Method for producing retroreflective three-dimensional molded body

Abstract

To provide a method for producing a retroreflective three-dimensional molded body in which retroreflectivity is less likely to decrease at curved portions, a support easily conforms to the three-dimensional shape, and the three-dimensional shape is easily maintained.SOLUTION: The method includes the following steps: preparing a retroreflective material comprising an adhesive layer 2 made of an acrylic-based adhesive, transparent microbeads 4 embedded in the adhesive layer 2, and a reflective layer 3 provided between the adhesive layer 2 and the transparent microbeads 4; preparing a support 1 comprising a stretchable knitted fabric woven or knitted from core-sheath type multifilament yarns in which the core component is polyethylene terephthalate and the sheath component is a low-melting-point polyester copolymer; forming a laminate by bringing the adhesive layer 2 of the retroreflective material into contact with the support 1 and laminating the retroreflective material and the support 1; heating the laminate to soften or melt the sheath component, thereby fusing the core-sheath type multifilament yarns together and molding the laminate into a three-dimensional shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a three-dimensional retroreflective molded article, and more particularly to a method for molding a retroreflective material into a three-dimensional object without impairing the retroreflective function. [Background technology]

[0002] Retroreflective materials have been widely used for indicating traffic signs, etc. Furthermore, from the perspective of ensuring the safety of people working at night, it is common for police, fire departments, civil engineering and construction workers, etc. to wear retroreflective materials in the form of sashes or armbands. All of these retroreflective materials are supplied in flat shapes.

[0003] A planar retroreflective material comprises an adhesive resin layer made of a synthetic resin such as polyethylene terephthalate, transparent microspheres embedded in the adhesive resin layer, and a reflective layer disposed between the transparent microspheres and the adhesive resin layer. The support for this retroreflective material is made of a polyester-cotton taffeta fabric laminated and bonded to the adhesive resin layer (see Patent Document 1, Example 1). Therefore, when attempting to mold this into a three-dimensional shape, the adhesive resin layer is destroyed, resulting in reduced retroreflectivity, particularly in curved sections. Furthermore, because the support is made of taffeta fabric, it is difficult to conform to a three-dimensional shape, making it difficult to maintain the three-dimensional shape, and the support is prone to tearing and wrinkling.

[0004] [Patent Document 1] Patent No. 5612790 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a method for producing a three-dimensionally molded retroreflective body in which, when three-dimensionally molded, retroreflectivity is less likely to decrease at curved sections, and the support body easily conforms to the three-dimensional shape and easily maintains the three-dimensional shape. [Means for solving the problem]

[0006] The present invention solves the above-mentioned problems by employing specific adhesive layers and supports. Specifically, the present invention relates to a method for producing a three-dimensional retroreflective body, comprising the steps of: preparing a retroreflective material having an adhesive layer made of an acrylic pressure-sensitive adhesive, transparent microspheres embedded in the adhesive layer, and a reflective layer provided between the adhesive layer and the transparent microspheres; preparing a support body made of an extensible knitted fabric knitted with sheath-core multifilament yarns having a core component made of a high-melting point polymer and a sheath component made of a low-melting point polymer, the core component being not fused to the sheath-core multifilament yarns; abutting the adhesive layer of the retroreflective material against the support body to laminate the retroreflective material and the support body to obtain a laminate; and applying heat to the laminate body to soften or melt the sheath component to fuse the core-sheath multifilament yarns to each other and molding the laminate body into a three-dimensional shape.

[0007] The fixing layer 2 used in the present invention is made of an acrylic adhesive. Because acrylic adhesives have viscoelasticity, they conform well to the shape of the three-dimensional object even when deformed. Conventional acrylic adhesives can be used, with those primarily composed of acrylic ester copolymers being particularly preferred. Conventional acrylic ester copolymers can also be used. For example, copolymers of n-butyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate can be used. To adjust the viscoelasticity of acrylic adhesives primarily composed of acrylic ester copolymers, polyisocyanate compounds may be added and cured as appropriate. It is preferable to slightly cure or semi-cure the acrylic ester copolymer by adjusting the degree of curing, i.e., the amount of polyisocyanate compounds such as diisocyanate compounds.

[0008] The fixing layer 2 may contain additives such as dyes, pigments, phosphorescent pigments, inorganic fillers, etc. depending on the application and required functions of the resulting retroreflective three-dimensional molded article. The thickness of the fixing layer 2 is, for example, about 15 to 300 μm, preferably about 20 to 200 μm, as long as the transparent microspheres 4 can be embedded and held in place.

