DLC coating

Abstract

To provide a DLC coating with excellent stain resistance against inorganic materials. [Solution] A DLC coating is formed on a substrate, wherein the DLC coating forms an upper region and a lower region in the depth direction from the surface of the coating, and the sp of the upper region 3 The average value of the ratio is the sp of the lower region. 3 Higher than the average ratio, the sp of the upper region 3 The average ratio is between 55% and 90%, and the upper region is a surface modification region. The problem is solved by a DLC coating.

Description

[Technical Field]

[0001] This invention relates to a diamond-like carbon (DLC) coating, and more particularly to a DLC coating with excellent stain resistance. [Background technology]

[0002] Traditionally, DLC coatings have been applied to the surfaces of parts requiring wear resistance, such as sliding components in internal combustion engines, to improve wear resistance. In recent years, however, DLC coatings have also been used as coating materials for components other than sliding parts, due to their excellent gas barrier properties resulting from the density of the coating surface.

[0003] For example, Patent Document 1 discloses that by forming a DLC coating on the inner surface of the inner container, it is possible to achieve excellent abrasion resistance and corrosion resistance, as well as prevent the adhesion of dirt and odors. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-199013 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The technology disclosed in Patent Document 1 involves applying a DLC coating, which has excellent abrasion resistance and corrosion resistance and can prevent the adhesion of dirt and odors, to the inside of an insulated container. However, the types of dirt that can adhere have not been specifically considered, and since the target of the coating is an insulated container, it is assumed that it is mainly intended to protect against organic dirt such as food. In other words, its antifouling properties against inorganic dirt have not been considered. This invention provides a DLC coating with excellent stain resistance against inorganic materials. [Means for solving the problem]

[0006] In order to solve the above problems, the present inventors have conducted studies and found that a DLC film in which the outermost surface is modified and the sp 3 ratio in the surface modification region is increased exhibits antifouling properties against inorganic substances and can solve the above problems, thereby completing the present invention. In the present specification, the sp 3 ratio refers to the sp ratio measured by TEM-EELS (Transmission Electron Microscope - Electron Energy Loss Spectroscopy), which is a combination of a transmission electron microscope (TEM) and electron energy loss spectroscopy (EELS). 3 / (sp 2 +sp 3 ) structure ratio (hereinafter, simply referred to as the sp 3 ratio), and the sp 2 ratio (refers to the sp 2 / (sp 2 +sp 3 ) structure ratio).

[0007] One embodiment of the present invention is a DLC film formed on a substrate, wherein the DLC film forms an upper region and a lower region in the depth direction from the outermost surface of the film, and the average value of the sp 3 ratio in the upper region is higher than the average value of the sp 3 ratio in the lower region, the average value of the sp 3 ratio in the upper region is 55% or more and 90% or less, and the upper region is a surface modification region, the DLC film.

[0008] It is preferable that the DLC film has a scale adhesion rate of 70% or less as a result of performing a sliding test under the following test conditions and measuring the scale adhering to the surface of the DLC film, and it is preferable that the depth direction length of the upper region of the DLC film is 10 nm or more and 200 nm or less. <Test Conditions> 20 μ L of water containing 75 mg / L of silica is dropped onto a SUS304 test piece with a size of 30 mm□ and a weight of 70 g, and dried at 100°C for 5 minutes to deposit scale on the test piece. Lay a Kim towel (manufactured by Nippon Paper Crecia) on the table, and place the test piece with scale deposits on the Kim towel so that the surface of the test piece faces the Kim towel. Then, slide it 2 m at a speed of 1 m / sec without applying a load to the test piece.

[0009] In addition, the DLC film preferably has a surface resistance value of 1×10 10 Ω / □ or more in the upper region, and preferably has an intensity ratio (ID / IG) of the D band to the G band obtained from the Raman spectrum of 1.6 or less. * a * b * The value of L in the color system * is preferably 5 or more, the value of a * is preferably -1.7 or more, and the value of b * is preferably -2 or less.

Advantages of the Invention

[0010] According to the present invention, a DLC film excellent in antifouling property and also excellent in adhesion can be provided. In addition, a DLC film having good insulating properties can be provided.

Brief Description of the Drawings

[0011] [Figure 1] A schematic cross-sectional view of a DLC film formed on a substrate is shown. [Figure 2] It is a TEM image of the cross section of the DLC film of Example 3 (photograph for substituting drawing).

