Method and apparatus for coating the inner wall of a tubular substrate

Abstract

Method for coating an inner wall of a tubular substrate (900, 1000, 1300) with vaporized coating material by means of chemical vapor deposition or by means of physical vapor deposition, wherein at least one end of the tubular substrate (900, 1000, 1300) has an opening (901, 1001, 1002, 1301) through which the coating material can penetrate the tubular substrate (900, 1000, 1300), and wherein the method comprises the following steps: - Imprinting a temperature profile along the longitudinal direction of the wall of the tubular substrate (900, 1000, 1300) by means of a temperature control device comprising a plurality of temperature control elements (903-906, 1003-1008, 1104, 1107, 1303, 1304) arranged along the longitudinal direction of the tubular substrate (900, 1000, 1300), wherein each of the temperature control elements (903-906, 1003-1008, 1104, 1107, 1303, 1304) is designed to be heated or cooled to a predetermined temperature, wherein the temperature in the area near the at least one opening (901, 1001, 1002, 1301) of the tubular substrate (900, 1000, 1300) is higher than the temperature at the areas of the inner wall furthest from the at least one opening (901, 1001, 1002, 1301); - Deposition of the coating material on the inner wall of the tubular substrate (900, 1000, 1300), wherein, with increasing distance from the at least one opening (901, 1001, 1002, 1301), the concentration of the coating material inside the tubular substrate (900, 1000, 1300) decreases as a result of the deposition of the coating material on the inner wall of the tubular substrate (900, 1000, 1300).

Description

[0001] The invention relates to a method for coating an inner wall of a tubular substrate with evaporated coating material and a coating device for coating an inner wall of a tubular substrate with evaporated coating material.

[0002] In many technological fields, the surface properties of products and workpieces are modified and adapted to specific requirements through the targeted application of coatings. Such surface finishing allows the product or workpiece to be tailored to the demands of its intended use. A particular challenge is applying a coating of uniform thickness to even complex, three-dimensional surfaces.

[0003] One particular challenge is coating the inner walls of tubular substrates such as hoses and pipes, as well as cavities, hollow spaces, and blind holes, with a coating of uniform thickness. In the field of medical technology, for example, the coating of the inner walls of catheters, cannulas, capillaries, ureteral stents, artificial bladders, and other hoses, tubes, and cavities is important. Such products can, for instance, be coated with a material that improves biocompatibility or with an antimicrobial coating.

[0004] German patent application DE 29 28 980 A1 describes a process for forming a metal oxide film on the inner surface of glass tubes. The process comprises drawing a glass tube from a container of molten glass, wherein the glass in the tube area is above its softening temperature, and subsequently, the vertical movement gradually becomes a horizontal movement while a glass tube is formed by drawing and rolling. Simultaneously, an evaporated metal compound is injected into the tube area along with an oxidizing agent that reacts with the metal compound to form an oxide of the metal, which is deposited on the inner surface of the glass tube as a coating or film.

[0005] German patent application DE 24 45 564 A1 describes a method for coating the inner surfaces of hollow bodies, particularly tubes. This method employs a chemical vapor deposition (CVD) process, in which the hollow bodies are heated zone by zone to a deposition temperature, so that the coating is applied only to the heated zones. Preferably, metal acetylacetonates, metal carbonyls, or metal halides are decomposed in a carrier gas stream.

[0006] European patent application EP 0 064 785 A1 describes a method and an arrangement for the internal coating of a tube by reactive deposition from a gas mixture activated by a plasma. Tubes made of an electrically insulating material such as SiO2 are internally coated by reactive deposition from a gas mixture flowing through the tube. The deposition is activated by a plasma within the tube that moves along its length. The plasma is generated within the tube by high-frequency electrical energy, which is capacitively coupled into the gas phase by means of two flames acting at two longitudinally spaced points on the outside of the tube. These points move along the tube during the reactive deposition. A high-frequency generator is electrically connected to the burners that generate the flames.

[0007] German patent application DE 28 29 568 A1 describes a process for the uniform, firmly adhering deposition of refractory metal layers onto inductively heated inner surfaces of metal tubes by gas-phase reduction of their halides with hydrogen, as well as an apparatus for carrying out this process. The metal tube to be coated is heated by means of a fixed induction coil whose coil spacing is variable and adjustable, and is gas-tightly connected to a halide evaporator. During the process, a boat loaded with the metal halide is introduced into the evaporator at a controlled speed to meter the halide vapor, and hydrogen is introduced into the evaporator to adjust the reaction gas mixture. During the coating process, the gas outlet is open to the outside atmosphere at a slight internal overpressure.

[0008] US patent 5,686,157A describes a plastic container coated with a multilayer barrier coating. The multilayer barrier coating is useful for providing an effective barrier against gas permeability in containers and for extending the shelf life of containers, particularly evacuated plastic blood collection devices.

[0009] In the article "Polymerization of Para-Xylylene Derivatives (Parylene Polymerization). I. Deposition Kinetics for Parylene N and Parylene C" by P. Kramer et al., Journal of Polymer Science: Polymer Chemistry Edition, Vol. 22, 1984, pp. 475-491, Wiley Online Library [online], URL: The kinetic aspects of parylene N and parylene C are investigated in https: / / doi.org / 10.1002 / pol.1984.170220218. As described in this article, the conversion of the starting material (dimer of p-xylylene or chloro-para-xylylene) to polymer occurs at approximately 100%. Consequently, the total polymer formed in a closed system is directly proportional to the amount of dimer used. However, the percentage of the total polymer formed that is deposited on the substrate surfaces in the deposition chamber, as well as the polymer film growth rate, depend on operating conditions such as the substrate temperature, the dimer sublimation temperature, the flow pattern of the reactive species, and other factors. Because parylene C is a heavier and more polar molecule, it tends to deposition more readily in the deposition chamber than parylene N. Parylene C also has a higher ceiling temperature for deposition than parylene N.This situation was investigated from the perspective of excess thermal energy hindering polymer formation (deposition) due to the extremely high entropy change required for polymer deposition. It was shown that the addition of a cool (i.e., room temperature) inert gas increases the deposition of parylene N on substrate surfaces within the deposition chamber. The increase in deposition and the acceleration of the deposition rate (film growth) were found to be related to the size and molecular weight of the inert gas molecules, as well as directly to the inert gas pressure maintained within the system.

[0010] The object of the invention is to provide a method and a device for coating an inner wall of a tubular substrate, which enable a uniform coating of the inner wall of tubular substrates.

[0011] The object of the invention is achieved by a method for coating an inner wall of a tubular substrate with evaporated coating material according to claim 1 and by a coating device for coating an inner wall of a tubular substrate with evaporated coating material according to claim 17.

