Coating systems for plastic processing applications

Abstract

The present invention relates to a multi-layer coating exhibiting good corrosion resistance and good wear resistance. The multi-layer coating has A and B layers deposited to form a sequence of the type ...A / B / A / B / A.... The A layers are CrN-based or CrN layers and the B layers are CrON-based or CrON layers. The multi-layer coating exhibits a controlled layer thickness ratio of the A and B layers. The multi-layer coating comprises at least two different coating parts with the A and B layers adjusted to have different layer thickness ratios.

Description

[Technical Field]

[0001] This invention relates to a coating system for plastic processing applications. [Background technology]

[0002] Plastic processing applications such as injection molding or extrusion molding involve various stages where metal tools physically come into contact with the plastic. Therefore, tools such as extrusion molds are subjected to a combination of attacks, including corrosion and wear. Corrosive media caused by plastics can originate from, for example, plasticizers, colorants, and free hydrochloric acid used in the plastic. Simultaneously, tool wear is increasing due to the growing interest in the use of glass fiber reinforced plastics in various plastic processing applications, including injection-molded parts for the automotive industry. Glass fiber reinforced plastics with a glass fiber content exceeding 30% are highly abrasive, reducing tool life.

[0003] To extend the lifespan of tools used in plastic processing applications, there is a demand for PVD coatings that combine wear resistance and corrosion resistance.

[0004] In International Publication No. 2020099605, Bolvardi proposes a coating system that meets the requirements for plastic processing applications. This coating system is • A lower layer comprising at least one corrosion-resistant material layer, preferably one or more AlCrO layers as the corrosion-resistant layer, • An upper layer comprising one or more wear-resistant material layers, preferably one or more CrON layers as wear-resistant layers, A transition layer is provided between the first layer and the second layer, It is equipped with.

[0005] Furthermore, Bolvardi states in International Publication No. 2020099605 that multilayer coatings of the ...CrN / CrON / CrN / CrON... type provide good wear resistance, but their corrosion resistance is poor.

[0006] Despite the advancements achieved by prior art, the increasing demand for further improvements to sustainably achieve the required tool performance in plastic processing applications necessitates addressing these needs with additional coating solutions. [Overview of the project] [Problems that the invention aims to solve]

[0007] The objective of the present invention is to provide a sustainably manufactured coating system that achieves a good combination of corrosion resistance and wear resistance suitable for improving the performance of tools used in plastic processing applications.

[0008] A further object of the present invention is to provide a molding tool having a surface that is exposed to contact with plastics during plastic processing. Herein, this surface is treated and / or coated before use (before being used in plastic processing applications) to exhibit a suitable combination of good abrasion resistance and good corrosion resistance during use. [Means for solving the problem]

[0009] The object of the present invention is to provide a multilayer coating comprising multiple layers deposited in an overlapping manner. Here, • Individual chromium nitride-based (CrN-based) layers or individual chromium nitride (CrN) layers, • Individual chromium oxynitride-based (CrON-based) layers or individual chromium oxynitride (CrON) layers These are deposited in a sequence of the type ...CrN / CrON / CrN / CrON / CrN..., overlapping each other. Here, the ratio of the thicknesses of the two overlapping layers is adjusted along the thickness of the multilayer coating.

[0010] To simplify the explanation of the present invention, each CrN-based layer or each CrN layer is referred to as layer A, and each CrON-based layer or each CrON layer is referred to as layer B.

[0011] The statement, "The ratio of the thicknesses of two layers deposited in an overlapping manner is adjusted along with the thickness of the multilayer coating," refers to a specific variation in the ratio of the thicknesses of one A layer and one B layer when two individual layers, i.e., one A layer, are deposited on top of one B layer.

[0012] Even when the same coating process parameters are set, slight inherent variations in coating conditions during coating deposition can cause slight changes in the thickness of individual layers (layer A or layer B). Therefore, it should be noted that the thickness of individual layers (layer A or layer B) is the average thickness of individual layers (layer A or layer B).