Embodiments for Carrying Out the Invention

[0012] One embodiment of the present invention is a DLC film formed on a substrate, and its description will be given using FIG. 1. In FIG. 1, a DLC film 2 is formed on a substrate 1. The substrate 1 is not particularly limited as long as it is a material on which a DLC film can be formed. Typically, it is a metal material, but it is not limited thereto, and it may be a glass material or a resin material. Between the substrate 1 and the DLC coating 2, there may be another layer, such as an underlayer or intermediate layer, which can be used during DLC ​​coating formation. The underlayer may be a DLC coating layer or a layer other than the DLC coating. Examples of layers other than the DLC coating include SiC films, W films, Ti films, and Cr films.

[0013] The DLC coating 2 has an upper region 2a and a lower region 2b extending from the surface of the coating (upper part in the figure) in the depth direction (lower part in the figure). In other words, the surface of the DLC coating 2 can be said to have undergone surface modification treatment. The length of the upper region 2a of the DLC coating in the depth direction is not particularly limited, but it is preferably 10 nm to 200 nm, and more preferably 20 nm to 150 nm. By setting it within the above range, sufficient antifouling properties can be achieved and it is also economical.

[0014] As a surface modification treatment, the surface of the DLC coating 2 is modified to the above sp 3 Any process that can achieve the ratio is acceptable. This could be a process that reduces the surface roughness of DLC coating 2 and makes the surface smooth, or a process that applies energy to DLC coating 2 that can change its color. For example, polishing processes such as buffing and lapping may be performed, shot peening may be performed, or burnishing may be performed. One example is to perform surface polishing with #1500 wet sandpaper under a load of 10N for a polishing time of 5 minutes, and then buff polishing with diamond abrasive grains.

[0015] The DLC coating 2 that has undergone this surface modification treatment will have a different color compared to before the surface modification treatment. The change in color was measured according to JIS Z 8722, for example, L * a * b * L in color systems * The value of is 5 or greater, and a * The value of is -1.7 or greater, and b * The value of may be -2 or less.

[0016] In this embodiment, the DLC coating 2 is surface-modified, so that from the surface of the coating in the depth direction, an upper region 2a that has undergone surface modification and a lower region 2b that is the original DLC coating are formed. 3 The average value of the ratio is the sp of the lower region 2b. 3 Higher than the average ratio, the sp in the upper region 2a 3 The average ratio is between 50% and 90%, preferably between 55% and 90%. DLC coating 2 having these characteristics has high resistance to inorganic stains. Specifically, sliding tests were conducted under the following test conditions, and the amount of limescale adhering to the DLC coating surface was measured. The results showed that the limescale adhesion rate was 70% or less. Preferably, the limescale adhesion rate is 60% or less, and more preferably 50% or less.

[0017] <Test Conditions> 20 μL of water containing 75 mg / L of silica was dropped onto a 30 mm square, 70 g SUS304 test piece, and dried at 100°C for 5 minutes to allow limescale to accumulate on the test piece. Place a Kimtowel (manufactured by Nippon Paper Crecia) on a table, and position the test specimen on the Kimtowel so that the side of the specimen with limescale buildup faces the Kimtowel. Afterward, the test specimen is slid 2 meters at a speed of 1 m / sec without applying any load.

[0018] The limescale buildup rate is measured using the following method. <Method for measuring limescale buildup> After testing, the test specimen is placed on the stage of a microscope (Keyence VHV-5000), the objective lens is set to 30x magnification, the illumination is fully on, the shutter speed is set to 32 out of 255 steps, and the target limescale is focused on and displayed on the monitor to recognize the outermost edge of the limescale. Subsequently, using the automatic area measurement function, the extraction target was defined as a "bright object" based on the brightness condition, and the threshold was set to +24 within the range of -206 to +206 to extract the bright area inside the outermost edge of the limescale. In the region extracted as a "bright object" based on brightness, the area was 1973 μm. 2After removing smaller, single areas using a filter function (because these are droplets of DLC coating 2 that were mistakenly extracted as limescale), the area of ​​the areas extracted as "bright areas" is totaled and measured, and this area is defined as the limescale adhesion area. When the area enclosed by the innermost region of the limescale displayed on the monitor is used as the denominator, and the area defined as the limescale adhesion area is used as the numerator, this fraction is defined as the limescale adhesion rate.

[0019] In this specification, sp 3 The average ratio is measured using TEM-EELS, which combines transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS). Observation of the DLC coating 2 in this embodiment using TEM-EELS reveals that the DLC coating 2 forms a gradient from the upper region 2a to the lower region 2b, with a shift from a region with a high diamond content to a region with a high graphite content. This is shown in Figure 2 and will be explained in the examples. In other words, the DLC coating 2 in this embodiment is not a DLC coating with a multi-layer structure formed by lamination, but rather a single DLC coating with a surface modification treatment applied to its surface.