[0012] The method according to the embodiments of the invention serves to coat the inner wall of a tubular substrate with vaporized coating material by means of chemical vapor deposition or physical vapor deposition. At least one end of the tubular substrate has an opening through which the coating material can penetrate the tubular substrate.The method comprises imprinting a temperature profile along the longitudinal direction of the wall of the tubular substrate by means of a temperature control device comprising a plurality of temperature control elements arranged along the longitudinal direction of the tubular substrate, each of the temperature control elements being designed to be heated or cooled to a predetermined temperature, wherein the temperature in the area near the at least one opening of the tubular substrate is higher than the temperature in the areas of the inner wall further away from the at least one opening, and depositing the coating material on the inner wall of the tubular substrate, wherein, with increasing distance from the at least one opening, the concentration of the coating material inside the tubular substrate decreases as a result of the deposition of the coating material on the inner wall of the tubular substrate.

[0013] When coating the inner wall of a tubular substrate, the vaporized coating material penetrates the interior of the tubular substrate through at least one opening and is then deposited on the inner wall. Due to the deposition of the coating material, its concentration decreases from the at least one opening to the areas further away from it.

[0014] To achieve a coating that is as uniform as possible along the longitudinal direction of the inner wall despite this concentration gradient, a temperature profile is applied to the tubular substrate. The temperature is comparatively high in the area of ​​the at least one opening and decreases towards the areas of the inner wall further away from the at least one opening. In the area near the at least one opening, the relatively high temperature reduces the deposition rate. Towards the areas further away from the at least one opening, the temperature decreases, leading to a certain increase in the deposition rate. Therefore, the temperature profile allows for targeted control of the deposition rate along the longitudinal direction of the inner wall of the tubular substrate, thus creating the conditions for a homogeneous deposition of the coating material.This allows for better control of layer growth on the inner wall, and improves the quality of the inner coating of the tubular substrate.

[0015] This is important, for example, in the field of medical technology, where there are a number of applications where the inner wall of hoses, tubes, catheters, cannulas, capillaries, ureteral stents, etc., is to be coated.

[0016] The invention will now be described in more detail with reference to several exemplary embodiments illustrated in the drawing. The drawing shows... Fig. 1A a tubular substrate on whose inner wall a coating is deposited; Fig. 1B a blind hole on whose inner wall a coating is deposited; Fig. 2 the construction of a steam injection system; Fig. 3A the structure of a parylene dimer; Fig. 3B the structure of the parylene monomer; Fig. 3C the structure of polyparylenes; Fig. 4A a blind hole, where the position along the blind hole is denoted by x; Fig. 4B the diffusion of nitrogen into the Fig. 4A shown blind hole as a function of time; Fig. 5 the thickness d of a deposited layer as a function of the position x along the blind hole; Fig. 6 a representation of the error function erf(z) and the complementary error function erfc(z) as a function of z; Fig. 7A a comparison of the relative concentration c(x,t) / c0 as a function of x with loss and without loss for the diffusion times t1=0.01 sec, t2=0.1 sec, t3=1 sec; Fig. 7B a comparison of the relative concentration c(x,t) / c0 as a function of x with loss and without loss for the diffusion times t3= 1 sec, t4=10 sec; Fig. 7C a comparison of the relative concentration c(x,t) / c0 as a function of x with loss and without loss for the diffusion times t4=10 sec, t5=20 sec; Fig. 8 a representation of the deposition rate as a function of the substrate temperature; Fig. 9A a representation of a hose to be coated with a plurality of temperature control elements, wherein the first end of the hose is open and the second end of the hose is closed; Fig. 9B that goes to the hose from Fig. 9A corresponding temperature profile, which enables a uniform coating of the inner wall of the hose; Fig. 10A a representation of a hose to be coated with a plurality of temperature control elements, wherein both the first end and the second end of the hose are open; Fig. 10B one to the in Fig. The temperature profile of hose 10A shown here allows for a uniform coating of the inner wall of the hose; Fig. 11 a coating device designed to determine the corresponding layer thickness profile for a given temperature profile; Fig. 12 a temperature control block with a plurality of separately temperature-controlled sections; Fig. 13 a hose with an opening, wherein two heating elements are arranged near the opening; and Fig. 14 the temperature profile and the profile of the relative layer thickness as a function of position x for the in Fig. 13 hoses shown.

[0017] In Fig. Figure 1A shows a thin tube 100, the inner wall of which is to be provided with a thin coating 101. As in Fig. As can be seen in Figure 1A, the length S1 of the hose 100 is significantly greater than the diameter d1, so that: S1 >> d1. The hose 100 is open at both ends, and therefore the coating material can penetrate into the interior of the hose 100 from the two openings 102, 103 in order to apply a coating 101 to the inner wall of the hose 100 as uniformly as possible.

[0018] At the in Fig. In the geometry shown in Figure 1B, the inner wall of a blind hole 104 is to be coated with a coating 105 of as uniform a thickness as possible. The length S2 of the blind hole 104 is significantly larger than the diameter d2, such that S2 >> d2. The blind hole 104 is closed at the rear end, and therefore the coating material can only penetrate into the interior of the blind hole 104 from the opening 106 in order to apply a coating 105 of as uniform a thickness as possible to the inner wall of the blind hole 104.

[0019] In addition to the in Fig. 1A and Fig. In addition to the geometries shown in 1B, other, possibly irregularly shaped cavities, hollow spaces, etc. are also conceivable, whose inner walls are to be provided with a uniform coating.

[0020] For applying a coating to a substrate, a variety of different coating technologies are known, including, for example, the processes of physical vapor deposition (PVD) and chemical vapor deposition (CVD), whereby in chemical vapor deposition (CVD) an additional chemical reaction takes place on the substrate surface.

[0021] To achieve a uniform surface coating for complex geometries, shading of poorly accessible areas of the inner wall should be avoided. For coating inner walls, and especially those in Fig. 1A and Fig. The geometries shown in 1B are therefore particularly suitable for those coating technologies in which the particles of the coating material are subject to a certain surface diffusion before reaching their final position, so that a certain homogenization of the layer thickness occurs.

[0022] These coating processes include, in particular, chemical vapor deposition (CVD) processes, in which at least one chemical reaction takes place on the surface of the workpiece to be coated. The particles deposited on the substrate surface by condensation do not remain in the position where they meet the substrate, but move along the surface, depending on their energy, to find an energetically more favorable location. These are areas on the crystal surface with as many neighbors as possible (higher binding energy).

[0023] Chemical vapor deposition (CVD) processes enable, for example, conformal coating, allowing for the uniform coating of complex three-dimensionally shaped surfaces, cavities, and inner walls. This allows, for instance, the uniform coating of even the finest recesses in wafers or hollow bodies on their inner surfaces.

[0024] Low-pressure CVD (Low Pressure Chemical Vapor Deposition, LPCVD) is particularly suitable for coating internal walls.

