Laser decoration method

Abstract

To enhance the visibility of decoration by suppressing black discoloration of an exposed aluminum base material in a laser-decorating method in which a coated film layer is formed on a surface of an aluminum base material via a surface treatment layer, and decoration is applied by irradiating the coated film layer with laser light.SOLUTION: In a laser-decorating method in which a coated film layer is formed on a surface of an aluminum base material via a surface treatment layer, and decoration is applied by irradiating the coated film layer with laser light, the color of the coated film layer at an irradiation position of a laser light is set to a color having a higher absorption rate of the wavelength of the laser light.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a laser decoration method. [Background technology]

[0002] Metal substrates having a coating film formed on the surface are irradiated with laser light to perform decoration such as marking on various products. One conventional technique is known in which a thick film is formed on the surface of a metal substrate, and when laser light is irradiated, the thick film is removed to a depth that does not reach the surface of the metal substrate, thereby performing marking (see Patent Document 1 below).

[0003] Another known prior art technique involves forming a light-transmitting coating film on a surface-treated metal substrate, and irradiating the coating film with laser light to form a discoloration layer in the area where the coating film faces the metal substrate (see Patent Document 2 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-181658 A [Patent Document 2] Japanese Patent Application Publication No. 2-41785 Summary of the Invention [Problem to be solved by the invention]

[0005] The former conventional technique described above requires a thick coating film and fine adjustment of the intensity of the irradiated laser light, making it difficult to apply to the decoration of a coating film layer formed on the outer surface of a can container, etc. In addition, the latter conventional technique described above is limited to a transparent coating film, so it cannot be applied to the decoration of a coating film layer colored in various colors.

[0006] In addition, the metal substrate in metal products such as can containers is an aluminum substrate, and a coating layer is formed on top of a surface treatment layer. When this coating layer is irradiated with laser light to perform decoration such as marking, the coating layer is often removed at the position irradiated with the laser light, and the surface treatment layer is also removed, exposing the aluminum substrate to the surface. In such a state, it has been confirmed that the exposed surface of the aluminum substrate turns black (hereinafter, blackening) when a hot water sterilization treatment or the like is subsequently performed, which causes a problem of reduced visibility of the decoration.

[0007] The present invention aims to address such problems. That is, in a laser decoration method in which a coating layer is formed on the surface of an aluminum base material such as a can container via a surface treatment layer, and the coating layer is irradiated with laser light to decorate the surface, the present invention aims to improve the visibility of the decoration by preventing the exposed aluminum base material from turning black. [Means for solving the problem]

[0008] In order to solve such problems, the present invention has the following configuration. In a laser decoration method in which a coating layer is formed on the surface of an aluminum substrate via a surface treatment layer, and the coating layer is decorated by irradiating the coating layer with laser light, a wavelength of laser light that peels off the coating layer but leaves the surface treatment layer is The wavelength of the laser light is in the near infrared region, and the color of the coating layer is black. 1. A method for producing a metal product using a laser beam, comprising the step of selecting Effect of the Invention

[0009] According to the laser decoration method of the present invention having such characteristics, it is possible to prevent the decorated portion from turning black due to irradiation with laser light, and to improve the visibility of the decoration. [Brief description of the drawings]

[0010] [Figure 1]An explanatory diagram showing the state of the decorative pattern created by irradiation with laser light ((a) is the case of a coating layer of a color with low absorptivity for the wavelength of laser light, and (b) is the case of a coating layer of a color with high absorptivity for the wavelength of laser light). [Diagram 2] An explanatory diagram showing the spectral reflectance of each color of a coating layer (near infrared region). [Diagram 3] An explanatory diagram showing the spectral reflectance of each color of a coating layer (from ultraviolet to visible light range). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, the embodiment of the present invention is premised on a metal product to be decorated, which is a metal product having a surface treatment layer L2 formed on the surface of an aluminum base material L3 and a coating layer L1 formed thereon, and which is decorated (marked) with characters, patterns, etc. by irradiating the coating layer L1 with laser light. Here, the coating layer L1 is partially removed by irradiation with laser light to reveal the metal surface of one or both of the surface treatment layer L2 and the aluminum base material L3, thereby allowing the decorative pattern to be visually recognized by the contrast between the coating layer L1 and the metal surface.

[0012] In this case, if hot water sterilization or the like is performed after decoration by laser light irradiation, blackened areas will appear in the decorative pattern, and if blackened areas occur over a large area of ​​the decorative pattern, the visibility (contrast) of the decorative pattern will decrease, as shown in Figure 1(a). It is thought that the blackening occurs when an oxide film grows on the aluminum base material, and metal ions (Ca, Mg, Si, etc.) contained in the sterilized water are absorbed into the oxide film, causing discoloration.

[0013] Here, it was discovered that even when laser decoration was performed with a similar laser light intensity and then a similar treatment was performed, the area of ​​the blackened area in the decorative pattern was sometimes large, as shown in Figure 1(a), and sometimes small, as shown in Figure 1(b). Upon investigating the cause of this, it was found that the area of ​​the blackened area could be reduced if the remaining area of ​​the surface treatment layer in the decorative pattern could be increased.

