WO2019185756A1 - Procédé de traitement d'éléments obtenus par un procédé de fabrication additive - Google Patents

Procédé de traitement d'éléments obtenus par un procédé de fabrication additive Download PDF

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Publication number
WO2019185756A1
WO2019185756A1 PCT/EP2019/057795 EP2019057795W WO2019185756A1 WO 2019185756 A1 WO2019185756 A1 WO 2019185756A1 EP 2019057795 W EP2019057795 W EP 2019057795W WO 2019185756 A1 WO2019185756 A1 WO 2019185756A1
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Prior art keywords
solution
temperature
elements
acid
aqueous solution
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PCT/EP2019/057795
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English (en)
Inventor
Tobias Abstreiter
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Technische Universität München
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Priority claimed from EP18181049.0A external-priority patent/EP3587080A1/fr
Application filed by Technische Universität München filed Critical Technische Universität München
Publication of WO2019185756A1 publication Critical patent/WO2019185756A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C71/00—After-treatment of articles without altering their shape; Apparatus therefor
    • B29C71/0009—After-treatment of articles without altering their shape; Apparatus therefor using liquids, e.g. solvents, swelling agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y40/00—Auxiliary operations or equipment, e.g. for material handling
    • B33Y40/20—Post-treatment, e.g. curing, coating or polishing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C71/00—After-treatment of articles without altering their shape; Apparatus therefor
    • B29C71/0009—After-treatment of articles without altering their shape; Apparatus therefor using liquids, e.g. solvents, swelling agents
    • B29C2071/0018—Absorbing ingredients, e.g. drugs, flavourings, UV screeners, embedded in the articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/30—Auxiliary operations or equipment
    • B29C64/35—Cleaning
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2077/00—Use of PA, i.e. polyamides, e.g. polyesteramides or derivatives thereof, as moulding material

Definitions

  • the present invention is concerned with a method for treatment of polyamide comprising elements obtained by an additive manufacturing process.
  • Additive processes for preparing elements for various applications have become very popular.
  • Additive processes also known as three-dimensional (3D) printing processes are available in different forms starting from building materials in liquid, viscous, solid or powder form.
  • 3D printing processes uses building material in powder form which is selectively solidified by first sintering, melting, fusing, or binding the powder at selected sites for producing elements. Elements are built by depositing powdery material layer after layer.
  • the building material can be a polymer, metal, ceramic , or a composite material.
  • One class of polymers that is useful for additive manufacturing is the class of polyamide polymers and polyamide blends.
  • An element is formed by applying a layer of material in powder form to a building platform, and then based on computer generated data the powder in those parts of the layer which shall become part of the element, is selectively heated or bonded, for example the powder is fused or melted by infrared radiation, sintered by a laser beam, or is bonded by a binder material.
  • the platform is then lowered, another layer of material in powder form is added and again melted, fused, or bonded. These steps are repeated until the element has been built.
  • Selective heating can be obtained by laser beam, as for example in selective laser sintering (SLS), or by infrared radiation, such as in multi-jet fusion (MJF) processes.
  • Selective solidifying can be obtained by binder-jetting processes among others. The main principle of these solidifying processes is the use of a powder which is treated to solidify at predetermined sites to yield the product.
  • Additive sintering processes are particularly useful for producing elements with delicate structures, fine channels and/or complex forms.
  • a class of polymers that is highly desirable for additive manufacturing is polyamide, a highly robust polymer which is resistant to the environment, and has good mechanical properties. Therefore, polyamide in powder form is a useful building material and is used in multi-jet fusion (MJF) and selective laser sintering (SLS) processes.
  • MJF multi-jet fusion
  • SLS selective laser sintering
  • US 2017/0327658 discloses a process for surface treatment of an object wherein the object is dipped in concentrated acid to impregnate the surface and then is heated to a temperature between 140 and 180°C, until melting of the surface is obtained. This treatment is very harsh and can result in formation of holes or cracks in the surface.
  • DE 10 2014 102 137 discloses a process for treatment and dyeing of surfaces wherein an object is dipped in a hot solution comprising a dye for up to 6 hours wherein the dye solution has a temperature between 60 and 180°C.
