Light guide rod and method for manufacturing light guide rod

Abstract

To provide a light guide rod that has high light emission luminance, has flexibility, and has a small environment load, and a method for manufacturing the light guide rod.SOLUTION: A light guide rod 100 comprises a core layer 1 made primarily of acrylic resin, and a clad layer 2 with a lower refractive index than that of the core layer 1, and guides light incident from one end surface in a longitudinal direction and emits light from an outer peripheral surface or the other end face, where neither the core layer 1 nor the clad layer 2 contains fluorine. This configuration can provide high light emission luminance, flexibility, and a small environmental load.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a light guiding rod that can guide light incident from one end face in the longitudinal direction and emit the guided light from the outer peripheral surface or the other end face. [Background technology]

[0002] There are various types of signs and advertisements for stores and buildings, and neon lights have been used to display letters and figures even at night. However, because neon lights are made of glass tubes and are not flexible, they cannot be deformed into different shapes after being manufactured in a predetermined shape. Therefore, they must be individually manufactured to fit the desired shape, which causes inconveniences such as delays in delivery and increased manufacturing costs.

[0003] Therefore, light guide rods, which are made of flexible, light-transmitting resin processed into a rod shape, are being used as an alternative to neon lights. When light is incident on one end of a light guide rod, it undergoes repeated total reflection inside the rod, guiding the light in the longitudinal direction and emitting it from the opposite end. On the other hand, it is also possible to scatter some of the light that would otherwise be totally reflected, so that it can be emitted from the outer surface. In this way, end-emitting light guide rods that guide light in the longitudinal direction and emit light from the end surfaces, and peripheral-emitting light guide rods that emit light from the outer periphery, are flexible and can guide light through total reflection even when bent to a certain extent, so they can be deformed into various shapes and used.

[0004] In order for the light guide rod to efficiently totally reflect light and guide it in the longitudinal direction, the refractive index of the clad layer, which forms the total reflection surface, must be lower than that of the core layer, which guides the light.In addition, it must be made of a flexible material to achieve flexibility. In order to achieve both of these, fluorine-based resins are used in resin light guide rods.

[0005] The applicant of the present application has previously filed many patent applications relating to light guide rods that use a fluororesin for the cladding layer. For example, Patent Document 1 discloses a technique in which a copolymer of ethylene and tetrafluoroethylene, a copolymer of hexafluoropropylene, tetrafluoroethylene and ethylene, or polyvinylidene fluoride is used as the fluororesin for the cladding layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-166067 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in recent years, the environmental impact of PFAS (Perfluorooctaphenylalanine Sulfate, or PFAS) has become a concern. PFAS is a general term for numerous fluorinated organic compounds, most of which are difficult to decompose in nature, and it has been pointed out that they can accumulate in the environment over long periods of time if they run off into the soil.

[0008] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a light guide rod and a manufacturing method thereof that has high luminous brightness, is flexible, and has a low environmental impact. [Means for solving the problem]

[0009] The means adopted by the present inventors to solve the above problems will be described below. The light guide rod of the present invention comprises a core layer primarily made of acrylic resin and a clad layer having a lower refractive index than the core layer, and guides light incident from one end face in the longitudinal direction and emits light from the outer surface or the other end face. It is characterized in that neither the core layer nor the cladding layer contains fluorine.

[0010] Since neither the core layer nor the clad layer contains fluorine, the light guide rod does not contain PFAS, which can accumulate in the environment over long periods of time. The core layer is made of a fluorine-free acrylic resin, which provides high light transmittance and makes it easy to achieve a refractive index difference with the clad layer. In addition, the core layer has a smaller diameter than the clad layer, allowing it to be configured with sufficient flexibility.

[0011] In addition to the above means, the present invention also employs a means for solving the above-mentioned problems in which the clad layer is made of paint and the paint contains particulate matter having a lower refractive index than the core layer.