[0013] The inventors have found the following using a multilayer coating of type A / B / A / B / A... including the above-described A and B layers. By adjusting the thickness of layer A relative to the thickness of layer B, such that the average thickness of layer A is greater than the average thickness of layer B, the corrosion resistance of the multilayer coating can be improved. By adjusting the thickness of layer A relative to the thickness of layer B, such that the average thickness of layer A is thinner than the average thickness of layer B, the wear resistance of the multilayer coating can be similarly improved. • By adjusting the ratio of the thicknesses of layer A and layer B and depositing a multilayer coating, both the wear resistance and corrosion resistance of the multilayer coating can be improved. Here, the multilayer coating includes at least two different coating portions, each adjusted so that the ratio of the thicknesses of layer A and layer B differs along the overall thickness of the multilayer coating. In particular, the multilayer coating is • The lower multilayer coating portion has an average layer thickness of layer A that is thicker than the average layer thickness of layer B, • The upper multilayer coating portion has an average layer thickness of layer A that is thinner than the average layer thickness of layer B, It can include, When a multilayer coating is deposited on the substrate surface, preferably the lower multilayer coating portion is deposited closer to the substrate surface than the upper multilayer coating portion.

[0014] In the context of the present invention, the CrN-based layer or CrN layer (also referred to as layer A in the context of the present invention) is a chromium nitride layer that may contain other chemical elements as doping elements or alloying elements. Such a layer may have, for example, an average chemical composition given by the following formula: · (Cr a X b ) q (N d Z e ) r Here, a, b, d, and e are coefficients representing the proportions of the atomic concentrations of Cr, X, N, and Z, respectively, and q and r are coefficients representing stoichiometry (r / q=1), hyperstoichiometry (r / q>1), or substoichiometry (r / q<1). Cr is the chemical element chromium. • N is the chemical element nitrogen, X is one or more chemical elements selected from Ti, Zr, Hf, Sc, Y, V, Nb, Ta, In, Si, Ge, Sn, Al, Mo, W, Ni, Pd, Pt, Cu, Ag, Au, B. · Z is one or more chemical elements selected from carbon (C) and oxygen (O). When X is O, or when X contains O, the concentration of O in the total of N + Z shall not exceed 5 in atomic percentage. Specifically, for example, when X = O, e can be at most 5, that is, when X = O, 0 ≦ e ≦ 5, which means · a + b = 100, where 0 ≦ b ≦ 20, preferably 0 ≦ b ≦ 15, more preferably 0 ≦ b ≦ 10 or 0 ≦ b ≦ 5, · d + e = 100, where 0 ≦ e ≦ 30, preferably 0 ≦ e ≦ 20, more preferably 0 ≦ e ≦ 10 or 0 ≦ e ≦ 5, · 0.90 < r / q° ≦ 1.10.

[0015] In the context of the present invention, the CrON layer is a chromium oxynitride layer that may contain other chemical elements as doping elements or alloy elements. Such a layer can have, for example, an average chemical composition according to the following formula: · (Cr f D t ) g (O h N j C m ) u Here, f, t, h, j, and m are coefficients representing the ratios of the atomic concentrations of Cr, D, O, N, and Q, respectively, and g and u are coefficients representing stoichiometry (u / g = 1), super-stoichiometry (u / g > 1), or sub-stoichiometry (u / g < 1). Also, · Cr is the chemical element chromium, · N is the chemical element nitrogen, · D is one or more chemical elements selected from Ti, Zr, Hf, Sc, Y, V, Nb, Ta, In, Si, Ge, Sn, Al, Mo, W, Ni, Pd, Pt, Cu, Ag, Au, B, · C is the chemical element carbon (C), · f + t = 100, where 0 ≦ t ≦ 20, preferably 0 ≦ t ≦ 15, more preferably 0 ≦ t ≦ 10 or 0 ≦ t ≦ 5, · h + j + m = 100, where 5 < j ≤ 70, preferably 5 < j ≤ 60, more preferably 10 ≤ j ≤ 60 or 10 ≤ j ≤ 55, 0 ≤ m ≤ 15, preferably 0 ≤ e ≤ 10, · 0.90 < r / q° ≤ 1.10.