[0020] The DLC coating 2 in this form is sp 3 While the average ratio is high, it is also possible to make a thick film, and the film thickness may be 2 μm to 15 μm or 3 μm to 10 μm. 3 When the average ratio is high, it is difficult to make the DLC coating thick due to delamination caused by increased internal stress, but in this form of DLC coating, sp is only on the outermost surface. 3 By creating a coating with a high ratio, it becomes possible to form a thick film.

[0021] The surface roughness of the upper region 2a of the DLC coating is not particularly limited, but Ra may be reduced by surface modification treatment, and Ra is preferably 0.1 μm or less, and more preferably 0.05 μm or less.

[0022] In the upper region 2a of the DLC coating, the intensity ratio of the D band to the G band (ID / IG) determined from the Raman spectroscopy spectrum is preferably 1.6 or less, more preferably 1.3 or less, and even more preferably 1.0 or less.

[0023] The upper region 2a of the DLC coating has improved insulation properties due to surface modification treatment, resulting in a surface resistance value of 1 × 10⁻⁶. 10 It may be Ω / □ or greater, and 5 × 10 10 The impedance may be greater than or equal to Ω / □. DLC is carbon and is generally a conductor, but the structure of the upper region approaches that of a diamond structure through surface modification treatment, thus acquiring insulating properties. Therefore, the DLC coating 2 in this embodiment can be described as a laminated structure of a conductor and an insulator.

[0024] The DLC coating 2 of this embodiment has the properties described above and can be manufactured by forming an existing DLC ​​coating and applying a surface modification treatment to its surface. The method for forming the DLC coating is not particularly limited, and one example is a method of forming the DLC coating using the filtered cathode vacuum arc (FCVA) method. The FCVA method may form the DLC coating with a single structure, or it may be formed by changing the applied pulse bias voltage or by depositing the coating multiple times without changing the pulse bias voltage.

[0025] The surface modification treatment after forming the DLC coating is not particularly limited as long as it is a surface modification treatment that results in the average value of the sp3 ratio described above. For example, polishing processes such as buffing and lapping may be performed, shot peening may be performed, or burnishing may be performed.

[0026] Because this form of DLC coating has excellent stain-resistant properties, it is suitable for application to the surfaces of water-related components in bathrooms, kitchens, and other areas (faucets, drain fittings, shower heads, shower bars, handrails, drains, mirrors, bathroom walls, floors, doors, windows, etc.). Furthermore, because the upper region of the DLC coating has a structure similar to that of a diamond, it is resistant to scratches, and the upper region has a unique blue color, resulting in superior aesthetic appeal. [Examples]

[0027] Next, the present invention will be described in more detail using examples and comparative examples. However, the present invention is not limited to the following examples.

[0028] (Deposition of DLC coating) With the substrate placed inside the filtered arc ion plating apparatus, the apparatus was evacuated to reduce the pressure, and then the substrate was heated. Subsequently, ion bombardment was performed using argon ions while a pulse bias voltage in the range of -500 to -1500V was applied to the substrate. Next, a Ti coating was formed on the substrate as an adhesive layer using a sputtering method. Next, a first amorphous carbon layer and a second amorphous carbon layer were alternately deposited and stacked on the Ti coating. Here, the first amorphous carbon layer was deposited using a sputtering method, applying a bias voltage to the substrate within the range of -50 to -300V, and using a carbon target in an argon gas atmosphere. Furthermore, the second amorphous carbon layer was deposited using a filtered arc method, applying a pulse bias voltage within the range of -500 to -1500V to the substrate while using a carbon target. During the deposition of both the first and second amorphous carbon layers, no hydrogen-containing gas was introduced into the deposition chamber to prevent hydrogen from being incorporated into the films. Furthermore, the thickness of the first amorphous carbon layer was set to 2-8 nm, and the thickness of the second amorphous carbon layer was set to 350-400 nm. Then, one first amorphous carbon layer and one second amorphous carbon layer were formed as a pair of two layers, and these pairs of two layers were repeatedly stacked until a film of the desired thickness was achieved.

[0029] (Surface modification treatment) The obtained DLC coatings were subjected to surface modification treatment. The surface modification treatment involved surface polishing using #1500 wet sandpaper under a load of 10N for 5 minutes, followed by buff polishing with diamond abrasive particles. Furthermore, by changing the surface modification treatment conditions as shown in Table 1, DLC coatings for Examples 2 and 3, and Comparative Examples 1-3 were obtained. In Example 2, the surface modification treatment involved surface polishing using #1500 wet sandpaper with a load of 10N and a polishing time of 2 minutes, followed by buff polishing with diamond abrasive grains. In Example 3, the surface modification treatment involved shot peening for 60 seconds using a polycarbonate media (particle size 500μm) that did not contain abrasive grains, at a spray pressure of 0.2MPa.

