Laser marking method

Abstract

To highly accurately print an image on a resin composition.SOLUTION: A laser marking method irradiates a processed surface F of an object 1 composed of a resin composition with a laser beam 2 and thereby prints an image thereon, and irradiates the processed surface F with the laser beam 2 in the state where a heat radiation member 4 for transmitting the laser beam 2 is installed on the processed surface F of the object 1, wherein thermal conductivity of the heat radiation member 4 is higher than thermal conductivity of the object 1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for processing the surface of a resin composition with a laser.

Background Art

[0002] Conventionally, various techniques have been proposed for printing images such as characters and patterns (so-called laser marking) by irradiating the surface of an object such as metal or wood with a laser to change the color of the surface.

[0003] Here, in recent years, from the viewpoint of ensuring the traceability of products and production, there has been a demand to directly print a solid number, a barcode, etc. on the surface of a product. The surface of a product is often made of a resin composition. However, resin compositions generally have high water repellency. Therefore, it may be difficult to print an image on the resin composition with ink.

[0004] Therefore, a technique for printing an image on a resin composition using a laser has been disclosed (for example, Patent Document 1). In the technique of Patent Document 1, a resin composition is directly irradiated with a laser. Then, the portion of the surface of the resin composition irradiated with the laser melts and changes color, and a desired image is printed. When the resin composition melts, heat is transferred from the surface of the resin composition to the surrounding air.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the thermal conductivity of air is low, and heat transfer from the surface of the resin composition to the surrounding air is poor. As a result, the temperature of the surface of the resin composition irradiated with the laser rises rapidly. Furthermore, the resin composition itself often has low thermal conductivity. Then, the portion melted by the laser irradiation instantaneously vaporizes, resulting in severe damage (excessive deformation and discoloration). That is, the problem that the image cannot be printed with high precision occurs. In particular, when printing an image on an object made of a resin composition in the form of a thin film with a thickness of 1 mm or less, damage such as perforation and cutting is easily caused. In view of the above circumstances, the present invention aims to print an image with high precision on a resin composition using a laser.

Means for Solving the Problems

[0007] A laser marking method for printing an image by irradiating a laser on the surface of an object made of a resin composition, wherein the laser is irradiated on the surface with a heat dissipation member that transmits the laser installed on the surface of the object, and the thermal conductivity of the heat dissipation member is higher than that of the object.

Effects of the Invention

[0008] The laser marking method according to a preferred embodiment of the present invention can reduce damage to the resin composition. Consequently, it becomes possible to print an image with high precision on the resin composition.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0010] The present invention is a laser marking method for printing an image (for example, characters or patterns) (so-called laser marking) by irradiating the surface of an object with a laser.

[0011] The object according to the present invention is made of a resin composition. The resin composition has a resin material as a main component (for example, 90% by mass or more of the whole). There is no particular limitation on the resin material, and any known material such as a thermoplastic resin, a thermosetting resin, and a photocurable resin is used alone or in combination of two or more. For example, polyethylene, vinyl chloride resin, polypropylene, styrene resin, ABS resin, polyvinyl alcohol, acrylic resin, acrylonitrile-styrene resin, vinylidene chloride resin, fluororesin, polycarbonate, polyamide, acetal resin, polyphenylene oxide, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, epoxy resin, phenol resin, unsaturated polyester resin, urethane resin, silicone resin, diallyl phthalate resin, etc. are exemplified as the resin material.

[0012] In addition, arbitrary additives can be blended in the resin composition in addition to the resin material. Examples of the additives include a flame retardant, a lubricant, a heat stabilizer, a dye, a pigment, a mold release agent, an antioxidant, a plasticizer, etc. The types of the resin composition and the additives are arbitrary as long as laser marking can be performed on the resin composition.

[0013] FIG. 1 is a schematic diagram schematically showing the laser marking method according to the present embodiment. In the following description, the surface of the object 1 on which the image is printed is denoted as "processing surface F". As illustrated in FIG. 1, in the laser marking method according to the present embodiment, the laser 2 is irradiated onto the processing surface F with the heat dissipation member 4 installed on the processing surface F. The laser 2 is scanned along a locus corresponding to a desired image, and is transmitted through the heat dissipation member 4 and irradiated onto the object 1. Then, the image is printed by melting and discoloring the portion of the processing surface F irradiated with the laser 2.

[0014] Irradiation of the laser 2 onto the processing surface F is performed by any known laser processing apparatus capable of irradiating light having a wavelength absorbed by the resin composition as the object 1. For example, a laser processing apparatus that irradiates infrared rays having a wavelength in the range of 780 nm or more and 1 mm or less is used. From the viewpoint of printing a fine image with high precision, a CO2 laser processing apparatus capable of limiting the irradiation of the laser 2 to a fine region is preferable.

[0015] The heat radiating member 4 is a member for radiating heat generated in the object 1 (particularly in the vicinity of the processing surface F) by the irradiation of the laser 2. Specifically, the heat radiating member 4 is installed in a state of being in contact with the processing surface F of the object 1. The heat radiating member 4 according to the present embodiment transmits the laser 2. The heat radiating member 4 is formed of a material having a transmittance of 20% or more, preferably 50% or more, and more preferably 70% or more at the oscillation wavelength (peak wavelength) of the laser 2. The laser 2 passes through the heat radiating member 4 and is absorbed by the object 1.