[0016] In other words, the average layer thickness ratio LTR is defined by the following formula:

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Brief Description of the Drawings

[0017] Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. [Figure 1] It is a schematic diagram of a coating design including a lower multi-layer coating portion 100 and an upper multi-layer coating portion 200, where layer A is shown in light gray and layer B is shown in dark gray. [Figure 2] It is a schematic diagram of a coating design including a lower multi-layer coating portion 100 and an upper multi-layer coating portion 200, where layer A is shown in light gray and layer B is shown in dark gray. [Figure 3] It is a schematic diagram of a coating design including a lower multi-layer coating portion 100, an intermediate multi-layer coating portion 150, and an upper multi-layer coating portion 200, where layer A is shown in light gray and layer B is shown in dark gray. [Figure 4] It is a schematic diagram of a coating design including a lower multi-layer coating portion 100, an intermediate multi-layer coating portion 150, and an upper multi-layer coating portion 200, where layer A is shown in light gray and layer B is shown in dark gray. [Figure 5] It is a diagram showing the wear scar depth after SRV measurement for evaluating wear resistance. The less the wear, the shallower the wear scar depth, that is, the higher the wear resistance, the lower the bar in the graph. The values are normalized with respect to the results corresponding to the examples. Example 1 is a comparative example, and Examples 2 and 3 are examples of the present invention. [Figure 6]These are steel samples recorded at different time intervals during NSST testing. [Modes for carrying out the invention]

[0018] Therefore, in the lower multilayer coating portion 100, the average layer thickness ratio LTR 100 is defined by considering the average layer thickness of layer A in the lower multilayer coating portion 100, i.e., the average layer thickness of layer A 100, and the average layer thickness of layer B in the lower multilayer coating portion 100, i.e., the average layer thickness of layer B 100:

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[0019] Similarly, in the upper multilayer coating portion 200, the average layer thickness ratio LTR200 is defined by considering the average layer thickness of layer A in the upper multilayer coating portion 200, i.e., the average layer thickness of layer A 200, and the average layer thickness of layer B in the upper multilayer coating portion 200, i.e., the average layer thickness of layer B 200:

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[0020] The inventors observed a significant improvement in the combination of corrosion resistance and wear resistance when, in the fabrication of a multilayer coating having at least two multilayer coating portions, the average layer thickness ratio LTR100 in the lower multilayer coating portion 100 is greater than the average layer thickness ratio LTR200 in the upper multilayer coating portion 200, i.e., LTR100 > LTR200.

[0021] In particular, in a preferred embodiment of the present invention, a multilayer coating is fabricated to have at least two multilayer coating portions, including a lower multilayer coating portion 100 having an average layer thickness ratio LTR 100 > 1 and an upper multilayer coating portion 200 having an average layer thickness ratio LTR 200 < 1, and a remarkably good combination of high corrosion resistance and high wear resistance was obtained.

[0022] Furthermore, the multilayer coating according to the present invention may include further coated portions or further coated layers.

[0023] According to a more preferred embodiment of the present invention, the multilayer coating includes an intermediate multilayer coating portion 150 deposited between a lower multilayer coating portion 100 and an upper multilayer coating portion 200.

[0024] The average layer thickness ratio LTR150 of the intermediate multilayer coating portion 150 is defined by considering the average layer thickness of layer A in the intermediate multilayer coating portion 150, i.e., the average layer thickness of layer A 150, and the average layer thickness of layer B in the intermediate multilayer coating portion 150, i.e., the average layer thickness of layer B 150:

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[0025] In a more preferred embodiment, the multilayer coating includes four or more multilayer coating portions, where the first multilayer coating portion is a lower multilayer coating portion 100, and the last multilayer coating portion is an upper multilayer coating portion 200. Each multilayer coating portion also has a different average layer thickness ratio (LTR), and the LTR decreases gradually (continuously or stepwise) from the lower multilayer coating portion to the upper multilayer coating portion.

