Method for forming thin film portion using laser

Abstract

To provide a method of forming a thin film part with laser which can form a thin film part on a sheet-like workpiece stably.SOLUTION: When a laser beam L is radiated from the front surface side of a workpiece 10 to perform laser processing, melting of the back surface side of the workpiece is inhibited by means 20 for inhibiting temperature rise in a laser radiation position of the workpiece to form a thin film part 15 at the laser radiation position P of the workpiece. Further, it is preferable that the means for inhibiting the temperature rise be a base member 20A which is disposed contacting tightly with the back surface side of the workpiece.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for forming a thin film portion on a workpiece by irradiating the workpiece with a laser beam. [Background technology]

[0002] For example, molded products made from synthetic resin sheets such as polypropylene (PP) and polyethylene terephthalate (PET) are used for food containers that hold processed foods sold at convenience stores, supermarkets, etc. In recent years, the issue of microplastics has been attracting attention, and in order to reduce the environmental burden, it has been recommended to reduce the use of synthetic resin materials and reuse them.

[0003] For food containers made of synthetic resin, making them smaller (reducing the volume) is an effective way to improve the convenience of disposal, recovery, etc. after use. For example, a structure in which a plurality of bent parts are formed in the body of a container, making the container more likely to be crushed when the container is pushed in from above, is known as a way to make the container smaller (see Patent Document 1). In this way, in order to make a synthetic resin molded product smaller in volume, a portion that can be easily deformed by applying force, such as the bent parts, is provided. However, the bent parts make the molded product more complicated in structure, and improvements were required.

[0004] As a means for allowing a molded product to have a simple structure while being easily deformed, for example, perforations or thin film portions can be formed in the deformed portion. Perforations can be easily formed by mechanical processing or laser processing, but when they are provided in a food container, leakage of contents or entry of foreign matter from the outside is likely to occur. In contrast, thin film portions are thought to enable appropriate deformation without the risk of leakage of contents or entry of foreign matter.

[0005] Incidentally, laser processing is known to be extremely effective as a processing technique for synthetic resins, being fast and low cost. However, while a synthetic resin sheet, for example, is thin and can be easily melted by irradiation with a laser beam, it is not easy to control the laser processing so as to form a thin film portion of an appropriate thickness without penetrating the sheet, due to fluctuations in irradiation conditions. Therefore, the present inventors have conducted extensive research and have found a method for stably forming a thin film portion without penetrating the sheet when irradiating a workpiece with a laser beam. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-141468 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above points, and provides a method for forming a thin film portion by using a laser, which is capable of stably forming a thin film portion on a workpiece. [Means for solving the problem]

[0008] That is, the invention of claim 1 relates to a method for laser processing a workpiece by irradiating the workpiece with a laser beam from the surface side thereof, The temperature rise suppression means is made of a base member arranged in close contact with the back surface of the workpiece. Suppresses temperature rise at the laser irradiation position of the workpiece do The present invention relates to a method for forming a thin film portion by using a laser, which is characterized in that melting of the back side of the workpiece is suppressed, thereby forming a thin film portion at the laser irradiated position of the workpiece.

[0009] The invention of claim 2 is as follows: 2. The method for forming a thin film portion by laser according to claim 1, wherein the temperature rise suppression means is placed in close contact with the back surface of the workpiece by vacuum suction. relates to.

[0010] The invention of claim 3 is a claim in which the base member is a metal plate. 1 or 2 relates to a method for forming a thin film portion using a laser.

[0011] The invention of claim 4 relates to the method for forming a thin film portion by using a laser according to claim 3, wherein the metal plate is made of any one of copper, aluminum, brass, iron, and stainless steel.