[0025] For coating internal walls, metal-organic chemical vapor deposition (MOCVD or OMCVD) is particularly suitable, in which the chemical deposition occurs from metal-organic starting compounds. A subgroup of MOCVD is metal-organic vapor-phase epitaxy (MOVPE), which produces crystalline layers of very high quality.

[0026] Furthermore, plasma-enhanced chemical vapor deposition (PECVD) is a special variant of chemical vapor deposition used for coating internal walls. In this process, a plasma is ignited in the coating chamber to support the deposition process. This can be done either inductively (inductively-coupled PECVD, ICPECVD) or capacitively (capacitance-coupled PECVD). Besides these direct plasma processes, there is also remote plasma-enhanced CVD (RPECVD), in which the plasma is spatially separated from the substrate. The terms "downstream plasma" and "afterglow plasma" also describe processes in which the interaction between plasma and substrate takes place at a location remote from the plasma. This reduces the substrate's exposure to ion bombardment and radiation.

[0027] Chemical vapor infiltration (CVI) is a process that utilizes the particular advantage of CVD technology, namely its ability to uniformly coat even porous materials. This method is used, for example, for coating fiber bundles.

[0028] Physical vapor deposition (PVD) processes can also be used to coat internal walls. In these processes, the vaporized coating material is deposited on the substrate surface without a chemical reaction. Even with these methods, a certain degree of surface diffusion occurs. The particles deposited on the substrate surface by condensation move along the surface, depending on their energy, to find an energetically more favorable location. These are areas on the crystal surface with as many neighbors as possible. Satisfactory layer homogeneity on internal walls can also be achieved with physical vapor deposition (PVD) processes.

[0029] In Fig. Figure 2 shows the setup of an evaporation system suitable, among other things, for chemical vapor deposition (CVD) processes. The core of the evaporation system is a coating chamber 200, in which the evaporation process is carried out. The substrate 201 to be coated is located inside the coating chamber 200 and is held by a suitable holder 202. The evaporation process is preferably carried out at a pressure of approximately 0.5 Pa to approximately 50 Pa, i.e., at a pressure in the range of fine vacuum. To generate the fine vacuum, the coating chamber 200 is connected to a vacuum pump 204 via a cold trap 203.

[0030] The vacuum pump 204 could, for example, be a mechanically operated vacuum pump, such as a rotary vane pump. Using a rotary vane pump, the required fine vacuum in the range of approximately 0.5 Pa to approximately 50 Pa can be generated within the coating chamber 200.

[0031] The cold trap 203 is designed to condense the vaporized material contained in the pumped-out gas so that it cannot reach the vacuum pump 204. For this purpose, the walls of the cold trap 203 are cooled down to, for example, -90°C, which can be achieved, for example, by means of compressor cooling.

[0032] At the in Fig. In the vapor deposition system shown in Figure 2, the coating material is evaporated in an evaporator unit 205. A heated evaporator 206, often also referred to as a "boat," is arranged in the evaporator unit 205. The coating material 207 is heated by the heated evaporator 206 and transferred into the gas phase. Preferably, the heated evaporator 206 is heated by means of an electric resistance heater.

[0033] From the evaporator unit 205, the vaporized material passes to a pyrolysis unit 208, which is often also referred to as a "cracker unit." The temperature in the pyrolysis unit 208 is approximately 700°C. This high temperature breaks down the vaporized molecules into smaller, reactive molecules or particles. For example, in the case of a parylene coating, parylene is vaporized in the evaporator unit 205 in the form of parylene dimers, which are then broken down into highly reactive parylene monomers in the pyrolysis unit 208. The smaller, reactive molecules or particles produced in the pyrolysis unit 208 by breaking down the vaporized molecules then pass to the coating chamber 200, where they are deposited on the surface of the substrate 201 and react.

[0034] The chemical deposition of the coating material onto the substrate 201 can be additionally supported by a plasma. In this case, it is referred to as plasma-enhanced chemical vapor deposition (PECVD). The plasma required for this in the coating chamber 200 is generated by irradiation with an alternating electromagnetic field. To generate this alternating electromagnetic field, the [component] Fig. Figure 2 shows a deposition system with a magnetron 209, which generates electromagnetic radiation in the microwave range in a resonance chamber 210. This electromagnetic radiation can be coupled into the coating chamber 200 via a microwave window 211.

[0035] The vapor deposition system can additionally include a mass spectrometer 212 for analyzing the gas phase in the coating chamber 200. The composition of the vaporized coating material, as well as impurities and moisture, can be quantitatively determined using the mass spectrometer 212.

[0036] Furthermore, the vapor deposition system can be used by Fig. The system includes two different sensors for recording various operating parameters. For example, the vapor deposition system can include a pressure sensor that measures the pressure within the coating chamber 200. A temperature sensor can be provided within the evaporator unit 205 to measure the temperature of the heated evaporator 206, thus enabling temperature control. Furthermore, a deposition sensor can be arranged within the coating chamber 200 to measure the instantaneous deposition rate of the vapor material deposited on the substrate 201. For example, the deposition sensor can include a quartz crystal whose oscillation frequency changes as a result of material deposition. In this way, it is possible to precisely measure and control the layer growth.

[0037] The following discussion will focus on the vapor deposition of parylene as an example. Parylene coatings are of great importance in medical technology because parylene is biocompatible and exhibits high compatibility with the body's own tissue. Therefore, implants, catheters, cannulas, aids, and prostheses that come into prolonged contact with human tissue are coated with parylene to improve biocompatibility. For example, stents used to dilate and keep blood vessels open can be coated with a layer of parylene. Another example is an artificial bladder, which is coated with a parylene layer to enhance biocompatibility.

[0038] The chemical structure of parylene is described in the Fig. 3A-3C shown. Fig. Figure 3A shows the parylene dimer, which consists of two parylene monomers linked via their carbon atoms. In the parylene material found in the evaporator unit, the parylene exists in the form of dimers.

[0039] Various types of parylene are available, differing in that they are distinguished by one or more substitutions of chemical groups on the ring or bridge. In the following, "parylene" will be used as a collective term for all variants of parylene.

[0040] To initiate polymerization, it is necessary to break down the dimer into two reactive monomers. This takes place in the pyrolysis or cracking unit 208, which is located in Fig. 2 is shown in the diagram. In the pyrolysis unit 208, the dimers are broken down into reactive monomers by the influence of high temperature. Fig. 3B is the monomer of parylene shown.

[0041] During the coating process, the parylene, which after passing through the pyrolysis unit 208 exists almost entirely in the form of parylene monomers, condenses onto the substrate to be coated. There, the highly reactive parylene monomers react to form polyparylene chains. Fig. Figure 3C shows the chemical structure of a polymer formed from n monomers.

[0042] The following discussion will focus on coating the inner wall of a blind hole using chemical vapor deposition or physical vapor deposition. The insights gained can then be applied to coating the inner walls of tubular substrates, hoses, pipes, and especially cannulas, capillaries, catheters, etc.

