Corrosion-resistant permanent magnets and intravascular blood pumps containing these magnets

Abstract

To provide a permanent magnet for intravascular blood pumps with improved corrosion resistance. [Solution] The corrosion-resistant permanent magnet 1 includes a composite coating 16 covering its surface, the composite coating 16 including a first layer structure 17 and, optionally, a second layer structure 18 on the first layer structure, the first layer structure 17 consisting of an aluminum layer 44, a first linker layer 42, and a first organic layer 43, and the second layer structure 18 consisting of an aluminum oxide layer 51, a second linker layer 52, and a second organic layer 53. The organic layer is made of poly(2-chloro-p-xylylene). The corrosion-resistant permanent magnet is corrosion-resistant due to the composite coating.

Description

Technical Field

[0001] The present invention relates to the corrosion prevention of permanent magnets. In particular, the present invention relates to a permanent magnet provided with a protective coating that makes the magnet corrosion-resistant, and a method for manufacturing a corrosion-resistant permanent magnet. The present invention also relates to an intravascular blood pump including the corrosion-resistant permanent magnet of the present invention. Although the present invention can be applied to all types of permanent magnets, rare earth permanent magnets are preferred, and neodymium iron boron (NdFeB) permanent magnets are particularly preferred.

Background Art

[0002] Intravascular blood pumps support the blood flow within a patient's blood vessels. These are, for example, percutaneously inserted into the femoral artery and guided through the body's vascular system to their destination, such as the ventricle of the heart.

[0003] A blood pump typically includes a pump casing having a blood flow inlet and a blood flow outlet. To generate blood flow from the blood flow inlet to the blood flow outlet, an impeller or rotor is supported within the pump casing so as to rotate around a rotation axis, and the impeller is provided with one or more blades for transporting blood.

[0004] An exemplary blood pump is shown in FIG. 1. FIG. 1 is a schematic longitudinal sectional view of an exemplary intravascular blood pump 10. This blood pump includes a motor part 11 and a pump part 12, which are coaxially arranged with each other and have a rod-like structural form. The pump part is extended by a flexible suction hose (not shown) having an opening for allowing blood to flow into the pump at its end and / or its side wall. A catheter 14 is connected to the end of the blood pump 10 opposite to the suction hose, optionally in combination with a guide wire for directing the blood pump to its destination.

[0005] The exemplary intravascular blood pump shown in Figure 1 comprises a motor unit 11 and a pump unit 12 that are securely connected to each other. The motor unit 11 has an elongated housing 20 that houses an electric motor 21. The electric motor has a rotor and a stator. The stator is the stationary part of the motor's electromagnetic circuit, and the rotor is the moving part. Either the rotor or the stator contains conductive windings, and the other contains permanent magnets. The current flowing through the windings interacts with the magnetic field of the permanent magnets to create an electromagnetic field that generates a force to rotate the rotor. In the exemplary blood pump of Figure 1, the stator 24 of the electric motor 21 has, in the usual manner, a number of windings arranged circumferentially along its longitudinal direction and a magnetic return path 28. This is securely coupled to the motor housing. The stator 24 surrounds the rotor 1, which is coupled to the motor shaft 25 and consists of permanent magnets magnetized in the active direction. The motor shaft 25 extends beyond the entire length of the motor housing 20 and protrudes from the end of the latter. There is an impeller 34, or pump blades, with protruding blades 36, which rotate within a tubular pump housing 32, and the pump housing 32 is also securely coupled to the motor housing 20.

[0006] A flexible catheter 14 is attached to the proximal end of the motor housing 20, closely fitted to it. In this disclosure, “proximal” and “distal” refer to the position as seen from the physician inserting the intravascular blood pump, i.e., the distal end is the impeller side. An electrical cable 23 for supplying power to and controlling the electric motor 21 extends through the catheter 14. Furthermore, a purge fluid line 29 extends into the catheter 14, penetrating the proximal end wall 22 of the motor housing 20. The purge fluid (shown by a thick arrow in the schematic diagram) is supplied into the motor housing 20 through the purge fluid line 29, flows through the gap 26 between the rotor 1 and the stator 24, and is discharged from the end face 30 of the distal end of the motor housing. The purge pressure is selected to be higher than the blood pressure therein to prevent blood from entering the motor housing. Depending on the application, the purge fluid pressure is between 300 and 1400 mmHg at the point where the pressure is applied to the motor.

[0007] For purging, a fluid with a viscosity higher than that of water (η = 0.75 mPa·s at 37°C), particularly a purging fluid with a viscosity of 1.2 mPa·s or higher at 37°C, is suitable. For example, a 5% to 40% glucose aqueous solution intended for injection can be used, but physiological saline is also suitable.

[0008] As the impeller 34 rotates, blood (indicated by the white arrow in the schematic diagram) is drawn in through the end face suction opening 37 of the pump housing 32 and transported axially backward within the pump housing 32. The blood then flows out of the pump unit 12 through the outlet opening 38 of the pump housing 32 and further flows along the motor housing 20. It is also possible to operate the pump unit in the reverse transport direction to draw the blood along the motor housing 20 and discharge it from the opening 37.

[0009] The motor shaft 25 is attached to radial bearings 27 and 31, one end of which is at the proximal end of the motor housing and the other end of which is at the distal end of the motor housing. Furthermore, the motor shaft 25 is also attached axially to an axial bearing 39. If the blood pump is used to transport blood in the reverse direction, or only in the reverse direction, a similar axial bearing 39 is also provided at the proximal end of the motor housing 20.

[0010] Of course, the blood pump described above is merely an example, and the present invention is applicable to various blood pumps that include electric motors, i.e., those that require permanent magnets. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] European Patent No. 3319098 [Overview of the project] [Problems that the invention aims to solve]

[0012] Intravascular blood pumps must meet numerous requirements. Because they are placed inside the body, they need to be as small as possible. The smallest pumps currently in use have an outer diameter of approximately 4 mm. Despite this, these pumps must deliver high flow rates within the human blood circulation. Therefore, these tiny pumps need to be high-performance engines.

[0013] Furthermore, implantable blood pumps must not adversely affect the biological environment, such as the blood they pump or the surrounding tissues. Therefore, these pumps must be biocompatible in a broad sense; that is, they must not contain or produce harmful substances that could damage the body or its components, nor generate excessive heat.

[0014] Furthermore, replacing the pump is a burden for the patient. For this reason, and of course for economic reasons, intravascular blood pumps need to have a long service life.

[0015] The materials and design of intravascular blood pumps must be appropriately selected and tailored in detail to meet these various requirements.

[0016] Selecting a permanent magnet suitable for electric motors is crucial. For pump efficiency and lifespan, the magnet needs to possess a strong magnetic field, i.e., high residual magnetism, high demagnetization resistance, i.e., high coercivity, and high saturation magnetization. In this regard, rare-earth permanent magnets, specifically those containing neodymium as a rare-earth metal, particularly neodymium-iron-boron (NdFeB) permanent magnets, are the preferred choice. Other rare-earth iron-boron permanent magnets can also be used.

[0017] The stronger the magnet, the smaller the magnet can be while still generating sufficient rotational force. In other words, stronger magnets allow for smaller electric motors. NdFeB permanent magnets are currently the strongest permanent magnets available. This makes them ideal for use in intravascular blood pumps.

[0018] It is well known that the magnetic properties of rare-earth metal magnets, such as NdFeB magnets, vary depending on the detailed alloy composition, microstructure, and manufacturing method used. NdFeB magnets are available as polymer-bonded magnets and sintered magnets. Sintered magnets have superior magnetic properties. They are manufactured by alloying the raw materials, grinding them into powder, compressing them, and sintering them. An external magnetic field is applied to magnetize the material during or after manufacturing. A well-studied magnet is Nd2Fe. 14 This is a microcrystalline sintered material in which B crystals are surrounded by a thin layer particularly rich in neodymium.

[0019] Neodymium iron boron magnets possess magnetic properties particularly well-suited for use in the electric motors of intravascular blood pumps, but they also have significant drawbacks. Specifically, commercially available NdFeB magnets, mainly composed of neodymium, iron, and boron, especially sintered neodymium iron boron magnets with a highly active neodymium-rich phase at the grain boundaries, are highly susceptible to corrosion. These magnets can corrode, for example, due to oxygen and moisture in the air, and particularly at the grain boundaries. Corrosion significantly reduces magnetic properties, and if corrosion progresses during use, the performance of the blood pump using the magnet will deteriorate. This phenomenon is exacerbated by the tendency of neodymium iron boron magnets to act as absorbers of corrosion products, leading to structural breakdown, flaking of fragments from the magnet's surface, and ultimately, the collapse of the magnet.

