Methods for producing three-dimensional structures or structural elements on substrate surfaces

Abstract

A method for producing three-dimensional structures or structural elements, in which a pasty composition comprising a polymer as the organic component B1, a powdered material having a solid content in the range of 60 wt% to 95 wt% in the composition, and at least two different solvents C1 and C2, which form a solvent mixture, wherein a first solvent C1 has a boiling point that is lower than the boiling point of the further solvent(s) C2, is formed, in the form of at least one layer printed onto the surface of a substrate, maintaining a temperature at which the first solvent C1 evaporates, thus increasing the viscosity of the pasty composition, followed by mechanical processing or plastic deformation by applying additional force to achieve a predetermined outer contour of the respective structure or structural element, and at least one further solvent C2 subsequently being removed during a heat treatment leading to complete drying at a higher temperature, above the boiling point of the first solvent C1, so that no solvent remains in the dried structure or structural element. and Following this, a thermal treatment is carried out in which all organic components are removed and the powdered material is sintered.

Description

[0001] The invention relates to a method for producing three-dimensional structures or structural elements on substrate surfaces, which preferably have advantageous electrochemical and mechanical properties. Using pasty compositions, for example, self-supporting functional layers or functional layers arranged on a substrate, in particular for forming strip-shaped electrically conductive functional elements, can be produced by applying the pasty compositions and subsequently curing these masses. The invention can advantageously be used in the production of structures or structural elements on electrochemical cells or sensors. Bonded joints can also be produced using a pasty composition.

[0002] In the production of various electronic or electrical components, functional layers are applied via physical or chemical vapor deposition. These techniques allow the production of very fine and particularly thin structures. However, they are not particularly suitable for cost-effective mass production. Various functional elements can be produced more cheaply using screen printing, roller printing, or pad printing. However, these technologies have the disadvantage that only limited aspect ratios of the printed structures can be achieved. An aspect ratio is the ratio of the height of a structure, i.e. the thickness of a structure, for example a functional layer, to its width. The above-mentioned printing processes have the fundamental disadvantage that high layer thicknesses cannot be achieved, especially with narrow line widths. This can, for example,lead to the following disadvantage that a sufficiently low electrical resistance can only be achieved with wider structures and / or a higher number of usable structures. When realizing narrow structures, the interaction between the printed composition, which is used in a pasty consistency for the formation, and the substrate must also be taken into account. The paste and the substrate essentially influence the possible wide flow of the applied structures. In this case, the printed structures show a tendency to run with narrow and tall structure formation. This limits the aspect ratio and the width of a structure or structural element becomes considerably larger than is the case directly during formation of the structure or structural element.

[0003] With wider structures or structural elements, another undesirable effect can often occur, such as structural collapse. The moist layer, which is present with the pasty composition directly during formation, sinks into the center of the printed structure, forming a depression or valley, so that the vertically upward-facing surface of a structure or structural element is concavely curved and may be formed with individual trench-shaped depressions or craters. This leads to additional work, in particular mechanical processing (e.g. grinding, milling) of printed and dried structures or even sintered structures. However, suitable machining processes are complex, since the brittleness of the material and, if applicable, the thermal expansion of the printed structure can lead to premature deformation.Poor adhesion of a structure formed on a substrate can lead to damage or even total failure, i.e., scrap. At the very least, this requires a correspondingly high amount of time. Machining in the green state can also result in a structure or structural element being detached from the substrate on which it was formed, in an undesirable, undefined form.

[0004] To avoid such situations, the dried paste should have very good mechanical properties, which, however, is usually not achievable or only with great effort and associated high costs.

[0005] For example, it is known from US 2002 / 0195746 A1 to bring solid particles into different states of strength and viscosity using a polymer and a solvent in order to produce three-dimensional components.

[0006] US 2009 / 0008055 A1 and US 2016 / 0040025 A1 concern technical solutions for the production of three-dimensional components in which powder and polymer are applied layer by layer and the respective layers are locally exposed to a liquid mixture in a differentiated manner and thereby solidified there.