[0043] In Fig. Figure 4A schematically represents a blind hole 400 with an opening 401. The position x along the blind hole 400 is plotted along the right axis. The depth of the blind hole is denoted by S. At the opening 401 of the blind hole 400, x = 0, and at the bottom of the blind hole 400, x = S.

[0044] In chemical vapor deposition (CVD), two velocities are important for the deposition rate: firstly, the transport velocity at which the reactants are carried to the surface, and secondly, the reaction velocity at which the reactants react at the surface.

[0045] In physical vapor deposition (PVD), two velocities are important for the deposition rate: firstly, the transport velocity at which the particles are led to the surface, and secondly, the deposition velocity at which the particles adhere to the surface.

[0046] The transport of the vaporized coating material from the source to the desired location on the surface occurs through diffusion. If the source is a liquid or a gas from which the reactants can be continuously replenished, it is referred to as an "inexhaustible source." With regard to the coating material, we will initially assume an "inexhaustible source." However, it will become apparent that this assumption requires correction.

[0047] Diffusion is based on the random, undirected movement of particles due to their thermal energy. With an uneven distribution, statistically more particles move from areas of high concentration to areas of low concentration or particle density than vice versa. This results in a net macroscopic transport of matter.

[0048] The macroscopic transport of substances caused by diffusion is described by Fick's first law: J=−D∂c∂x where ∂c / ∂x denotes an initial concentration gradient, D denotes the diffusion coefficient, and J denotes a particle flux density or particle flux that opposes and equalizes the concentration gradient. The diffusion coefficient D indicates the magnitude of the particle flux caused by the concentration gradient ∂c / ∂x. The higher the diffusion coefficient D, the stronger the diffusion caused by concentration differences.

[0049] The diffusion coefficient D can be expressed as D=13⋅v¯⋅λ where v denotes the mean thermal velocity of the particles and λ denotes the mean free path. The mean thermal velocity v of the particles increases with increasing temperature. The mean free path λ is inversely proportional to the particle density n: λ=1n⋅σ

[0050] Here, n denotes the particle density and σ the total cross-section of the gas particles, which depends primarily on the size of the gas particles. The fewer particles present in a given volume, the less frequently collisions occur between the particles, and consequently, the greater the mean free path λ. The dependence of the mean free path λ on the particle density n implies that the mean free path λ depends on the pressure p of the medium. The lower the pressure p in the coating chamber, the lower the particle density n, and the greater the mean free path λ.

[0051] The diffusion coefficient D can therefore be significantly influenced by both the temperature T and the pressure p. As the temperature T increases, the mean thermal velocity v of the particles increases, which directly leads to a higher diffusion coefficient D. A decrease in pressure p leads to an increase in the mean free path λ, which also results in an increase in the diffusion coefficient D. Therefore, mass transport by diffusion can be increased by raising the temperature and lowering the pressure.

[0052] The time course of a diffusion process is described by Fick's second law. Fick's second law states: ∂c∂t=−∂J∂x=∂∂x(D∂c∂x)

[0053] For constant diffusion coefficients D, the following results: ∂c∂t=D∂2c∂x2

[0054] Fick's second law establishes a relationship between the temporal and spatial equalization of concentration differences.

[0055] The following example, using Fick's second law, will illustrate the time course of the penetration of a gas into the Fig. The blind hole 400 shown in section 4A illustrates this. Nitrogen (N2) will be used as an example, which has a cross-sectional area σ = 45 Å. 2 It possesses. At room temperature, the nitrogen molecules have an average speed v = 500 m / s.

[0056] At a pressure of 75 mTorr (equivalent to 10 Pa) the particle density is n(75 mTorr) = 2.7 × 10 15 cm -3 , which results in a mean free path λ(75 mTorr) = 0.3 mm. For this pressure of 75 mTorr, the diffusion coefficient D can be determined as follows: D=13⋅v¯⋅λ=500 cm2 / s

[0057] For this example, the penetration of nitrogen into the Fig. The blind hole 400 shown in 4A can be illustrated as a function of time. For this purpose, see in Fig. Figure 4B shows the particle density N(x,t) / N0 as a function of the position x along the blind hole for six consecutive time points. At time t1 = 0, no nitrogen has yet entered the blind hole 400; accordingly, the particle density N(x,t1=0) / N0 within the blind hole is consistently zero. Curve 402 shows the particle density as a function of the position x at time t2 = 0.1 seconds. It can be seen that the nitrogen has already penetrated the blind hole 400 to some extent. Curves 403 to 406 show the particle density as a function of the position x at times t3 = 0.5 seconds, t4 = 1 second, t5 = 10 seconds, and t6 = 100 seconds.

[0058] Based on Fig. Figure 4B shows that, due to diffusion, the nitrogen concentration inside and outside the blind hole is almost completely equalized after approximately 100 seconds. In the example presented, a near-complete equalization of concentration can therefore be achieved within approximately 100 seconds. If these results obtained for nitrogen are applied to the respective coating material, for example, to monomeric parylene molecules, then one can conclude that, assuming an inexhaustible source, a sufficient concentration of the coating material should be present throughout the entire depth of the blind hole due to diffusion.

[0059] However, a different picture emerges when looking at the actual deposition rates achieved in the deposition of parylene on the inner wall of a blind hole. This is shown in Fig. Figure 5 plots the layer thickness deposited on the inner wall as a function of position within the blind hole for two different samples. It can be seen that in region 500, close to the opening 401 of the blind hole, a relatively high layer thickness of approximately 400 nm to 1000 nm is obtained. In contrast, in region 501, further away from the opening 401, a significantly lower deposition rate and consequently a significantly lower layer thickness of approximately 200 nm to 400 nm are obtained.

[0060] The reason for this behavior is that the particles of the coating material are removed from the gas phase by the chemical reaction on the surface of the inner wall. This results in a sharp decrease in the concentration of the film-forming species in the area near opening 401 of the blind hole. In the rear region of the blind hole, the concentration of the coating material is already very low, and therefore a very low deposition rate and consequently a small film thickness result in this area.

[0061] The CVD deposition of a polyparylene film in a blind hole approximately 30 cm deep demonstrates that the deposition process cannot be described by the "inexhaustible source" model. Rather, the chemical reaction with the substrate surface significantly reduces the concentration of the coating material in the area near the opening of the blind hole. Therefore, the coating material cannot penetrate to the rear end of the blind hole in a sufficient concentration.

