Light shielding layer formation method
The method employs a transfer device and film to form a light-shielding layer on light-transmissive resin molded articles with fine concavo-convex structures, overcoming previous challenges by creating a bonded layer that follows the intricate shape, achieving a hologram-like effect and enhancing the article's appearance and durability.
Patent Information
- Application Number
- JP2023200744
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-11-28
- Publication Date
- 2025-06-09
AI Technical Summary
Existing methods struggle to effectively form a light-shielding layer on molded articles made of light-transmissive resin with fine concavo-convex structures, as conventional techniques like silk printing clog the fine structures and transfer films fail to follow the intricate shapes.
A method using a transfer device and a transfer film with an ink layer laminated on a base material, where the transfer film is stretched over a kiln, subjected to reduced pressure, and then bonded to the molded article using saturated steam and pressure, forming a thermocompression-bonded light-shielding layer that follows the concavo-convex structure.
This method allows for the effective formation of a light-shielding layer on molded articles with fine concavo-convex structures, achieving a hologram-like color effect while ensuring the structural integrity and aesthetic appeal of the molded article.
Smart Images
Figure 2025086636000001_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for forming a light shielding layer.
Background Art
[0002] In some cases, a layer for shielding light is formed on one of the front and back surfaces of a molded body made of a resin having light transmissivity. For example, in a flat electronic device such as a smartphone, assuming that the surface on which the display is disposed on one surface of the flat housing is the front surface and the other surface is the back surface, a back cover is disposed on the back surface. In a smartphone, while it is difficult to differentiate from other products because the display is arranged in the entire area on the front surface, the back surface can be differentiated from other products by devising the design and material of the back cover.
[0003] And in some cases, a resin molded product having light transmissivity (hereinafter, a light transmissive resin molded product) is used for the back cover. As a result, the back surface of the smartphone has a high-class feeling with a gloss like glass. And, unlike glass, the resin material of the light transmissive resin molded product is less likely to crack due to impact. The electronic device can be made lighter. It can also be molded into a complex shape.
[0004] By the way, when a back cover made of a molded body of a light transmissive resin is used on one surface of an electronic device, in order to prevent the electronic circuit inside the housing or the base of the housing without surface treatment such as decoration or gloss from being seen through from the outside, a light shielding layer is often provided on the inner surface (hereinafter, the back surface) of the back cover. This light shielding layer is formed by applying ink by printing or by using a transfer film described in Non-Patent Document 1 below. Note that Non-Patent Document 2 below describes "vacuum transfer", which is a method of transferring a transfer film.
Prior Art Documents
Non-Patent Documents
[0005]
Non-Patent Document 1
Non-Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[0006] In recent years, products adopting designs such as "hologram finish" and "rainbow color" have attracted attention. In these products, a film having a spectroscopic function (hereinafter referred to as a hologram finish film) is adhered to the surface of the housing. Roughly speaking, it is formed by forming a reflective layer made of a metal thin film by vapor deposition or the like on a film having fine stripe-shaped irregularities. The fine irregularities function substantially as a diffraction grating, and the light spectroscopically separated by the reflective layer formed along the shape of the irregularities interferes, so that the film looks like a rainbow color. And the color tone and the area of its color development change according to the viewing angle.
[0007] Therefore, if a molded article made of a light-transmissive resin can be given the same color effect as a hologram-like film, the aesthetic appearance can be made more excellent. However, it has been found that when a fine concavo-convex structure capable of exhibiting a spectroscopic function is formed on the back surface of a molded article made of a light-transmissive resin, it is impossible to effectively form a light-shielding layer. Specifically, although it is not difficult to form a reflective layer made of a metal thin film along the fine structure, since the reflective layer is extremely thin, it cannot sufficiently block the light incident from the surface, and thus a light-shielding layer is still required. When a light-shielding layer is formed by silk printing or the like, the grooves of the fine concavo-convexities are clogged with ink, and the light incident from the surface is not spectroscopically separated, and the "hologram-like" color tone cannot be obtained. When the shape of the molded article is a shallow dish shape having a flat bottom surface and a concavo-convex structure is formed on the bottom surface, ink accumulates in the curved portions around the bottom surface, resulting in unevenness in color and density. In addition, in a fine concavo-convex structure, the thickness of the protruding portions of the concavo-convexities is extremely thin, and the protruding portions are eroded by the solvent contained in the ink, and the concavo-convex structure collapses.
