Cover material for LED light source

Abstract

To provide a methacryl resin molded article and a methacryl resin composition which are superior in both light diffusion and light transmission.SOLUTION: A methacryl resin molded article has a total light transmittance of 40% or more when made into a flat sheet with a thickness of 2 mm, and also has a relative brightness (5° / 0°) of 70% or more. A methacryl resin composition comprises 0.7 pts.mass or more of a silicone resin-derived diffusion agent relative to 100 pts.mass of a methacryl resin.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a methacrylic resin molded body and a methacrylic resin composition having excellent light diffusibility and light transmittance.

Background Art

[0002] Methacrylic resin (PMMA) is a thermoplastic resin excellent in optical properties, weather resistance, chemical resistance, hardness, etc., and is widely used as a molding material for vehicle members, building members, members for housing equipment, commercial members, etc.

[0003] Among the uses of methacrylic resins, in lighting fixture covers for members for housing equipment and acrylic plates for displays in commercial members, in recent years, in order to enhance the commercial value, it is required that the light brightness is uniform throughout and the image of the light source cannot be seen through. In order to eliminate the image of the light source, it is only necessary to improve the light diffusibility. That is, increasing the light diffusibility indicates the direction in which the image of the light source disappears, and the luminance distribution ratio ((luminance value at the darkest point) / (luminance value at the brightest point)), which is a measure of the light diffusibility, and the value of the light diffusion rate described later also increase. However, when the light diffusibility of the material is increased to the extent that the image of the light source is eliminated, there is a problem that the light transmittance rapidly decreases and the brightness of the light source is extremely impaired.

[0004] In response to such requirements, as a light diffusing material that has no image of the light source when used as an actual product and has a light transmittance equivalent to the conventional characteristics, it is composed of a light diffusing resin composition containing a specific light diffusing agent, and when it is a flat sheet with a thickness of 2 mm, a light diffusing resin molded body has been proposed that satisfies the condition that the total light transmittance is 60% or more and the luminance distribution ratio of the sheet is 0.8 or more (Patent Document 1). Here, the luminance distribution ratio corresponds to, for example, the ratio of the maximum value to the minimum value within the measurement range when measuring the luminance distribution pattern on the surface by installing a light diffusing material in front of a lighting source equipped with two fluorescent tubes. Patent Document 1 states that the closer the value of this luminance distribution ratio is to 1, the closer it becomes to a perfect diffuser, and the image and brightness non-uniformity of the light source disappear.

[0005] Patent Document 2 proposes an acrylic resin sheet with excellent light diffusion properties that contains a specific light diffusing agent and satisfies the conditions of having a total light transmittance of 50% or more and a light diffusion rate of 80% or more. Here, light diffusivity is a measure of the light diffusion performance of a milky white translucent plate (diffuser plate). As shown in Figure 2, it is determined by transmitting light through a test piece and using the formula described later, based on the DIN 5036 standard. Patent Document 2 states that the closer the value of this light diffusivity is to 100%, the closer it is to a perfect diffuser, and the non-uniformity of the image and brightness of the light source disappears. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-73296 [Patent Document 2] Japanese Patent Application Publication No. 11-172019 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, with the recent proliferation of highly directional LED light sources, conventional luminance distribution ratios and light diffusion rates are no longer effective indicators of light diffusion, failing to reflect the light source's transparency and thus lacking correlation with actual visual observation. Therefore, a more suitable indicator for light diffusion is needed.

[0008] The present invention has been made in view of the above-mentioned conventional circumstances, and aims to provide a methacrylic resin molded article and a methacrylic resin composition that can achieve both high light diffusion and light transmission even when using a highly directional LED light source. [Means for solving the problem]

[0009] As a result of repeated studies to solve the above problems, the inventors of the present invention have found that by using relative luminance (5° / 0°) as an indicator of light diffusion, rather than the conventional luminance distribution ratio or light diffusion rate, it is possible to evaluate light diffusion more accurately for any light source. This invention was achieved based on the above findings, and its gist is as follows.

[0010] [1] A methacrylic resin molded article characterized in that, when formed as a flat sheet with a thickness of 2 mm, the total light transmittance is 40% or more, and the relative luminance (5° / 0°) is 70% or more.

[0011] [2] The methacrylic resin molded article according to [1], wherein the relative brightness (5° / 0°) is 80% or more.

[0012] [3] The methacrylic resin molded article according to [1] or [2], wherein the total light transmittance is 50% or more.