[0030] Regarding the obtained DLC coating, the depth of the surface-modified upper region and the sp of the upper region were determined. 3 The average ratio, surface resistance, surface color, and ID / IG ratio were measured. The measurement results are shown in Table 1.

[0031] (Stain resistance evaluation test) The DLC coatings of Examples 1-3 and Comparative Examples 1-3 were subjected to stain resistance evaluation tests under the following test conditions. The results are shown in Table 1. <Test Conditions> A 30mm square, 70g SUS304 test piece was dropped with 20μL of water containing 75mg / L silica, and dried at 100°C for 5 minutes to deposit limescale on the test piece. A Kimwipe (manufactured by Nippon Paper Crecia) was placed on a table, and the test piece was positioned on the Kimwipe so that the surface of the test piece with limescale deposits faced the Kimwipe. The test piece was then slid 2m at a speed of 1m / sec without applying any load.

[0032] <Judgment Criteria> After the test, the test specimen was placed on the stage of a microscope (Keyence VHV-5000), and with the objective lens at 30x magnification and the illumination at full power, the settings were changed to 32 out of 255 steps and the shutter speed to 70 out of 255 steps. The target limescale was then focused on and displayed on the monitor to identify the outermost edge of the limescale. Subsequently, using the automatic area measurement function, the extraction target was defined as a "bright object" based on the brightness condition, and the threshold was set to +24 within the range of -206 to +206 to extract the bright area inside the outermost edge of the limescale. In the region extracted as a "bright object" based on brightness, the area was 1973 μm. 2 After removing smaller, single areas using a filter function (because these were droplets of DLC coating 2 that were mistakenly extracted as limescale), the area of ​​the areas extracted as "bright areas" was totaled and measured, and this area was defined as the limescale adhesion area. The area enclosed by the innermost region of the limescale displayed on the monitor was used as the denominator, and the area defined as the limescale adhesion area was used as the numerator. This fraction was defined as the limescale adhesion rate. A limescale adhesion rate of 70% or less was considered acceptable.

[0033] [Table 1]

[0034] Figure 2 shows a cross-sectional TEM image of the DLC coating according to Example 3. Furthermore, EELS measurements were taken at the locations indicated by analysis points 2-9 in the direction of the arrows in Figure 2. 2 The ratios are shown in Table 2. This sp 2 From the ratio, it can be seen that the DLC coating in this embodiment forms a gradient from the upper region to the lower region, with a higher concentration of diamond components and a higher concentration of graphite components.

[0035] [Table 2]

Claims

1. A DLC coating formed on a substrate, The DLC coating has an upper region and a lower region extending in the depth direction from the outermost surface of the coating, and the sp of the upper region ３ The average value of the ratio is the sp of the lower region ３ The sp of the upper region is higher than the average ratio. ３ A DLC coating in which the average ratio is between 55% and 90%, and the upper region is a surface modification region.

2. The DLC coating according to claim 1, wherein a sliding test is performed on the DLC coating under the following test conditions, and the amount of limescale adhering to the surface of the DLC coating is measured, and the limescale adhesion rate is 70% or less. <Exam Conditions> 20 μL of water containing 75 mg / L of silica was dropped onto a 30 mm square, 70 g SUS304 test piece, and dried at 100°C for 5 minutes to deposit limescale on the test piece. Place a Kimtowel (manufactured by Nippon Paper Crecia) on a table, and position the test specimen on the Kimtowel so that the side of the specimen with limescale buildup faces the Kimtowel. Afterward, the test piece is slid 2 meters at a speed of 1 m / sec without applying any load.

3. The DLC coating according to claim 1 or 2, wherein the depth direction length of the upper region of the DLC coating is 10 nm or more and 200 nm or less.

4. The surface resistance value of the upper region is 1 × 10 １０ A DLC coating according to claim 1 or 2, wherein the Ω / □ ratio is 1 or greater.

5. The DLC coating according to claim 1 or 2, wherein the intensity ratio of the D band to the G band (ID / IG) determined from the Raman spectroscopic spectrum of the upper region is 1.6 or less.

6. The upper region is L ＊ a ＊ b ＊ In the color system, the value of L ＊ is 5 or more, the value of a ＊ is -1.7 or more, and the value of b ＊ is -2 or less. The DLC film according to claim 1 or 2

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