[0012] By forming the cladding layer as a coating film using paint, it is possible to select materials other than thermoplastic resins, including those that do not contain fluorine. In addition, by dispersing particles with a lower refractive index than the core layer in the paint, the refractive index of the entire coating film can be lowered.

[0013] As another means adopted by the present invention to solve the above-mentioned problems, the paint may be configured in the above-mentioned configuration so that silica particles are contained in the urethane (meth)acrylate binder. In this invention, "(meth)acrylate" means either acrylate or methacrylate. In addition, the urethane (meth)acrylate used in this invention also includes a mixture of urethane (meth)acrylate and a (meth)acrylate monomer as the main component.

[0014] Urethane (meth)acrylate is an oligomer containing acrylic groups and urethane bonds. The acrylic groups have the property of hardening, and the urethane bonds have the property of softening, making it a substance that can be made flexible and strong. Furthermore, various hardness, strength, and flexibility can be adjusted by combining polyols, isocyanates, and acrylates. Furthermore, the presence of an acrylic group allows rapid curing by ultraviolet light.

[0015] However, because urethane (meth)acrylate contains acrylic groups, its refractive index is close to that of the acrylic resin used in the core layer, and therefore, if urethane (meth)acrylate is used directly in the cladding layer, the critical angle at which total reflection occurs becomes large. Therefore, silica particles are dispersed as granular matter in urethane (meth)acrylate. Silica particles are spherical silica (silicon dioxide) particles with a lower refractive index than the acrylic resin in the core layer. Therefore, dispersing silica particles in urethane (meth)acrylate reduces the critical angle, increasing the amount of light that undergoes total reflection and improving light guide efficiency.

[0016] As another means adopted by the present invention to solve the above-mentioned problems, the cladding layer can be formed from a coating film having a thickness of 10 nm or more and less than 200 nm. Unlike extrusion molding, by using paint to create a cladding layer with a thickness of 10 nm to less than 200 nm, it is possible to relatively increase the diameter of the core layer for a given diameter of the entire light guide rod. A relatively larger diameter of the core layer increases the efficiency of light incidence from the light source and the light-emitting area for edge emission.

[0017] As another means adopted by the present invention to solve the above-mentioned problems, it is also possible to configure the coating material to contain 10% by mass or more of hollow silica particles. Hollow silica is a balloon-shaped silica particle having a gas layer inside a spherical silica layer, and is characterized by a lower refractive index than solid silica particles that do not contain a gas layer. By dispersing hollow silica particles in urethane (meth)acrylate, the refractive index of the cladding layer can be further reduced, and the critical angle can be further reduced.

[0018] On the other hand, the means adopted by the present invention to solve the above-mentioned problems is a manufacturing method of a light guiding rod that has a core layer made primarily of acrylic resin and a clad layer with a lower refractive index than the core layer, and that guides light incident from one end face in the longitudinal direction and emits light from the outer surface or the other end face. In this manufacturing method, a core member that forms the core layer is molded by extrusion molding, and then a fluorine-free paint is applied to the molded core member, and the paint applied around the core layer is cured to form the cladding layer.

[0019] By molding the core member by extrusion molding, it is possible to form a long body having a uniform cross-sectional shape. Then, by applying a fluorine-free paint to the core member formed by extrusion molding and curing it, a cladding layer consisting of a coating film of the paint can be formed around the core member. By applying the paint to the core member, it is possible to form the cladding layer using a material other than a fluorine-free thermoplastic resin. [Effects of the Invention]

[0020] As mentioned above, the light guide rod of the present invention has a structure in which neither the core layer, which is primarily made of acrylic resin, nor the clad layer, which has a lower refractive index than the core layer, contains fluorine. The above-described configuration has the effect of providing high luminance and flexibility, as well as reducing the environmental impact. [Brief explanation of the drawings]

[0021] [Figure 1] 1A and 1B are perspective and cross-sectional views showing a light guide rod of the present invention. [Figure 2] 1A to 1C are explanatory diagrams showing a method for manufacturing a light guiding rod according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] An embodiment of the present invention will be described below with reference to FIGS. It should be noted that each drawing is drawn in a schematic manner for the purpose of explanation, and some dimensions and shapes are shown exaggerated or simplified.

