Metal-resin composite molded article, method for processing metal member, and method for manufacturing metal-resin composite molded article

Abstract

One embodiment of the present invention is a metal-resin composite molded article in which a metal member and a thermoplastic resin are joined. In the metal-resin composite molding, recesses and projections are formed on a joining surface of one surface of the metal member that is joined to the thermoplastic resin, substantially spherical clusters are formed on the joined surface portion, and the arithmetic average curvature of the vertexes of the clusters is 2500-5000 (1 / mm).

Description

Technical Field

[0001] The present invention relates to a technique for joining a metal member and a thermoplastic resin. Background Art

[0002] By using a combination of materials with different properties such as a conductive material such as metal and an electrically insulating material such as resin, components that have been lightened, strengthened, or highly functionalized are used in various fields. For example, a metal-resin composite molded product in which a metal member and a thermoplastic resin are joined is used for interior components of an automobile such as a console box around a dashboard, engine peripheral components, interior decoration components, housings of electronic devices such as digital cameras and mobile phones, interface connection parts, power terminal parts, and the like.

[0003] As a method of joining different materials such as metal and resin to each other, processes such as adhesion and screw fastening are generally known, but the number of processes and components increases, so they are not preferable. Therefore, various proposals are known as methods for joining a metal material and a resin material.

[0004] For example, Japanese Patent No. 4020957 describes the following method: laser processing is performed along a certain scanning direction on the surface of a metal material, and laser processing is performed on another scanning direction intersecting with the scanning direction, so that different types of materials are joined to the surface. Japanese Unexamined Patent Application Publication No. 2020-116806 describes the following method: when forming unevenness on the surface of a metal plate, the undercut rate of the unevenness is within a specified range, thereby improving the joining strength when a resin molded product is joined to the surface. Japanese Unexamined Patent Application Publication No. 2013-71312 describes the following composite molded body, which is a composite molded body of metal and resin in which a pit-shaped depression is formed on a metal by a laser beam or the like, and granular sputtering is formed on a cap-shaped raised portion that melts and scatters on the metal surface. Japanese Patent No. 6819798 describes a composite structure in which a surface-roughened metal member and a PPS member are joined. When measuring any five points on the surface of the surface-roughened metal member with a confocal microscope according to ISO 25178, the developed area ratio (Sdr) of the interface is in the range of 5 or more on average, and the melt viscosity of the PPS resin is in the range of 15 to 500 [Pa·s]. Summary of the Invention

[0005] Problems to be Solved by the Invention

[0006] However, for existing methods of joining a metal material and a resin material, it is not possible to sufficiently ensure the airtightness of the joint portion between the metal material and the resin material, and improvement in this regard is required.

[0007] Therefore, an object of the present invention is to improve the airtightness of the joint portion when joining a metal member and a resin member.

[0008] Solution for solving problems

[0009] The first aspect of the present invention is a metal-resin composite molded product in which a metal member and a thermoplastic resin are joined. In this metal-resin composite molded product, for the surface property of the surface portion of one surface of the metal member that is joined to the thermoplastic resin, the arithmetic mean curvature of the apex is 2500 to 5000 (1 / mm).

[0010] The second aspect of the present invention is a method for processing a metal member. In this processing method, by irradiating the surface of the metal member with a high-energy beam, a surface property is formed such that the arithmetic mean curvature of the apex of the surface becomes 2500 to 5000 (1 / mm).

[0011] The third aspect of the present invention is a method for manufacturing a metal-resin composite molded product in which a metal member and a thermoplastic resin are joined. In this manufacturing method, a surface property is formed such that the arithmetic mean curvature of the apex of the surface of the metal member becomes 2500 to 5000 (1 / mm) by irradiating the surface of the metal member with a high-energy beam. Then, the metal member is inserted into a mold, and the thermoplastic resin is injection-molded, whereby the thermoplastic resin is joined to the aforementioned surface of the metal member.

[0012] Effects of the invention

[0013] According to one aspect of the present invention, the airtightness of the joined portion can be improved when a metal member and a resin member are joined. Description of the drawings

[0014] Figure 1 It is a diagram schematically showing a method for processing a metal member according to an embodiment.