[0009] The transparent microspheres 4 are spread over the entire surface of the adhesive layer 2 without overlapping. The refractive index of the transparent microspheres 4 is approximately 1.6 to 2.5. By using transparent microspheres 4 with such a refractive index, it is possible to focus on the reflective layer and provide excellent retroreflective performance. From the viewpoint of providing even better retroreflective performance, the refractive index of the transparent microspheres 4 is preferably 1.8 to 2.2, more preferably 1.9 to 2.1. The average particle size of the transparent microspheres 4 is preferably 30 to 200 μm, and preferably a small average particle size of approximately 45 to 65 μm. Transparent microspheres 4 with a small average particle size exhibit better retroreflective performance at curved portions of the resulting three-dimensional retroreflective molded article. The average particle size of the transparent microspheres 4 is determined by measuring the maximum diameter of 30 transparent microspheres 4 using a microscope at a magnification of 500x and calculating the average value.

[0010] The material of the transparent microspheres 4 is not particularly limited as long as it has the refractive index described above, and may be made of glass, resin, or the like. However, glass transparent microspheres 4 are excellent in transparency, chemical resistance, washing resistance, weather resistance, etc., and are therefore preferably used in the present invention. The number of transparent microspheres 4 embedded per unit area may be appropriately determined depending on the desired retroreflective performance. For example, 2 The number of transparent microspheres 4 may be about 50 to 500, preferably about 100 to 250.

[0011] The reflective layer 3 is disposed between the transparent microspheres 4 and the adhesive layer 2 and serves to retroreflect light incident from the transparent microspheres 4. While the material of the reflective layer 3 is not particularly limited, a metal film is preferred. Specific examples of metals that can be used to form the metal film include aluminum, zinc oxide, titanium, zinc, silica, tin, nickel, and silver. Among these metals, aluminum is preferred for its superior retroreflective performance. While the thickness of the reflective layer 3 is not particularly limited, it is preferably approximately 100 to 2000 Å, preferably approximately 600 to 1500 Å. A transparent resin layer (not shown) may be disposed between the transparent microspheres 4 and the reflective layer 3. The provision of the transparent resin layer makes it possible to adjust the reflective brightness and change the color tone of the emitted light. Furthermore, when the reflective layer 3 is a metal film, the transparent resin layer further protects the reflective layer 3 from corrosion. As described above, a retroreflective material comprising the transparent microspheres 4, the reflective layer 3, and the adhesive layer 2 is obtained. A synthetic resin film may be laminated on the surface of the transparent microspheres 4 as a release substrate.

[0012] The support 1 laminated to the retroreflective material is made of an extensible knitted fabric. The extensible knitted fabric is preferably a weft knitted fabric, and particularly preferably a circular knitted fabric. A weft knitted fabric is made by connecting loops, which are stitches, in the weft direction, and is easily stretchable in both the weft and warp directions due to deformation of each loop, making it preferable for use in the present invention. An extensible knitted fabric can be obtained by knitting a core-sheath multifilament yarn on a knitting machine such as a weft knitting machine, such as a circular knitting machine.

[0013] The sheath-core multifilament yarn constituting the stretchable knitted fabric is formed by bundling multiple sheath-core filaments whose core component is made of a high-melting-point polymer and whose sheath component is made of a low-melting-point polymer. The difference in melting point between the high-melting-point polymer and the low-melting-point polymer is preferably 50°C or more. If the difference in melting point is less than 50°C, when the low-melting-point polymer is softened or melted, the high-melting-point polymer may also soften, making it difficult to maintain the original fiber shape. Specific examples of combinations of high-melting-point polymer and low-melting-point polymer include polyethylene terephthalate / low-melting-point polyester copolymer, polyethylene terephthalate / polypropylene, polyethylene terephthalate / polyethylene, nylon 6 / low-melting-point polyester copolymer, and polypropylene / polyethylene, with polyethylene terephthalate / low-melting-point polyester copolymer being particularly preferred. Any low-melting-point polyester copolymer can be used as long as it has a melting point lower than that of polyethylene terephthalate. Generally, it is preferable to use a copolymer containing ethylene glycol, terephthalic acid, 1,4-butanediol, and diethylene glycol, and optionally caprolactone, as the low-melting point polyester copolymer. In the sheath-core filament, the weight ratio of the core component to the sheath component is approximately 0.3 to 3:1 (weight ratio). If the weight ratio of the core component is too low, the shape retention of the resulting three-dimensional retroreflective molded body tends to decrease. If the weight ratio of the core component is too high, the degree of fusion between the sheath-core multifilament yarns decreases, and the shape retention of the resulting three-dimensional retroreflective molded body tends to decrease. The core component and sheath component are preferably arranged concentrically. If they are arranged eccentrically, they are more likely to shrink when heated, which tends to cause the resulting three-dimensional retroreflective molded body to shrink. In general, a core-sheath multifilament yarn has a filament fineness of about 3 to 15 decitex, and is formed by bundling about 20 to 70 of these filaments together, with a total fineness of about 100 to 500 decitex.