[0026] Preferably, multiple CrN layers within a single coating portion have approximately the same coating thickness, and preferably, multiple CrON layers within a single coating portion have approximately the same coating thickness. However, variations may occur due to the rotation of the substrate and the relative orientation of the deposition source in the PVD deposition apparatus.

[0027] Preferably, the thickness of one bilayer, i.e., the total thickness of one B layer and one A layer deposited so as to overlap each other, is in the range of 30 nm to 500 nm, more preferably in the range of 100 nm to 200 nm. For example, the thickness of the bilayer can be 150 nm.

[0028] The overall thickness of the multilayer coating is preferably in the range of 1 μm to 30 μm, more preferably in the range of 2 μm to 20 μm, and even more preferably in the range of 5 μm to 10 μm.

[0029] The thickness of one multilayer coating portion, for example, the thickness of the lower multilayer coating portion 100 or the thickness of the upper multilayer coating portion 200, is preferably not less than 10% of the total thickness of the multilayer coating.

[0030] Preferably, the coating contains a cubic fcc-CrN phase, which can be characterized, for example, by X-ray diffraction.

[0031] Preferably, the coating has an indentation hardness greater than 20 GPa, particularly in the range of 25 GPa to 35 GPa.

[0032] Furthermore, the coating according to the present invention may include a bottom coating layer deposited between the substrate surface on which the multilayer coating is deposited and the lower multilayer coating portion.

[0033] For example, to improve the adhesion of the coating to the substrate surface, the bottom coating layer can be directly deposited onto the substrate surface. In this case, the bottom coating layer can be, for example, a CrN layer or a Cr layer, or a layer containing either CrN or Cr.

[0034] Furthermore, the coating according to the present invention may include a top coating layer deposited on the coating above the upper multilayer coating portion.

[0035] For example, to further improve surface properties, the top coating layer can be directly deposited as the outermost layer on top of the upper multilayer coating portion.

[0036] For example, the top coating layer can be a CrON layer to reduce the tendency for adhesion to plastic materials.

[0037] The coating application described above can be combined with a nitriding pretreatment. This can be done using a separate vacuum or atmospheric nitriding process before coating the first surface layer, or it can be done in situ.

[0038] The coating of the present invention can be deposited using known PVD techniques.

[0039] It was found that using a negative bias voltage (e.g., a negative bias voltage in the range of 10V to 150V (absolute value)) applied to the substrate during the deposition of the multilayer coating was advantageous.

[0040] [Examples of the present invention and comparative examples] This specification, including the accompanying drawings and examples, is not intended to limit the invention, but is provided to aid in understanding the invention. Therefore, the examples in this specification should not be understood as limiting the invention.

[0041] The INNOVENTA mega PVD deposition system from Oerlikon Balzers was used for the deposition of the coatings of the present invention in the examples described below, as well as for the deposition of the comparative examples.

[0042] The following examples of the coatings of the present invention were deposited by arc deposition from a Cr target. The multilayer structure was obtained by alternating between a pure N2 atmosphere for depositing CrN and a mixed N2 / O2 atmosphere. By repeating the sequence of pure N2 atmosphere and N2 / O2 mixed atmosphere several times, a coating was obtained that included a sequence of multiple bilayers consisting of individual layers of CrN and CrON.

[0043] The ratio of CrN to CrON layer thicknesses was adjusted (i.e., controlled) by adjusting the duration of the deposition sequence in a pure N2 atmosphere and the time spent in a mixed N2 / O2 atmosphere.

[0044] Figures 5 and 6 show the results of corrosion resistance and abrasion resistance tests on substrates coated with the comparative example from Example 1, and the two comparative examples from Examples 2 and 3.

[0045] [Comparative Example 1] Multilayer coatings containing CrN and CrON layers with an average layer thickness ratio (LTR) of 1, i.e., CrN and CrON layers in which the average layer thickness of each CrN layer is the same as that of each CrON layer (same average layer thickness value), were deposited and tested. In some tests, particularly those shown in Figures 5 and 6, a bottom layer of CrN was deposited between the substrate surface and the multilayer coating.