[0007] It is therefore an object of the invention to provide possibilities for producing self-supporting or three-dimensional structures or structural elements arranged on a substrate, which can preferably be formed as functional layers usable in electrochemical components, which are cost-effective and with which in particular a large aspect ratio can be achieved in conjunction with a near-net-shape formation before a heat treatment in which sintering of a solid contained in a pasty composition occurs.

[0008] This object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in subordinate claims. The pasty composition usable in the invention is preferably a heterogeneous mixture formed from a powdered solid A, an organic polymer B1, optionally a plasticizer / softener / leveling agent / wetting and / or dispersing additive B2, and at least two solvents C1 and C2 for organic components B1 and B2. One of the solvents C1 has a boiling point at which evaporation of the first solvent C1 occurs, which is lower than the boiling point of another solvent C2. The boiling point of the first solvent C1 should be at least 10 K lower than the boiling point of another solvent C2.

[0009] The pasty composition can be formed into the desired geometric shape, particularly advantageously layer by layer, using a generative manufacturing process, and solidified in this form by preferential evaporation of the first solvent C1 immediately after the formation of a layer with which a structure or structural element is formed. The formation of the structure or structural elements can be achieved with a single layer, particularly by means of stencil printing, or with several individual layers formed one above the other, for example, using other printing processes, wherein the process of evaporating the first solvent C1 should be carried out for each individual layer immediately after the formation of a layer.The at least one additional solvent C2 is only added later during a heat treatment that leads to complete drying and at a higher temperature, which is above the boiling point of the additional solvent(s) C2 and, of course, also above the boiling point of the first solvent C1. After this heat treatment, no solvent is contained in the dried structure or any structural element.

[0010] A pasty composition can be realized with powdered solids based on electrically conductive oxides, mixed oxides, spinels, perovskites, metals, or their mixtures in particle form with particle sizes ranging between 0.1 µm and 10 µm. The multicomponent organic solvent mixture is formed with different solvents C1 and C2. At least one solvent C1 should be selected from the group with which an RER (relative evaporation rate) value above 1 can be maintained. The value for the term RER (relative evaporation rate) is a parameter for comparing the evaporation of a solvent with a standard sample (usually n-butyl acetate). A solvent with an RER value above 1 represents a solvent with a high evaporation rate.Generally speaking, the term “solvents with a high evaporation rate” or “volatile solvents” is intended to mean that a known drying process in the solvent mixture causes the pasty composition to evaporate at least almost completely.

[0011] However, at least one additional solvent C2, which was contained in the solvent mixture, remains in the pasty composition after the formation of a layer, which merely reduces the viscosity of the pasty composition, while still allowing plastic deformation of the pasty composition through additional force and / or simplified mechanical material removal. However, plastic deformation, which occurs solely due to gravitational forces, no longer occurs after the evaporation of the first solvent C1, so that, apart from shrinkage occurring during sintering, no further deformation of the structure or structural element formed by printing one or more layers occurs without additional processing.

[0012] Particularly for the formation of functional layers with narrow structures or structural elements, in particular with a height to width ratio (aspect ratio) a > 0.3), it is advantageous to carry out a drying process at room temperatures, i.e. below 30°. The drying, during which a first solvent C1 evaporates completely, should take place in the shortest possible time and this time should be less than 0.5 h, preferably less than 20 min and particularly preferably less than 5 min. In this case, the spread of the pasty composition can be prevented by enabling rapid curing or hardening at least on the surface or in a region close to the surface by evaporating the first solvent C1 at a high evaporation rate after the pasty composition has been applied, so that the applied pasty composition becomes dimensionally stable in a short time.This dimensional stability can be achieved in particular by forming a mechanically stable skin.

[0013] In any case, the viscosity should be reduced by evaporating the first solvent C1, so that the solvent(s) C2 still remaining in the pasty composition may still allow for plastic deformability or simplified processing by removing material from the surface of a structure or structural element that has not yet been sintered.