[0015] Figure 2 It is a diagram showing an exemplary cluster image formed in the laser irradiation portion of the metal member.

[0016] Figure 3 It is a diagram schematically explaining the interface state between the metal member and the resin member that conforms to the size of the Spc of the surface of the resin member in a metal-resin composite molded product according to an embodiment.

[0017] Figure 4 It is a diagram showing the shape of a test piece used in the airtightness test.

[0018] Figure 5 It is a diagram showing the schematic configuration of a test apparatus for the airtightness test.

[0019] Figure 6 Based on the test results of the airtightness test of the examples and comparative examples, the Spc of the surface of the resin member is plotted and Figure 5Graph showing the relationship of the detected pressure in the test device. Detailed implementation mode

[0020] Hereinafter, a metal-resin composite molded product according to an embodiment of the present invention will be described.

[0021] A metal-resin composite molded product according to an embodiment is formed by joining a metal member and a thermoplastic resin. In this metal-resin composite molded product, irregularities are formed on the joint surface that is joined to the thermoplastic resin on one surface of the metal member.

[0022] In one embodiment, the irregularities on the joint surface are formed by clusters that are substantially spherical. For "substantially spherical", the respective shapes of the clusters are not limited to spheres, and also include ellipsoids, shapes in which a part of a sphere or an ellipsoid is missing, etc.

[0023] The substantially spherical clusters can be formed by irradiating the surface of the metal member with, for example, a laser. For example, by irradiating the surface of the metal member with a laser under specified irradiation conditions, spherical clusters can be formed on the metal surface.

[0024] The inventors of the present application conducted in-depth research and found that: by making the surface property of the joint surface that is joined to the thermoplastic resin on one surface of the metal member be the desired surface roughness, the airtightness of the joint surface between the metal and the resin of the metal-resin composite molded product is improved more than before. In the following embodiments, the case where the desired surface roughness is achieved by forming substantially spherical clusters on the joint surface between the metal member and the thermoplastic resin will be described, but it is not limited thereto. As long as the desired surface roughness can be achieved on the joint surface between the metal member and the thermoplastic resin, the surface treatment method for achieving it is not limited.

[0025] It should be noted that the shape of the metal-resin composite molded product is not particularly limited, and the present invention can be applied to metal-resin composite molded products of any shape.

[0026] The metal member contained in the metal-resin composite molded product is not limited, and examples include aluminum, copper, silver, gold, iron, titanium, nickel, magnesium, zinc, and carbon steel, stainless steel, etc. belonging to their alloys.

[0027] In addition, surface treatment such as anodizing treatment and painting can also be performed on the surface of the metal material. From the aspects of light weight and strength, aluminum, magnesium, copper, and titanium are preferred. In applications such as terminals that require conductivity, aluminum and copper are more preferred, and copper is particularly preferred. In addition, in applications that require thin-wall stiffness, magnesium and titanium are preferred, and titanium is particularly preferred.

[0028] The resin contained in the metal-resin composite molded product is preferably a thermoplastic resin that is easy to process by injection molding.

[0029] Examples of suitable thermoplastic resins include polyoxymethylene (POM), polyamide (PA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polycarbonate (PC), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyetheretherketone (PEEK), styrene resin, acrylic resin, etc.

[0030] The method of joining the metal member and the resin is not limited, and joining can be performed by injection molding. For example, joining can be performed by insert molding in which a metal material is an insert member.

[0031] Figure 1 The processing method of the metal member of one embodiment is schematically shown.

[0032] As Figure 1 As shown, when the metal member is irradiated with a laser, the metal on the surface of the metal member melts due to the high-energy beam based on the laser, and after being extruded to the outside of the irradiation portion, it solidifies into a spherical shape due to surface tension, thereby forming irregularities on the surface of the metal member. In one embodiment, spheres generated by laser scanning the surface of the metal member at a minute interval overlap to form a cluster. Alternatively, the sublimated or scattered liquid metal particles of the metal member solidify (recondense) and deposit to form a spherical cluster. Figure 2 An exemplary image of the cluster formed in the laser irradiation portion when the metal member is irradiated with a laser is shown.