[0013] [4] A methacrylic resin composition characterized by containing 0.7 parts by mass or more of a silicone resin-derived diffusion agent per 100 parts by mass of methacrylic resin.

[0014] [5] The methacrylic resin composition according to [4], wherein the content of the silicone resin-derived diffusion agent is 0.75 parts by mass or more and 4.0 parts by mass or less.

[0015] [6] The methacrylic resin composition according to [4] or [5], wherein the volume average particle size of the silicone resin-derived diffusion agent is 1.0 to 3.0 μm.

[0016] [7] The methacrylic resin composition according to any one of [4] to [6], wherein the refractive index of the diffusing agent derived from the silicone resin is 1.00 to 2.00.

[0017] A methacrylic resin molded article obtained by molding a methacrylic resin composition described in any of [8] [4] to [7].

Advantages of the Invention

[0018] According to the present invention, even when a highly directional LED light source is used, it is possible to provide a methacrylic resin molded body and a methacrylic resin composition that can achieve both high light diffusibility and light transmittance. Therefore, according to the present invention, it is possible to provide a lighting product with high commercial value in which the image of the light source is not visible through and the brightness of the light source is not impaired.

Brief Description of the Drawings

[0019] [Figure 1] FIG. 1(a) is a diagram for explaining the relative luminance (5° / 0°), which is an index of light diffusibility in the present invention, and FIG. 1(b) is a diagram showing an example of the emitted light luminance distribution. [Figure 2] It is a diagram for explaining the conventional light diffusion rate. [Figure 3] It is an explanatory diagram of an evaluation method for the presence or absence of light transmission through a light source. [Figure 4] It is a graph showing the relationship between the total light transmittance and the relative luminance (5° / 0°) in the examples. [Figure 5] It is a diagram showing a camera image in the evaluation of light transmission through the light source of the sample in the examples.

Modes for Carrying Out the Invention

[0020] Hereinafter, the embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments and can be variously modified and implemented within the scope of the gist.

[0021] [Methacrylic Resin Molded Body] The methacrylic resin molded body of the present invention is characterized in that when it is a flat sheet with a thickness of 2 mm, the total light transmittance (hereinafter, may be simply referred to as "total light transmittance") is 40% or more, and the relative luminance (5° / 0°) (hereinafter, may be simply referred to as "relative luminance (5° / 0°)") is 70% or more.

[0022] <Mechanism> The luminance distribution ratio in Patent Document 1 refers, for example, to the ratio of the maximum and minimum luminance values ​​within a measurement range when a light-diffusing material is placed in front of an illumination light source equipped with two fluorescent tubes, and the luminance distribution pattern on that surface is measured. Furthermore, the light diffusivity in Patent Document 2 is a measure of the light diffusion performance of a milky white translucent plate (diffuser plate), and as shown in Figure 2, it is determined by transmitting light through a test piece and using the following formula based on the DIN 5036 standard.

[0023]

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[0024] However, with conventional luminance distribution ratios and diffuse rates, the image of the light source may not disappear regardless of whether the value is large or small. The inventors have confirmed that luminance distribution ratios and light diffuse rates are unsuitable as indicators of light diffusion. This is thought to be because the luminance distribution ratio is calculated using only the maximum and minimum values ​​of luminance, and does not adequately reflect the unevenness of luminance. Furthermore, the light diffuse rate does not calculate the case of luminance directly below (θ=0°), and therefore cannot adequately reflect the degree to which the image of the light source is visible.

[0025] In this invention, instead of using conventional luminance distribution ratios or light diffusivity, as shown in Figure 1(a), the output light luminance is measured when light (incident light (parallel rays)) is transmitted through a test piece, and the relative luminance (5° / 0°) calculated by the following formula is used as an indicator of light diffusivity, that is, the degree to which the image of the light source is visible. Relative luminance (5° / 0°) = L(5°) / L(0°) × 100(%) L(5°): Luminance at an angle θ=5° with the normal to the test specimen. L(0°): Brightness at the normal to the test specimen (angle θ=0°).