[0014] Particularly suitable examples of first solvents C1, preferably with an RER value above 1, are hexane, cyclohexane, methyl acetate, ethyl acetate, benzene, methyl ethyl ketone, isopropanol, ethanol and methanol.

[0015] An additional solvent C2 with an RER (relative evaporation rate) value of less than 1 cannot adversely affect the solubility of polymer B1 and other organic additives, such as plasticizer / plasticizer / leveling agent / wetting and dispersing additive B2. On the other hand, these additional solvents C2 can influence the long-term stability of the pasty composition as well as its thixotropic properties. The thixotropic properties can thus have a beneficial effect on the formation of the ultimately desired outer contour of a structure or structural element, particularly when plastic deformability or material removal is to occur on a not-yet-sintered structure or structural element. Thus, plastic deformation can be achieved with a mold acting on a not-yet-sintered, plastically deformable structure or structural element.Material removal can be achieved through machining, particularly by grinding or milling. This involves significantly lower forces and moments than would be the case with machining after sintering, thus preventing the detachment of structures or structural elements from a substrate surface and / or damage to a structure or structural element due to unwanted material removal.

[0016] Butyl carbitol, monoethylene glycol, diethylene glycol, 1,2-propanediol, butanol, 3-methoxy-1-butanol, terpineol, or pineol can be used as additional solvents C2. These chemical compounds can be used alone or in combination with at least two of these chemical compounds in a solvent mixture with a first solvent C1.

[0017] The amount of solvent mixture used can be selected within a wide range of 3% to 40% by mass, depending on the other variable components that make up the paste-like composition and the desired results or properties. For most applications, the organic solvent mixtures used can be comprised of 5% to 95% by mass of a first solvent C1 with an RER value greater than 1 and at least one further organic solvent C2 with a proportion in the range of 5% to 95% by mass, which has an RER value less than 1.

[0018] An organic polymer B1 and optionally at least one plasticizer / plasticizer / leveling agent / wetting and dispersing additive B2 are dissolved in the solvent mixture. The plasticizer / plasticizer / leveling agent / wetting and dispersing additive B2 can be utilized to improve the strength of a structure or structural element after application and drying of the paste-like composition. The following organic polymers B1 can be used, which have proven particularly suitable for forming structures or structural elements using a printing process: ethyl cellulose of types N-4 to N-300, methyl methacrylate, n-butyl methacrylate, acrylic polymers, or alkyd resins. The paste-like composition can be composed of one or more other organic components, such as a plasticizer / plasticizer / leveling agent / wetting and dispersing additive B2.In particular, the following components can be included as B2: 1,2,3,4-tetrahydronaphthalene, dimethylcyclohexyl phthalate, naphthalene, N-oleoylsarcosine, 1,2-cyclohexanedicarboxylic acid di-isononyl ester, trihydroxystearin, octadecylamine, triethanolamine, oleic acid, and / or stearic acid. The amount of the additional organic component(s) B2 can be selected in the range of 0.05% to 6.0% by mass, depending on the other variables of the system and the desired properties of the pasty composition.

[0019] The material for the solid can be any powder. The material can function as an electrical resistor, electrical conductor, or electrical insulator. Particularly preferred is a contact system using electrically conductive oxides, mixed oxides, spinels, perovskites, metals, glasses, or mixtures thereof. The solid content of the pasty composition, i.e., the functionally active phase in the pasty composition, should be kept in the range between 60 mass% and 95 mass%, preferably 65 mass% and 85 mass%. The average particle size should be 50 in the range 0.1 µm to 10 µm, preferably between 0.5 µm and 5 µm.

[0020] The use of a pasty composition according to the invention can prevent the printed structures or structural elements from flowing after application to the substrate. In addition, improved adhesion to the substrate can be achieved, allowing a reduction in volume (contraction) of the applied structure or structural element without loss of adhesion.