[0020] Unfortunately, susceptibility to corrosion is a property common to all rare earth metals. Therefore, as explained earlier with NdFeB magnets, all rare earth metal permanent magnets have the undesirable tendency to corrode. For currently available magnets, it can generally be said that the stronger the magnet, the more susceptible it becomes to corrosion.

[0021] In an intravascular blood pump, the magnet must operate in a corrosive environment, that is, in the purge fluid flowing between the rotor and the stator (see Fig. 1). As described above, the purge fluid is generally an aqueous fluid and, in some cases, a fluid containing chlorides. Chlorides are highly corrosive to rare earth metal-based magnets, and furthermore, water and oxygen dissolved in water cause severe corrosion within a very short period of time, on the order of just a few hours.

[0022] It is clear that it is necessary to protect rare earth metal-based permanent magnets, such as neodymium iron boron magnets, for intravascular blood pumps from corrosion.

[0023] Various means for protecting neodymium iron boron magnets and other rare earth metal-based magnets from corrosion are known. For example, a protective coating can be applied to the magnet to improve its corrosion resistance.

[0024] Common coatings are nickel coatings and epoxy resin-based coatings. In particular, in blood pumps, titanium coatings and parylene coatings are known. However, these coatings also have drawbacks. Even if biocompatible metals and organic resins such as titanium and parylene are selected respectively, there is a problem that the metal coating has to be made relatively thick in order to obtain a sufficient protective effect. As a result, the gap between the magnet and the winding in the electric motor of the blood pump has to be relatively large. A large gap has a significant adverse effect on the performance of the electric motor. A large gap requires a larger motor current, and a large motor current may generate undesirable heat that can lead to damage to blood and tissue.

[0025] Furthermore, organic materials such as parylene have a thermal expansion coefficient that is quite different from that of the magnet. Therefore, due to temperature changes during the use of the magnet, cracks and / or delamination of the coating often occur.

[0026] European Patent No. 3319098A1 discloses a coating for permanent magnets comprising a metal layer, a metal oxide layer, a linker layer, and a poly(2-chloro-p-xylylene) layer, the metal oxide layer being several nanometers thick, similar to those naturally formed when an aluminum layer is exposed to air. This coating provides good corrosion protection. However, the manufacturing process is not highly reproducible, and in particular, when the coating is thin, an undesirable number of magnets with insufficient corrosion protection are produced. Further improvements are desired.

[0027] Currently, no biocompatible coatings for permanent magnets, such as neodymium-iron-boron magnets, are known that satisfactorily meet all the requirements for use in intravascular blood pumps. Such coatings must be corrosion-resistant, thin yet dense, free from cracking or other defects during use, and adhere securely and closely to the magnets. Furthermore, the coating process should ideally produce highly reproducible results, meaning fewer magnets need to be selected. Of course, the coating must be biocompatible and cover the entire magnet, or at least any part of the magnet exposed to corrosive environments during use, with a uniform thickness. This is particularly necessary because many magnets have porous surfaces and include edges. In short, rare-earth metal magnets, such as neodymium-iron-boron magnets, for use in intravascular blood pumps constitute components that cannot be easily coated with a uniform thickness. [Means for solving the problem]

[0028] This invention provides a solution to the above-mentioned problems.

[0029] This invention presents a permanent magnet with a protective coating and a method for manufacturing this protective coating with high reproducibility, which reliably prevents corrosion of the magnet during long-term use in intravascular blood pumps. Because the protective coating is particularly thin, it enables the manufacture of very small magnets and, consequently, very small blood pumps.

[0030] The subject matter of the present invention includes a corrosion-resistant permanent magnet having the features set forth in independent claim 1, a method for manufacturing a corrosion-resistant permanent magnet having the features set forth in independent claim 16, and an intravascular blood pump having the features set forth in independent claim 26. Embodiments of the present invention are listed below.

[0031] 1. A corrosion-resistant permanent magnet, and this magnet is, A magnetic body and A composite coating provided on the magnetic body and covering its surface, Includes, The composite coating includes a first layer structure on the magnetic body and, optionally, a second layer structure on the first layer structure. Each layer structure is, Inorganic layer and A linker layer on an inorganic layer, An organic layer consisting of poly(2-chloro-p-xylylene) on the linker layer, This includes, in the order listed, The first layer of the inorganic structure includes either an aluminum layer on a magnetic body, or an aluminum layer on a magnetic body and an aluminum oxide layer on the aluminum layer. The inorganic layer of the second layer structure includes at least one of an aluminum layer and an aluminum oxide layer. The composite coating comprises at least one aluminum oxide layer with a thickness of at least 50 nm. 2. The magnet of Embodiment 1, wherein a linker layer is provided between the first layer structure and the second layer structure. 3. The magnet of Embodiment 1 or 2, wherein the inorganic layer of the second layer structure is an aluminum oxide layer. 4. Any one of the embodiments 1 to 3, wherein the magnet body is a sintered magnet body. 5. A magnet according to any one of Embodiments 1 to 4, wherein the magnetic body is rare earth metal-based. 6. The magnet of Embodiment 5, wherein the rare earth metal is neodymium. 7. A magnet according to any one of Embodiments 1 to 6, wherein the magnetic body is a rare earth metal iron-boron permanent magnet. 8. A magnet of Embodiment 6 or 7, wherein the magnetic body is Nd2Fe 14 B crystal and Nd2Fe 14 A sintered magnet comprising a neodymium iron boron material surrounding a B crystal, wherein the neodymium iron boron material is Nd2Fe 14 It is richer in neodymium than B crystals. 9. A magnet according to any one of embodiments 1 to 8, wherein the magnetic body is rod-shaped with all edges rounded. 10. A magnet according to any one of Embodiments 1 to 9, wherein the linker forming at least one of the linker layers is selected from silanes and silanes having thiol, phosphine, or disulfide groups. 11. The magnet of Embodiment 10 is selected from trimethoxy and triethoxysilanes having an acryloyloxy or methacryloyloxy functional group, or from linkers having a bistrimethoxysilyl functional group. 12. The magnet of Embodiment 10, wherein the silanes have hydride functional groups. 13. The magnet of Embodiment 10, wherein the linker is selected from 3-(2-pyridylethyl)thiopropyltrimethoxysilane, 3-(4-pyridylethyl)thiopropyltrimethoxysilane, and 2-(diphenylphosphino)ethyltriethoxysilane. 14. A magnet according to any one of Embodiments 1 to 13, wherein the thickness of the aluminum layer of the first layer structure and / or second layer structure is 0.5 μm to 15 μm. 15. The magnet of Embodiment 14, wherein the thickness of the aluminum layer of the first layer structure and / or second layer structure is 1 μm to 10 μm, or 1 μm to 5 μm. 16. A magnet according to any one of Embodiments 1 to 15, wherein the thickness of the aluminum oxide layer of the first layer structure and / or second layer structure is 50 nm to 200 nm. 17. A magnet according to Embodiment 16, wherein the thickness of the aluminum oxide layer of the first layer structure and / or second layer structure is 80 nm to 120 nm. 18. A magnet according to any one of Embodiments 1 to 17, wherein the first layer structure and / or second layer structure comprises an inorganic layer including an aluminum layer and an aluminum oxide layer, and the combined thickness of the aluminum layer and aluminum oxide layer of the first layer structure and / or second layer structure is in the range of 5 μm to 15 μm. 19. A magnet according to any one of embodiments 1 to 18, wherein at least one of the linker layers is a single layer, or at least one of the linker layers has a thickness of 20 nm to 50 nm. 20. A magnet according to any one of Embodiments 1 to 19, wherein the thickness of the layers made of poly(2-chloro-p-xylylene) in the first layer structure and / or second layer structure is in the range of 5 μm to 20 μm. 21. A magnet according to any one of Embodiments 1 to 20, wherein the thickness of the composite coating is 200 μm or less, or 50 μm or less. 22. Any one of the embodiments 1 to 21, wherein all layers of the composite coating are completely spread over all surfaces of the magnetic body. 23. A method for manufacturing a corrosion-resistant permanent magnet, wherein this method is The process of preparing an unmagnetized magnet, A first layer structure is formed on a magnet by a process of depositing an inorganic layer on the surface of the magnet, depositing a linker layer on the inorganic layer, and depositing a poly(2-chloro-p-xylylene) layer on the linker layer. If necessary, the process involves depositing an inorganic layer on the first layer structure, depositing a linker layer on the inorganic layer, and depositing a poly(2-chloro-p-xylylene) layer on the linker layer to form a second layer structure on the first layer structure. The process of magnetizing a magnetic material, Includes, The process of depositing the first layer of inorganic structure includes either a step of depositing an aluminum layer on a magnet body, or a step of depositing an aluminum layer on a magnet body and an aluminum oxide layer on the aluminum layer. The process of depositing the second layer inorganic structure includes a step of depositing an aluminum layer on the first layer structure, or a step of depositing an aluminum oxide layer on the first layer structure, or a step of depositing an aluminum layer on the first layer structure and an aluminum oxide layer on the aluminum layer. At least one aluminum layer is deposited by physical vapor deposition, At least one aluminum oxide layer is deposited to a thickness of at least 50 nm using atomic layer deposition. 24. The method of Embodiment 23, wherein a linker layer is deposited on the first layer structure. 25. The method of Embodiment 23 or 24, wherein an aluminum oxide layer is deposited as the inorganic layer of the second layer structure. 26. A method according to any one of embodiments 23 to 25, wherein the magnetic body is a magnetic body defined in any one of embodiments 4 to 9. 27. A method according to any one of embodiments 23 to 26, wherein two aluminum layers are formed, and one of the aluminum layers is formed by ion deposition, plasma deposition, or atomic layer deposition. 28. A method according to any one of embodiments 23 to 27, wherein an aluminum oxide layer having a first layer structure and / or a second layer structure is produced from AlX3 as a first precursor compound and H2O as a second precursor compound, where X represents a lower alkyl group (which may be the same or different), or a hydrogen atom and a lower alkyl group (which may be the same or different), or a halogen atom (which may be the same or different). 29. The method of Embodiment 28, wherein AlX3 is selected from the group consisting of trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), dimethylaluminum (DMAIH), and AlCl3. 30. A method according to any one of embodiments 23 to 29, wherein at least one linker layer is formed by a step of coating the linker with plasma-based physical deposition or a step of depositing the linker from a solution. 31. Any one of the embodiments 23 to 30, wherein at least one linker in the linker layer is a linker defined in any one of embodiments 10 to 13. 32. A method according to any one of embodiments 23 to 31, wherein a layer of poly(2-chloro-p-xylylene) having a first layer structure and / or a second layer structure is formed by plasma deposition of dichloro[2.2]paracyclophane. 33. A method according to any one of embodiments 23 to 32, wherein the layers of the first layer structure and / or the second layer structure have the thickness defined in any one of embodiments 14 to 21. 34. An intravascular blood pump comprising an electric motor, wherein the electric motor comprises a permanent magnet as defined in any one of Embodiments 1 to 22. [Brief explanation of the drawing]