[0023] As shown in FIG. 1, the light guiding bar 100 of the present invention includes a core layer 1 made primarily of a fluorine-free acrylic resin, and a clad layer 2 made primarily of a fluorine-free urethane (meth)acrylate. The core layer 1 may have a circular cross-sectional shape as shown in FIG. 1, but may also have other shapes such as a rectangular, elliptical, semicircular, polygonal, or irregular shape.

[0024] The core layer 1 may be made of a thermoplastic resin containing an acrylic resin as a main component. As the acrylic resin, one or more types of hard acrylic resins such as polymethyl methacrylate (PMMA), polyethyl methacrylate, polyisobutyl methacrylate, or polyt-butyl methacrylate can be used. Also usable are one or more acrylic elastomers such as a block copolymer of methyl methacrylate-n-butyl acrylate-benzyl acrylate, a block copolymer of methyl methacrylate and butyl acrylate (MMA-BA block copolymer), a block copolymer of methyl acrylate and butyl acrylate, or an acrylic block copolymer composed of methyl methacrylate (methyl acrylate), an acrylic ester, and an aromatic acrylic ester. Furthermore, it is also possible to use a mixture of the above-mentioned hard acrylic resin and acrylic elastomer resin.

[0025] The yellowing of the emitted light color of the light guide bar 100 can also be suppressed by adding a bluing agent (blue pigment or purple pigment) to the core layer 1. The amount of bluing agent added is preferably 0.1 ppm to 10 ppm by weight relative to the resin material of the core layer 1. However, this additive should be one that does not contain fluorine.

[0026] Resins used as paints can be used as the material for the clad layer 2. Examples of paints that can be used include urethane paint, acrylic paint, epoxy paint, polyester paint, and silicone paint. Among these, urethane paint is preferred from the viewpoint of flexibility, and paint using urethane (meth)acrylate, which can be cured by ultraviolet light, is particularly preferred from the viewpoint of adhesion to the acrylic resin, which is the main material of the core layer 1 mentioned above.

[0027] The cladding layer 2 can also be made to suppress yellowing of the luminous color of the light guide bar 100 by adding a bluing agent. The amount of bluing agent to be added is the same as that of the core layer. Initiators and other additives can also be added. However, these additives should not contain fluorine.

[0028] In addition, granular materials with a low refractive index are contained in the coating material of the cladding layer 2. Hollow acrylic particles containing air or silica particles can be used as the granular materials with a low refractive index. Among these, silica particles, which are made of a material with a low refractive index, are preferred, and hollow silica particles containing an air layer are particularly preferred because of their low refractive index.

[0029] In the cladding layer 2, the proportion of urethane (meth)acrylate in the entire cladding layer 2 is preferably 20% by mass or more but less than 95% by mass, more preferably 30% by mass or more but less than 85% by mass, and even more preferably 40% by mass or more but less than 80% by mass. If the proportion of urethane (meth)acrylate is less than 20% by mass, the proportion of additives and other resins will be high, which may reduce flexibility and strength. On the other hand, if the proportion of urethane (meth)acrylate is 95% by mass or more, the proportion of low-refractive-index particulate matter will be low, making it impossible to lower the refractive index.

[0030] Furthermore, the hollow silica particles preferably account for 5% by mass or more, and more preferably 10% by mass or more, of the entire cladding layer 2. If the hollow silica particles account for less than 5% by mass, the refractive index of the cladding layer 2 cannot be reduced.

[0031] In the embodiment shown in FIG. 1, when PMMA is used for the core layer 1 and urethane (meth)acrylate containing hollow silica particles is used for the clad layer 2, the refractive index of the clad layer 2 is smaller than that of the core layer 1. Therefore, of the light incident on the core layer 1, light incident at various angles can be totally reflected by the clad layer 2. This allows more light to be guided.