[0021] The pasty composition may exhibit thixotropic properties, which, due to its viscosity, can reduce the risk of fracture under shear forces, while significantly increasing strength and dimensional stability in the unstressed state. Due to these properties, a specific viscosity of the pasty composition should be maintained before and after printing to achieve and maintain a correspondingly large aspect ratio. Accordingly, a pasty composition should have a viscosity at a temperature in the range of 20°C to 30°C in the range of 40 Pas to 300 Pas at a shear rate η of 10 s -1 At a shear rate η of 100 s -1 A viscosity of 10 Pas to 35 Pas should be maintained.

[0022] In order to prevent the often occurring undesirable problems (such as the wide flow of a printed stripe, a column or a dot), a viscosity increase in the range of 60 Pas to 450 Pas (measured value related to a shear rate η of 10 s -1 ) to cure the surface of a structure or structural element after application / printing. The respective viscosity increase can be influenced by the composition of the paste and by the drying process.

[0023] A pasty composition can be used to form a structural element on a substrate, for example, in the form of a web or a column. The entire surface can also be printed, preferably using screen printing, stencil printing, pad printing, 3D printing, or a dispenser. Printing can be done in one or more layers. Multiple layers can be applied sequentially or on top of one another. After each individual layer has been formed, drying should be carried out, during which at least a large portion of the first solvent C1 is evaporated.

[0024] In the following, the invention will be explained using examples. Example 1 Preparation of a pasty composition for producing a web-shaped contact layer between an interconnector and a cathode of a high-temperature fuel cell

[0025] In a closed stirred vessel, 50 g of 1,2,3,4-tetrahydronaphthalene as B2, 5 g of benzyl alkyl phthalate as B2, 3 g of butyl glycolate as C2, 0.5 g of naphthalene as B2, 36.5 g of terpineol as additional solvent C2, 2 g of ethyl cellulose type N-7 as B1, and 6 g of ethyl acetate as C1 are mixed and heated. An organic mixture is obtained which is fluid at room temperature and can be stored without any significant change in its flow properties. 80 g of perovskite powder (e.g., La) is mixed into 20 g of the above-mentioned organic mixture. 0.8 Sr 0.2 Mn 0.9 Co 0.1 O3) with an average particle diameter d 50of 5 µm using a stirrer, dissolver, mortar mill, or speed mixer. The resulting paste-like composition is then homogenized in a three-roll mill. The produced paste is applied to the surface of an interconnector as a substrate using screen or stencil printing or a dispenser. After drying, during which the first solvent C1 has been at least completely evaporated at 25-75°C, the structure formed on the cathode surface with the paste-like composition can be mechanically processed on its surface, preferably smoothing and leveling the surface before a heat treatment leading to sintering is carried out. Example 2

[0026] In the preparation of a pasty composition for a contact layer formed with webs between an interconnector and a cathode of the high-temperature fuel cell, 15 g of methyl methacrylate and / or n-butyl methacrylate as organic polymer B1, 80 g of terpineol as additional solvent C2, 2 g of butyl carbitol as additional solvent C2 and 5 g of isopropanol as solvent C1 are mixed and heated in a closed stirred vessel. An organic mixture is obtained which is flowable at room temperature and could be stored without any major change in its flow properties. 80 g of perovskite powder (e.g. La 0.8 Sr 0.2 Mn 0.9 Co 0.1 O3) with an average particle size d 50of 5 µm and 1 g of 2,4,7,9-tetramethyl-5-decyne-4,7-diol as B2 are mixed into the mixture using a stirrer, dissolver, mortar mill, or speed mixer. The pasty composition is then homogenized using a roller mill. The produced paste is applied to a surface of the interconnector as the substrate using screen or stencil printing or a dispenser. After drying, during which at least the first solvent C1 has been almost completely evaporated, it can be processed mechanically or by plastic deformation using an attachable mold, before a heat treatment leading to sintering is carried out.

