and cured. In the curing step, the ultraviolet reflective resin composition is poured into the cavity of a mold that has been heated in advance to the curing temperature of the ultraviolet reflective resin composition (for example, 80 to 250°C, preferably 120 to 200°C) and cured. The heating time varies depending on the heating temperature, but is, for example, in the range of 10 seconds to 30 minutes. Finally, the cured ultraviolet reflective resin composition is obtained by removing it from the mold.

[0053] (effect) As described above, the ultraviolet reflective resin composition and its cured product according to this embodiment contain the specified aluminum oxide powder and silica powder, and the ratio of the viscosity of the ultraviolet reflective resin composition at 23°C and a shear rate of 0.1 (1 / s) to the viscosity of the ultraviolet reflective resin composition at 23°C and a shear rate of 10 (1 / s) is within the range of 1.5 to 50. Therefore, it is possible to suppress sedimentation of the aluminum oxide powder for a long period of time while maintaining moldability. [Example]

[0054] The present invention will be further described below with reference to examples and comparative examples, but the technical scope of the present invention is not limited thereto.

[0055] 1. Study of aluminum oxide powder and silica powder (Relationship between shear rate and viscosity) As a preliminary experiment, the relationship between shear rate and viscosity of the UV-reflecting resin composition was investigated. If the viscosity of the UV-reflecting resin composition is low at high shear rates, it is easy to mold, while if the viscosity of the UV-reflecting resin composition is high at low shear rates, the aluminum oxide powder is less likely to settle. Figure 1 is a graph showing the relationship between shear rate and viscosity of the UV-reflecting resin composition. The horizontal axis of Figure 1 represents shear rate (1 / s), and the vertical axis represents the viscosity (Pa·s) of the UV-reflecting resin composition. In Figure 1, open square symbols represent the results for UV-reflecting resin composition a of the example in Table 1, filled circle symbols represent the results for UV-reflecting resin composition b of the comparative example in Table 1, open circle symbols represent the results for UV-reflecting resin composition c of the comparative example in Table 1, and filled square symbols represent the results for UV-reflecting resin composition d of the comparative example in Table 1. The viscosity at each shear rate was measured using the method described above.

[0056] A commercially available addition-type silicone resin was used as the silicone resin. This resin contains (A) an organopolysiloxane having at least two alkenyl groups per molecule, (B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and (E) a curing catalyst. (D) Silica powder with a volume average particle diameter of 12 nm was used. (C) Aluminum oxide powder with a volume average particle diameter of 0.7 μm was used.

[0057] The compositions of the respective ultraviolet reflective resin compositions are shown in Table 1.

[0058] [Table 1]

[0059] As shown in Table 1 and FIG. 1 , UV-reflecting resin composition a, which contained silicone resin, silica powder, and aluminum oxide powder, had a low viscosity at 23°C and a shear rate of 10 (1 / s), but a high viscosity at 23°C and a shear rate of 0.1 (1 / s). On the other hand, UV-reflecting resin compositions b to d, which did not contain silica powder or aluminum oxide powder, had a low viscosity at 23°C and a shear rate of 10 (1 / s), and also had a low viscosity at 23°C and a shear rate of 0.1 (1 / s). This indicates that the viscosity of UV-reflecting resin compositions containing silicone resin, silica powder, and aluminum oxide powder changes depending on the shear rate. It was also found that the compositions were easy to mold and the aluminum oxide powder was less likely to settle out depending on the shear rate.

[0060] (Study of the effect of suppressing sedimentation) As a preliminary experiment, we investigated the combination of aluminum oxide powder content and silica powder content that could effectively inhibit the settling of aluminum oxide powder. The silicone resin, aluminum oxide powder content, and silica powder content used were the same as those used in the "Relationship between Shear Rate and Viscosity" section above. The aluminum oxide powder content was 0, 10, 50, and 70 parts by mass per 100 parts by mass of silicone resin. The silica powder content was 0, 0.5, 1, 2, 5, and 7 parts by mass per 100 parts by mass of silicone resin. The ratio of the viscosity of each UV-reflecting resin composition at a shear rate of 0.1 (1 / s) at 23°C to the viscosity of each UV-reflecting resin composition at a shear rate of 10 (1 / s) at 23°C was calculated. Each resin composition was placed in a transparent sample bottle and visually inspected after one month to confirm the effect of inhibiting the settling of aluminum oxide powder.

[0061] Table 2 shows the ratio of the viscosity of each UV-reflecting resin composition at 23°C and a shear rate of 0.1 (1 / s) to the viscosity of the UV-reflecting resin composition at 23°C and a shear rate of 10 (1 / s).

[0062] [Table 2]

[0063] As shown in Table 2, it was found that the effect of suppressing the settling of aluminum oxide powder in the ultraviolet reflective resin composition was exhibited only when the viscosity ratio was within a predetermined range.