[0008] On the other hand, if a light-shielding layer is formed using a transfer film, clogging of the eyes, accumulation of ink, deterioration by a solvent, etc. do not occur. However, in a conventional transfer method as described in Non-Patent Document 2, the transfer film cannot follow the fine concavo-convexities, and it is still difficult to make it "hologram-like".
[0009] Therefore, one object of the present invention is to provide a method for effectively forming a light-shielding layer by a transfer film on a molded article made of a translucent resin having a fine concavo-convex structure with a reflective layer made of a metal thin film formed on the surface.
Means for Solving the Problems
[0010] One aspect of the present invention for achieving the above object is a method for forming a light-shielding layer on the surface layer side of a reflective layer for a molded article made of a light-transmissive resin having a concavo-convex structure formed on one main surface and a reflective layer made of a metal thin film laminated along the shape of the concavo-convex structure, using a transfer device and a transfer film, The transfer device includes an openable and closable kiln composed of a first kiln and a second kiln, capable of reducing and increasing the pressure inside the kiln, and capable of introducing saturated steam into the kiln. The transfer film is formed by laminating an ink layer on a base material. An arrangement step of arranging the molded body in the first kiln and stretching the transfer film over the first kiln. A pressure reduction step of reducing the pressure inside the first kiln with the transfer film stretched over it. A steam introduction step of introducing saturated steam into the second kiln while closing the first kiln and the second kiln. A pressurization step of pressurizing the inside of the second kiln. including In the arrangement step, the ink layer of the transfer film is faced to the surface of the molded body where the concavo-convex structure is formed, and while covering the molded body with the transfer film, the space of the first kiln is closed. The transfer film is adhered along the surface shape of the molded body by the pressure reduction step. The saturated steam at a predetermined temperature introduced in the steam introduction step and the pressure inside the second kiln by the pressurization step cause the ink layer of the transfer film to be thermocompression-bonded along the shape of the concavo-convex structure in the molded body as the light shielding layer. It is a method for forming a light shielding layer.
[0011] The ink layer may be formed of a plurality of layers, and the layer on the surface layer side may be a colored layer that is a color other than black or white. Further, the colored layer may be a complementary color of the light transmitted through the translucent resin.
[0012] The ink layer may be formed of a plurality of layers, with an achromatic layer other than black arranged on the base layer side and a black layer arranged on the surface layer side with respect to the achromatic layer, as a method for forming a light shielding layer.
[0013] The transfer film is formed by laminating the ink layer on the surface layer side of the base layer serving as the base material via a release layer, and may be a method for forming a light-shielding layer including a base layer peeling step of peeling the base layer from the transfer film thermocompression-bonded by the reduced-pressure step.
[0014] Furthermore, the release layer is configured to contain a UV paint, and the method for forming a light-shielding layer may include an ultraviolet curing step of curing the UV paint after the base layer peeling step.
[0015] The transfer film is formed by directly laminating the ink layer on the surface layer side of the base layer serving as the base material, and in the transfer film, it may be a method for forming a light-shielding layer including a film cutting step of cutting areas other than the areas thermocompression-bonded by the reduced-pressure step.
[0016] Regarding the one main surface as the front surface, the method for forming a light-shielding layer may be such that the molded body disperses light incident from the rear to the front by the uneven structure.
Advantages of the Invention
[0017] According to the present invention, a method is provided for effectively forming a light-shielding layer by a transfer film on a molded body made of a translucent resin having a fine uneven structure with a reflective layer made of a metal thin film formed on the surface. Other advantages will be clarified in the following description.