[0033] Here, when the laser output power (energy per unit time) is low, the metal on the metal surface does not melt, or sublimation and scattering of liquid metal particles do not occur. Therefore, the laser output power for forming the spherical cluster is appropriately determined according to the metal material used in the metal member. In addition, in order to make the molten metal extruded to the outside of the laser irradiation portion form minute spheres, the laser scanning pitch is preferably 30 μm or less, more preferably 20 μm or less, and further preferably 10 μm or less.

[0034] It should be noted that the energy provided to the metal surface per unit time per unit area is determined according to the laser output power and the irradiation speed. Therefore, in addition to the laser output power, the irradiation speed also becomes a factor in forming the spherical cluster. According to the laser output power and the irradiation speed, a local temperature rise in a very short time occurs on the metal surface, thereby forming a spherical cluster.

[0035] In addition, from the viewpoint of sufficiently ensuring airtightness when joining with the resin, it is preferable to form spherical clusters on the entire surface of the joining surface of the metal member and the resin. For this purpose, it is best to make the laser scanning pitch smaller than the irradiation diameter of the laser.

[0036] In the present disclosure, the "high energy beam" refers to a beam of energy per unit time that is high enough to form spherical clusters on the surface of a metal component.

[0037] Typically, the high energy beam is a laser, but it is not limited thereto, and it can also be a beam generated by an electron gun.

[0038] A method for manufacturing a metal-resin composite molded product according to an embodiment is as follows: By irradiating a high energy beam such as a laser on the surface of a metal component to form irregularities on the surface of the metal component, and then melting and joining the metal component with irregularities formed on its surface to a thermoplastic resin. In one embodiment, substantially spherical clusters are formed on the surface (bonding surface) of the metal component.

[0039] By forming spherical clusters on the bonding surface of the metal component with the resin, when the metal component and the thermoplastic resin are insert-molded, the molten resin is incorporated into the part of the spherical clusters, and the adhesion between the metal and the resin becomes higher at the molding stage. Therefore, in the manufactured metal-resin composite molded product, a higher airtightness than before can be achieved at the bonding surface of the metal component.

[0040] The range where spherical clusters are formed on the surface of the metal component is preferably the entire surface of the bonding surface of the metal component with the resin, but it is not limited thereto. For example, if spherical clusters are formed in most of the bonding surface, such as in a range of 70% to 80% or more of the bonding surface, a sufficiently high airtightness can be ensured at the bonding surface of the metal component.

[0041] For example, when the entire surface of the bonding surface of the metal component with the resin is the irradiation target of the laser, if the scanning pitch of the laser is larger than the irradiation diameter of the laser, an area where the laser is not irradiated is generated on the bonding surface. In this case, when the area where the laser is not irradiated on the bonding surface is relatively small, a sufficiently high airtightness can also be ensured at the bonding surface of the metal component.

[0042] The inventors of the present application further focused on the shape of the spherical clusters formed on the surface of the metal component, and advanced research on the relationship between various surface roughness parameters of the surface of the metal component and the airtightness of the bonding surface of the metal component with the resin. As a result, it was found that by making the Spc (arithmetic mean curvature of the peak vertex) of the vertex of the spherical cluster within a specified range, the airtightness can be significantly improved. Spc (arithmetic mean curvature of the peak vertex) is a parameter of the surface characteristics specified in ISO25178, and represents the average of the principal curvatures of the peak vertices formed on the surface of the evaluation object.

[0043] The reason for the improvement of the airtightness of the bonding surface of the metal component with the resin by making the Spc of the vertex of the spherical cluster within a specified range is speculated as follows. Figure 3 It is speculated as follows.

[0044] Figure 3 This is a schematic diagram showing the bonding surface between a metal member and a resin for the cases of large Spc values (“Spc large”), medium Spc values (“Spc medium”), and small Spc values (“Spc small”) at the vertices of spherical clusters formed on the surface of the metal member. It is speculated that in the case of large Spc, the vertices of the spherical clusters become sharp, and when the thermoplastic resin cools, indentations (shrinkage) are generated. However, since the vertices of the clusters are sharp, gaps are likely to occur between the resin and the metal at the bonding surface of these vertices, which is disadvantageous in terms of airtightness. On the other hand, in the case of small Spc, the spherical clusters as a whole have a gently varying surface shape, so the surface area of the joint part is small, and the adhesion between the metal and the resin is not very high during the molding stage. Therefore, in the case of medium Spc, the incorporation of the molten resin into the part of the spherical clusters on the surface of the metal member becomes sufficient incorporation, and the adhesion between the metal and the resin becomes extremely high during the molding stage.