[0026] Figure 1(a) shows an example of the output light luminance distribution. A to D in Figure 1 are as follows, and E shows the luminance directly below the light source. A large difference between the luminance near the source (θ=5°) and the luminance directly below (θ=0°) indicates greater light transmission. A: Perfectly diffuse (luminance distribution is hemispherical) It appears to have a uniform brightness no matter what direction you view it from. It has the highest luminance distribution ratio and diffuseness, and the least transparency. B: It has the second highest luminance distribution ratio and diffusion rate after A, and the second lowest transparency after A. C: While it has the lowest luminance distribution ratio and diffuseness, its transparency is the second lowest after B. D: The luminance distribution ratio and diffuseness are higher than C and lower than B, but it has the greatest transparency. In other words, regarding the luminance distribution ratio and diffusion rate, C <D<B<A The order is highest, but regarding the transparency of the light source image, A <B<C<D In that order, the order is largest. That is, regarding preventing the image of the light source from showing through, D <C<B<A This order is preferable. Therefore, it was found that values ​​expressed by luminance distribution ratio and diffusion rate may not be appropriate as indicators for judging the transparency of the light source image. This is because, as shown in D in Figure 1(b), the emitted light luminance distribution is not hemispherical, but may have an inflection point in the range of θ=0° to 5°. In such cases, the difference between the luminance directly below the emitted light (θ=5°) and the luminance directly below it (θ=0°) becomes large, and the transparency of the light source increases. Therefore, the relative luminance (5° / 0°) that takes the above-mentioned circumstances into account is an indicator of light diffusion that appropriately reflects and quantifies the transparency of the light source's image.

[0027] <Total light transmittance / relative luminance (5° / 0°)> The methacrylic resin molded article of the present invention exhibits excellent light transmittance if its total light transmittance is 40% or more. From the viewpoint of light transmittance, this total light transmittance is preferably 50% or more, and more preferably 60% or more. From the viewpoint of light transmittance, a higher total light transmittance is preferable, but from the viewpoint of ensuring the following relative brightness (5° / 0°), the upper limit of the total light transmittance is usually 95% or less.

[0028] The relative brightness (5° / 0°) of the methacrylic resin molded article of the present invention being 70% or higher indicates that the difference between the brightness directly below the emitted light (θ=5°) and the brightness directly below it (θ=0°) is small enough to sufficiently obscure the image of the light source, resulting in excellent light diffusion and prevention of the light source's image from showing through. From this viewpoint, a higher relative brightness (5° / 0°) is preferable, preferably 80% or higher, and particularly preferably 90% or higher.

[0029] In this invention, the total light transmittance and relative luminance (5° / 0°) are specifically measured by the method described in the Examples section below.

[0030] In this invention, a "flat sheet with a thickness of 2 mm" is used in the evaluation of total light transmittance and relative luminance (5° / 0°). However, the shape and dimensions of the methacrylic resin molded article of this invention are not limited to a flat sheet with a thickness of 2 mm. In terms of shape, it may be a sheet with a curved surface or a sheet with a bent portion. Furthermore, from the viewpoint of light diffusion, the thickness is preferably 0.1 mm or more, and more preferably 1 mm or more. Furthermore, from the viewpoint of light transmission, the thickness is preferably 10 mm or less, and more preferably 5 mm or less.

[0031] There are no particular limitations on the method for producing the methacrylic resin molded article of the present invention that satisfies such total light transmittance and relative luminance (5° / 0°), but preferably, the methacrylic resin molded article of the present invention is produced by molding the methacrylic resin composition of the present invention as described below.

[0032] [Methacrylic resin composition] The methacrylic resin composition of the present invention is characterized by containing 0.7 parts by mass or more of a silicone resin-derived diffusion agent per 100 parts by mass of methacrylic resin. If the content of the silicone resin-derived diffuser is below the above lower limit, it is not possible to obtain a methacrylic resin molded article with excellent light diffusion properties. From the viewpoint of light diffusion, the content of the silicone resin-derived diffuser in the methacrylic resin composition of the present invention is preferably 0.75 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of the methacrylic resin. On the other hand, if the content of the silicone resin-derived diffuser is too high, the light transmittance tends to decrease, so the content of the silicone resin-derived diffuser in the methacrylic resin composition of the present invention is preferably 4.0 parts by mass or less, and more preferably 3.0 parts by mass or less, per 100 parts by mass of the methacrylic resin.

[0033] The silicone resin constituting the diffusion agent is a polymer in which siloxane bonds, in which silicon atoms and oxygen atoms bonded to organic groups are alternately repeated, form a three-dimensional network structure. Preferred organic groups bonded to the silicon atoms include alkyl groups such as methyl, ethyl, propyl, and butyl groups, as well as carboxyl, carbonyl, ester, and ether groups, which have affinity for the methacrylic resin or its monomer used in this invention. A typical example of an organic group is the methyl group.