[0032] [Figure 1] This is a schematic longitudinal cross-sectional view showing an exemplary embodiment of an intravascular blood pump. [Figure 2] This is a schematic cross-sectional view showing a part of a magnet according to the present invention, the magnet having a composite coating including a single-layer structure. [Figure 3] This is a schematic cross-sectional view showing a part of a magnet according to the present invention, the magnet comprising a composite coating including a first layer structure and a second layer structure. [Figure 4a] This is a schematic diagram showing an exemplary integrated magnet according to the present invention. [Figure 4b] Figure 4a is a partial cross-sectional view showing details of the magnet. [Figure 5] This is a schematic top view showing an exemplary segmented magnet according to the present invention. [Modes for carrying out the invention]

[0033] If the magnet passes the tests described in the Experiment section, it is considered corrosion-resistant in the sense of this invention.

[0034] According to the present invention, a powerful permanent magnet includes a coating that either completely surrounds the magnetic body or covers at least its surface, which is exposed to fluid when the magnet is operated in an intravascular blood pump. This coating makes the magnet corrosion-resistant while it is used in an intravascular blood pump. A preferred magnetic body, as previously mentioned, mainly consists of neodymium, iron, and boron, with a fine tetragonal magnetic structure Nd2Fe 14 This is a sintered magnet consisting of a B crystal and a neodymium-rich nonmagnetic phase surrounding it. Typically, the main phase is Nd2Fe. 14 The B crystals have an average crystal diameter ranging from 1 to 80 μm. The non-magnetic neodymium-rich phase accounts for 1 to 50 volume percent of the magnet. These magnets are readily available commercially. They are preferred because they have high magnetic properties, and are particularly strong, i.e., have high magnetic flux density. For the reasons mentioned above, particularly strong magnets are required for applications in intravascular blood pumps. However, in principle, the corrosion-resistant coating of the present invention is applicable to any material requiring protection against corrosion, for example, different rare-earth iron-boron magnetic materials and other magnetic materials.

[0035] The coating of the present invention is a composite coating applied to the surface of a magnet, i.e., an actual magnetic material. This composite coating has a layered structure comprising, in the order listed, an inorganic layer, a linker layer on the inorganic layer, and an organic layer made of poly(2-chloro-p-xylylene) on the linker layer. The inorganic layer is provided on the surface of the magnet. The inorganic layer includes either an aluminum layer or a combination of an aluminum layer and an aluminum oxide layer. In either case, the aluminum layer is the layer provided on the surface of the magnet.

[0036] A layer structure comprising an aluminum layer on the surface of a magnet, an aluminum oxide layer on the aluminum layer if necessary, a linker layer on the aluminum layer or aluminum oxide layer, and an organic layer on the linker layer can constitute a composite coating, or only the first part thereof. That is, a further (second) layer structure can be provided on the first layer structure to cover the surface of the organic layer of the first layer structure. The second layer structure is similar to the first layer structure, but does not need to be identical to the first layer structure.

[0037] The second layer structure includes, in the order listed, an inorganic layer on the organic layer of the first layer structure, a linker layer on the inorganic layer, and an organic layer made of poly(2-chloro-p-xylylene) on the linker layer. The inorganic layer of the second layer structure includes an aluminum layer, an aluminum oxide layer, or a combination of an aluminum layer and an aluminum oxide layer. Either the aluminum layer or the aluminum oxide layer can be provided on the organic layer of the first layer structure.

[0038] To enhance the bonding between the first layer (organic layer) and the second layer (inorganic layer), an additional linker layer can be provided between the first and second layers.

[0039] In a composite coating comprising a first-layer structure and a second-layer structure, the same or different compounds can be used for the linker layer, and the corresponding layers of the first-layer structure and the second-layer structure may have the same or different thicknesses. However, this composite coating includes at least one aluminum oxide layer having a thickness of at least 50 nm. In a composite coating comprising a first-layer structure and a second-layer structure, the aluminum oxide layer having a thickness of at least 50 nm can be a component of the first-layer structure or the second-layer structure. Alternatively, both layer structures may include an aluminum oxide layer having a thickness of at least 50 nm.

[0040] In the following, even if only one single-layer structure is provided on the magnet body, the components of the first layer structure, or the single-layer structure, will be referred to as the first inorganic layer (first aluminum layer, first aluminum oxide layer), the first linker layer, and the first organic layer. Similarly, the components of the second layer structure will be referred to as the second inorganic layer (second aluminum layer, second aluminum oxide layer), the second linker layer, and the second organic layer. If a linker layer exists between the first and second layer structures, this will be referred to as a further linker layer.

[0041] Rare earth metal magnets purchased from suppliers are generally protected with a phosphate coating. This phosphate coating can be removed, for example, by washing with acid, before applying the composite coating. However, the phosphate coating may remain on the magnet, as it does not interfere with the coating or covering process of the present invention. Preferably, the phosphate coating is not removed. If the phosphate coating is not removed, one step can be omitted, and the introduction of impurities during such a step can be avoided. However, it is preferable to clean the magnet before coating the first layer structure (or each a single layer structure) of aluminum layer. Cleaning is preferably carried out by washing the magnet with an organic solvent, such as alcohol. Particularly preferred cleaning agents are isopropanol and a mixture of isopropanol and ethanol. After washing with an organic solvent, the magnet is dried, for example, in a vacuum or in an air stream.

[0042] After cleaning and drying, an aluminum layer is applied to the surface of the magnet.

[0043] The method for coating the aluminum layer is not particularly limited in principle. Examples of coating methods include dry and wet methods.

[0044] An exemplary wet process is, for example, galvanic deposition (electroplating) from an ionic liquid, a method commonly used in the art. Electroplating is a very common coating method for aluminum and is considered an easily controllable and low-cost method that yields high-quality coatings with high reproducibility. However, galvanic deposition has been found to be less advantageous for the purposes of the present invention. The present invention particularly requires a high-quality coating, and it is believed that galvanic deposition cannot produce an aluminum coating of the desired quality with the desired reproducibility.