  • the process comprises at least three steps wherein in a first step the objects are pretreated by milling, grinding, or polishing. After this step formic acid vapor can be applied to further smoothen the surface.
  • the elements are dyed by using a mixture of dye and water having a temperature of at least 60° and up to 180°C.
  • the surface of the object is impregnated and/or sealed by applying a polymer solution. This process has disadvantages.
  • polyamide comprising elements obtained by an additive manufacturing process with a smooth surface by treating the elements with a process comprising at least two steps, as defined in claim 1 , which allows to smoothen surfaces in elements with very delicate parts, with high complexity, with channels, holes and fine structures in a time and cost effective way.
  • the parts have high quality and the mechanical strength is not or hardly impaired by the method of the present invention. Only by using at least steps a), and b) a smooth surface can be obtained.
  • the method of the present invention can be used for elements that have been obtained by additive manufacturing processes, wherein a polymer, such as polyamide, is used as building material to form an element.
  • a polymer such as polyamide
  • the elements are built as described above, for example by using an energy source like a laser or infrared radiation to create a solid structure from a powder.
  • the powder bed supports the elements which allows to prepare very delicate structures by this technique.
  • the method as defined in the claims is versatile and allows to adapt the conditions according to the properties that are desirable for an element. Moreover, the method of the present invention has an influence on the color of the elements to be treated and allows to get white, black, or colored elements by adapting the conditions of the treatment as will be explained below.
  • additive manufacturing refers to a process where polyamide is first melted, fused, sintered, or bonded and then solidified at predetermined sites. In other words, it is a process, where a polyamide is selectively formed into a solid material.
  • additive manufacturing refers to a process where a polymer powder is solidified in a predetermined shape or pattern to build an object or element.
  • additive manufacturing among others comprises selective laser sintering (SLS) methods, infrared radiation based methods, such as multi-jet fusion (MJF) processes, selective solidifying methods like binder-jetting processes including high speed sintering.
  • polyamide when used in this application refers to a product that has been obtained by additive manufacturing with polyamide, in particular with polyamide powder as building material.
  • polyamide comprises one type of polyamide or a mixture of two or more types of polyamide as well as polyamide blends.
  • polyamide powder comprises one type of polyamide powder or a powder mixture of two or more types of polyamide as well as polyamide blends, i.e. blends of one or more polyamide powders with other powders, like other polymer powders, metal powders, ceramic powders, fibers, etc.
  • the temperature refers to the temperature of this liquid.
  • the application of a“liquid at x°C“ means that the liquid has the temperature when it is applied and that the temperature of the liquid is maintained for the indicated time period, for example by heating means, such as a heating bath.
  • applying or “application” is used with regard to the treatment with nitric acid or a solution
  • this shall mean that the liquid is applied to the element such that the element is fully or partially wetted or contacted by the liquid.
  • This can be obtained by means as known to the skilled person, for example by dipping elements into the liquid such that the element is fully surrounded by the liquid or such that selected parts are wetted by the liquid.
  • Applying a solution can also be in the form of vapor. It is important that the liquid contacts the whole surface of an element and can also flow into channels, holes etc., or, if this intended, contacts selected parts of the surface.
  • Solidifying of a powder can be obtained by fusing, sintering, melting, or binding a powder.
  • the surface roughness of a material or element refers to the texture on the surface. It is quantified by deviations in the profile, i.e. deviations in a direction that is normal to the surface. Measured values for the profile result from scanning the actual profile with a probe. Surface imperfections, such as cracks, scratches and dents, should not be part of the profile and should not be included in the measured value.
  • R a values i.e. arithmetical mean roughness values except the context tells otherwise.
  • Any type of pure water, like demineralized water, deionized water, or distilled water is also referred to as E-water.
  • a functionalizing agent refers to an agent that adds or introduces a function to the element or the surface of the element, respectively.
  • the function can be a chemical, physical, esthetical etc. function.
  • a functionalizing solution is a solution comprising at least one functionalizing agent.
  • base refers to an inorganic or organic compound that is soluble in water and when dissolved in water yields a solution with a pH of greater than 7. Examples are hydroxides of alkali and alkaline earth metals.