[0034] The diffusing agent derived from silicone resin is preferably in the form of fine particles rather than amorphous particles in order to satisfy the aforementioned total light transmittance and relative luminance (5° / 0°), and in particular, its shape is preferably ellipsoidal or spherical. The volume-average particle size of the silicone resin-derived diffuser is preferably in the range of 1.0 to 3.0 μm, and more preferably in the range of 1.5 to 2.5 μm. If the volume-average particle size of the silicone resin-derived diffuser is too small, the light transmittance will be poor, and it may not be possible to achieve a total light transmittance of 40% or more. If the volume-average particle size of the silicone resin-derived diffuser is too large, the light diffusion will be poor, and it may not be possible to achieve a relative brightness (5° / 0°) of 70% or more. Here, the volume-average particle size of the silicone resin-derived diffuser is calculated by measuring the particle size of diffuser particles contained in a certain volume measured by laser diffraction scattering, and then calculating the average value. However, for commercially available products, the catalog value can be used.

[0035] Furthermore, the refractive index of the silicone resin-derived diffuser is preferably 1.00 to 2.00, and particularly preferably 1.2 to 1.6. If the refractive index of the silicone resin-derived diffuser is within the above range, a methacrylic resin molded article with excellent light transmittance and light diffusion can be obtained. Here, the refractive index of the silicone resin-derived diffuser is the measurement value for the sodium d line (589 nm).

[0036] <Methacrylic resin> The methacrylic resin that forms the main component of the methacrylic resin composition of the present invention is a polymer containing repeating units derived from methyl methacrylate (MMA) (hereinafter referred to as "MMA units").

[0037] The lower limit of the MMA unit content in the methyl methacrylate polymer is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98.5% by mass or more, based on 100% by mass of the total mass of the methyl methacrylate polymer, from the viewpoint of good transparency, solvent resistance, etc. of the methacrylic resin composition. The upper limit of the MMA unit content is not particularly limited and may be 100% by mass.

[0038] The methyl methacrylate polymer may contain repeating units derived from other monomers copolymerizable with MMA (hereinafter referred to as "other monomers"), to the extent that it does not impair the transparency, solvent resistance, etc., of the methacrylic resin composition of the present invention.

[0039] Other monomers are not particularly limited as long as they are copolymerizable with MMA, and include alkyl methacrylates other than MMA such as ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, and 2-ethylhexyl methacrylate; alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; unsaturated acids such as methacrylic acid and acrylic acid; aromatic vinyl compounds such as styrene and α-methylstyrene; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; maleic anhydride; and maleimide compounds such as phenylmaleimide and cyclohexylmaleimide. These may be used individually or in combination of two or more.

[0040] <Other ingredients> The methacrylic resin composition of the present invention may contain, in addition to the methacrylic resin and a diffusing agent derived from a silicone resin, transparent resins other than methacrylic resins and various other additives, to the extent that the objectives of the present invention are not impaired. The transparent resin is not particularly limited as long as it has a high light transmittance in at least the visible light region (for example, a visible light transmittance of 60% or more), and known transparent resins can be used. Examples of transparent resins other than methacrylic resins include one or more types of polycarbonate resin, polystyrene resin, and polyvinyl chloride resin. These may be used individually or in combination of two or more types.

[0041] Other additives include stabilizers such as UV absorbers and antioxidants, antistatic agents to prevent dust and other particles from adhering, release agents to facilitate separation from the mold, lubricants to improve fluidity, and inorganic pigments and fluorescent whitening agents other than those derived from silicone resin.

[0042] <Methacrylic resin composition manufacturing method and molding method> The methacrylic resin composition of the present invention can be used to produce a target methacrylic resin molded article, i.e., a methacrylic resin molded article with a total light transmittance of 40% or more and a relative brightness (5° / 0°) of 70% or more, by mixing a methacrylic resin, a silicone resin-derived diffusion agent, and other components used as needed in a Henschel mixer or the like, and then molding it into a predetermined shape by injection molding or extrusion molding.

[0043] As mentioned above, the wall thickness of the methacrylic resin molded article of the present invention is preferably 2 mm, but is not limited to 2 mm.