[0014] The adhesive layer 2 of the retroreflective material is laminated against the support 1, and a laminate is obtained in which the support 1, adhesive layer 2, reflective layer 3, and transparent microspheres 4 are laminated in this order from the back side. In the present invention, an acrylic adhesive is used for the adhesive layer 2, so the retroreflective material and support 1 can be bonded together simply by applying pressure.

[0015] This laminate is heated to form it into a predetermined three-dimensional shape. Specifically, the laminate is deformed into the predetermined three-dimensional shape and then heated. Alternatively, the laminate may be deformed into the predetermined three-dimensional shape after being heated. Furthermore, pressure may be applied in addition to heat. The heat applied to the laminate is a temperature at which the sheath components of the sheath-core multifilament yarns that make up the stretchable knitted fabric, which is the support 1, soften or melt. Specifically, when heated to a temperature of 170°C to 210°C, the sheath components soften or melt. As the sheath components soften or melt, they fuse together, causing the sheath-core multifilament yarns to fuse together, and then the laminate is cooled to obtain a three-dimensional retroreflective molded body that retains the predetermined three-dimensional shape.

[0016] The retroreflective three-dimensional molded articles obtained by the method of the present invention can be used for a variety of purposes, particularly as equipment for nighttime performances such as plays, concerts, and sports events. They can also be used as outdoor exteriors or three-dimensional structures (objects). They can also be used as indoor interior materials, decorations, lighting covers, etc. [Effects of the Invention]

[0017] The method for producing a three-dimensional retroreflective molded body according to the present invention uses a viscoelastic acrylic adhesive as the adhesive layer for the retroreflective material and an extensible knitted fabric as the support, so that both the retroreflective material and the support conform well to the three-dimensional shape during three-dimensional molding. This results in less deterioration of retroreflectivity and less wrinkling at curved portions of the three-dimensional shape. Furthermore, because the extensible knitted fabric is made of sheath-core multifilament yarns, which are fused together, the resulting three-dimensional retroreflective molded body has good shape retention.

[0018] Example 1 [Preparing retroreflective materials] A release substrate consisting of a 75 μm-thick polyester film laminated with a 40 μm-thick polyethylene film was heated at 200°C for 2 minutes to melt the polyethylene film. Transparent microspheres with an average particle size of 55 μm and a refractive index of 1.93 were then spread over the molten polyethylene film without overlapping, and the film was allowed to cool to solidify. Aluminum was then deposited onto the transparent microspheres by vacuum deposition to form a 700 Å-thick reflective layer. A 40 μm thick adhesive composition was applied to the reflective layer, consisting of an acrylic adhesive ("AS-5510" manufactured by Lion Specialty Chemicals Co., Ltd.) primarily composed of an acrylic ester copolymer and a curing agent ("Curing Agent L-45K" manufactured by Soken Chemical & Engineering Co., Ltd.) primarily composed of a diisocyanate compound. The acrylic adhesive was then semi-cured to form an adhesive layer, yielding a retroreflective material.

[0019] [Preparation of support] The core component was polyethylene terephthalate, a copolymer of ethylene glycol and terephthalic acid (melting point 256°C, intrinsic viscosity [η] 0.75). The sheath component was a low-melting-point polyester copolymer containing terephthalic acid, ε-caprolactone, ethylene glycol, 1,4-butanediol, and diethylene glycol (melting point 160°C, intrinsic viscosity [η] 0.65). The copolymer molar ratios were 86.8 mol% terephthalic acid, 13.2 mol% ε-caprolactone, 50.0 mol% ethylene glycol, 49.2 mol% 1,4-butanediol, and 0.8 mol% diethylene glycol. The intrinsic viscosity [η] was measured using an equal weight mixture of phenol and tetrachloroethane as the solvent at a concentration of 0.5 g / dL and a liquid temperature of 20°C.

[0020] The above-mentioned polyethylene terephthalate and low-melting point polyester copolymer were fed into a composite melt spinning apparatus equipped with a core-sheath composite spinneret with a hole diameter of 0.6 mm and 48 holes, and composite melt spinning was carried out at a nozzle temperature of 280°C with a polyethylene terephthalate:low-melting point polyester copolymer weight ratio of 2.7:1 to obtain concentric core-sheath filaments. The resulting yarn, in which 48 core-sheath filaments were bundled, was subjected to cooling, drawing, and relaxation treatments in the usual manner to obtain a core-sheath multifilament yarn of 280 dtex / 48 filaments. This core-sheath multifilament yarn was threaded on a 22-gauge circular knitting machine with a 33-inch pot diameter, and spun to a weight of 198 g / m. 2 A stretchable circular knitted fabric of 100g was obtained.