Brief Description of the Drawings
[0018]
Figure 1
Figure 2
Figure 3A
Figure 3B
Figure 4
Figure 5A
Figure 5B
Figure 6A
Figure 6B
Figure 6C
Figure 7
Figure 8
Modes for Carrying Out the Invention
[0019] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings used in the following description, the same or similar parts may be denoted by the same reference numerals, and redundant descriptions may be omitted. Depending on the drawings, unnecessary reference numerals may be omitted in the description. ===Example=== <Back cover> As a product to which the light-shielding layer forming method according to the embodiment is applied, a rear cover of a smartphone can be cited. FIG. 1 shows an exploded view of the smartphone 10 disassembled into the rear cover 1 and the rest of the smartphone body 11. In the smartphone 10 shown in FIG. 1, the smartphone body 11 has a display disposed on one main surface side of a generally rectangular flat housing, and a camera lens 14 and the like are disposed on the other surface 13. Here, the thickness direction of the flat housing 12 is defined as the front-rear direction, and the front-rear directions are defined based on the fact that the display is disposed on the front side. The front-rear direction of the rear cover 1 is defined with reference to the state of being attached to the smartphone body 11. Therefore, the rear surface 2 of the rear cover 1 becomes the outer surface of the smartphone 10, and the front surface 3 of the rear cover 1 becomes the surface facing the rear surface 13 of the smartphone body 11. Also, for convenience, hereinafter, in the rectangular flat smartphone body 11 and rear cover 1, the longitudinal direction of the rectangular plane is defined as the vertical direction, and the short-side direction is defined as the left-right direction.
[0020] In the smartphone body 11 shown in FIG. 1, the housing 12 is made of a material such as resin, and the rear surface 13 of the housing 12 has the base of the material exposed as it is. The rear cover 1 is in the shape of a rectangular plate and has a hole (hereinafter sometimes referred to as a "window portion 4") for exposing components attached to the smartphone body 11, such as the lens 14, to the outside. And the rear cover 1 has the function of hiding the base of the housing 12 of the smartphone body 11, which lacks a high-class feeling, and making it excellent in appearance.
[0021] The back cover 1 has a structure formed on its rear surface (hereinafter sometimes referred to as the "back surface 3") for expressing the above-described hologram-like color tone when viewed from the outside in order to enhance the aesthetics of the smartphone 10. Generally speaking, the back cover 1 has a structure in which a reflective layer made of a metal thin film and a light-shielding layer made of an ink layer transferred from a transfer film are laminated in this order on one main surface of a plate-shaped substrate made of a translucent resin material (for example, polycarbonate). A fine uneven structure is formed on one main surface of the substrate, and the reflective layer and the light-shielding layer cover the one main surface of the substrate while following the uneven structure. And this embodiment forms this light-shielding layer.
[0022] Fig. 2 schematically shows the structure of the back surface 3 of the back cover 1. As shown in Fig. 2, on the front surface, which is one main surface of the substrate 20, a large number of grooves 21 with a depth d = 3.7 μm are formed side by side at a pitch p = 56 μm so as to be parallel to each other. The thickness of the reflective layer 22 is, for example, 50 to 100 nm, and the light-shielding layer 23 is, for example, about 8.5 to 9.5 μm. And the back cover 1 exhibits a hologram-like color tone when viewed from the rear due to the structure shown in Fig. 2.
[0023] Figs. 3A and 3B more specifically show the aspect of the back surface 3 of the back cover 1. Fig. 3A is a micrograph of the back surface 3 of the back cover 1, and Fig. 3B shows the surface roughness measured by scanning the back surface 3 of the back cover 1 with a laser microscope along the line a-a in Fig. 3A. As shown in Fig. 3A, the uneven shape of the groove 21 can be clearly distinguished. That is, it can be confirmed that the light-shielding layer 23 is also formed so as to follow this uneven shape together with the reflective layer 22. And it can also be seen from the measurement result of the surface roughness shown in Fig. 3B that the reflective layer 22 and the light-shielding layer 23 follow the uneven shape of the substrate 20.