[0045] Specifically, the Spc at the vertices of the spherical clusters on the surface of the metal member is preferably in the range of 2500 - 5000 (1 / mm), more preferably in the range of 3000 - 5000 (1 / mm), and most preferably in the range of 3500 - 5000 (1 / mm).

[0046] When adjusting so that the Spc falls within the desired range, the energy provided to the bonding surface between the metal member and the resin by laser irradiation is controlled. When using pulsed laser as the laser, if the average output power is set as P and the frequency is set as f, the energy E per pulse is represented by P / f. Therefore, by adjusting the average output power P (so-called laser output power) and / or the frequency f, the energy provided to the bonding surface between the metal member and the resin can be controlled. For example, if the frequency of the pulsed laser is increased, the energy per pulse imparted to the surface of the metal member becomes smaller, so there is a tendency for Spc to decrease. Conversely, if the frequency of the pulsed laser is decreased, the energy per pulse imparted to the surface of the metal member becomes larger, and there is a tendency for Spc to increase. However, if the energy becomes large enough, Spc reaches saturation. In addition, even under the same laser irradiation conditions, there is a possibility that Spc changes according to environmental conditions (for example, if the environmental temperature is low, it is considered that there is a possibility of Spc decreasing). Therefore, it is necessary to confirm whether the Spc is within the desired range after laser irradiation. Specific Examples

[0048] Hereinafter, examples of the metal-resin composite molded product will be described.

[0049] In the examples, as test pieces, metal-resin composite molded products 10 having the Figure 4 shown shape were fabricated (hereinafter referred to as “test pieces 10”).

[0050] As shown Figure 4 in Figure 4 , the test piece 10 is composed of an annular metal member 11 having an inner hole in the center and a resin molded product 12 disposed in the inner hole of the metal member 11. The outer diameter of the metal member 11 is The diameter of the inner hole is and the thickness is 1 mm. The outer diameter of the resin molded product 12 is and the thickness is 3 mm.

[0051] As the metal member 11 and the resin molded product 12, the following materials are used.

[0052] · Metal member: Aluminum A5052, Copper C1100

[0053] · Thermoplastic resin:

[0054] Polyphenylene sulfide (PPS) (Durafide (registered trademark) 1140A6 (manufactured by Polyplastics Co., Ltd.))

[0055] Polybutylene terephthalate (PBT) (Duranex (registered trademark) 930MA (manufactured by Polyplastics Co., Ltd.))

[0056] Polyphenylene sulfide (PPS) (Durafide (registered trademark) 6150T73 (manufactured by Polyplastics Co., Ltd.))

[0057] Before bonding to the resin molded product 12, using a laser processing machine (ML-7350DL manufactured by AMADAWELD TECH), the surface of the metal member 11 to range (bonding surface with the resin molded product 12) is laser-treated in a concentric circle pattern.

[0058] The laser irradiation conditions of Examples 1 to 6 are shown in Table 1 described later. The laser irradiation conditions of Comparative Examples 1 to 11 are shown in Tables 2 and 3 described later. Although not described in the table, for all Examples and Comparative Examples, the irradiation pitch of the laser is set to 10 μm and the irradiation diameter is set to 58 μm. The pitch is the interval between the concentric circles of the scanned laser. Since the pitch is smaller than the irradiation diameter, the entire bonding surface is irradiated with the laser.

[0059] For all Examples and Comparative Examples, the surface of the metal member 11 was observed with a SEM (scanning electron microscope), and as a result, spherical clusters were confirmed to be formed on the entire surface. Furthermore, using a laser microscope VK-X3000 manufactured by KEYENCE CORPORATION, the Spc of the vertices of the spherical clusters formed on the surface of the metal member 11 was measured (refer to Tables 1 to 3).

[0060] In Comparative Examples 1, 7, and 8, the laser output power was relatively low and the frequency was high. Therefore, it can be seen that the energy of each pulse imparted to the surface of the metal member 11 became small and the Spc was low.