[0045] Exemplary dry methods include physical vapor deposition (PVD) and ion vapor deposition (IVD), as well as plasma coating and atomic layer deposition (ALD). IVD produces an aluminum layer with a columnar structure. Peening is desirable before depositing further layers on top of it. Such aluminum layers also do not possess the desired quality. PVD, particularly Arc-PVD, is a recommended method for producing the aluminum layer of the composite coating of the present invention. PVD can produce an aluminum layer with the desired quality and thickness in a reasonable time and at a reasonable cost. In particular, PVD produces a homogeneous aluminum layer. For this reason, the composite coating of the present invention includes at least one aluminum layer deposited by PVD, preferably Arc-PVD. In a composite coating containing two or more aluminum layers, the additional aluminum layer can be deposited by another method, such as IVD, but preferably both aluminum layers are deposited by PVD to take advantage of the benefit of having a homogeneous aluminum barrier at different locations within the composite coating.

[0046] Exemplary reaction conditions for the PVD process to coat the first or second aluminum layer include a temperature in the range of about 200°C to 260°C and an inert gas atmosphere, such as an argon gas atmosphere.

[0047] ALD can be applied similarly, but it is time-consuming and costly.

[0048] The exemplary aluminum layers have a thickness of 0.5 μm to 15 μm. From the viewpoint of obtaining optimal corrosion protection, it is desirable for each of the one or more aluminum layers to be thicker, but the thicker the layer, the more time is required for coating (making the process more expensive), and as mentioned earlier, thicker coatings are disadvantageous in that the distance between the magnet and winding in the electric motor of the blood pump increases. For this reason, the preferred thickness is 15 μm or less. On the other hand, composite coatings containing aluminum layers less than 0.5 μm thick cannot reliably obtain sufficient corrosion protection. This is also true for coatings with two or more aluminum layers. Therefore, the preferred thickness is 0.5 μm or more. Regardless of whether the aluminum layer is in the first layer structure or the second layer structure, the more preferred thickness of the aluminum layer is 1 μm to 10 μm, and the particularly preferred thickness is 1 μm to 5 μm.

[0049] When aluminum is exposed to air, a passive oxide layer forms. This naturally formed oxide layer is only a few nanometers thick, usually about 2 to 3 nm, and adheres well to the underlying aluminum metal layer. It has been found that significantly increasing the thickness of the aluminum oxide layer beyond that of the natural aluminum oxide layer can improve the corrosion protection effect of composite coatings containing the aluminum layer. The preferred thickness range is 50 to 200 nm. While not strictly necessary, forming the aluminum oxide layer on top of the underlying aluminum layer is advantageous. Rather, the aluminum oxide layer can be formed on top of an organic layer, such as a poly(2-chloro-p-xylylene) layer in the underlying first layer structure, or on top of a linker layer in the first layer structure.

[0050] In this invention, the aluminum oxide layer is preferably coated by atomic layer deposition (ALD). In principle, other deposition methods such as anodizing are also possible, which can produce aluminum oxide layers with a maximum thickness of 1 μm at low cost. However, composite coatings containing aluminum oxide produced by anodizing are inferior in terms of the durability of their corrosion prevention effect. This is thought to be due to the microscopic structure of the aluminum oxide layer. In anodizing, a layer is created in which fine channels containing ions extend throughout the entire layer. These channels must be blocked by the overcoating layer, and if some channels remain open, or if some channels are exposed due to wear or corrosion of the overcoating layer while the coated magnet is in use, each channel becomes an entry point for corrosive purging liquid. This drawback can be somewhat compensated for by making the coating thicker, for example, 500 to 1,000 nm.

[0051] Methods for obtaining a channelless aluminum oxide layer, such as PVD and IVD, are more preferred, as they allow for a reduction in the thickness of the aluminum oxide layer to, for example, a range of about 200 to 500 nm while providing sufficient corrosion protection.

[0052] However, the preferred method for forming the aluminum oxide layer is atomic layer deposition (ALD). Therefore, the composite coating of the present invention includes at least one aluminum oxide layer deposited by atomic layer deposition. This aluminum oxide layer has a thickness of at least 50 nm and can constitute a first layer structure or a second layer structure. Regardless of whether the aluminum oxide layer is a component of the first or second layer structure, it is deposited by the ALD method until it is a layer with a thickness of at least 50 nm, preferably 50 nm to 200 nm, and more preferably 80 nm to 120 nm. In a composite coating including a first layer structure and a second layer structure, only one of the layer structures must include an aluminum oxide layer deposited by ALD to a thickness of at least 50 nm. The other layer structure may or may not include an aluminum oxide layer, and if it does, this layer may be deposited by ALD or other methods.

[0053] ALD (Advanced Laser Deposition) is a thin-film deposition method that grows thin films on a substrate by alternately exposing the substrate surface to gaseous substances, or so-called precursors. The precursors are introduced into the reactor containing the substrate to be coated in a series of continuous, non-overlapping pulses; in other words, multiple precursors are never present in the reactor simultaneously.

[0054] In each cycle, the precursor introduced into the reactor is adsorbed onto the surface of the substrate to be coated until all available reaction sites on the surface are consumed. Next, the excess precursor is removed from the reactor. Then, a second precursor, different from the first precursor, is introduced into the reactor, adsorbed onto the substrate surface, and chemically reacted with the previously adsorbed first precursor. Next, the excess precursor and gaseous reaction products are again removed from the reactor. Depending on the type of layer to be deposited, yet another precursor, different from the first and second precursors, can be introduced into the reactor, adsorbed and reacted, and the excess precursor and reaction products can be removed from the reactor.

[0055] Exposure to all precursors once is referred to as one ALD cycle.

[0056] Ideally, each ALD cycle generates a single layer of the coating material. In other words, ALD allows for atomic-level control of the layer thickness and composition. This enables the coating of large substrates with complex shapes with a uniform, easily conformable coating that does not have defects that could make the composite coating susceptible to corrosive attack.

[0057] In this invention, an artificially created aluminum oxide layer can be formed on an aluminum layer, on a natural oxide layer already formed on an aluminum layer, on an organic layer with a first layer structure, or on a linker layer between the first and second layer structures. Preferred precursor materials for carrying out the ALD process are AlX3 and water (gaseous). In AlX3, X represents a lower alkyl group (which may be the same or different), or a lower alkyl group (which may be the same or different) and hydrogen, or a halogen atom (which may be the same or different). Particularly preferred AlX3 compounds are trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), dimethylaluminum (DMAIH), and aluminum trichloride (AlCl3).

[0058] In an exemplary ALD process for producing a first-layer, second-layer, or both aluminum oxide layer, a magnet is placed in the reaction chamber, and AlX3, added to a suitable inert carrier gas, such as argon, is introduced into the reaction chamber at a suitable temperature, e.g., about 300°C. The AlX3 is adsorbed almost instantaneously onto the surface (aluminum or naturally formed aluminum oxide or organic or linker layer), and excess AlX3 and carrier gas are removed by evacuating to, for example, about 0.1 to 0.01 Pa. Then, moist air is introduced. The water contained in the air is adsorbed onto the surface and reacts with the AlX3, generating aluminum oxide and HX on the surface. The reaction chamber is again evacuated to about 0.1 to 0.01 Pa to remove the air, excess AlX3, and further HX.

[0059] A complete ALD cycle takes approximately 10 to 12 seconds and produces an aluminum oxide coating layer with a thickness of approximately 0.1 nm. Therefore, to produce a particularly preferred aluminum oxide layer with a thickness of approximately 100 nm, an ALD processing time of approximately 3 hours is required.

[0060] The combined thickness of the aluminum / aluminum oxide layer is preferably small, i.e., about 15 μm or less. A thickness of 10 μm or less is particularly preferred.

[0061] To enhance the corrosion-preventive effect obtained by the inorganic layer, the inorganic layer is combined with a poly(p-xylylene) polymer layer. Poly(p-xylylene) polymer is known by the trade name parylene. Parylene is known to react with surfaces containing hydroxyl groups and form a thin, pinhole-free film. Furthermore, it has a low dielectric constant (approximately 3), which is advantageous for implantable blood pumps. A composite coating containing an aluminum and / or aluminum oxide layer and a parylene layer is biocompatible and also provides corrosion prevention. However, the adhesion of the parylene layer to the aluminum or aluminum oxide layer is not strong enough under the operating conditions of an intravascular blood pump. The parylene layer begins to peel off in an unacceptably short time, exposing the aluminum or aluminum oxide layer. The inorganic layer does not adequately protect the magnet, and thus corrosion of the magnet begins.