[0024] Incidentally, the reflective layer 22 can be formed by vapor-depositing a metal (such as tin, indium, aluminum, etc.). The light-shielding layer 23 can be formed, for example, using the transfer film described in JP-A-2013-126740. The invention described in the publication is the base material for the transfer film, and the transfer film has a structure in which an ink layer (hereinafter referred to as an ink layer) is laminated via a release layer. FIG. 4 shows an example of the structure of the transfer film 30 applied to the method of this embodiment. FIG. 4 shows a cross-section of the transfer film 30 and has a laminated structure including a base layer 31 as a base material, an ink layer 32, and a release layer 33 interposed between the ink layer 32 and the base layer 31. In the transfer film 30 used in the method of the embodiment, there are four ink layers 32 from the surface layer side toward the base layer 31. When the surface layer side is the first layer 32a, the first layer 32a is a layer for adjusting the hue of the hologram tone (hereinafter sometimes referred to as the "colored layer 32a"). For example, it is colored with a complementary color (for example, green) to cancel out a part of the hue of each color (for example, purple) spectroscopically separated by the fine structure. The second layer 32b and the third layer 32c are colored black and are layers for concealing the inside of the smartphone housing and the substrate (hereinafter sometimes referred to as the "black layers (32b, 32c)"). The fourth layer 32d is colored white, and the fourth layer 32d is a layer for filling the pinhole in case a pinhole penetrating the two black layers (32b, 32c) occurs (hereinafter sometimes referred to as the "pinhole-concealing layer 32d"). Incidentally, the pinhole-concealing layer 32d is not limited to white and may be achromatic other than black, such as gray.
[0025] Then, when the transfer film 30 is heated while being pressed from the base layer 31 side toward the ink layer 32 in a state where the ink layer 32 is in contact with an object to be transferred (hereinafter sometimes referred to as the "transfer object"), the ink layer 32 adheres to the transfer object. Then, when the transfer film 30 is peeled off toward the base layer 31 side, the ink layer 32 is peeled off from the base layer 31 together with the release layer 33, and the release layer 33 and the ink layer 32 are transferred to the transfer object. Therefore, the actual light-shielding layer 23 is the ink layer 32 including the release layer 33. However, since the thickness of the release layer 33 is extremely thin at about 0.5 μm and the colored ink layer 32 functions to shield light, hereinafter, unless otherwise specified, the light-shielding layer 23 and the ink layer 32 will be described as being synonymous.
[0026] In the example shown in FIG. 4, the black layers (32b, 32c) were composed of two layers, but may be a single layer as long as they can sufficiently shield light and surely prevent the occurrence of pinholes. Also, although the four layers (32a to 32d) constituting the ink layer 32 have the same thickness, for example, the black layers (32b, 32c) may be a single layer that is thicker than the other layers (32a, 32d). <Transfer device> On the back surface 3 of the back cover 1, the light-shielding layer 23 composed of the above-described four-layer ink layer 32 is transferred by the method of this embodiment. To form the light-shielding layer 23, a dedicated device (hereinafter sometimes referred to as the "transfer device") for transferring the ink layer 32 of the transfer film 30 to the back surface of the back cover 1 is used. FIGS. 5A and 5B show the schematic structure of the transfer device 40. As shown in FIG. 5A, the transfer device 40 includes a kiln 41 and external devices (43a to 43c) connected to the kiln 41 via pipelines (42a to 42c). Note that a valve mechanism (not shown) is interposed in the middle of the pipelines (42a to 42c). The kiln 41 is composed of a first kiln 41a and a second kiln 41b that can be opened and closed with respect to each other. FIGS. 5A and 5B show the state where the kiln 41 is open and the state where it is closed, respectively. Note that the basic structure and operation of the transfer device 40 are the same as those described in, for example, Japanese Patent Application Laid-Open No. 2011-230418.