[0012] The invention of claim 5 relates to the method for forming a thin film portion by using a laser according to any one of claims 1 to 4, wherein the workpiece is a sheet-like object containing a synthetic resin material. Effect of the Invention

[0013] According to the method for forming a thin film portion by a laser according to the invention of claim 1, when performing laser processing by irradiating a laser beam from the front side of a workpiece, The temperature rise suppression means is made of a base member arranged in close contact with the back surface of the workpiece. Suppresses temperature rise at the laser irradiation position of the workpiece do In order to prevent melting of the back side of the workpiece, thereby forming a thin film portion at the laser irradiation position of the workpiece, The temperature rise suppression effect can be effectively applied to the back side of the workpiece. Even if the irradiation conditions of the laser processing change, the back side of the workpiece will not be penetrated, and a thin film portion can be formed easily and stably.

[0014] According to the method for forming a thin film portion by using a laser according to the invention of claim 2, in the invention of claim 1, Since the temperature rise suppression means is disposed in intimate contact with the back surface side of the workpiece by vacuum suction, the base member can be in intimate contact with the back surface side of the workpiece.

[0015] According to the method for forming a thin film portion by a laser according to the invention of claim 3, 1 or In the second aspect of the present invention, the base member is a metal plate, which has high thermal conductivity and high reflectance and is suitable as a base member, and the base member is less likely to be damaged or deformed during laser processing.

[0016] According to the method for forming a thin film portion by a laser of the invention of claim 4, in the invention of claim 3, the metal plate is made of any of copper, aluminum, brass, iron, and stainless steel, which is easily available, easy to handle, economical, and suitable for industrial use.

[0017] According to the method for forming a thin film portion by using a laser of the invention of claim 5, in the inventions of claims 1 to 4, the workpiece is a sheet-like object containing a synthetic resin material, so that laser processing can be easily performed. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view of a method for forming a thin film portion by using a laser according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged schematic cross-sectional view of a thin film portion of the workpiece. [Diagram 3] 13 is a graph showing the results of measuring the thickness of a thin film portion when laser processing is performed using a copper plate base member. [Figure 4] 13 is a graph showing the results of measuring the thickness of a thin film portion when laser processing is performed without using a base member. [Diagram 5] 13 is a graph showing the results of measuring the thickness of a thin film portion when laser processing is performed using an aluminum plate as a base member. [Figure 6] 13 is a graph showing the results of measuring the thickness of a thin film portion when laser processing is performed using a brass plate as a base member. [Figure 7] 13 is a graph showing the results of measuring the thickness of a thin film portion when laser processing is performed using a steel plate as a base member. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] 1 is a schematic cross-sectional view showing a method for forming a thin film portion by a laser according to one embodiment of the present invention. In this embodiment, when a laser beam L is irradiated from the front side of a sheet-like workpiece 10 to perform laser processing, melting of the back side of the workpiece 10 is suppressed by means 20 for suppressing a temperature rise at the laser irradiation position P of the workpiece 10, thereby forming a thin film portion 15 at the laser irradiation position P of the workpiece 10.

[0020] Examples of the laser processing include known processing methods using an appropriate laser such as a CO2 laser (carbon dioxide laser). The output of the laser is not particularly limited, and may be a continuous wave (CW) laser or a pulsed laser, but a continuous wave laser capable of high-speed processing is suitable for industrial use such as mass production and is therefore preferred.

[0021] The workpiece 10 is a sheet-like object made of a material containing a synthetic resin material that is easily laser-machined by irradiation with a laser beam L. Examples of the workpiece 10 include sheet materials made of known synthetic resin materials such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET). These resin materials are easy to obtain and have excellent formability, making them suitable for industrial use. From the viewpoint of reducing environmental impact, it is also possible to use sheet materials made of synthetic resin materials containing inorganic fillers such as talc (filler-containing polypropylene; PPF, etc.). The thickness of the workpiece 10 is appropriate, but is, for example, about 0.2 to 1 mm.