[0062] In accordance with the present invention, this scenario is prevented by combining several means (installation of an interfacial layer connecting the inorganic layer and the parylene layer, use of a specific parylene compound, installation of at least one aluminum layer having a homogeneous structure as obtained by physical vapor deposition, and installation of at least one relatively thick aluminum oxide layer having a dense and virtually defect-free structure as obtained by ALD deposition).

[0063] Compounds that form an interfacial layer within the first and / or second layer structure, or between the first and second layer structures, i.e., linker compounds, must be difunctional. Difunctionality means that the linker compound has two functional groups or molecular parts with different functionalities (reactivity), where one functional group or molecular part reacts, for example, with a hydroxyl group on the surface of the inorganic layer and bonds to the inorganic layer, and the other functional group or molecular part bonds to parylene, thereby firmly bonding the inorganic layer and the organic parylene layer. The bond can be a covalent bond or other bond, such as van der Waals forces.

[0064] Linkers are known that have a functional group or moiety that bonds to a metal or metal oxide and a functional group or moiety that bonds to parylene. Exemplary linkers include silane compounds, mercaptans, phosphines, disulfides, and silanes having thiol, phosphine, or disulfide groups. In the present invention, the linker is preferably an alkoxysilane such as methoxysilanes and ethoxysilanes, for example, a silane represented by the structural formula (H3CO)3Si-R, where R is, for example, methacrylate, alkylamine, phenylamine, or epoxyalkyl. To bond to parylene, the linker preferably has an acryloyloxy or methacryloyloxy functional group. The carbon chain length between the silyl moiety and the (meth)acryloyloxy moiety of the linker typically contains 1 to 16 carbon atoms (methyl, ethyl, propyl, butyl, pentyl…). The hydrocarbon chain is generally saturated, but may contain one or more unsaturated bonds. A particularly preferred linker is Silquest's 3-(trimethoxysilyl)propyl methacrylate (A-174), but other silane compounds such as Silquest's G-170 (vinyl-functionalized silane coupling agent) are also suitable. Furthermore, linkers with bistrimethoxysilyl or bistriethoxysilyl functionality, such as bis(trimethoxysilylethyl)benzene, may also be used.

[0065] The bifunctional linker is preferably coated onto the surface (aluminum or aluminum oxide with a first or second layer structure, or a parylene layer with a first layer structure) by plasma coating, physical vapor deposition without plasma, or by applying an aprotic solution, alcohol, or aqueous solution of the bifunctional linker compound to the surface to be coated. Dry coating of a silane compound in a plasma chamber creates a glassy layer containing Si-O-Si-O chains that are aligned almost parallel to the inorganic surface and bonded to the surface via oxygen atoms. Organic residues face the opposite side of the surface and can be used for bonding with parylene. Physical vapor deposition and wet coating form an interface layer with a similar structure but without a glassy appearance.

[0066] Plasma deposition results in a dense layer with good adhesion to parylene. Physical deposition without plasma produces a layer with better adhesion to parylene but lower density than the plasma-deposited layer. Wet coating produces a very dense monolayer with an irregular network structure, high degree of crosslinking, and a high proportion of silicon-bonded oxygen. This layer also adheres very well to the parylene layer. Therefore, wet coating is particularly preferred.

[0067] Alternatively, plasma coating can be combined with physical vapor deposition (without plasma) or wet coating processes; that is, a glassy interface layer can be formed first by plasma vapor deposition, and then a second linker layer can be formed by physical vapor deposition or wet coating to create a composite linker layer. In such a composite linker layer, the silicon atoms of the glassy layer are covalently bonded to the oxygen atoms of the second layer, and the organic residues of the second layer (methacrylate, alkylamine, epoxyalkyl, etc.) can be used for bonding with parylene by covalent bonding or by other means, such as van der Waals forces.

[0068] The interfacial layer typically has a thickness in the range of 10 to 100 nm, preferably 20 to 50 nm. Alternatively, only a single layer may be applied. The single layer can be obtained by coating a solution of the linker compound and evaporating the solvent.

[0069] In the first layer structure, and in the second layer structure if one exists, the parylene layer, i.e., the poly(p-xylylene) polymer layer, is formed on the interface layer. The poly(p-xylylene) polymer has the following structural formula. [ka] In the formula, n is the degree of polymerization.

[0070] The precursors of poly(p-xylylene) compounds are the [2.2] paracyclophanes, which have the following structural formula. [ka]

[0071] Dimeric compounds, such as precursors to parylene N, parylene C, parylene D, and parylene F, are commercially available. In parylene N, X and all of R1 through R4 are hydrogen; in parylene C, one of R1 through R4 is chlorine and the other residues R and X are hydrogen; in parylene D, two of R1 through R4 are chlorine and all other residues are hydrogen; and in parylene F, residue X is fluorine and residues R1 through R4 are hydrogen. Parylene layers are typically used as moisture barriers and dielectric barriers.

[0072] Under vacuum and high temperature (approximately 500°C or higher, depending on the specific parylene), the dimer decomposes to generate the corresponding p-xylylene radicals. These monomers polymerize to form poly(p-xylylene) polymers, on the one hand, and to bond to the interfacial layer via functional groups, such as methacrylate groups, on the other hand. Alternatively, they can simply adhere to the hydrophobic portions of the interfacial layer.

[0073] According to the present invention, it has been found that coating the composite coating of the present invention with parylene C, in which one of R1 to R4 is chlorine, as a cover layer for the first layer structure, or an optional second layer structure, forms a coating that makes the magnetic material corrosion-resistant under the conditions encountered by intravascular blood pumps. The parylene C layer is preferably coated by plasma deposition, and the thickness of the layer is preferably in the range of 5 to 25 μm, more preferably 10 to 20 μm. A thickness of about 15 μm is particularly preferred.

[0074] When parylene C is directly applied to the surface of a magnetic material, cracking and delamination of the protective parylene C layer, as well as corrosion of the magnetic material, are observed within a few days. Similarly, when parylene C is applied to an aluminum layer or an aluminum / aluminum oxide layer, corrosion of the magnetic material is observed within an unacceptably short time due to delamination under conditions within an intravascular blood pump. Furthermore, parylene compounds other than parylene C do not provide sufficient corrosion protection even when used with adhesion promoters, for example, when applied to a silane-based interface layer.

[0075] The composite coating of the present invention exhibits excellent adhesion to magnetic materials and, having a structure composed of both inorganic and organic components, provides an effective barrier against both inorganic and organic substances. This barrier property is further enhanced by the particularly homogeneous structure of the PVD-deposited aluminum layer and the particularly dense structure of the ALD-deposited aluminum oxide layer. The glassy interface layer also possesses barrier properties.

[0076] In embodiments of the present invention, the corrosion prevention effect of the magnetic material is further enhanced by specifically adapting the shape of the magnet body to allow for the formation of a coating of uniform thickness over the magnet body. For this purpose, the magnet body has no sharp angles and has a rounded shape, such as a gentle edge. Preferably, the magnet body is rod-shaped with a groove extending longitudinally through it to receive the motor shaft of the intravascular blood pump, and the opposing front surfaces of the magnet body are inclined toward the groove. In the intravascular blood pump, the groove receives and is fixed to the motor shaft, so it is not necessary to cover the groove with a composite coating. Of course, the groove may still be covered for safety.

[0077] The magnetic body may be a single component or may consist of several segments. In the latter case, each segment is provided with the coating of the present invention to a uniform thickness, either completely surrounding it or at least on its exposed surface. Preferably, each segment has a smooth edge.

[0078] The present invention will be further described with reference to the attached figures.

[0079] The drawings are not to scale. These should not be construed as limiting the invention in any way.

[0080] The intravascular blood pump 10 shown in Figure 1 was described earlier. The pump has a conventional structure, but it includes a corrosion-resistant permanent magnet 1 according to the present invention.

[0081] In the pump shown in Figure 1, magnet 1 is rod-shaped, with opposing front surfaces that are flat and parallel to each other. The composite coating according to the present invention can effectively protect a magnet body with sharp angles, as shown in Figure 1, from corrosion over a long period of time, but in the present invention, it is preferable to use a magnet body with the shape shown in Figure 4. Each layer of the composite coating is completely spread over the composite coating layer applied to the front of each.