[0027] Here, it is assumed that the front-back direction, left-right direction, and up-down direction in the back cover 1 coincide with the respective directions in the kiln 41 of the transfer device 40, and in a state where the kiln 41 is closed, the first kiln 41a and the second kiln 41b face each other in the vertical up-down direction. Also, it is assumed that the second kiln 41b is arranged vertically above the first kiln 41a. And in FIGS. 5A and 5B, the cross-sectional shape of the kiln 41 when viewed from the up-down direction is shown.
[0028] The first kiln 41a has a rectangular box-shaped recess 44a with the rear (vertically downward) as the bottom surface, and the opening of the recess (hereinafter sometimes referred to as the "first recess 44a") is covered by a lid portion 45 in which a large number of holes 46 are formed. Also, the first kiln 41a is movable in the up-down direction (in the depth direction of the drawing in the figure). Note that the moving direction of the first kiln 41a is not limited to the up-down direction. For example, it may be in the left-right direction (in the left-right direction of the drawing in the figure). In any case, in the transfer device 40 used in the method of the embodiment, the first kiln 41a can move within a plane with the vertical up-down direction as the normal.
[0029] The second kiln 41b has a rectangular box-shaped recess (hereinafter sometimes referred to as the "second recess 44b") with the rear (vertically downward) open, and is movable in the front-back direction (vertical up-down direction). Then, while facing the openings of the recesses (44a, 44b) of the first kiln 41a and the second kiln 41b, when the second kiln 41b is retracted (moved vertically downward) to close the kiln 41, as shown in FIG. 5B, a storage space 44 closed by the first recess 44a and the second recess 44b respectively is formed.
[0030] The transfer device 40 includes, as external devices (43a to 43c), a vacuum pump 43a, a water vapor generator 43b, and a pressurizing device 43c. Further, the first kiln 41a has an exhaust port 47a to which a pipeline 42a from the vacuum pump 43a is connected while communicating the first recess 44a with the outside. The second kiln 41b has a water vapor inlet 47b connected to a pipeline 42b from the water vapor generator 43b and an air inlet 47c connected to a pipeline 42c from the pressurizing device 43c. Thereby, the transfer device 40 can perform decompression, filling with water vapor, and pressurization on the storage space 44. <Procedure for forming the light shielding layer> The following shows the procedure for transferring the ink layer 32 of the transfer film 30 to the back surface 3 of the back cover 1 using the transfer device 40 shown in FIGS. 5A and 5B. First, a molded body 50 that will finally become the back cover 1 is prepared. The molded body 50 is shown in FIGS. 6A to 6C. In FIGS. 6A to 6C, the front-back, up-down, and left-right directions of the molded body 50 and the back cover 1 are made to coincide. FIG. 6A is an external view of the molded body 50, FIG. 6B is a plan view when the molded body 50 is viewed from the front, and FIG. 6C is a cross-sectional view taken along the b-b arrow in FIG. 6B.
[0031] As shown in FIG. 6A, the molded body 50 has a shallow rectangular dish shape with a flange 51, and the rectangular bottom 52 is the region that will finally become the back cover 1. And the front surface of the rectangular dish-shaped molded body 50 (hereinafter, may be referred to as "bottom surface 53") becomes the back surface 3 of the back cover 1. The molded body 50 is, for example, a transparent resin molded body made of polycarbonate or the like, and an uneven structure composed of the above-mentioned many grooves 21 and a reflective layer 22 made of a metal thin film are previously formed on the bottom surface 53 thereof.
[0032] As shown in Fig. 6B, the outer dimensions of the molded body 50 are a vertical length L1 = 210 mm and a horizontal width W1 = 105 mm. And in this molded body 50, the region of the bottom portion 52 that becomes the back cover 1 has a vertical length L2 = 178 mm and a horizontal width W2 = 80 mm. Also, as shown in Fig. 6C, the molded body 50 has a wall thickness t = 0.65 mm and a height H = 4 mm. Note that the groove 21 is formed so as to extend in a direction where θ = 45° with respect to the horizontal direction as indicated by the white double-headed arrow in Fig. 6B.