[0027] The three-dimensional web structure obtained according to Examples 1 or 2 has a structure width of 3 mm and a layer thickness of the web lines in the range between 200 µm and 550 µm, preferably 300 µm to 350 µm. To realize these structures, a pasty composition according to the invention was used, the viscosity of which initially was approximately 60 Pas and increased to 110 Pas after 10 minutes of drying in air.

Claims

[1] A process for producing three-dimensional structures or structural elements, in which a pasty composition containing a polymer as organic component B1, a powdery material which has a solid content in the range of 60% to 95% by mass in the composition, and at least two different solvents C1 and C2, which form a solvent mixture, wherein a first solvent C1 has a boiling point which is lower than the boiling point of the further solvent(s) C2, in the form of at least one layer onto the surface of a substrate and maintaining a temperature at which the first solvent C1 evaporates, so that the viscosity of the pasty composition is increased, and then mechanical processing or plastic deformation is carried out by additional force, in which a predetermined outer contour of the respective structure or structural element is achieved, and the at least one further solvent C2 is later removed during a heat treatment which leads to complete drying and at a higher temperature which is above the boiling point of the first solvent C1, so that no solvent is contained in a dried structure or structural element, and Subsequently, a thermal treatment is carried out in which all organic components are removed and the powdered material is sintered. [2] Method according to claim 1, characterized by that the printing is carried out by means of screen printing, stencil printing, pad printing or dispensers with a respective layer thickness of at least 100 µm and / or a height to width ratio α in the range 0.05 ≤ a ≤ 1.0 is maintained. [3] Method according to one of the preceding claims, characterized by that a pasty composition is used which additionally contains a plasticizer / softener / leveling agent / wetting and dispersing additive B2. [4] Method according to one of the preceding claims, characterized by that a pasty composition in the a first solvent C1 selected from hexane, cyclohexane, methyl acetate, ethyl acetate, benzene, methyl ethyl ketone, isopropanol, ethanol and methanol and / or another solvent C2 selected from; butyl carbitol, monoethylene glycol, diethylene glycol, 1,2-propanediol, butanol, 3-methoxy-1-butanol, terpineol and pineol and / or an organic polymer B1 selected from ethyl cellulose of type N-4 to N-300, methyl methacrylates, n-butyl methacrylates, acrylic polymers and alkyd resins and / or a plasticizer / plasticizer / leveling agent / wetting and dispersing additive B2 which is selected from 1,2,3,4-tetrahydronaphthalene, dimethylcyclohexyl phthalate, naphthalene, N-oleoylsarcosine, 1,2-cyclohexanedicarboxylic acid di-isononyl ester, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, trihydroxystearin, octadecylamine, triethanolamine, oleic acid and stearic acid is used. [5] Method according to one of the preceding claims, characterized by that a temperature in the range 20 °C to 30 °C results in a viscosity in the range of 40 Pas to 300 Pas at a shear rate γ of 10 s -1 and a viscosity in the range of 10 Pas to 35 Pas at a shear rate γ of 100 s -1 is adhered to. [6] Method according to one of the preceding claims, characterized by that a pasty composition is used which contains a first and at least one further solvent C1 and C2 with a proportion in the range 3 mass% to 40.0 mass% and a first solvent C1 with a proportion in the range 5.0 mass% to 95.0 mass%. [7] Method according to one of the preceding claims, characterized bythat a pasty composition is used which contains 0.05 mass% to 6.0 mass% of plasticizer / plasticizer / leveling agent / wetting and dispersing additive B2 and 0.05 mass% to 8.0 mass% of organic polymers B1. [8] Method according to one of the preceding claims, characterized by that an oxide, a mixed oxide, a spinel, a perovskite, a metal and / or a glass or a mixture thereof is used as powdered solid A. [9] Method according to one of the preceding claims, characterized by that solid with an average particle size d 50 in the range between 0.1 µm and 10 µm. [10] Method according to one of the preceding claims, characterized by that a first solvent C1 is used whose boiling point is at least 10 K lower than the boiling point of the further solvent(s) C2.