[0046] [Example 2 of the present invention] Regarding another multilayer coating of the present invention, which includes a CrN layer A and a CrON layer B, a multilayer coating formed by two different multilayer coating portions, including a lower multilayer coating portion with an LTR of 2 to 1.3 and an upper multilayer coating portion with an LTR of 0.8 to 0.3, was deposited and tested. In several tests, particularly those shown in Figures 5 and 6, a bottom layer of CrN was deposited between the substrate surface and the multilayer coating. In the tests shown in Figures 5 and 6, the LTR in the lower multilayer coating portion was 1.55 to 1.75, and the LTR in the upper multilayer coating portion was 0.4 to 0.7.

[0047] [Example 3 of the present invention] The only difference between Example 2 and Example 3 is that the multilayer coating was deposited in the additional multilayer coating portion, more precisely in the intermediate multilayer coating portion with an LTR of 1.2 to 0.9. In the tests shown in Figures 5 and 6, the LTR in the intermediate multilayer coating portion was approximately 1.

[0048] [Explanation of the exam] The wear resistance of the coating was investigated using vibratory friction wear (SRV) measurement. An Al2O3 ball was used to perform reciprocating vibration at a constant force (50N) at 10Hz for 60 minutes. The depth of the resulting wear marks was measured. The results are shown in Figure 5. The shallower the wear mark, the higher the wear resistance. As shown in Figure 5, the coating of the present invention (see Examples 2 and 3 in Figure 5) showed higher wear resistance than the comparative coating (see Example 1 in Figure 5) prepared according to the prior art.

[0049] To evaluate the corrosion resistance of the coatings, the coatings of the present invention and comparative coatings prepared according to the prior art were tested using a neutral salt spray test (NSST). The coatings were applied to a substrate made of cold-worked steel with a strength of 1.2842 containing 0.4% Cr. As shown in Figure 6, pitting corrosion occurred in the main part of the surface of the comparative coating (see Example 1 in Figure 6) after 72 to 96 hours. The coating of the present invention (see Example 2 in Figure 6) showed good corrosion resistance.

[0050] These two tests confirmed that the coating of the present invention possesses both good corrosion resistance and high wear resistance.

Claims

1. .. .. .. A / B / A / B / A multilayer coating having A and B layers deposited to form a sequence of type A, where the A layer is a CrN-based layer or a CrN layer, the B layer is a CrON-based layer or a CrON layer, the multilayer coating exhibits a controlled ratio of the thicknesses of the A and B layers, and the multilayer coating comprises at least two different coating portions having the A and B layers adjusted to have different thickness ratios along the overall thickness of the multilayer coating. The aforementioned multilayer coating is - A lower multilayer coating portion (100) having an average layer thickness ratio LTR100 of the average layer thickness of the A layer (A100) to the average layer thickness of the B layer (B100), - An upper multilayer coating portion (200) having an average layer thickness ratio LTR200 of the average layer thickness of the A layer to the average layer thickness of the B layer, Includes, - Characterized by LTR100 > LTR200, Multilayer coating.

2. The multilayer coating according to claim 1, characterized in that when the multilayer coating is deposited on the substrate surface, the lower multilayer coating portion (100) is deposited closer to the substrate surface than the upper multilayer coating portion (200).

3. a. In the lower multilayer coating portion (100), the average layer thickness ratio LTR100 between the A layer (A100) and the B layer (B100) is greater than 1, i.e., LTR100 > 1. b. The upper multilayer coating portion (200) is characterized in that the average layer thickness ratio LTR200 between the A layer (A200) and the B layer (B200) is LTR200 < 1. The multilayer coating according to claim 2.

4. A multilayer coating according to any one of claims 1 to 3, characterized by including a further coated portion or a further coated layer.

5. The multilayer coating according to claim 4, characterized in that it includes an intermediate multilayer coating portion (150) deposited between the lower multilayer coating portion (100) and the upper multilayer coating portion (200).

6. The multilayer coating according to claim 5, characterized in that in the intermediate multilayer coating portion (150), the average layer thickness ratio LTR150 between the A layer and the B layer satisfies LTR100 > LTR150 > LTR200.

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