[0033] Fig. 7 shows the procedure for forming the light-shielding layer 23 on the bottom surface 53 of the above-mentioned molded body 50 using the transfer device 40. First, the above-mentioned molded body 50 is placed in the first kiln 41a (s1). Specifically, the jig 60 is placed on the front surface (vertical upper surface) of the lid portion 45 of the first kiln 41a, and the molded body 50 is placed on the jig 60. At this time, the first kiln 41a is moved to a position where it does not face the second kiln 41b in the front-rear direction (vertical up-down direction) in order to ensure the safety of the operation and facilitate the installation of the molded body 50. Also, the transfer film 30 is arranged behind (vertically downward) the second kiln 41b so that the ink layer faces backward (vertically downward).
[0034] Next, while moving the first kiln 41a to a position where it faces the second kiln 41b in the front-rear direction (vertical direction), the vacuum pump 43a is operated to exhaust the air in the first recess 44a of the first kiln 41a through the exhaust port 47a. Note that the jig 60 is formed with holes 61 that penetrate both the front and rear surfaces, similar to the lid portion 45, and the molded body 50 is adsorbed to the front surface (vertical upper surface side) of the lid portion 45 together with the jig 60 as the pressure in the first recess 44a is reduced. Then, when the first kiln 41a and the second kiln 41b face each other in the front-rear direction (vertical direction), the transfer film 30 is stretched across the opening of the first recess 44a of the first kiln 41a so that the bottom surface 53 side of the molded body 50 and the lid portion 45 are covered (s2). When the transfer film 30 is stretched across the first kiln 41a, the air between the transfer film 30 and the molded body 50 is also exhausted as the pressure in the first recess 44a is reduced, and the transfer film 30 is arranged along the shape of the molded body 50.
[0035] When the kiln 41 is closed (S3), the degree of vacuum in the first recess 44a of the first kiln 41a in the storage space 44 further increases, and due to the pressure difference between the depressurized first recess 44a and the second recess 44b of the second kiln 41b that is close to atmospheric pressure, the transfer film 30 adheres more closely along the outer shape of the molded body 50. If the kiln 41 is closed, the evacuation of the first recess 44a of the first kiln 41a is continued, and as shown by the dotted hatching in the figure, saturated steam from the steam generator 43b is introduced into the second recess 44b of the second kiln 41b through the steam inlet 47b (S4). Note that the final degree of vacuum in the first recess 44a of the first kiln 41a is, for example, -99.8 KPa to -100.5 KPa.
[0036] When the temperature of the saturated steam in the second kiln 41b reaches a predetermined temperature (for example, 115°C to 120°C), the introduction of the saturated steam and the evacuation operation are stopped, and compressed air from the pressure pump 43c is introduced into the second recess 44b through the air inlet 47c so that the inside of the second recess 44b becomes a predetermined air pressure (for example, 0.5 MPa) (S5). Thereby, the transfer film 30 is thermocompression-bonded to the front side of the molded body 50. Then, the inside of the storage space 44 of the kiln 41 is returned to atmospheric pressure, the kiln 41 is opened (S6), and the molded body 50 with the transfer film 30 adhered is taken out together with the jig 60 (S7). Then, the base layer 31 side of the transfer film 30 is peeled off. In this way, a molded body 50 onto which the four-layer ink layer 32 serving as the release layer 33 and the light-shielding layer 23 is transferred is obtained (S8).
[0037] In addition, in order to complete the back cover 1 using the molded body 50, the side surface around the bottom 52 of the molded body 50 including the flange 51 is cut to cut out only the bottom 52. Further, when it is necessary to provide a window portion 4 for exposing the lens 14 of the camera of the smartphone 10 to the outside as in the back cover 1 shown in FIG. 1, after cutting out the bottom 52 of the molded body 50, the window portion 4 may be formed on the bottom 52 by cutting or laser processing or the like.