[0062] If the particles of the coating material are lost as a result of the reaction at the surface during diffusion, Fick's second law (see formula (5)) must be supplemented by a loss term -L·c. In this loss term -L·c, L denotes a temperature-dependent loss rate, and c denotes the concentration of the particles of the coating material. Fick's second law supplemented by the loss term -L·c then reads: ∂c∂t=D∂2c∂x2−L⋅c

[0063] This equation represents a mathematical model for a diffusion process in which the concentration of particles decreases during diffusion due to deposition or chemical reactions with the substrate surface. Equation (7) can be solved using standard methods. The concentration c(x,t) as a function of position and time is given by: c(x,t)c0=12⋅exp(−xLD)⋅erfc(x2⋅Dt−Lt)++12⋅exp(+xLD)⋅erfc(x2⋅Dt+Lt)

[0064] In this solution, c(x,t) denotes the concentration of the coating material as a function of position and time, while c0 denotes the base concentration. The function erfc(z) appearing in this solution is the so-called complementary error function, which can be derived from the error function erf(z). The error function erf(z) is the integral from 0 to z over e -y2 (Gaussian bell curve): erf(z)=2π∫0ze−y2dy

[0065] In Fig. Figure 6 shows the error function erf(z) represented as curve 600. For z → -∞, the error function erf(z) approaches -1. For z → +∞, the error function erf(z) approaches +1. limz→−∞erf(z)=−1limz→+∞erf(z)=+1

[0066] The complementary error function erfc(z) appearing in the solution is related to the error function erf(z) as follows: erfc(z)=1−erf(z)

[0067] In Fig. Figure 6 shows the complementary error function erfc(z) as curve 601. For z → -∞, the complementary error function erfc(z) approaches +2, and for z → +∞, erfc(z) approaches 0. limz→−∞erfc(z)=+2limz→+∞erfc(z)=0 Looking at the solution for c(x,t) in equation (8), it becomes clear that the exponential function is independent of time, whereas the time dependence is contained in the complementary error functions erfc(z). In the following, equation (8) will be considered for two limiting cases, namely... 1) for the case L → 0 (no losses) and 2) in the case L >> D / S 2 , where L denotes the loss rate, D the diffusion coefficient and S the depth of the blind hole or the length of the tubular substrate.

[0068] In the case of L >> D / S 2The rate of deposition or reaction at the surface is higher than the influx of particles to the substrate surface due to diffusion. In this case, the particles react immediately at the surface (CVD) or are deposited on the surface (PVD). Compared to diffusion to the substrate surface, deposition or reaction at the substrate surface occurs relatively quickly. The diffusion of the vaporized coating material to the substrate surface therefore determines (and limits) the rate of the deposition process. The rate-determining step for the deposition process is the diffusion of the coating material to the substrate surface. Such deposition behavior is referred to as diffusion-controlled deposition. 1) No losses, L → 0

[0069] For the case L → 0, the solution for c(x,t) from equation (8) is: c(x,t)c0=erfc(x2⋅Dt)

[0070] For large time periods (t → ∞), c(x,t) = c0, meaning a constant concentration of the coating material across the entire longitudinal extent of the blind hole. This corresponds to the equation in Fig. 4B behavior shown. 2) Diffusion-controlled separation behavior, the losses are greater than diffusion, L >> D / S 2

[0071] In the case of diffusion-controlled separation behavior with L >> D / S 2 , so in the case of high losses, the behavior is described overall by equation (8): c(x,t)c0=12⋅exp(−xLD)⋅erfc(x2⋅Dt−Lt)++12⋅exp(+xLD)⋅erfc(x2⋅Dt+Lt)

[0072] In the limiting case for large times t → ∞, c(x,t) is obtained. c(x,t)c0=exp(−xLD)

[0073] For long periods, the concentration of the coating material in the blind hole is therefore described by an exponential decrease.

[0074] In the Fig. 7A, Fig. 7B, Fig. In 7C, an attempt was made to illustrate the behavior described by equation (8) by determining the relative concentration c(x,t) / c0 as a function of x for different diffusion times t in the case with high loss (L >> D / S). 2 ) and are shown for comparison in the case without loss (L=0). Fig. 7A, Fig. 7B, Fig. 7C show the relative concentrations c(x,t) / c0 with loss (L=1 sec) -1 ) and without loss (L=0) for five diffusion times t1=0.01 sec, t2=0.1 sec, t3=1 sec, t4=10 sec and t5=20 sec. For all in Fig. 7A, Fig. 7B, Fig. The diffusion rate shown in curve 7C is D=10 cm. 2 / sec.

[0075] Fig. 7A shows the relative concentration c(x,t) / c0 as a function of x for the three diffusion times t1 = 0.01 sec, t2 = 0.1 sec, and t3 = 1 sec. Curve 701A represents the concentration with loss (L = 1 sec). -1) at time t1=0.01 sec. Curve 701B represents the concentration without loss (L=0) at time t1=0.01 sec. Curves 701A and 701B lie on top of each other, so the loss term has no effect at t1=0.01 sec.

[0076] At time t2=0.1 sec, the concentration is reduced with loss (L=1 sec). -1 The concentration at zero loss (L=0) is represented by curve 702A, while the concentration without loss is represented by curve 702B. Curves 702A and 702B are superimposed. The loss term also has no effect for t2=0.1 sec.

[0077] The loss term only becomes noticeable at longer diffusion times. For a diffusion time t3 = 1 sec, curve 703A shows the concentration with loss (L = 1 sec). -1 ) represents, recognizable below curve 703B, which shows the concentration without loss (L=0).

[0078] In Fig. Figure 7B shows curves 703A and 703B for the diffusion time t3 = 1 sec, again on a different scale, together with curves 704A and 704B for the diffusion time t4 = 10 sec. As already mentioned in Fig. The curve shown in 7A is 703A, which shows the concentration with loss (L=1 sec). -1 ) is shown below curve 703B, which shows the concentration without loss (L=0). For the diffusion time t4= 10 sec, curve 704A lies below, which shows the concentration with loss (L=1 sec). -1 ) is also shown below curve 704B, which shows the concentration without loss (L=0). It can be seen that with increasing diffusion time, the distance between curves 703A and 704A (with loss) and curves 703B and 704B (without loss) becomes increasingly larger.

[0079] This trend continues in Fig. 7C continued. In Fig. Figure 7C shows curves 704A and 704B for a diffusion time t4 = 10 sec, again on a different scale, together with curves 705A and 705B for a diffusion time t5 = 20 sec. It can be seen that with increasing diffusion time, the distance between curves 704A and 705A decreases with a loss (L = 1 sec). -1 ) and curves 704B, 705B without loss (L=0) are further magnified. It can also be seen that curves 704A, 705A appear as superimposed straight lines in the logarithmic plot. The reason for this is that the concentration with loss for large times t4=10 sec, t5=20 sec can increasingly be described by the time-independent exponential function according to equation (14): c(x,t)c0=exp(−xLD)

[0080] The deposition or reaction of the coating material at the surface is described in Fick's second law by the loss term -L·c. In the computational model, this deposition or reaction of the coating material also leads to a sharp decrease in the concentration of the coating material in the blind hole with increasing distance from the opening (see equation (14)). This sharp drop in concentration results in an uneven coating within the blind hole.