[0016] The thermal conductivity of the heat radiating member 4 is higher than that of the object 1. Further, the thermal conductivity of the heat radiating member 4 is preferably higher than the thermal conductivity of the air in the space where the object 1 is present. Specifically, the thermal conductivity of the heat radiating member 4 is, for example, 1 W / mK or more, preferably 10 W / mK or more, and more preferably 50 W / mK or more. The upper limit value of the thermal conductivity of the heat radiating member 4 is not particularly limited, but is, for example, 150 W / mK or less.

[0017] Note that the thermal conductivity of the object 1 varies depending on the type of the resin composition used for the object 1, but is, for example, 0.2 to 0.4 W / mK. The thermal conductivity of air is, for example, 0.0257 W / mK at 20 degrees.

[0018] As understood from the above description, the material of the heat radiating member 4 is appropriately selected according to the oscillation wavelength of the laser 2 used and the thermal conductivity of the object 1 used.

[0019] For example, when using a laser 2 with an oscillation wavelength in the range of 9 to 11 μm (for example, a CO2 laser with an oscillation wavelength of about 10.6 μm), it is preferable to use, for example, silicon, germanium, zinc selenide, zinc sulfide, etc. that transmit the laser 2 as the heat dissipation member 4.

[0020] When using a laser 2 with an oscillation wavelength in the range of 4 to 6 μm (for example, a CO laser with an oscillation wavelength of about 5 μm), it is preferable to use, for example, silicon, calcium fluoride, magnesium fluoride, barium fluoride, magnesium oxide, etc. that transmit the laser 2 as the heat dissipation member 4.

[0021] When using a laser 2 with an oscillation wavelength in the range of 1 to 3 μm (for example, a thulium-doped laser with an oscillation wavelength of about 1.9 μm or a fiber laser with an oscillation wavelength of about 1.06 μm), it is preferable to use, for example, quartz, sapphire, calcium fluoride, magnesium fluoride, barium fluoride, borosilicate glass, etc. that transmit the laser 2 as the heat dissipation member 4.

[0022] Note that the material of the heat dissipation member 4 is not limited to the above examples. Any material that transmits the laser 2 and has a higher thermal conductivity than the object 1 can be used as the material of the heat dissipation member 4. For example, a heat dissipation member 4 containing a plurality of types of materials and various additives may be used.

[0023] The thickness of the heat dissipation member 4 is appropriately selected according to the material of the heat dissipation member 4 and is not particularly limited. From the viewpoint of suppressing the absorption and scattering of the laser 2 by the heat dissipation member 4 and allowing the laser to reach the object 1 sufficiently, the thickness of the heat dissipation member 4 is preferably, for example, 0.5 to 4.0 mm, and more preferably 1.0 to 2.0 mm.

[0024] Here, assume a laser marking method (hereinafter referred to as "comparative example") in which the laser 2 is directly irradiated onto the surface of the object 1 made of a resin composition. FIG. 2 is a schematic diagram schematically showing the laser marking method according to the comparative example. As shown in FIG. 2, in the comparative example, the processed surface F of the object 1 is in contact with the air.

[0025] However, the thermal conductivity of air is low, and heat transfer from the processed surface F to the surrounding air is poor. Then, the temperature of the processed surface F irradiated with the laser 2 rises rapidly. Furthermore, the resin composition itself often has low thermal conductivity. As a result, in the laser marking method of the comparative example, the portion (hereinafter referred to as "melted portion") 3 melted by the irradiation of the laser 2 instantaneously vaporizes and the damage (for example, excessive deformation and discoloration) becomes severe.

[0026] Also, when the temperature of the object 1 rises and exceeds the decomposition point, foaming occurs within the melted portion 3 to form a foamed portion. In the comparative example, since heat transfer from the processed surface F to the surrounding air is poor, the melted portion 3 becomes extensive. Then, the foamed portions are also formed over a wide range. As a result, the foamed portions are formed over the thickness of the object 1, causing damage such as perforation and cutting. In the laser marking method of the comparative example, particularly when printing an image on a thin-film object 1 having a thickness of 1 mm or less, damage such as perforation and cutting is easily caused.

[0027] As understood from the above description, in the comparative example, there is a problem that the object 1 is damaged and the image cannot be printed with high precision.

[0028] FIG. 3 shows a photograph of an object when an image (QR code (registered trademark)) is actually printed by the laser marking method according to the comparative example. In the comparative example, an object made of a fluororesin (semi-transparent) having a thickness of about 0.1 mm was used, and a laser having an oscillation wavelength of about 10.6 μm (mark speed: 500 mm / s, laser power: 50%) was used. As shown in FIG. 3, it can be confirmed that in the comparative example, the portion irradiated with the laser is excessively deformed and discolored, and further causes perforation and cutting.