[0061] After the laser treatment of the metal member 11, under the following conditions, the metal member 11 was joined by insert molding as an insert member, whereby it was molded into Figure 4 the test piece 10 shown.

[0062] · Injection molding machine: TR100EH manufactured by Sodick Co., Ltd.

[0063] · Barrel temperature: 320 °C (for 1140A6 and 6150T73), 260 °C (for 930MA)

[0064] · Mold temperature: 150 °C

[0065] · Injection speed: 15 mm / s

[0066] · Holding pressure: 50 MPa

[0067] Next, an airtightness test was performed on the molded test pieces 10 of the examples and comparative examples. The configuration of the test apparatus for the airtightness test (helium leak test, vacuum method) is shown in Figure 5 .

[0068] As Figure 5 shown, the jig 2 and the test piece 10 are arranged in the chamber 3 sealed from the outside. The jig 2 has a bottomed rectangular parallelepiped shape, and the test piece 10 is arranged on the upper part, so that the inside of the jig 2 and the remaining part inside the chamber 3 are sealed. The valve 6 is opened, and the inside of the jig 2 is evacuated by the vacuum pump 5. Then, the valve 6 is closed, and the chamber 3 is filled with helium from the helium gas cylinder 4. The helium leaking from the joint portion of the test piece 10 in the chamber 3 is detected by the helium detector 7. The control device 8 displays the detection result of the helium.

[0069] Note that a helium leak detector G-FINE manufactured by Cosmo Instruments Co., Ltd. and an L300i manufactured by INFICON Co., Ltd. are used as the helium detector 7.

[0070] The pressure of helium in the chamber 3 is made 400 kPa, and the vacuum pressure in the jig 2 is made 100 kPa. When the airtightness of the joint portion between the metal member 11 and the resin molded product 12 of the test piece 10 is low, the helium in the chamber 3 flows into the jig 2 and is detected by the helium detector 7. In this test, the pressure of the helium detected by the helium detector 7 (detection pressure) is 1.0×10 -7(=1.0E-7)Pa·m 3 / s or more is considered as airtightness NG, and less than 1.0×10 -7 (=1.0E-7)Pa·m 3 / s, the airtightness is judged to be OK.

[0071] Regarding the detection pressure of the airtightness test on the test piece, Table 1 shows the results of Examples 1 to 6, and Tables 2 and 3 show the results of Comparative Examples 1 to 11.

[0072] [Table 1]

[0073] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Resin 1140A6 1140A6 930MA 1140A6 6150T73 6150T73 Metal A5052 C1100 A5052 A5052 C1100 C1100 Laser output power (W) 11.3 11.3 19.5 9.6 19.5 44.0 Frequency (kHz) 50 50 5 50 50 50 Irradiation speed (mm / s) 1000 1000 1000 1000 1000 1000 Laser scanning pitch (μm) 10 10 10 20 10 10 Spc (1 / mm) 4799 3701 4627 4003 3896 4999 <![CDATA[Detection pressure (Pa·m 3 / s)]]> 1.0E-10 1.0E-11 1.0E-9 1.0E-10 1.0E-10 1.0E-10

[0074] [Table 2]

[0075] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Resin 1140A6 1140A6 1140A6 1140A6 1140A6 1140A6 Metal A5052 A5052 A5052 A5052 A5052 A5052 Laser output power (W) 11.3 15.5 19.5 44 44 44 Frequency (kHz) 100 50 50 50 50 50 Irradiation speed (mm / s) 1000 1000 1000 1000 500 100 Laser scanning pitch (μm) 10 10 10 10 10 10 Spc (1 / mm) 2091 5208 5427 5871 6341 7419 <![CDATA[Detection pressure (Pa·m 3 / s)]]> 1.0E-5 1.0E-7 1.0E-6 1.0E-5 1.0E-5 1.0E-5

[0076] [Table 3]

[0077] Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Comparative Example 11 Resin 1140A6 930MA 930MA 930MA 930MA Metal C1100 A5052 A5052 A5052 A5052 Laser output power (W) 16 16 32 32 32 Frequency (kHz) 100 100 50 50 50 Irradiation speed (mm / s) 1000 1000 1000 500 100 Laser scanning pitch (μm) 10 10 10 10 10 Spc (1 / mm) 1200 2091 5871 6341 7419 <![CDATA[Detection pressure (Pa·m 3 / s)]]> 1.0E-5 1.0E-5 1.0E-6 1.0E-6 1.0E-5

[0078] Figure 6 This is a graph in which the relationship between the detection pressure of the airtightness test and the Spc of the apex of the spherical cluster formed on the surface of the metal member 11 is plotted for Examples 1 to 6 and Comparative Examples 1 to 11.