[0081] The question therefore arises as to how a uniformly thick coating of the inner wall of pipes, hoses, cannulas, capillaries, catheters and similar tubular substrates can be achieved despite the drop in concentration.

[0082] According to the embodiments of the present invention, it can be used to take advantage of the fact that in chemical vapor deposition (CVD) and physical vapor deposition (PVD) processes the deposition rate has a strong dependence on the temperature at the substrate surface: Since evaporation is fundamentally an endothermic process, the opposite is true for condensation. A similar principle applies to the desorption and adsorption of particles that are upstream or downstream of a potential chemical reaction (Langmuir's theory). According to Le Chatelier's principle, the equilibrium can therefore be shifted to the desired side; thus, increasing the temperature shifts it to the more energetic side (vapor), and decreasing the temperature shifts it to the less energetic side (condensate).

[0083] In Fig. Figure 8 shows the dependence of the deposition rate on the substrate temperature for polyparylene of the type parylene-N. The substrate temperature in degrees Celsius is plotted along the horizontal axis, and the deposition rate in angstroms per minute is plotted along the vertical axis. The deposition behavior is described by a so-called ceiling temperature T. C characterized by the fact that in Fig. Figure 8 is shown. Above the ceiling temperature, the deposition of a film from the vapor phase is no longer possible. This ceiling temperature, for example, lies between 30°C and 90°C for the various parylene grades. In the case of the Fig. In the example shown for polyparylene type N, the ceiling temperature T is... C at approximately 25°C. Above a substrate temperature of approximately 25°C, layer deposition is therefore not possible.

[0084] Based on Fig. It can also be seen in section 8 that below the ceiling temperature T CThe deposition rate increases linearly with decreasing substrate temperature. This makes it possible to adjust the deposition rate to a desired value by varying the substrate temperature. Lowering the substrate temperature leads to a corresponding increase in the deposition rate, while raising the substrate temperature results in a corresponding decrease. This dependence of the deposition rate on the substrate temperature can be used to achieve a uniform coating of the inner wall of a hose, tube, cannula, capillary, catheter, or other tubular substrate.

[0085] In Fig. Figure 9A shows a hose 900, on whose inner wall a coating is to be applied by means of chemical vapor deposition. The first end of the hose 900 has an opening 901 through which the coating material can penetrate into the interior of the hose 900. The second end of the hose 900 is designed as a closed end 902. Therefore, the inner wall of the hose 900 to be coated has a blind hole geometry. According to the Fig. Based on the separation characteristic shown in Figure 5, the separation rate is expected to be relatively high near the opening 901 and to decrease steadily towards the closed end 902. To counteract this inhomogeneity of the separation rate and to achieve uniform separation along the entire longitudinal direction of the hose 900, a temperature profile is applied along the longitudinal direction of the hose 900. For this purpose, several temperature control elements 903-906 are arranged along the longitudinal extent of the hose 900, with which the temperature of the inner wall of the hose 900 in the corresponding segments can be set independently of one another to specific predetermined temperature values. Preferably, the temperature control elements 903-906 are designed as heating or cooling jackets.

[0086] In the area near opening 901, the separation rate would be very high, as shown by Fig. 5 can be seen. In order to obtain a homogeneous separator rate over the entire length of hose 900, the separator rate would therefore have to be reduced in the area near opening 901. Accordingly Fig. 8. Such a reduction in the separation rate can be achieved by heating the inner wall. If the substrate temperature is increased towards the ceiling temperature T. C As the temperature increases, the separation rate decreases. Accordingly, the temperature control elements 903 and 904 are designed to heat the area near the opening 901.

[0087] The further one moves away from opening 901 and towards the closed end 902, the more the separation rate decreases. Therefore, the separation rate should be increased in the section of hose 900 furthest from opening 901. This can be achieved accordingly. Fig. 8. This occurs through cooling of the inner wall. The lower the substrate temperature, the higher the separation rate. To achieve a separation rate that is as constant as possible over the entire longitudinal extension of the tube 900, the two temperature control elements 905 and 906 are therefore designed either not to heat the substrate or even to cool it further.

[0088] A suitable temperature profile to achieve a separation rate that is as constant as possible over the entire length of this 900 mm hose therefore includes one or more of the following measures: - Heating the area of ​​the hose located near opening 901; - Cooling the area of ​​the hose furthest from opening 901.

[0089] In Fig. Figure 9B shows a suitable temperature profile schematically. Along the horizontal axis, position x is plotted along the longitudinal direction of the tube 900, and along the vertical axis, the temperature imparted to the inner wall by the temperature control elements 903-906 is plotted. Position x=0 denotes the position of the opening 901 of the tube 900, while position x=S denotes the position of the closed end 902 of the tube 900. It can be seen that the temperature of the inner wall is relatively high near the opening 901 and decreases continuously towards the closed end 902. With such a temperature profile, a uniform separation rate can be achieved along the entire longitudinal direction of the tube 900.

[0090] If the hose 900 is coated over a certain period of time, the largely homogeneous deposition rate and the correspondingly uniform layer growth result in a uniform thickness of the coating on the inside of the hose 900.

[0091] This is of particular technological importance for coating the inside of pipes, hoses, cannulas, catheters, capillaries, ureteral stents, etc. In the medical technology sector, such products are usually made of polyurethane, silicone, or other polymer materials. Applying a coating can improve biocompatibility. Furthermore, an antimicrobial coating, especially on the inner wall, can prevent contamination by bacteria, viruses, fungi, etc.

[0092] Furthermore, the described coating process can also be used to coat the inside of tubular substrates such as tubes, capillaries, cannulas, etc., made of glass, metal, or ceramic. In particular, the coating process would also be applicable to a tubular substrate through which a vacuum is drawn on one side and film-forming vapor is introduced on the other, and which can withstand the external pressure.

[0093] In Fig. Figure 10A shows a hose 1000 as a further example, which has an opening 1001, 1002 at each end. The coating material can therefore penetrate the interior of the hose 1000 from both ends. A plurality of temperature control elements 1003-1008 are arranged along the longitudinal direction of the hose 1000. The temperature control elements 1003-1008 can, for example, be designed as heating or cooling sleeves.

[0094] At the in Fig. In the embodiment shown in Figure 10A, the coating material can penetrate the interior of the tube 1000 from both openings 1001 and 1002. Therefore, the deposition rate is very high near the two openings 1001 and 1002, whereas it is significantly lower in the central region of the tube 1000. To achieve a uniform deposition rate along the entire length of the tube 1000, it is proposed to selectively increase the temperature in the areas near the openings 1001 and 1002 in order to reduce the deposition rate in these areas. Therefore, the temperature control elements 1003, 1004 and 1007, 1008 arranged near the openings 1001, 1002 should be designed to heat the inner wall of the hose 1000 in the areas near the openings 1001, 1002.