[0029] Hereinafter, the laser marking method according to the present invention will be described in detail. As illustrated in FIG. 1, the laser 2 is irradiated from the side of the heat dissipation member 4. Then, the laser 2 transmitted through the heat dissipation member 4 is absorbed by the object 1 and converted into heat to form the melted portion 3. At this time, the heat generated near the processing surface F is transferred by heat conduction to the heat dissipation member 4 having a higher thermal conductivity than the object 1 (moving as shown by the dashed arrow in FIG. 1). Therefore, an excessive temperature rise on the processing surface F is suppressed. Specifically, it is possible to suppress the temperature of the processing surface F from exceeding the melting point of the object 1 (resin composition). As a result of suppressing the excessive temperature rise, the inside of the object 1 can be heated to a higher temperature without causing damage (excessive deformation or discoloration) to the object 1.

[0030] Furthermore, when the inside of the object 1 is heated to a high temperature, the temperature of the object 1 exceeds the decomposition point. When it exceeds the decomposition point, a foamed portion 5 is formed within the melted portion 3 and discolors. In the present invention, since the temperature rise on the processing surface F is suppressed, the range of the melted portion 3 can be limited. And the range of the foamed portion 5 formed within the melted portion 3 can also be limited. Specifically, the range of the foamed portion 5 can be made less than the wall thickness of the object 1. Therefore, the occurrence of damage such as perforation or cutting in the object 1 can be suppressed.

[0031] As understood from the above description, according to the laser marking method of the present invention, damage to the object 1 can be suppressed, so that an image can be printed with high precision. In the present invention, in particular, when the object 1 is in a thin film shape with a thickness of 1 mm or less, it can be suitably used without causing perforation or cutting.

[0032] FIG. 3 also shows a photograph of the case where an image is printed under the same conditions as in the comparative example by the laser marking method according to an example (hereinafter referred to as “example”) of the present embodiment. In the example, silicon was used as the heat dissipation member 4. The thermal conductivity of silicon is 148 W / mK, and the thermal conductivity of the fluororesin as the object 1 is 0.25 W / mK. As shown in FIG. 3, in the example, it can be confirmed that excessive deformation or damage does not occur in the object 1 and an image (the portion that has turned white and discolored) can be printed with high precision.

[0033] In particular, when the object 1 is made of a resin composition that is translucent or transparent, there is a problem that the discoloration by the laser 2 is light and the visibility is poor. Therefore, in order to develop a deep color, it is necessary to cause excessive foaming. However, a resin composition that is translucent or transparent has a narrow temperature range from melting to crystallization, and there is a prominent problem that it easily causes damage such as perforation and cutting. As a result, it is difficult to set the irradiation conditions of the laser 2 to enable appropriate coloring while suppressing damage to the object 1.

[0034] In the present invention, even when the object 1 is made of a resin composition that is translucent or transparent, since the heat generated in the object 1 can be dissipated by the heat dissipation member 4, there is an advantage that an image can be appropriately printed. That is, when the object 1 is made of a resin composition that is translucent or transparent, the present invention is preferably used.

[0035] In the present invention, the translucent resin composition transmits 10% or more and less than 90% of visible light (wavelength range 360 to 780 nm), and transparent transmits 90% or more of visible light.

[0036] Further, when the object 1 is made of a resin composition containing a resin composition having high water repellency, when trying to print an image using ink, there is a problem that the ink is repelled and does not adhere, making it difficult to print an image. On the other hand, in the present invention, an image can be appropriately printed by irradiating the resin composition having high water repellency with the laser 2.

[0037] In particular, in the case of a resin composition mainly composed of a fluororesin (90% by mass or more of the whole), it is translucent or transparent and has very high water repellency. Therefore, the present invention can be preferably used particularly when the object 1 is a resin composition mainly composed of a fluororesin.

[0038] As understood from the above description, according to the laser marking method of the present invention, due to the heat dissipation effect of the heat dissipation member 4 provided on the processing surface F, while suppressing the temperature of the processing surface F from exceeding the melting point of the object 1, it is possible to heat and discolor the object 1 until it exceeds the decomposition point within a limited range inside the object 1. Therefore, damage to the processing surface F can be suppressed and an image can be printed with high precision.

[0039] In addition, the present invention can also be applied when printing an image on the surface of the object 1 in a structure in which the object 1 made of a resin composition is provided on the surface of a base material made of a material other than a resin composition (for example, pulp).

Explanation of Reference Numerals

[0040] 1: Object 2: Laser 3: Melted Portion 4: Heat Dissipation Member 5: Foaming Portion F: Processing Surface

Claims

1. A laser marking method for printing an image by irradiating a surface of an object made of a resin composition with a laser, while installing a heat dissipation member that transmits the laser on the surface of the object, irradiating the surface with the laser, wherein the thermal conductivity of the heat dissipation member is higher than that of the object. Laser marking method.

2. The object has a visible light transmittance of 10% or more. The laser marking method according to Claim 1.

3. The resin composition contains a fluororesin. The laser marking method according to Claim 1 or Claim 2.

4. The thickness of the object is 1 mm or less. The laser marking method according to any one of Claims 1 to 3.

5. The thermal conductivity of the heat dissipation member is lower than that of air. The laser marking method according to any one of Claims 1 to 4.

Images