[0032] If a light diffusing agent such as rubbery acrylic beads is contained in either or both of the core layer 1 and the cladding layer 2, the light incident on the light guide rod 100 is guided in the longitudinal direction, and the light diffused at the boundary surface of the cladding layer 2 is emitted from the peripheral surface. In this way, by using a light diffusing agent, a peripheral surface emitting type light guide rod can be made.

[0033] On the other hand, if a non-light-transmitting coating layer is provided around the cladding layer 2, the light incident on the light guiding rod 100 is guided in the longitudinal direction and then exits from the opposite end face. In this way, by providing a light-blocking coating layer on the outside of the cladding layer 2 without using a light diffusing agent, an end-emitting light guiding rod can be obtained.

[0034] The above-described light guiding rod 100 can be manufactured by the method shown in FIG. First, as shown in Fig. 2, a core material C that will become the core layer 1 is formed by extrusion molding. Depending on the shape of a mold M used for extrusion molding, the cross-sectional shape of the core material C can be made into various shapes. In the embodiment shown in FIG. 2, the core material C has a circular cross section as shown in FIG. 1, and PMMA is used as the resin.

[0035] Next, the core material C is immersed in the paint in the container T. The paint is made of urethane (meth)acrylate as a binder material and hollow silica particles dispersed therein. Then, the core material C immersed in the paint is pulled up vertically at a constant speed. By pulling up vertically, the paint adheres evenly to the periphery of the core material C. Furthermore, by keeping the pulling up speed constant, the paint also adheres evenly to the longitudinal direction of the core material C.

[0036] Finally, while the substrate is still pulled up, the coating material is cured by ultraviolet light emitted from an ultraviolet irradiation device U to form the clad layer 2. Thereafter, various coating layers may be formed on the outside of the clad layer 2 as required.

[0037] If the lifting speed is slow, much of the paint adhering to the core material C will flow off before it hardens under UV light, resulting in a thin coating. Conversely, if the lifting speed is fast, not much of the paint adhering to the core material C will flow off before it hardens, resulting in a thick coating. It is preferable to make the lifting speed as slow as possible to make the coating film thin.

[0038] In the embodiment shown in Figure 2, the extruded core material C is continuously introduced into the container T, but it is also possible to cut the extruded core material C to a predetermined length, and then fix and hang multiple cut core materials C·C... on a jig, and simultaneously immerse them in the paint in the container T and then lift them out. The paint may also be applied to the core material C using a spray gun, or other application methods such as roll coating, curtain coating, or flow coating may be selected. Furthermore, the cladding layer 2 may be made into a multi-layer structure by applying and curing paint again after forming the cladding layer 2. In this case, the refractive index and thickness of the cladding layer 2 may be the same or different. [Example]

[0039] "Brightness evaluation test" Next, the luminance of the samples of specific examples 1 to 5 of the light guiding rod of the present invention was compared with that of the samples of comparative examples 1 and 2, which are light guiding rods of the prior art. Each sample had a length of 300 m and a core layer diameter of 3.0 mm (also approximately 3 mm overall), and the luminance was measured at the output end opposite the input end. The measurement was performed using a spectroradiometer (Konica Minolta CS-2000) placed at the end of the light guide rod. The light source used was an LED light source with a luminance of 37.4 cd measured by the luminance meter. [Table 1]

[0040] "Example 1" Example 1 was configured to use a core layer having a diameter of 3.0 mm and a circular cross section, and to have a clad layer with a thickness of 60 nm provided around the core layer. The core layer was made of PMMA, and the clad layer was made of 70% by mass of urethane (meth)acrylate and 30% by mass of hollow silica particles. In addition, 5% by mass of an initiator was also added to the urethane (meth)acrylate. The refractive index of the core layer is 1.49, and the refractive index of the cladding layer is 1.41.