[0021] [Preparation of laminate and production of retroreflective three-dimensional molded body] A stretchable circular knit fabric was laminated onto the adhesive layer of the retroreflective material, and pressure was applied to bond the retroreflective material and the stretchable circular knit fabric. The release substrate was then removed to obtain a laminate. This laminate was placed over the outside of a stainless steel bowl with a top diameter of 120 mm, a bottom diameter of 80 mm, and a height of 45 mm. The laminate was secured to the top of the bowl with metal clips, adjusting the size to avoid wrinkles. The product was then placed in an oven heated to 180°C and heat-treated at 180°C for 15 minutes. After heat treatment, the product was cooled to room temperature, and the bowl was removed to obtain a three-dimensional retroreflective molded product. The resulting three-dimensional retroreflective molded product was wrinkle-free and had good retroreflectivity on its curved surface.

[0022] Example 2 A retroreflective three-dimensional molded object was obtained in the same manner as in Example 1, except that zinc oxide was vapor-deposited onto transparent microspheres by vacuum deposition to form a reflective layer 1500 Å thick. The obtained three-dimensional retroreflective molded object was wrinkle-free and had good retroreflectivity on its curved surface.

[0023] Example 3 A laminate was obtained using the same method as in Example 2, except that a pressure-sensitive adhesive composition containing carbon black was used. A U-shaped piece of wood measuring 100 mm in length, 95 mm in width, and 20 mm in thickness was covered with aluminum foil, and the laminate was then placed on top of it. The periphery and top surface of the U-shaped piece of wood were then heated with a heat gun to the extent that the sheath component of the core-sheath multifilament yarn constituting the stretchable circular knitted fabric melted. The piece was then cooled at room temperature, yielding a U-shaped three-dimensional retroreflective molded object. The resulting three-dimensional retroreflective molded object had good retroreflectivity on the curved surface, but contained some wrinkles.

[0024] Comparative Example 1 A 15 μm thick polyurethane resin was applied onto the reflective layer to form an adhesive layer made of a cured polyurethane resin, and a retroreflective three-dimensional molded body was obtained in the same manner as in Example 1. The obtained retroreflective three-dimensional molded body was wrinkled and was not of any practical use.

[0025] Comparative Example 2 A three-dimensional retroreflective molded body was obtained in the same manner as in Example 2, except that a 15 μm thick polyurethane resin was applied onto the reflective layer to form an adhesive layer made of a cured polyurethane resin. The obtained three-dimensional retroreflective molded body was wrinkled and was not of any practical use.

[0026] Comparative Example 3 A resin composition containing carbon black added to a polyurethane resin was applied to a thickness of 15 μm onto the reflective layer to form an adhesive layer made of a cured polyurethane resin. Except for this, a retroreflective three-dimensional molded body was obtained in the same manner as in Example 3. The obtained retroreflective three-dimensional molded body was wrinkled and was not of any practical use. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic cross-sectional view of an example of a laminate used in the present invention. [Explanation of symbols]

[0028] 1 Support 2. Adhesion layer 3 Reflection layer 4 transparent microspheres

Claims

1. a step of preparing a retroreflective material including an adhesive layer made of an acrylic adhesive, transparent microspheres embedded in the adhesive layer, and a reflective layer provided between the adhesive layer and the transparent microspheres; a step of preparing a support made of an extensible knitted fabric which is knitted with a sheath-core multifilament yarn having a core component made of a high-melting point polymer and a sheath component made of a low-melting point polymer, and in which the sheath-core multifilament yarns are not fused to each other; a step of contacting the adhesive layer of the retroreflective material with the support and laminating the retroreflective material and the support to obtain a laminate; A method for producing a retroreflective three-dimensional molded body, characterized in that heat is applied to the laminate to soften or melt the sheath component, thereby fusing the core-sheath multifilament yarns together and molding the laminate into a three-dimensional shape.

2. 2. The method for producing a three-dimensional retroreflective molded article according to claim 1, wherein the acrylic adhesive contains an acrylic ester copolymer as a main component.

3. 3. The method for producing a retroreflective three-dimensional molded article according to claim 2, wherein the acrylic ester copolymer is cured with a polyisocyanate compound.

4. 2. The method for producing a three-dimensional retroreflective molded article according to claim 1, wherein the stretchable knitted fabric is a weft knitted fabric.

5. 5. The method for producing a three-dimensional retroreflective molded article according to claim 4, wherein the weft knitted fabric is a circular knitted fabric.

6. A laminate comprising a retroreflective material having an adhesive layer made of an acrylic adhesive, transparent microspheres embedded in the adhesive layer, and a reflective layer provided between the adhesive layer and the transparent microspheres, and a support bonded to the adhesive layer, The support is a laminate used in the manufacturing method of a retroreflective three-dimensional molded body described in claim 1, which is an extensible knitted fabric knitted with a core-sheath multifilament yarn whose core component is made of a high-melting point polymer and whose sheath component is made of a low-melting point polymer, and in which the core-sheath multifilament yarns are not fused to each other.

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