[0038] Fig. 8 shows an electron micrograph of a cross-section when the completed back cover 1 is cut. The cross-section corresponds to the c-c arrow-view cross-section in Fig. 6B. Also, when cutting, a cutting blade is applied to the back surface 3 of the back cover 1. And as shown in Fig. 8, it can be confirmed that in the back cover 1 produced by applying the method of the embodiment, the light-shielding layer 23 is formed along the shape of the uneven structure. Furthermore, in the electron micrograph shown in Fig. 8, even though the top of the uneven structure has been crushed by the pressure applied to the back surface 3 of the back cover 1 when cutting the back cover 1, the light-shielding layer 23 has not peeled off. That is, it can be seen that the light-shielding layer 23 formed by the method of the embodiment has a large adhesive strength. Note that since the electron micrograph shown in Fig. 8 is set at a magnification that makes the light-shielding layer 23 and the uneven structure clear, the extremely thin metal thin film 22 cannot be clearly discriminated from this electron micrograph.
[0039] Thus, according to the method for forming the light-shielding layer 23 according to the embodiment, a reflection layer 22 made of a metal thin film is formed on the surface, and for a molded body made of a translucent resin having an extremely fine uneven structure 21 that functions as a diffraction grating, the light-shielding layer 23 formed of the ink layer 32 of the transfer film 30 can be surely formed. Thereby, it is possible to provide an aesthetic appearance that could not be achieved with an ink layer 32 transferred by silk printing or a conventional transfer method for a resin molded body such as the back cover 1 of the smartphone 10. ===Other Embodiments=== The method according to the above embodiment is applicable not only to the back cover 1 of the smartphone 10 but also to a translucent resin molded body having a fine uneven structure 21 on the surface and a reflection layer 22 formed along the uneven structure 21. And the translucent resin molded body to which the method according to the embodiment is applied only needs to have translucency and does not have to be colorless and transparent. Of course, the shape of the resin molded body is not limited to a flat plate shape. For example, it may be a shallow dish shape in which the flange 51 is cut off from the molded body 50 shown in Figs. 6A to 6C. The bottom 53 does not have to be a flat surface. For example, a fine uneven structure may be formed on the inner surface of a bowl shape.
[0040] In the above embodiment, in order to obtain the aesthetic appearance of the hologram tone, a fine concavo-convex structure that functions as a diffraction grating was formed on the back surface 3 of the back cover 1. However, the concavo-convex structure may be fine characters, patterns, or the like. In any case, with the method according to the embodiment, the light shielding layer 23 can be surely formed even with a concavo-convex structure that cannot be followed by the conventional method.
[0041] In the above embodiment, the transfer film 30 having the four-layer ink layer 32 composed of a total of three colors was used. However, the colors of the respective layers (32a to 32d) are not limited to those in the above embodiment. For example, if there is no need to adjust the color tone, the colored layer 32a may be omitted, or the colored layer 32a may be made black. In any case, it is only necessary that the internal state of the device covered by the resin molded body having translucency is not seen through outward or the aesthetic appearance is not deteriorated by pinholes.
[0042] In the above embodiment, the release layer 33 was disposed on the surface layer of the back surface of the back cover 1. However, the release layer 33 may be constituted by a UV paint. Alternatively, a UV paint may be mixed with the resin material constituting the release layer 33. Thereby, if the UV paint is cured by irradiating ultraviolet rays after the formation of the light shielding layer 23, the release layer 33 becomes a hard coat layer covering the ink layer 32 and has a function of suppressing the peeling of the ink layer 32 due to friction, warm water, or the like.
[0043] In the above embodiment, the base layer 31 of the transfer film 30 was peeled off and the ink layer 32 and the release layer 33 were transferred to the back surface 3 of the back cover 2. However, if the base layer 31 is thin enough to follow the concavo-convex structure, the extra transfer film 30 may be cut without peeling the base layer 31, and the base layer 31 may be thermocompression-bonded together with the ink layer 32. Thereby, the base layer 31 can prevent the molded body 50 from being damaged by a strong impact or the like as a protective layer. In addition, when the ink layer 32 is thermocompression-bonded together with the base layer 31, the release layer 33 of the transfer film 30 is unnecessary.