[0064] (Reflectivity study) Next, the UV reflectance of the cured products of each UV-reflecting resin composition was examined. Figure 2 is a graph showing the relationship between UV wavelength (nm) and diffuse reflectance (%). A UV-reflecting resin composition was prepared containing 100 parts by mass of silicone resin, 2 parts by mass of silica powder, and 30 parts by mass of aluminum oxide powder. The silicone resin and silica powder were the same as those used in the "Relationship between shear rate and viscosity" section above. The aluminum oxide powders used were AA-1.5 (Sumitomo Chemical Co., Ltd.), AP-1 (Harzok Japan Co., Ltd.), and DAW-07 (Denka Company Limited), each containing 150 ppm or less of the total impurities Fe, Ga, Ti, and Zn and having a volume average particle size of 1.7 μm.

[0065] In Figure 2, the solid line shows the results for the UV-reflecting resin composition using AA-1.5 as the aluminum oxide powder, the dotted line shows the results for the UV-reflecting resin composition using AP-1 as the aluminum oxide powder, and the dashed-dotted line shows the results for the UV-reflecting resin composition using DAW-07 as the aluminum oxide powder. AP-1 is an aluminum oxide powder having a total content of Fe, Ga, Ti, and Zn of more than 150 ppm by mass and a volume average particle size of 1.0 μm. DAW-07 is an aluminum oxide powder having a total content of impurities Fe, Ga, Ti, and Zn of more than 150 ppm by mass and a volume average particle size of more than 10 μm.

[0066] As shown in Figure 2, the UV-reflecting resin composition using AA-1.5 as the aluminum oxide powder had a high diffuse reflectance. This was thought to be because the composition contained few impurities and had a volume average particle size within the specified range, which allowed UV rays to be reflected appropriately. On the other hand, the UV-reflecting resin compositions using AP-1 or DAW-07 as the aluminum oxide powder had a low UV diffuse reflectance.

[0067] 2. Preparation of Resin Composition (1) Material (A) Organopolysiloxane (main component) The organopolysiloxane used was a vinyl-terminated polydimethylsiloxane (DMS-V41; Gelest) whose both ends were blocked with dimethylvinylsiloxy groups and whose viscosity at 23°C was 10 Pa·s.

[0068] (B) Organohydrogenpolysiloxane (crosslinking agent) As the organohydrogenpolysiloxane, a methylhydrogenpolysiloxane (hydrogen 6.7 mmol / g) (HMS-501; Gelest) in which both ends were blocked with trimethylsiloxy groups was used.

[0069] (C) Aluminum oxide powder As the aluminum oxide powder, aluminum oxide (AA-1.5; Sumitomo Chemical Co., Ltd.) having a volume average particle size of 1.7 μm and a total content of impurities Fe, Ga, Ti, and Zn of 150 ppm by mass was used.

[0070] (D) Silica powder (D-1) Silica powder having a volume average particle size of 12 nm (AEROSIL (registered trademark) 200; Nippon Aerosil Co., Ltd.) was used. (D-2) Silica powder used was silica having a volume average particle size of 300 nm (SO-E1; Admatechs Co., Ltd.). (D-3) Silica powder used was silica having a volume average particle size of 1.5 μm (S150; Nippon Shokubai Co., Ltd.).

[0071] (E) Curing catalyst The curing catalyst used was a platinum-alkenylsiloxane complex Karstedt catalyst (479527; Sigma-Aldrich).

[0072] (F) Hardening inhibitor 2-Methyl-3-butyn-2-ol (M0180; Tokyo Chemical Industry Co., Ltd.) was used as a cure inhibitor.

[0073] (2) Preparation of UV-reflecting resin composition The UV-reflecting resin compositions were prepared by mixing equal amounts of the first and second materials. The first material contained (A) organopolysiloxane, (C) aluminum oxide powder, (D) silica powder, and component (E). The second material contained (A) organopolysiloxane, (B) organohydrogenpolysiloxane, (C) aluminum oxide powder, and (D) silica powder. The viscosities of the (C) aluminum oxide powder contained in the first and second materials were adjusted to prevent settling. Each UV-reflecting resin composition was prepared to have the composition shown in Tables 1 and 2. The ratio of the viscosity of the UV-reflecting resin composition at 23°C and a shear rate of 0.1 (1 / s) to the viscosity of the UV-reflecting resin composition at 23°C and a shear rate of 10 (1 / s) was determined according to the method described above.

[0074] (3) Evaluation of sedimentation The sedimentation property was evaluated by placing each resin composition in a sample bottle, leaving it to stand, and visually inspecting the state after one month and three months. The storage temperature was 23°C. The sedimentation property was evaluated according to the following criteria. ◯: Aluminum oxide powder did not settle. ×: Aluminum oxide powder was precipitated.