[0022] The thin film portion 15 is a portion formed by irradiation of the laser beam L from the front side of the workpiece 10 so as to be thinner than the thickness of the workpiece 10. As shown in Fig. 2, in this thin film portion 15, at the irradiation position P of the laser beam, the front side of the workpiece 10 is removed in a groove shape by the laser irradiation, and the back side is not melted and becomes a non-penetrating portion that maintains a predetermined thickness (T). The width and length of the thin film portion 15 can be appropriately designed.

[0023] The processed material 10, which is a sheet-like material containing a synthetic resin, is preferably used as a material for molded bodies such as containers for processed foods sold at convenience stores, etc. When the processed material 10 is molded and used as a food container, the thin film portion 15 is preferably formed on the body of the container. In such a container, by pushing the container from above, the thin film portion 15 functions as a deforming portion without a complex structure, making it possible to reduce the volume of the container. In addition, since the thin film portion 15 is a non-penetrating portion, there is no risk of foreign matter being mixed in or the contents leaking out when used as a container, and the strength of the container is not impaired.

[0024] The means 20 for suppressing temperature rise prevents the back side of the workpiece 10, which is opposite the front side irradiated with the laser beam, from reaching a temperature at which the back side would be melted by laser irradiation, thereby preventing melting of the back side of the workpiece 10.

[0025] During laser processing, the workpiece 10 is melted or evaporated at the laser irradiation position P by the heating of the laser irradiation, and is removed from the front side toward the back side. At this time, the temperature rise suppression means 20 acts on the back side corresponding to the laser irradiation position P of the workpiece 10, and it is considered that the temperature rise suppression effect exceeds the heating of the laser irradiation, and the part corresponding to the predetermined thickness (T) on the back side is kept at a temperature at which it will not melt. In this way, the back side of the workpiece 10 does not reach the melting temperature even during laser irradiation, so melting is suppressed. Therefore, the laser irradiation position P of the workpiece 10 becomes a thin film portion 15 where the front side has been removed and the back side is not penetrated.

[0026] The temperature rise suppression means 20 is not particularly limited as long as it is a means capable of controlling the temperature so that the back side of the workpiece 10 does not reach the melting temperature caused by laser irradiation during laser processing. For example, in addition to a base member such as a metal plate as shown in the examples, air-cooling means such as air blowing or assist gas, water-cooling means, and other appropriate temperature adjustment devices can be mentioned.

[0027] The temperature rise suppression means 20 is preferably a base member 20A that is placed in close contact with the back surface of the workpiece 10. This base member 20A is a plate-like member having a flat surface on which the workpiece 10 can be placed, and it is considered that a state of thermal equilibrium is formed between the back surface of the workpiece 10 and the base member 20A by placing the back surface of the workpiece 10 in close contact with the flat surface. Therefore, the base member 20A is preferably made of a material that has a thermal conductivity that is significantly higher than the thermal conductivity of the workpiece and has a high reflectance for the laser beam (is less likely to absorb the laser beam).

[0028] It is believed that the high thermal conductivity base member has a higher thermal conductivity than the workpiece, and therefore functions to maintain a thermal equilibrium state rather than a temperature rise caused by laser irradiation on the back surface of the workpiece 10. In addition, since the high reflectivity (low absorptivity) base member does not easily absorb the laser beam, the temperature rise caused by absorption of the laser beam is suppressed, and damage, deformation, etc. can be suppressed, and deterioration of the product quality, etc. can be prevented.

[0029] In practice, it is preferable to use a metal plate for the base member 20A. The metal plate has high thermal conductivity and high reflectance, and has a melting temperature higher than the sublimation temperature of the workpiece 10 containing a synthetic resin material. Therefore, even if the laser irradiation position P of the workpiece 10 is heated to the sublimation temperature during laser processing, the base member 20A is unlikely to be damaged or deformed. The metal plate is preferably made of any of copper, aluminum, brass, iron, and stainless steel. These metal plates are easily available, can be installed with little modification to existing equipment, and are easy to handle, making them suitable for industrial use.