Explanation of Reference Numerals
[0044] 1 Rear cover, 2 Rear surface of the rear cover, 3 Back surface of the rear cover, 4 Window portion 10 Smartphone, 11 Smartphone body, 12 Housing of the smartphone body 20 Substrate, 21 Concavo-convex structure (groove), 22 Reflective layer, 23 Light shielding layer 30 Transfer film, 31 Base layer, 32 Ink layer 32a First layer of the ink layer (coloring layer), 32b Second layer of the ink layer (black layer) 32c Third layer of the ink layer (black layer) 32d Fourth layer of the ink layer (pinhole concealment layer), 40 Transfer device, 41 Kiln 41a First kiln, 41b Second kiln, 42a - 42c Pipelines 43a External device (vacuum pump), 43b External device (water vapor generator) 43c External device (pressurizing device), 44 Storage space, 44a First recess 44b Second recess, 45 Cover portion, 46 Hole in the cover portion, 47a Exhaust port 47b Water vapor inlet, 47c Air inlet, 50 Formed body, 51 Flange of the formed body, 52 Bottom of the formed body, 53 Bottom surface of the formed body, 60 Jig
Claims
1. A method for forming a light-shielding layer on the surface layer side of a reflective layer composed of a metal thin film laminated along the shape of the uneven structure on a molded body made of a translucent resin having an uneven structure formed on one main surface, comprising: using a transfer device and a transfer film, wherein the transfer device includes an openable and closable kiln composed of a first kiln and a second kiln, capable of reducing and increasing the pressure inside the kiln, and capable of introducing saturated steam into the kiln, the transfer film is formed by laminating an ink layer on a base material, an arrangement step of arranging the molded body in the first kiln and stretching the transfer film over the first kiln, a pressure reduction step of reducing the pressure inside the first kiln in a state where the transfer film is stretched, a steam introduction step of introducing saturated steam into the second kiln while closing the first kiln and the second kiln, a pressurization step of pressurizing the inside of the second kiln, including: In the arrangement step, the ink layer of the transfer film is faced to the surface on which the uneven structure is formed in the molded body, and the space of the first kiln is closed while covering the molded body with the transfer film, adhering the transfer film along the surface shape of the molded body by the pressure reduction step, thermally pressing the ink layer of the transfer film as the light-shielding layer along the shape of the uneven structure in the molded body by the saturated steam at a predetermined temperature introduced in the steam introduction step and the pressure inside the second kiln by the pressurization step, A light-shielding layer forming method.
2. The light-shielding layer forming method according to claim 1, wherein the ink layer is formed of a plurality of layers, and the layer on the surface layer side is a colored layer having a color other than black or white.
3. The light-shielding layer forming method according to claim 2, wherein the colored layer is a complementary color of light transmitted through the translucent resin.
4. The light-shielding layer forming method according to claim 1, wherein the ink layer is formed of a plurality of layers, an achromatic layer other than black is disposed on the base layer side serving as the base material, and a black layer is disposed on the surface layer side with respect to the achromatic layer.
5. The light-shielding layer forming method according to claim 1, wherein the transfer film is formed by laminating the ink layer on the surface layer side of the base layer serving as the base material via a release layer, and includes a base layer peeling step of peeling the base layer from the transfer film thermally pressed by the pressure reduction step.
6. The light-shielding layer forming method according to claim 5, wherein the release layer is composed of a UV paint and includes an ultraviolet curing step of curing the UV paint after the base layer peeling step.
7. The light-shielding layer forming method according to claim 1, wherein the transfer film has the ink layer directly laminated on the surface layer side of the base layer serving as the base material, and in the transfer film, includes a film cutting step of cutting a region other than the region thermocompression-bonded by the reduced pressure step.
8. The light-shielding layer forming method according to any one of claims 1 to 7, wherein with the one main surface as the front surface, the molded body disperses light incident from the rear to the front by the uneven structure.