[0014] As shown in Figure 1(a), if the remaining area of ​​the surface treatment layer in the decorative pattern is small at the time of laser light irradiation, the area of ​​the blackened area in the decorative pattern will become larger in subsequent processing. Conversely, as shown in Figure 1(b), if the remaining area of ​​the surface treatment layer in the decorative pattern is large at the time of laser light irradiation, the area of ​​the blackened area in the decorative pattern will become smaller in subsequent processing.

[0015] We then thought that if we could actively create a difference between Figures 1(a) and 1(b), we could reduce the size of the blackened areas in the decorative pattern, as shown in Figure 1(b), and improve the visibility of the decorative pattern.As a result of our intensive research, we discovered that the difference between Figures 1(a) and 1(b) arises from the relationship between the "color" of the coating layer L1 and the "wavelength" of the irradiated laser light.

[0016] As shown in Fig. 1(a), the reason why the remaining area of ​​the surface-treated layer L2 in the decorative pattern formed by irradiation with laser light is small is believed to be because the laser light penetrates the coating layer L1 and damages the surface-treated layer L2 and the aluminum base material L3. In contrast, as shown in Fig. 1(b), the reason why the remaining area of ​​the surface-treated layer L2 in the decorative pattern formed by irradiation with laser light is large is believed to be because part of the laser light is absorbed by the coating layer L1, making it difficult to damage the surface-treated layer L2 and the aluminum base material L3.

[0017] The degree of absorption of laser light in the coating layer L1 varies depending on the "color" of the coating layer L1. Figure 2 shows the spectral reflectance of each color of the coating layer L1. The lower the reflectance here, the higher the absorption. When a fiber laser with a wavelength of 1064 nm is used as the laser light, "black" has the highest absorption rate, and the other colors (red, blue, green, yellow, clear (transparent)) have low absorption rates.

[0018] In this case, when laser decoration was actually performed using a fiber laser with a wavelength of 1064 nm and the "color" of the coating layer L1 was set to black, the area of ​​the blackened portion in the decorative pattern became smaller when hot water sterilization was then performed, as shown in Figure 1(b).In contrast, when similar laser decoration was performed with the "color" of the coating layer L1 set to red, for example, and then hot water sterilization was performed, the area of ​​the blackened portion in the decorative pattern became larger, as shown in Figure 1(a).

[0019] To summarize the results of such investigations, in a laser decoration method in which a coating layer L1 is formed on the surface of an aluminum base material L3 via a surface treatment layer L2, and the coating layer L1 is irradiated with laser light to perform decoration, the color of the coating layer L1 at the laser light irradiation position is set to a color that has a high absorption rate for the wavelength of the laser light, thereby preventing the subsequent occurrence of large blackened areas in the decorative pattern and the reduction in visibility of the decorative pattern. In particular, when the laser light is in the near-infrared range such as a fiber laser with a wavelength of 1064 nm, blackening in the decorative pattern can be effectively prevented by setting the "color" of the coating layer L1 to "black."

[0020] FIG. 3 shows the spectral reflectance of each color of the coating layer from the ultraviolet to visible light range. What is noteworthy here is the absorptance (reflectance) of each color in the ultraviolet range. In the ultraviolet range, most colors have high absorptance, except for clear (transparent). For this reason, by using a UV laser (e.g., wavelength 355 nm) as the laser light, the "color" of the coating layer L1 can effectively prevent blackening in the decorative pattern for each color (black, red, blue, green, yellow, etc.) except for clear.

[0021] [Table 1]

[0022] Table 1 above is an example showing the blackening suppression effect. A coating film layer L1 of each color was formed on an aluminum substrate L3 on which a surface treatment layer L2 was formed, and laser marking was performed using a fiber laser (wavelength: 1064 nm) and a UV laser (wavelength: 355 nm). After that, hot water sterilization was performed at 125 ° C for 30 minutes, and the blackening state of the laser marking was visually confirmed. In the laser marking using a fiber laser, the blackening suppression effect after hot water sterilization was confirmed in the black coating film layer L1, and in the laser marking using a UV laser, the blackening suppression effect after hot water sterilization was confirmed in the black, red, blue, green, and yellow coating film layers L1.

[0023] As described above, the laser decoration method according to the embodiment of the present invention makes it possible to perform highly visible laser decoration by appropriately selecting the relationship between the wavelength of the laser light used and the "color" of the coating layer L1. This laser decoration method is effective when performing laser decoration on the surface of a can container on which a coating layer has been formed, and even when a hot water sterilization treatment is then performed, it is possible to keep the blackened areas in the decorative pattern small and maintain a highly visible decorative pattern. [Explanation of symbols]

[0024] L1: coating layer, L2: surface treatment layer, L3: aluminum base material

Claims

1. A laser decoration method comprising forming a coating layer on a surface of an aluminum substrate via a surface treatment layer, and irradiating the coating layer with laser light to decorate the surface, comprising: A method for producing a metal product using laser light, comprising a step of selecting a wavelength of laser light that removes the coating layer but leaves the surface treatment layer in place, the wavelength of the laser light being in the near-infrared range and the color of the coating layer being black.

2. A laser decoration method comprising forming a coating layer on a surface of an aluminum substrate via a surface treatment layer, and irradiating the coating layer with laser light to decorate the surface, comprising: A method for producing a metal product using laser light, comprising a step of selecting a wavelength of laser light that removes the coating layer but leaves the surface treatment layer in place, the wavelength of the laser light being in the ultraviolet range, and the color of the coating layer being selected from red, blue, green, yellow, and black.

Images