[0082] Figure 2 is a schematic cross-sectional view showing a portion of a magnet 1 equipped with a composite coating 15 including a single-layer structure (i.e., a “first” layer structure). The composite coating 15 is formed on the surface 19' of an unmagnetized magnet body 19. The composite coating 15 includes a first aluminum layer 44 formed on the surface 19' of the magnet body 19 by physical vapor deposition. An aluminum oxide layer 45 is deposited on the surface 44' of the aluminum layer 44 by atomic layer deposition. The aluminum layer and the aluminum oxide layer together constitute the inorganic layer 41 of the composite coating 15. A linker layer 42 is formed on the surface 45' of the aluminum oxide layer, firmly bonding an organic layer 43 to the aluminum oxide layer 45. The organic layer 43 of the composite coating 15 consists of parylene C and covers the surface 42' of the linker layer 42.

[0083] Figure 3 is a schematic cross-sectional view showing a part of another magnet 1, which comprises a composite coating 16 including a first layer structure 17 and a second layer structure 18.

[0084] The first layer structure 17 consists of an aluminum layer 44, a first linker layer 42, and a first organic layer 43. The second layer structure 18 consists of an aluminum oxide layer 51, a second linker layer 52, and a second organic layer 53. The first aluminum layer 44 is formed on the surface 19' of the non-magnetized magnet body 19, the first linker layer 42 is formed on the surface 44' of the first aluminum layer 44, the first organic layer 43 is formed on the surface 42' of the first linker layer 42, the second aluminum oxide layer 51 is formed on the surface 43' of the first organic layer 43, the second linker layer 52 is formed on the surface 51' of the second aluminum oxide layer 51, and the second organic layer 53 is formed on the surface 52' of the second linker layer 52. The first and second organic layers are parylene C layers. The second organic layer 53 is the outermost layer of the composite coating 16.

[0085] The magnet 1 shown in Figure 3 has a composite coating 16 that includes a first layer structure 17 and a second layer structure 18, but it has only one aluminum layer (first aluminum layer 44) and only one aluminum oxide layer (second aluminum oxide layer 51). In this respect, composite coating 16 corresponds to composite coating 15 which has only one aluminum layer and only one aluminum oxide layer. Therefore, as in the case of composite coating 15, in order to obtain the optimal layer structure necessary for the best corrosion resistance, it is important to deposit the aluminum layer 44 by physical vapor deposition and deposit the aluminum oxide layer 51 to a thickness of at least 50 nm by atomic layer deposition.

[0086] When an additional aluminum oxide layer is provided between the first aluminum layer 44 and the first linker layer 42, it is not necessary to deposit the aluminum oxide layer by ALD, nor is it necessary for it to have a thickness of at least 50 nm, but it is preferable to deposit it by ALD to a thickness of at least 50 nm. Similarly, when an additional aluminum layer is provided between the first organic layer 43 and the second aluminum oxide layer 51, it is not necessary to deposit the aluminum layer by PVD, but it is preferable to do so.

[0087] In the composite coating 16 shown in Figure 3, the second layer structure 18 is formed directly on the first layer structure 17. However, in order to improve the bonding between the first layer structure 17 and the second layer structure 18, an additional linker layer may be applied to the surface 43' of the first organic layer 43 before coating with the second aluminum oxide layer 51, that is, the second layer structure 18 may be formed on the surface of the additional linker layer.

[0088] Figure 4a shows a rod-shaped, integrated magnet 1 with a hole or groove extending longitudinally through it. When this magnet is used in an intravascular blood pump 10 as shown in Figure 1, a motor shaft 25 is fitted into the groove. The opposing front surfaces 4 of the magnet are inclined toward the groove. The magnet 1 has a composite coating according to the present invention on the outer surface 2 exposed to the fluid flowing through the gap 26 and on the inclined front surface 4. The inner surface 3 adjacent to the motor shaft 25 may or may not be covered. The edge 5 of the transition between the outer surface 2 and the front surface 4, and the edge 6 of the transition between the front surface 4 and the inner surface 3 are covered. Because the edges are gentle, a uniform coating with good adhesion is easily formed. "N" and "S" indicate the north and south poles of the magnet.

[0089] Figure 4b is a partial cross-sectional view along the dashed line in Figure 4a. Figure 4b shows the magnetic portion within the circle in Figure 4a. Figure 4b clearly shows the smooth edges 5 and 6.

[0090] Figure 5 shows a segmented magnet 7. The magnet shown in Figure 5 has four segments 8 and 8'. Opposite segments 8 have the same magnetic polarity, as indicated by "N" in the top view of Figure 5, and similarly, opposite segments 8' have the same magnetic polarity, as indicated by "S" in the top view of Figure 5. As a result, adjacent segments 8 and 8' have opposite magnetic polarity.

[0091] Segments 8 and 8', like the integrated magnet shown in Figure 4, have an inner surface, an outer surface, opposing front surfaces, a transition edge between the outer surface and the front surface, and a transition edge between the front surface and the inner surface. Following the designation in Figure 4, the front surface is designated as 4', and the edges as 5' and 6', respectively. Furthermore, segments 8 and 8' have side surfaces 9 and 9' separated by a gap in the figure. Of course, when the magnet is in use, side surfaces 9 and 9' are in contact with each other. All surfaces of each segment of the magnet may be completely covered with the composite coating of the present invention, but it is not necessary to cover the side surfaces 9 and 9', which are not exposed because they are in contact with each other, and the inner surface, which is not exposed because it is in contact with the motor shaft. Preferably, all edges of all segments are smooth edges. [Examples]

[0092] Table 1 shows the results of corrosion tests on niobium-iron-boron magnets coated with various coatings. The same cylindrical, unmagnetized Nd2Fe magnets were 12 mm long and 2.8 mm in diameter. 14 Thirteen B sintered magnets were coated as described below and subjected to a corrosion test in an aqueous solution containing 0.9 wt% sodium chloride at 60°C. The test specimens were examined daily for 70 days. After 70 days, the test was terminated. When magnetic material corrodes, the coating lifts or deforms. In other words, the formation of lifting or blistering of the coating on the surface of the test specimen indicates corrosion of the magnetic material. The formation of a blister with a height of 0.1 mm and the lifting of the coating were defined as indicating damage to the magnet.

[0093] The test specimens were prepared using the following method.

[0094] All test specimens: Non-magnetized neodymium iron boron magnets (passivated with phosphate at the time of purchase) were washed with isopropanol and dried in an air stream. Next, the coating was applied, and after coating, the coated magnets were magnetized in a magnetic field. It is not appropriate to magnetize the magnets before applying the composite coating of the present invention. The coating thicknesses were approximately 1 μm, 2 μm, and 3 μm for the aluminum layers, approximately 60 nm for the aluminum oxide layers of test specimens 4, 5, and 6, approximately 100 nm for all other test specimens, approximately 1 μm for the silane layer, and approximately 15 μm (±2 μm) for the parylene layer (if coated).

[0095] Unless otherwise specified, the aluminum layer was coated with Arc-PVD, the aluminum oxide layer was coated with ALD using TEA as a precursor compound, the silane adhesion promoter (Silane A-174) was coated using an aqueous solution, and parylene C was also coated with plasma coating. The adhesion promoter constitutes the linker.

[0096] Test specimens 1 to 3: A dry magnetic body was coated with layers consisting of aluminum (layer thickness of 1 μm for test specimen 1, 2 μm for test specimen 2, and 3 μm for test specimen 3), aluminum oxide, adhesion promoter, and parylene C, in the order listed above.

[0097] Test specimens 4 to 6: A dry magnet body was coated with layers consisting of aluminum (layer thickness of 1 μm for test specimen 4, 2 μm for test specimen 5, and 3 μm for test specimen 6), an adhesion promoter, parylene C, aluminum oxide, an adhesion promoter, and parylene C, in the order listed above.

[0098] Test specimens 7 to 9: A dry magnetic body was coated with layers of aluminum (layer thickness of 1 μm for test specimen 7, 2 μm for test specimen 8, and 3 μm for test specimen 9), an adhesion promoter, and parylene C, in the order listed above.

[0099] Test specimens 10 to 12: Dry magnetic bodies were coated with layers of aluminum (layer thickness of 1 μm for test specimen 10, 2 μm for test specimen 11, and 3 μm for test specimen 12) and aluminum oxide, in the order listed above.

[0100] Test specimen 13: A dry magnet body was provided with layers of aluminum and aluminum oxide in the order listed above. The thickness of the aluminum layer was 1 μm, and the thickness of the aluminum oxide layer was 17 μm. The aluminum oxide was coated by electroplating.