[0030] The workpiece 10 is placed in close contact with the base member 20A by an appropriate method such as vacuum suction. In this embodiment, suction holes 21 are formed in a plurality of locations in the base member 20A, and the workpiece 10 and the base member 20A are vacuum-suctioned through the suction holes 21 to bring them into close contact. By bringing the workpiece 10 and the base member 20A into close contact with each other, the temperature rise suppression effect can be more efficiently exerted on the back side of the workpiece 10.

[0031] In the method for forming a thin film portion of the present invention, by using the base member 20A, the thickness T of the thin film portion 15 (the remaining thickness on the back side of the workpiece 10) is formed to be almost constant even if the energy of the laser irradiation increases. Therefore, the thin film portion 15 can be formed easily and stably without finely controlling the conditions of the laser irradiation.

[0032] In addition, the base member 20A can be used in a normal temperature (room temperature) environment, but if it is possible to prevent the back side of the workpiece 10 from reaching the melting temperature during laser processing and to prevent melting, it may be heated or cooled as appropriate. By controlling the temperature of the back side of the workpiece 10 that comes into contact with the base member 20A by heating or cooling, it is possible to adjust the thickness of the thin film portion 15 by adjusting the suppression of temperature rise on the back side. EXAMPLES

[0033] [Formation of thin film part] A CWCO2 laser (LP-431U manufactured by Panasonic Corporation) with a spot size of 100 μm and focal length of 111 mm was used to place a 300 μm thick transparent PP sheet (workpiece) on a base member made of a 10 mm thick copper plate that can be vacuum-suctioned, and vacuum-suction was performed at 21 kPa to bring the back side of the transparent PP sheet into close contact with the base member. The laser was focused on the surface of the transparent PP sheet and irradiated with a laser beam to perform one 10 mm long scan, thereby performing laser processing on the surface of the PP sheet. The laser irradiation conditions were a wavelength of 10.6 μm, an output of 30 W, and a laser scan speed of 60 to 150 mm / s. The copper plate used as the base member had a thermal conductivity of 401 W / m·K, an absorptivity of 1% at a wavelength of 10.6 μm, and a melting temperature of 1084°C.

[0034] After laser processing, a laser interferometer (Keyence Corporation; SI-F1000V and SI-F80) was used to measure the thickness of the center of the thin film formed on the PP sheet. Table 1 shows the measurement results, including the energy linear density P / S (energy per unit length; J / m) and the thickness (μm) of the thin film for each laser scanning speed, and Figure 3 shows a graph with the energy linear density (P / S: unit is J / m) on the horizontal axis and the thin film thickness (μm) on the vertical axis. In the energy linear density, P is the laser output (W) and S is the laser scanning speed (mm / s).

[0035] [Table 1]

[0036] As a comparative example, a base member was not placed on the back side of the workpiece, and laser processing was performed on the surface of a PP sheet by a conventional laser processing method in which the back side of the workpiece was air. The laser scan speed was 115 to 600 mm / s. The measurement results are shown in Table 2 and the graph in Figure 4.

[0037] [Table 2]

[0038] [Comparison of base materials] Instead of copper plates, aluminum plates, brass plates, and steel plates (JIS SS400) were used as base members, and laser processing was performed on the surface of the PP sheet. The thickness of each base member and the conditions of vacuum suction were the same as those for the copper plate, and the laser scanning speed was 75 to 120 mm / s. The measurement results are shown in Table 3 and the graphs in Figures 5 to 7. The aluminum plate has a thermal conductivity of 236 W / m K, an absorptivity of 1% at a wavelength of 10.6 μm, and a melting temperature of 660°C. The brass plate has a thermal conductivity of 111 W / m K, an absorptivity of 2% at a wavelength of 10.6 μm, and a melting temperature of 930°C. The steel plate has a thermal conductivity of 50 W / m K, an absorptivity of 10% at a wavelength of 10.6 μm, and a melting temperature of 1500°C.