[0075] (4) Evaluation of formability To evaluate moldability, the prepared UV reflective resin composition was placed in a two-component cartridge, attached to an air gun, and injected at 0.5 MPa air pressure into a mold with a 30 mm x 30 mm x 1 mm cubic cavity heated to 120°C. The composition was cured for 30 minutes and then further cured in a 150°C incubator for 2 hours. Finally, the composition was removed from the mold to obtain a 1 mm thick plate-shaped cured product. Moldability was evaluated according to the following criteria. ◯: A cured product was obtained with no filling defects and no visible bubbles. ×: Filling was insufficient or visible bubbles were generated.

[0076] (5) Reflectance evaluation The reflectance was evaluated by irradiating the molded cured plate-shaped product having a thickness of 1 mm with ultraviolet light having a predetermined central wavelength of 280 nm in the thickness direction, and measuring the reflectance of ultraviolet light.

[0077] Tables 3 and 4 show the components of each ultraviolet reflective resin composition and the evaluation results.

[0078] [Table 3]

[0079] [Table 4]

[0080] (6) Evaluation results As shown in Table 3, Example UV-reflective resin compositions 1 to 17, which contained (C) aluminum oxide powder having a volume average particle size of 0.1 to 10 μm and (D) silica powder having a volume average particle size of 1.0 μm or less, in which the aluminum oxide powder content was 10 to 200 parts by mass relative to 100 parts by mass of the combined mass of (A) and (B), and the silica powder content was 0.5 to 10 parts by mass relative to 100 parts by mass of the combined mass of (A) and (B), with a ratio of 1.5 to 50, exhibited good moldability, good suppression of sedimentation of the aluminum oxide powder, and good reflectance. Note that, to achieve the same level of anti-settling effect as in the Examples using silica powder having an average particle size of 1.0 μm or more, the silica content in the UV-reflective resin composition would be too high, sacrificing the reflectance-improving effect of aluminum oxide, which is not practical.

[0081] As shown in Table 4, comparative ultraviolet reflective resin compositions 26, 31, and 35, in which the silica powder content was more than 10 parts by mass and the ratio was more than 50, had poor moldability and the reflectance could not be measured. Comparative ultraviolet reflective resin composition 33, in which the silica powder content was 10 parts by mass or less but the ratio was more than 50, had poor moldability and the reflectance could not be measured. This is thought to be because the ratio was too high and the resin composition lost its fluidity.

[0082] Furthermore, as shown in Table 4, comparative ultraviolet reflective resin compositions 19 to 25, 27 to 31, 34 and 36, which had a ratio of less than 1.5, were poor in the effect of suppressing the settling of aluminum oxide powder.

[0083] As shown in Tables 3 and 4, a comparison of UV-reflecting resin compositions 2 and 3 of the Examples with UV-reflecting resin compositions 37 and 38 of the Reference Examples shows that simply adding the specified silica did not bring the ratio within the range of 1.5 to 50. A comparison of UV-reflecting resin compositions 2 and 3 of the Examples with UV-reflecting resin compositions 22 to 26 of the Comparative Examples and UV-reflecting resin compositions 37 and 38 of the Reference Examples shows that adding a specified silica in the presence of a specified aluminum oxide results in good moldability and sedimentation properties. [Industrial Applicability]

[0084] The ultraviolet reflective resin composition according to the present invention and its cured product are useful as materials for optical components that reflect ultraviolet light and are mounted in ultraviolet irradiation devices, for example.

Claims

1. An addition-curable ultraviolet reflective resin composition, (A) an organopolysiloxane having at least two alkenyl groups in each molecule; (B) an organohydrogenpolysiloxane having at least two hydrogen atoms bonded to silicon atoms in each molecule; (C) aluminum oxide powder having a volume average particle size of 0.1 to 10 μm; (D) silica powder having a volume average particle size of 1.0 μm or less; (E) a curing catalyst; and the content of the aluminum oxide powder is within a range of 10 to 200 parts by mass relative to 100 parts by mass of the total mass of (A) and (B); the content of the silica powder is within a range of 0.5 to 10 parts by mass relative to 100 parts by mass of the total mass of (A) and (B); the ratio of the viscosity of the ultraviolet reflective resin composition at 23°C and a shear rate of 0.1 (1 / s) to the viscosity of the ultraviolet reflective resin composition at 23°C and a shear rate of 10 (1 / s) is within the range of 1.5 to 50; Ultraviolet reflective resin composition.

2. 2. The ultraviolet reflective resin composition according to claim 1, wherein the total content of Fe, Ga, Ti, and Zn in the ultraviolet reflective resin composition is 150 ppm by mass or less.

3. A cured product obtained by curing the ultraviolet reflective resin composition according to claim 1 or 2.

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