[0101] [Table 1] Coated Nd2Fe in 0.9% NaCl solution at 60°C 14 Test results for magnet B. A magnet is considered damaged if the coating lifts or buckles by 0.1 mm. A magnet is considered to have passed the test if it lasts for at least 70 days before breaking. In this invention, a magnet is considered corrosion-resistant if it passes the test, that is, if the time until failure is at least 70 days.

[0102] Each of the test specimens 10 through 12, which consisted of an aluminum layer and an aluminum oxide layer (coated with ALD), but had a composite coating without an organic layer, all failed within two days, but longer than one day.

[0103] Test specimen 13, which had a very thick layer of aluminum oxide, also fractured in less than 24 hours. Test specimen 13 appeared intact after 12 hours.

[0104] Test specimens 7, 8, and 9 had a composite coating consisting of an aluminum layer, a parylene C layer, and an adhesion promoter between them. Test specimen 7, with a 1 μm thick aluminum layer, broke after 9 days; test specimen 8, with a 2 μm thick aluminum layer, broke after 36 days; and test specimen 9, with a 3 μm thick aluminum layer, passed the test but showed some buckling.

[0105] Test specimens 1, 2, and 3, each equipped with a composite coating (single-layer structure) according to the present invention, and whose coating consists of an aluminum layer, an aluminum oxide layer, a parylene C layer, and an adhesion promoter between them, showed no signs of corrosion even after 70 days (at which point the test was terminated).

[0106] Test specimens 4, 5, and 6, each equipped with the composite coating according to the present invention, and having a first layer structure and a second layer structure, each layer structure consisting of an inorganic layer, a linker layer on the inorganic layer, and an organic layer made of parylene C on the linker layer, behaved similarly to test specimens 1, 2, and 3. None of the test specimens 4, 5, and 6 showed any signs of corrosion at the end of the test, i.e., 70 days later.

[0107] The above test results clearly demonstrate that neodymium iron boron permanent magnets with a composite coating comprising a specific layer arrangement, namely, a first layer structure and optionally a second layer structure, as previously described, with at least one aluminum layer coated with PVD and at least one aluminum oxide layer coated with ALD with a thickness of at least 50 nm, exhibit excellent corrosion resistance even under harsh conditions and are advantageous for use in intravascular blood pumps. These test results also demonstrate that the coating method of the aluminum oxide layer affects corrosion resistance. Please refer to the comparison of test specimens 10 to 12 and test specimen 13.

[0108] Similarly, these test results indicate that the thickness of the aluminum layer affects corrosion resistance. This is evident when comparing test specimens 7, 8, and 9.

[0109] Furthermore, it is clear that in order to achieve optimal corrosion resistance, an aluminum layer, an aluminum oxide layer, a linker layer (adhesion promoter), and a parylene C layer must be present in combination.

[0110] To obtain the optimal corrosion prevention effect, it is desirable to apply the composite coating of the present invention to an unmagnetized magnet and magnetize the magnet only after the coating has been applied.

[0111] Test specimens 1, 2, 3, 4, 5, and 6 met the above conditions. Non-magnetized magnets were coated with the composite coating of the present invention, and all specimens were magnetized after coating. As a result, even after being placed in a 0.9 wt% NaCl solution at 60°C for at least 70 days, test specimens 1 to 6 showed no lifting of the coating, and buckling was less than 0.1 mm. Therefore, test specimens 1 to 6 are corrosion-resistant magnets in the sense of the present invention.

[0112] [Implementation Method] [Embodiment 1] A corrosion-resistant permanent magnet, wherein the magnet is A magnetic body and A composite coating provided on the aforementioned magnet body and covering its surface, Includes, The composite coating comprises a first layer structure on the magnet body and, optionally, a second layer structure on the first layer structure. Each of the aforementioned layer structures is Inorganic layer and The linker layer on the inorganic layer, An organic layer made of poly(2-chloro-p-xylylene) on the aforementioned linker layer, This includes, in the order listed, The inorganic layer of the first layer structure includes either an aluminum layer on the magnet body, or an aluminum layer on the magnet body and an aluminum oxide layer on the aluminum layer. The inorganic layer of the second layer structure includes at least one of an aluminum layer or an aluminum oxide layer. The composite coating comprises at least one aluminum oxide layer having a thickness of at least 50 nm. A magnet characterized by the following features. [Embodiment 2] A magnet according to Embodiment 1, characterized in that a linker layer is provided between the first layer structure and the second layer structure. [Embodiment 3] A magnet according to Embodiment 1 or 2, characterized in that the inorganic layer of the second layer structure is an aluminum oxide layer. [Embodiment 4] A magnet according to any one of embodiments 1 to 3, characterized in that the magnetic body is a sintered magnetic body. [Embodiment 5] A magnet according to any one of Embodiments 1 to 4, characterized in that the magnetic body is a rare earth metal iron-boron permanent magnet.

[0113] [Embodiment 6] A magnet according to any one of embodiments 1 to 5, characterized in that the magnetic body is rod-shaped with all edges rounded. [Embodiment 7] A magnet according to any one of Embodiments 1 to 6, characterized in that the linker forming at least one of the linker layers is selected from silanes and silanes having a thiol, phosphine, or disulfide group. [Embodiment 8] A magnet according to Embodiment 7, characterized in that the linker is selected from 3-(2-pyridylethyl)thiopropyltrimethoxysilane, 3-(4-pyridylethyl)thiopropyltrimethoxysilane, and 2-(diphenylphosphino)ethyltriethoxysilane. [Embodiment 9] A magnet according to any one of Embodiments 1 to 8, characterized in that the thickness of the aluminum layer of the first layer structure and / or the second layer structure is 0.5 μm to 15 μm, or 1 μm to 10 μm, or 1 μm to 5 μm. [Embodiment 10] A magnet according to any one of Embodiments 1 to 9, characterized in that the thickness of the aluminum oxide layer of the first layer structure and / or the second layer structure is 50 nm to 200 nm, or 80 nm to 120 nm.

[0114] [ment11] A magnet according to any one of Embodiments 1 to 10, characterized in that the combined thickness of the aluminum layer and the aluminum oxide layer of the first layer structure and / or the second layer structure is in the range of 5 μm to 15 μm. [Embodiment 12] A magnet according to any one of embodiments 1 to 11, characterized in that at least one of the linker layers is a single layer, or the linker layer has a thickness in the range of 20 nm to 50 nm. [Embodiment 13] A magnet according to any one of Embodiments 1 to 12, characterized in that the thickness of the poly(2-chloro-p-xylylene) layer of the first layer structure and / or the second layer structure is in the range of 5 μm to 20 μm. [Embodiment 14] A magnet according to any one of Embodiments 1 to 13, characterized in that the thickness of the composite coating is 200 μm or less, preferably 50 μm or less. [Embodiment 15] A magnet according to any one of embodiments 1 to 14, characterized in that all layers of the composite coating are completely spread over all surfaces of the magnetic body.

[0115] [Embodiment 16] A method for manufacturing a corrosion-resistant permanent magnet, wherein the method is The process of preparing an unmagnetized magnet, A step of forming a first layer structure on the magnet body by depositing an inorganic layer on the surface of the magnet body, depositing a linker layer on the inorganic layer, and depositing a poly(2-chloro-p-xylylene) layer on the linker layer, If necessary, the process involves depositing an inorganic layer on the first layer structure, depositing a linker layer on the inorganic layer, and depositing a poly(2-chloro-p-xylylene) layer on the linker layer to form a second layer structure on the first layer structure, The process of magnetizing the aforementioned magnet body, Includes, The step of depositing the inorganic layer of the first layer structure includes either a step of depositing an aluminum layer on the magnet body, or a step of depositing an aluminum layer on the magnet body and an aluminum oxide layer on the aluminum layer. The step of depositing the two-layer inorganic layer includes a step of depositing an aluminum layer on the first layer, or a step of depositing an aluminum oxide layer on the first layer, or a step of depositing an aluminum layer on the first layer and an aluminum oxide layer on the aluminum layer. At least one aluminum layer is deposited by physical vapor deposition, At least one aluminum oxide layer is deposited to a thickness of at least 50 nm using atomic layer deposition. A method characterized by the following: [Embodiment 17] A method according to Embodiment 16, characterized in that a linker layer is deposited on the first layer structure. [Embodiment 18] A method according to Embodiment 16 or 17, characterized in that an aluminum oxide layer is deposited as the inorganic layer of the second layer structure. [Embodiment 19] A method according to any one of embodiments 16 to 18, characterized in that the magnet body is a magnet body as defined in any one of claims 4 to 6. [Embodiment 20] A method according to any one of embodiments 16 to 19, characterized in that the aluminum oxide layer of the first layer structure and / or the second layer structure is produced from AlX3 as a first precursor compound and H2O as a second precursor compound, wherein X represents a lower alkyl group (which may be the same or different), or a hydrogen atom and a lower alkyl group (which may be the same or different), or a halogen atom (which may be the same or different).