[0044] [Application] The methacrylic resin molded articles of the present invention exhibit excellent light transmittance and light diffusion properties, preventing the image of the light source from showing through while achieving a high illumination effect. They are extremely useful industrially as outdoor signs, cover materials for outdoor lighting, materials for various displays, and vehicle parts. [Examples]

[0045] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

[0046] [raw materials] The raw materials used in the production of the methacrylic resin molded articles in the following examples are as follows.

[0047] <Methacrylic resin> Mitsubishi Chemical Corporation's "Acrypet (registered trademark) VH001"

[0048] <Diffusing agent> Solid silicone resin microparticles (volume average particle size: 2 μm, refractive index: 1.4)

[0049] [Measurement and evaluation methods for physical properties and characteristics] <Measurement of total light transmittance> Light transmittance (D65) was measured using a haze meter HM-150 manufactured by Murakami Color Technology Laboratory and evaluated according to the following criteria. A: Total light transmittance 40% or more B: Total light transmittance less than 40%

[0050] <Measurement of brightness (5° / 0°)> The output light luminance distribution was measured using a GONIO PHOTO METER GP-200, manufactured by Murakami Color Technology Laboratory. Light was shone perpendicularly (0°) onto the resin molded body, and the luminance was measured as the light receiving unit moved from 0° to 90°. The relative luminance at 5° was calculated, with the luminance at 0° (directly below) set to 100%, and evaluated according to the following criteria. A: Relative luminance (5° / 0°) 70% or higher B: Relative luminance (5° / 0°) less than 70%

[0051] <Evaluation of whether or not light source is transparent> As shown in Figure 3, two LED light sources 1A and 1B were installed with a distance of 18 mm between them, and the sample 2, a resin molded body with a thickness of 2 mm, was fixed at a distance of 25 mm from the LEDs. Furthermore, the CCD camera 3 was fixed so that the distance to the resin molded sample 2 was 840 mm. The light emitted from LED light sources 1A and 1B was observed through the resin molded sample 2 using a CCD camera 3, and evaluated according to the following criteria. ○: The light source is not visible through the image. ×: The light source is visible through the image. *: The methacrylic resin molded sample itself is dark, making it impossible to evaluate the transparency of the light source.

[0052] <Distinguishing between light and dark> When light was transmitted from an LED light source through a resin molded sample, samples where the outline of the resin molded material was visible were classified as "bright," and those where it was not visible were classified as "dark."

[0053] [Examples 1-4] A methacrylic resin composition was obtained by melt-kneading 100 parts by mass of methacrylic resin with the amount of the diffusion agent shown in Table 1 shown in Table 1, drying the resulting mixture with hot air at 80°C for approximately 4 hours, and then molding it into a 2 mm thick flat sheet using an injection molding machine (model name "FAS-T100D", manufactured by FANUC Corporation) to obtain a sample of a methacrylic resin molded body. The obtained methacrylic resin molded samples were subjected to the aforementioned measurements and evaluations, and the results are shown in Table 1. Furthermore, Figure 4 shows a graph of the relationship between total light transmittance and relative luminance (5° / 0°) in each example and comparative example, and Figure 5 shows camera images used to evaluate the transparency of the light source.

[0054] [Table 1]

[0055] As shown in Table 1, the methacrylic resin molded articles of Examples 1 to 4, which consist of a methacrylic resin composition containing a silicone resin-derived diffusing agent in a predetermined proportion and have a total light transmittance of 40% or more and a relative brightness (5° / 0°) of 70% or more, exhibit excellent light diffusion and light transmission properties, and can prevent the image of the light source from showing through without impairing the brightness of the light source. [Explanation of Symbols]

[0056] 1 LED 2. Sample of methacrylic resin molded product 3 CCD cameras

Claims

1. A methacrylic resin molded article is obtained by molding a methacrylic resin composition containing 0.75 parts by mass to 4.0 parts by mass of a silicone resin-derived diffusing agent having a volume-average particle size of 1.5 to 2.5 μm and a refractive index of 1.2 to 1.6 per 100 parts by mass of methacrylic resin, A cover material for an LED light source, made of a methacrylic resin molded body, having a total light transmittance of 40% or more and a relative luminance (5° / 0°) of 70% or more when formed as a flat sheet with a thickness of 2 mm.

2. The LED light source cover material according to claim 1, wherein the relative brightness (5° / 0°) is 80% or more.

3. The LED light source cover material according to claim 1 or 2, wherein the total light transmittance is 50% or more.

Images