[0041] "Example 2" Example 2 has the same configuration as Example 1, but differs in that the thickness of the cladding layer is 50 nm.

[0042] "Example 3" Example 3 had the same configuration as Example 1, but differed in that the thickness of the cladding layer was 40 nm.

[0043] Example 4 In Example 4, a core layer having a diameter of 3.0 mm and a circular cross section was used, and a clad layer having a thickness of 70 nm was provided around the core layer. The core layer was made of PMMA, and the clad layer was made of 45% by mass of urethane (meth)acrylate and 55% by mass of hollow silica particles. In addition, 5% by mass of an initiator was also added to the urethane (meth)acrylate. The refractive index of the core layer is 1.49, and the refractive index of the cladding layer is 1.36.

[0044] "Example 5" Example 5 had the same configuration as Example 4, but differed in that the thickness of the cladding layer was 55 nm.

[0045] "Comparative Example 1" Comparative Example 1 was configured to use a core layer having a diameter of 3.0 mm and a circular cross section, and to have a clad layer having a thickness of 0.25 mm provided around the core layer by extrusion molding. The core layer is made of PMMA, and the clad layer is made of a fluorine-containing resin, a copolymer of ethylene and tetrafluoroethylene (ETFE). The refractive index of the core layer is 1.49, and the refractive index of the cladding layer is 1.40.

[0046] "Comparative Example 2" Comparative Example 2 was configured with only a core layer having a diameter of 3.0 mm and a circular cross section. The core layer is made of PMMA. The refractive index of the core layer is 1.49.

[0047] "Test Results" Table 2 shows the test results for Examples 1 to 5 and Comparative Examples 1 and 2. [Table 2] As shown in Table 2, Comparative Example 2, which had only a core layer, had the lowest brightness, and Comparative Example 1, which used ETFE for the clad layer, had the next lowest brightness. In contrast, Examples 1 to 5 according to the present invention all had higher luminance than Comparative Examples 1 and 2. In particular, Example 3, in which the thickness of the cladding layer was 40 nm, had the highest brightness. All of Examples 1 to 5 were flexibly bendable.

[0048] As described above, in the present invention, since neither the core layer nor the clad layer contains fluorine, the light guide rod has a low environmental impact, yet has brightness equal to or greater than that of light guide rods made of conventional fluorine-based resins, and is flexible enough to be bent flexibly. [Explanation of symbols]

[0049] 100 light guide rod 1 Core layer 2. Cladding layer C Core Material M mold T container U Ultraviolet irradiation device

Claims

1. A light guide rod that includes a core layer made primarily of an acrylic resin and a clad layer having a refractive index lower than that of the core layer, guides light incident from one end face in the longitudinal direction, and emits light from the outer peripheral surface or the other end face, A light guide rod, characterized in that neither the core layer nor the clad layer contains fluorine.

2. the clad layer is formed by a coating film of paint, 2. The light guide rod according to claim 1, wherein the paint contains particles having a refractive index lower than that of the core layer.

3. 3. The light guide rod according to claim 2, wherein the paint contains urethane (meth)acrylate as a binder material and silica particles as granular matter.

4. 3. The light guide rod according to claim 2, wherein the clad layer is made of a coating film having a thickness of 10 nm or more and less than 200 nm.

5. 4. The light guide rod according to claim 2, wherein the paint contains 10% by mass or more of hollow silica particles.

6. A method for manufacturing a light guide rod that includes a core layer mainly made of an acrylic resin and a clad layer having a refractive index lower than that of the core layer, guides light incident from one end face in the longitudinal direction, and emits light from the outer peripheral surface or the other end face, a core member forming the core layer is formed by extrusion molding; Next, a fluorine-free paint is applied to the molded core member, A method for manufacturing a light guide rod, characterized in that the clad layer is formed by hardening paint attached to the periphery of the core layer.

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