[0079] Depend on Figure 6 It was confirmed that when the Spc of the apex of the cluster is 2500 to 5000 (1 / mm), the airtightness of the joint between the metal component and the resin is high (that is, the detection pressure is low). When the Spc of the apex of the cluster is 3000 to 5000 (1 / mm), the detection pressure of the airtightness test is preferably lower. When the Spc of the apex of the cluster is 3500 to 5000 (1 / mm), the detection pressure of the airtightness test is further lower, which is more preferred.

[0080] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. In addition, the above embodiments can be variously improved and modified within the scope not departing from the gist of the present invention.

[0081] The present invention is related to patent application No. 2022-178512 filed with the Japan Patent Office on November 8, 2022, and the entire contents of the application are incorporated into the specification of the present application by reference.

Claims

1. A metal-resin composite molded article, which is a metal-resin composite molded article in which a metal member and a thermoplastic resin are joined, wherein, the arithmetic mean curvature of the vertices of the surface portion of one surface of the metal member that is joined to the thermoplastic resin is 2500 to 5000 (1 / mm).

2. The metal-resin composite molded article according to claim 1, wherein, substantially spherical clusters are formed on the surface portion, and the arithmetic mean curvature of the vertices of the clusters is 2500 to 5000 (1 / mm).

3. The metal-resin composite molded article according to claim 1, wherein, the arithmetic mean curvature of the vertices of the surface portion is 3000 to 5000 (1 / mm).

4. The metal-resin composite molded article according to claim 1, wherein, the arithmetic mean curvature of the vertices of the surface portion is 3500 to 5000 (1 / mm).

5. A method for processing a metal member, the processing method is carried out as follows: By irradiating a high-energy beam on the surface of the metal member, the arithmetic mean curvature of the vertices of the surface is made 2500 to 5000 (1 / mm).

6. A method for processing a metal member, the processing method is carried out as follows: By irradiating a high-energy beam on the surface of the metal member, substantially spherical clusters with an arithmetic mean curvature of the vertices of 2500 to 5000 (1 / mm) are formed on the surface.

7. The method for processing a metal member according to claim 5, wherein, the arithmetic mean curvature of the vertices of the surface is 3000 to 5000 (1 / mm).

8. The method for processing a metal member according to claim 5, wherein, the arithmetic mean curvature of the vertices of the surface is 3500 to 5000 (1 / mm).

9. A method for manufacturing a metal-resin composite molded article, which is a method for manufacturing a metal-resin composite molded article in which a metal member and a thermoplastic resin are joined, the manufacturing method is carried out as follows: Insert a metal member whose surface has an arithmetic mean curvature of the vertices of 2500 to 5000 (1 / mm) by irradiating a high-energy beam on the surface of the metal member into a mold, and injection mold the thermoplastic resin, thereby joining the thermoplastic resin to the surface of the metal member.

10. A method for manufacturing a metal-resin composite molded article, which is a method for manufacturing a metal-resin composite molded article in which a metal member and a thermoplastic resin are joined, the manufacturing method is carried out as follows: By irradiating a high-energy beam on the surface of the metal member, substantially spherical clusters with an arithmetic mean curvature of the vertices of 2500 to 5000 (1 / mm) are formed on the surface, insert the metal member having substantially spherical clusters formed on the surface into a mold, and injection mold the thermoplastic resin, thereby joining the thermoplastic resin to the surface of the metal member.

11. The method for manufacturing a metal-resin composite molded article according to claim 9, wherein, the arithmetic mean curvature of the vertices of the surface is made 3000 to 5000 (1 / mm).

12. The method for manufacturing a metal-resin composite molded article according to claim 9, wherein, Make the arithmetic mean curvature of the vertices of the surface be 3500 - 5000 (1 / mm).

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