[0095] In the middle section of the hose, however, the separation rate is too low. To specifically increase the separation rate in the middle section of hose 1000, the inner wall in this area should not be heated or should even be cooled. Therefore, the temperature control elements 1005 and 1006 can be designed to specifically cool the inner wall in the middle section of hose 1000.

[0096] The corresponding temperature profile is in Fig. Figure 10B shows the position x along the longitudinal direction of hose 1000. The temperature is plotted along the vertical axis. Position x=0 corresponds to the position of the first opening 1001, and position x=S corresponds to the position of the second opening 1002. It can be seen that the temperature is relatively high in the area of ​​the two openings 1001 and 1002 and then decreases towards the middle of hose 1000.

[0097] The in Fig. 9A and Fig. The temperature control elements 903-906 and 1003-1008 shown in Figure 10A can, for example, be configured as heating and / or cooling sleeves. According to one possibility, the temperature control elements can have an arrangement of heating wires to implement resistance heating, whereby the current flowing through the heating wires is converted into ohmic heat. Another possibility is to provide a water heating or cooling system within each temperature control element, whereby a multi-circulating water line carries precisely temperature-controlled heating or cooling water. A further possibility for implementing the temperature control elements 903-906 and 1003-1008 is the use of Peltier elements. Peltier elements each have a heat-emitting side and a cooling side, so that Peltier elements can be used for both heating and cooling. Peltier elements are therefore very well suited for generating a predefined temperature profile.

[0098] In Fig. Figure 11 shows a specific coating device with which the deposition of coating material in a blind hole can be quantitatively determined. The coating device comprises an aluminum rail 1100 into which a blind hole 1101 is milled. The blind hole 1101 is covered by a plurality of glass plates 1102. For example, glass slides can be used to cover the blind hole 1101. During the coating process, vaporized coating material penetrates the blind hole 1101 from the opening 1103. After completion of the coating process, the layer thicknesses deposited on the slides are measured in order to determine the layer thickness profile along the blind hole 1101.

[0099] The in Fig. The coating device shown in Figure 11 is designed for the deposition of polyparylene-N. The ceiling temperature of polyparylene-N is very low; therefore, the rear region of the blind hole 1101 is cooled. For this purpose, a first Peltier element 1104 is arranged in the rear region of the blind hole 1101. The cold side of the first Peltier element 1104 is in thermal contact with the aluminum rail 1100, while the hot side of the first Peltier element 1104 faces away from the aluminum rail 1100. The hot side of the first Peltier element 1104 is thermally connected to a cooling rail 1105. The cooling rail 1105 is designed to dissipate the heat generated on the hot side of the first Peltier element 1104. The cooling rail 1105 is preferably made of a highly thermally conductive material such as stainless steel or copper. Above the first Peltier element 1104, the cooling rail 1105 is cooled by a water cooling system 1106 to dissipate the emitted heat.

[0100] A second Peltier element 1107 is arranged at the front end of the blind hole 1101. This element serves to heat the area around the opening 1103 of the blind hole 1101. The hot side of the second Peltier element 1107 is thermally connected to the aluminum rail 1100. The cold side of the second Peltier element 1107 faces away from the aluminum rail 1100 and is thermally connected to the cooling rail 1105. The resulting cold is transferred to the cooling rail 1105, providing additional cooling for the cooling rail 1105.

[0101] Using the two Peltier elements 1104 and 1107, a temperature profile is established along the blind hole 1101. The coating process is then carried out. The layer thickness distribution corresponding to this temperature profile can be determined using the glass plates 1102.

[0102] In Fig. Figure 12 shows a temperature control block 1200, which enables the simultaneous coating of the inner wall of multiple tubes, hoses, cannulas, capillaries, catheters, and similar tubular substrates. The temperature control block 1200 is designed to imprint a suitable temperature profile for coating the inner wall of several tubes, catheters, capillaries, etc., simultaneously. The temperature control block 1200 includes multiple recesses 1201, 1202 for receiving the tubular substrates to be coated. Fig. Although only two recesses are shown in Figure 12, significantly more recesses may be provided to enable a higher throughput during coating.

[0103] Tubes, catheters, capillaries, and other tubular substrates are typically made of a polymer material such as polyurethane or silicone, which has a relatively low thermal conductivity. Therefore, it takes a relatively long time for an externally applied temperature profile to penetrate to the inner wall of the respective tubular substrate. To ensure a stable temperature profile is maintained on the tubular substrates to be coated for a sufficiently long period, the temperature control block 1200 is divided into several independently temperature-controlled sections 1203, 1204, and 1205. Each of these sections is thermostatically controlled differently. For example, sections 1203, 1204, and 1205 are made of a highly thermally conductive metal such as copper or stainless steel.

[0104] To ensure that the individual sections 1203, 1204, and 1205 can be kept at different temperatures for extended periods, they are thermally insulated from one another. For this purpose, separating discs 1206 and 1207 made of a low-thermal-conductivity material, such as Teflon, are installed between the sections 1203, 1204, and 1205. This allows the individual sections 1203, 1204, and 1205 to be kept at different temperatures for extended periods without requiring significant heating or cooling power.

[0105] When the tubes, catheters, or capillaries inserted into recesses 1201 and 1202 are heated according to the desired temperature profile, the vaporized coating material is deposited on the inner walls of the tubes, catheters, or capillaries. The degree of dilution by the carrier gas, e.g., argon, can reduce the deposition rate to the necessary level.

[0106] However, it is not absolutely necessary to heat both the area near the opening and the area furthest from the opening. To achieve a homogeneous separation rate, it may be sufficient to perform only one of these measures. In particular, it may be sufficient to heat a hose to be coated on the inside in the area of ​​the opening.

[0107] One such embodiment is in Fig. 13 shown. Fig. Figure 13 shows a hose 1300, which has an opening 1301 at its first end and a closed end 1302 at its second end. A first heating element 1303 and a second heating element 1304 are arranged in the area near the opening 1301. Both heating elements 1303 and 1304 are implemented as resistance heating elements, each connected to a corresponding voltage source 1305 and 1306, respectively. The temperature in the various segments of the hose 1300 can be monitored using thermocouples 1307 and 1308.

[0108] Through the in Fig. As shown in Figure 13, selective heating of the area near opening 1301 can already achieve a satisfactory homogeneity of the deposition rate. This is shown in the diagram of Fig. 14 illustrated. Fig.Figure 14 shows the temperature profile 1400 along the length of the hose 1300 together with the profile 1401 of the relative layer thickness. The position x along the longitudinal extent of the hose 1300 to be coated is plotted along the right-hand axis.

[0109] The oven temperature for temperature profile 1400 is plotted in degrees Celsius along the vertical axis on the left edge. It can be seen that the two segments near the opening of hose 1300 are heated to temperatures of 75°C and 50°C respectively, whereas the rest of hose 1300 is not heated.