[0116] [Embodiment 21] A method according to Embodiment 20, characterized in that AlX3 is selected from the group consisting of trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), dimethylaluminum (DMAIH), and AlCl3. [Embodiment 22] A method according to any one of embodiments 16 to 21, characterized in that at least one of the linker layers is formed by a step of coating the linker using plasma-based physical deposition, non-plasma-based physical deposition, or from a solution. [Embodiment 23] A method according to any one of embodiments 16 to 22, characterized in that at least one linker in the linker layer is a linker defined in embodiment 7 or 8. [Embodiment 24] A method according to any one of embodiments 16 to 23, characterized in that the poly(2-chloro-p-xylylene) layers of the first layer structure and / or the second layer structure are formed by plasma deposition of dichloro[2.2]paracyclophane. [Embodiment 25] A method according to any one of embodiments 16 to 24, characterized in that the layers of the first layer structure and / or the second layer structure have the thickness defined in any one of embodiments 9 to 14.

[0117] [Embodiment 26] An intravascular blood pump comprising an electric motor, wherein the electric motor comprises a permanent magnet as described in any of Embodiments 1 to 15.

Claims

1. A corrosion-resistant permanent magnet, wherein the magnet is A magnetic body and A composite coating provided on the aforementioned magnet body and covering its surface, Includes, The composite coating comprises a first layer structure on the magnet body and, optionally, a second layer structure on the first layer structure. Each of the aforementioned layer structures is Inorganic layer and The linker layer on the inorganic layer, An organic layer made of poly(2-chloro-p-xylylene) on the aforementioned linker layer, This includes, in the order listed, The inorganic layer of the first layer structure includes an aluminum layer on the magnet body, or includes an aluminum layer on the magnet body and an aluminum oxide layer on the aluminum layer. The inorganic layer of the second layer structure includes at least one of an aluminum layer or an aluminum oxide layer. The composite coating comprises at least one aluminum oxide layer. A magnet characterized by the following features.

2. A magnet according to claim 1, wherein the thickness of the aluminum layer of the first layer structure and / or the second layer structure is 0.5 μm to 15 μm, 1 μm to 10 μm, or 1 μm to 5 μm.

3. A corrosion-resistant permanent magnet, wherein the magnet is A magnetic body and A composite coating provided on the aforementioned magnet body and covering its surface, Includes, The composite coating comprises a first layer structure on the magnet body and, optionally, a second layer structure on the first layer structure. Each of the aforementioned layer structures is Inorganic layer and The linker layer on the inorganic layer, An organic layer made of poly(2-chloro-p-xylylene) on the aforementioned linker layer, This includes, in the order listed, The inorganic layer of the first layer structure includes an aluminum layer on the magnet body, or includes an aluminum layer on the magnet body and an aluminum oxide layer on the aluminum layer. The inorganic layer of the second layer structure includes at least one of an aluminum layer or an aluminum oxide layer. The composite coating comprises at least one aluminum layer having a thickness of 3 μm to 15 μm. A magnet characterized by the following features.

4. A magnet according to claim 3, wherein the thickness of the aluminum layer of the first layer structure and / or the second layer structure is 3 μm to 10 μm or 3 μm to 5 μm.

5. A magnet according to any one of claims 1 to 4, wherein a linker layer is provided between the first layer structure and the second layer structure.

6. A magnet according to any one of claims 1 to 5, wherein the inorganic layer of the second layer structure is an aluminum oxide layer.

7. A magnet according to any one of claims 1 to 6, wherein the magnetic body is a sintered magnetic body.

8. A magnet according to any one of claims 1 to 7, wherein the magnetic body is a rare earth metal iron boron permanent magnet.

9. A magnet according to any one of claims 1 to 8, wherein the magnetic body is rod-shaped with all edges rounded.

10. A magnet according to any one of claims 1 to 9, wherein the linker forming at least one of the linker layers is selected from silanes and silanes having a thiol, phosphine, or disulfide group.

11. A magnet according to claim 10, wherein the linker is selected from 3-(2-pyridylethyl)thiopropyltrimethoxysilane, 3-(4-pyridylethyl)thiopropyltrimethoxysilane, and 2-(diphenylphosphino)ethyltriethoxysilane.

12. A magnet according to any one of claims 1 to 11, wherein the thickness of the aluminum oxide layer of the first layer structure and / or the second layer structure is 50 nm to 200 nm, or 80 nm to 120 nm.

13. A magnet according to any one of claims 1 to 12, wherein the combined thickness of the aluminum layer and the aluminum oxide layer of the first layer structure and / or the second layer structure is in the range of 5 μm to 15 μm.

14. A magnet according to any one of claims 1 to 13, wherein at least one of the linker layers is a single layer, or the linker layer has a thickness in the range of 20 nm to 50 nm.

15. A magnet according to any one of claims 1 to 14, wherein the thickness of the poly(2-chloro-p-xylylene) layer of the first layer structure and / or the second layer structure is in the range of 5 μm to 20 μm.

16. A magnet according to any one of claims 1 to 15, wherein the thickness of the composite coating is 200 μm or less, preferably 50 μm or less.

17. A magnet according to any one of claims 1 to 16, wherein all layers of the composite coating are spread completely over all surfaces of the magnetic body.

18. A method for manufacturing a corrosion-resistant permanent magnet, wherein the method is A step of forming a first layer structure on the magnet body by depositing an inorganic layer on the surface of the magnet body, depositing a linker layer on the inorganic layer, and depositing a poly(2-chloro-p-xylylene) layer on the linker layer, If necessary, the process involves depositing an inorganic layer on the first layer structure, depositing a linker layer on the inorganic layer, and depositing a poly(2-chloro-p-xylylene) layer on the linker layer to form a second layer structure on the first layer structure, Includes, The step of depositing the inorganic layer of the first layer structure includes either a step of depositing an aluminum layer on the magnet body, or a step of depositing an aluminum layer on the magnet body and an aluminum oxide layer on the aluminum layer. The step of depositing the two-layer inorganic layer includes a step of depositing an aluminum layer on the first layer, or a step of depositing an aluminum oxide layer on the first layer, or a step of depositing an aluminum layer on the first layer and an aluminum oxide layer on the aluminum layer. At least one aluminum layer is deposited by physical vapor deposition, A method for depositing at least one aluminum oxide layer using atomic layer deposition.

19. A method according to claim 18, further comprising the steps of preparing an unmagnetized magnet and magnetizing the magnet.

20. A method according to claim 18 or 19, wherein the at least one aluminum layer to be deposited by physical vapor deposition is deposited by physical vapor deposition to a thickness of 3 μm to 15 μm.

21. A method according to any one of claims 18 to 20, comprising depositing a linker layer on the first layer structure.

22. A method according to any one of claims 18 to 21, wherein an aluminum oxide layer is deposited as the inorganic layer of the second layer structure.

23. A method according to any one of claims 18 to 22, wherein the magnet body is a magnet body as defined in any one of claims 4 to 6.

24. A method according to any one of claims 18 to 23, wherein the aluminum oxide layer of the first layer structure and / or the second layer structure is AlX as the first precursor compound. ３ And H as the second precursor compound ２ A method for generating from O, wherein X represents a lower alkyl group (which may be the same or different), or a hydrogen atom and a lower alkyl group (which may be the same or different), or a halogen atom (which may be the same or different).

25. The method according to claim 24, wherein AlX ３ However, trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), dimethylaluminum (DMAlH), and AlCl ３ A method selected from a group consisting of the following.

26. A method according to any one of claims 18 to 25, wherein at least one of the linker layers is formed by a step of coating the linker using plasma-based physical deposition, or by non-plasma-based physical deposition, or from a solution.

27. A method according to any one of claims 18 to 26, wherein at least one linker in the linker layer is a linker as defined in claim 10 or 11.

28. A method according to any one of claims 18 to 27, wherein the poly(2-chloro-p-xylylene) layers of the first layer structure and / or the second layer structure are formed by plasma deposition of dichloro[2.2]paracyclophane.

29. A method according to any one of claims 18 to 28, characterized in that the layers of the first layer structure and / or the second layer structure have the thickness defined in any one of claims 2, 4, and 12 to 16.

30. An intravascular blood pump comprising an electric motor, wherein the electric motor comprises a permanent magnet as described in any one of claims 1 to 17.

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