[0039] [Table 3]

[0040] [Results and Discussion] First, in the comparative example using the conventional laser processing method not using a base member shown in Table 2 and Figure 4, it was confirmed that the thickness of the thin film portion decreased (the processed portion of the PP sheet became deeper) as the energy linear density (P / S) increased, and when the energy linear density (P / S) was 210 to 250 J / m, there were some parts of the thin film portion that were partially penetrated. Also, when the energy linear density (P / S) was 260 J / m, the laser processed portion penetrated completely, and it was not possible to form a thin film portion.

[0041] In contrast, when a copper plate was placed in close contact with the back side of the PP sheet as a base member, as can be seen from Table 1 and Figure 3, the thickness of the thin film portion decreased with an increase in the energy linear density (P / S), and the thin film portion was stably formed at a thickness of 50 to 60 μm when the energy linear density (P / S) was 280 J / m or more. As can be seen from the comparison with the comparative example, in the conventional method, if the laser was irradiated excessively, the laser-processed portion of the PP sheet would be penetrated, but by placing a copper plate (base member) in close contact with the back side of the PP sheet, it was found that even if the laser was irradiated excessively, the laser-processed portion (thin film portion) would not be penetrated and an almost constant thickness was maintained.

[0042] Furthermore, when aluminum, brass, or steel plates were used as the base member instead of copper plates, a non-penetrating thin film of approximately constant thickness was formed even when excessive laser irradiation was performed, just like with copper plates, as can be seen from Table 3 and Figures 5 to 7. The thermal conductivity of copper, aluminum, brass, and steel plates is all significantly higher than that of PP sheet (0.1 to 0.2 W / m K), and it was found that they can be suitably used as base members.

[0043] As shown and described above, in the method for forming a thin film portion by a laser according to the present invention, when a laser beam is irradiated from the front side of a workpiece to perform laser processing, a means for suppressing a temperature rise at the laser irradiation position of the workpiece is used to suppress melting of the back side of the workpiece and form a thin film portion at the laser irradiation position, so that even if the irradiation conditions for laser processing fluctuate and excessive laser irradiation is performed, the back side of the workpiece is not penetrated and a predetermined thickness can be maintained. Therefore, even if an error occurs in the output of the irradiated laser beam, a thin film portion can be appropriately formed. In other words, a thin film portion of approximately constant thickness can be stably formed without finely controlling the laser irradiation. In addition, if a base member such as a metal plate is placed in close contact with the back side of the workpiece, a thin film portion can be formed more simply, efficiently and stably. [Industrial Applicability]

[0044] As described above, the method for forming a thin film portion by a laser of the present invention can easily and stably form a thin film portion by laser processing without complex laser control. In addition to manufacturing commercially available food containers, it can be used for processing various products. [Explanation of symbols]

[0045] 10 Work material 15 Thin Film Section 20 Temperature rise suppression measures 20A Base material (metal plate) 21 Suction hole L Laser beam P Laser irradiation position T is the thickness of the thin film

Claims

1. A method for forming a thin film portion by a laser, characterized in that, when laser processing is performed by irradiating a laser beam from the front side of a workpiece, a temperature rise suppression means consisting of a base member arranged in close contact with the back side of the workpiece suppresses the temperature rise at the laser irradiation position of the workpiece, thereby preventing melting of the back side of the workpiece, thereby forming a thin film portion at the laser irradiation position of the workpiece.

2. A method for forming a thin film portion using a laser as described in claim 1, wherein the temperature rise suppression means is placed in close contact with the back side of the workpiece by vacuum suction.

3. 3. The method for forming a thin film portion by using a laser according to claim 1, wherein the base member is a metal plate.

4. 4. The method for forming a thin film portion by using a laser according to claim 3, wherein the metal plate is made of any one of copper, aluminum, brass, iron and stainless steel.

5. 5. The method for forming a thin film portion by using a laser according to claim 1, wherein the workpiece is a sheet-like object containing a synthetic resin material.

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