[0110] The scale for the relative layer thickness profile 1401 is plotted along the right edge of the vertical axis, with the relative layer thickness being referenced to the layer thickness at the position of the opening 1301. It can be seen that the relative layer thickness decreases only slightly from the opening 1301 to the closed end 1302 of the tube 1300, so that a layer thickness that is essentially constant over the entire length of the tube 1300 is deposited.

Claims

[1] A method for coating the inner wall of a tubular substrate (900, 1000, 1300) with vaporized coating material by means of chemical vapor deposition or by means of physical vapor deposition, wherein at least one end of the tubular substrate (900, 1000, 1300) has an opening (901, 1001, 1002, 1301) through which the coating material can penetrate the tubular substrate (900, 1000, 1300), and wherein the method comprises the following steps: - Imprinting a temperature profile along the longitudinal direction of the wall of the tubular substrate (900, 1000, 1300) by means of a temperature control device comprising a plurality of temperature control elements (903-906, 1003-1008, 1104, 1107, 1303, 1304) arranged along the longitudinal direction of the tubular substrate (900, 1000, 1300), wherein each of the temperature control elements (903-906, 1003-1008, 1104, 1107, 1303, 1304) is designed to be heated or cooled to a predetermined temperature, wherein the temperature in the area near the at least one opening (901, 1001, 1002, 1301) of the tubular substrate (900, 1000, 1300) is higher than the temperature at the areas of the inner wall furthest from the at least one opening (901, 1001, 1002, 1301); - Deposition of the coating material on the inner wall of the tubular substrate (900, 1000, 1300), wherein, with increasing distance from the at least one opening (901, 1001, 1002, 1301), the concentration of the coating material inside the tubular substrate (900, 1000, 1300) decreases as a result of the deposition of the coating material on the inner wall of the tubular substrate (900, 1000, 1300). [2] Method according to claim 1, characterized by , that the tubular substrate has an opening at the first end through which the coating material can penetrate the tubular substrate, with the tubular substrate being closed at the second end. [3] Method according to claim 2, characterized by , that the temperature is highest in the area of ​​the opening of the tubular substrate and decreases towards the closed second end. [4] Method according to claim 1, characterized bythat the tubular substrate has a first opening at the first end and a second opening at the second end, whereby the coating material can penetrate the tubular substrate through the openings from both ends. [5] Method according to claim 4, characterized by , that the temperature is highest in the area of ​​the openings of the tubular substrate and decreases towards the middle area of ​​the tubular substrate. [6] Method according to any one of claims 1 to 5, characterized by at least one of the following: - the diffusion of the coating material to the inner wall of the tubular substrate represents the rate-determining step in the deposition of the coating material; - the deposition or reaction of the coating material on the inner wall of the tubular substrate occurs comparatively faster than the diffusion of the coating material to the inner wall of the tubular substrate; - For the rate L of deposition or reaction of the coating material on the inner wall of the tubular substrate, L >> D / S applies. 2 , where D denotes the diffusion coefficient of the coating material and S the length of the tubular substrate. [7] Method according to any one of claims 1 to 6, characterized by , that the separation rate depends on the temperature of the inner wall, with the separation rate decreasing steadily with increasing temperature and the separation rate becoming zero when a ceiling temperature is reached. [8] Method according to any one of claims 1 to 7, characterized by, that in areas near the at least one opening there is a high concentration of coating material and the temperature is chosen to be higher there than in the areas further away from the at least one opening, where there is a comparatively low concentration of coating material. [9] Method according to any one of claims 1 to 8, characterized by , that the temperature profile is determined depending on the concentration of the coating material inside the tubular substrate, whereby the temperature at a position on the wall of the tubular substrate is chosen to be higher the higher the concentration of the coating material is there. [10] Method according to any one of claims 1 to 9, characterized by, that the temperature profile exhibits a decreasing temperature from the areas near the at least one opening to the areas further away from the at least one opening, thereby reducing the deposition of coating material in the area near the at least one opening and increasing the deposition of coating material in the areas further away from the at least one opening. [11] Method according to any one of claims 1 to 10, characterized by at least one of the following: - in the areas near the at least one opening, where the concentration of the coating material is comparatively high, the deposition rate is reduced by a comparatively high temperature of the inner wall; - In areas further away from at least one opening, where the concentration of the coating material is comparatively low, the deposition rate is increased by a comparatively low temperature of the inner wall. [12] Method according to any one of claims 1 to 11, characterized by at least one of the following: - By imprinting the temperature profile along the longitudinal direction of the inner wall of the tubular substrate, a largely homogeneous deposition rate is achieved; - The temperature profile is chosen so that a uniform layer thickness is deposited on the inner wall of the tubular substrate within a specified time. [13] Method according to any one of claims 1 to 12, characterized by at least one of the following: - the temperature control elements are thermostatically controlled temperature control elements; - the temperature control elements are heating and / or cooling sleeves; - The temperature control elements are designed to bring each segment of the tubular substrate to a predetermined temperature. [14] Method according to any one of claims 1 to 13, characterized by , that a temperature control element comprises at least one of the following: a resistance heater, a Peltier element, a water heater and / or a water cooler, heating or cooling coils. [15] Method according to any one of claims 1 to 14, characterized by , that the tubular substrate is one of the following: a hose, a tube, a cannula, a capillary, a catheter, a ureteral stent. [16] Method according to any one of claims 1 to 15, characterized by at least one of the following: - the tubular substrate consists of polyurethane or silicone or of glass, metal, ceramic; - the coating material is parylene, in particular parylene type N; - the process is carried out within a coating chamber; - the process is carried out within a coating chamber where a fine vacuum prevails. [17] Coating device for coating an inner wall of a tubular substrate (900, 1000, 1300) with vaporized coating material by means of chemical vapor deposition or by means of physical vapor deposition, wherein at least one end of the tubular substrate (900, 1000, 1300) has an opening (901, 1001, 1002, 1301) through which the coating material can penetrate the tubular substrate (900, 1000, 1300), and wherein the coating device comprises: - a temperature control device designed to imprint a temperature profile on the wall of the tubular substrate (900, 1000, 1300) along its longitudinal direction, wherein the temperature in the area near the at least one opening (901, 1001, 1002, 1301) of the tubular substrate (900, 1000, 1300) is higher than the temperature in the areas of the inner wall further away from the at least one opening (901, 1001, 1002, 1301), characterized by , that - the temperature control device comprises a plurality of temperature control elements (903-906, 1003-1008, 1104, 1107, 1303, 1304) arranged along the longitudinal direction of the tubular substrate (900, 1000, 1300), wherein each of the temperature control elements (903-906, 1003-1008, 1104, 1107, 1303, 1304) is designed to be heated or cooled to a predetermined temperature. [18] Coating device according to claim 17, characterized by at least one of the following: - the temperature control elements are thermostatically controlled temperature control elements; - the temperature control elements are heating and / or cooling sleeves; - The temperature control elements are designed to bring each segment of the tubular substrate to a predetermined temperature.

Images