  • a step as defined in the claims can be applied in one, two, or more runs, wherein “applied in one, two, or more runs” or carried out in one, two, or more runs” means that a processing step as defined is applied once, twice or more times, wherein each run can be the same or different than another run of this step.
  • the method of the present invention can have an influence on the color of the element.
  • These white elements treated by the method of the present invention are based on polyamide as building material.
  • Polyamide powder usually is white and, thus, elements for example produced by SLS are also white.
  • the elements by treating them with the method of the present invention can become off-white or get a yellowish tone.
  • Elements obtained with an MJF process usually are grey, the basic polyamide material is white but carbon black is added to improve the heating by infrared radiation and a white material is added to provide for accurate contours.
  • the elements at the surface become off-white to white. These elements can be dyed in many different tones because of their white or nearly white surface and because the surface layer has not been densified by mechanical treatment.
  • the favorable results are obtained only by using at least steps a) and b) of the method of the present invention. It has surprisingly been found that the surface of elements can be smoothened by first applying nitric acid on an element and thereafter removing it by applying an aqueous solution. By configuring concentration of nitric acid, temperatures and time periods of application and composition of the aqueous solution optimal results can be obtained.
  • the first step is important for smoothening the surface and/or for those elements, that have a grey color, for changing the color of the element to black or white.
  • the surface layer becomes softer and smoother.
  • the acid is removed in a manner that maintains smoothness, does not impair the elements and their surface hardens again.
  • the color changes during the treatment, but only in the upmost layer.
  • When treated with nitric acid the surface becomes black, when the nitric acid has been removed and the surface has been in contact with water it becomes off-white to white.
  • the surface becomes brighter when at the end it is treated with a finishing solution comprising alcohol, acid, base, or salt.
  • step a elements obtained by additive manufacturing are treated with nitric acid for a period of up to about 45 minutes, for example from about 1 to about 30 minutes at a temperature in the range of about 0°C to about 65°C, such as 10 to 55°C or 20 to 40°C. It has been found that concentrated nitric acid when used for a time period of at least 1 minute and at a temperature below 70°C provides for a smoothened surface without or essentially without damaging the surface or parts of the elements. The lower the temperature is the longer the time period of treatment with nitric acid should be.
  • One advantage of the method of the present invention is, that the method can be used at room temperature or slightly above. On the other hand, treatment can be very fast when a temperature in the range of 60 to 65°C is used.
  • Nitric acid is useful for smoothening the surface of complex elements, it was found that even channels, holes and delicate parts are smoothened when nitric acid is applied. Nitric acid can be used as long as it is concentrated enough. It has been found that nitric acid at a concentration between 40 and 85% is useful. Beyond 85% nitric acid is too strong and can damage the surface. Although a concentration of less than 40% could be used, this is not strong enough to smoothen the surface in channels and holes in an appropriate time period. When color change is important the application of nitric acid for a very short time can already be sufficient, such as about 1 second to about 30 minutes.
  • nitric acid for at least 1 minute, such as within a time period from about 1 to about 45 min. Less than 1 min might not be enough for finalizing the smoothening. More than 45 min can result in damage and destruction.
  • the time period used is also dependent on the application temperature. At lower application temperatures the time period can be longer whereas at higher temperatures the time period should be shorter. For example, when using a temperature in the range of about 10 to about 40°C the application time can be about 2 to about 45 minutes, such as about 5 to about 30 minutes, whereas when using a temperature in the range of about 45 to about 65°C the application time can be in the range of about 1 to about 15 minutes.
  • the skilled artisan can find the optimal combination of temperature and time for a specific type of element by routine experiments.
  • the method of the present invention allows to carry out the treatment at room temperature or slightly higher. This is an advantage compared to the methods of the prior art where high temperatures have to be used for preparing smooth surfaces.
  • a temperature between 20 and 50°C has been found particularly suitable and the best results are obtained in a temperature range between 30 and 40°C. If a temperature in the range of 30 to 40°C is used, a time period of 10 to 20 min is sufficient to obtain an optimal surface smoothening. For lower temperature the time period can be up to 30 min, whereas for temperatures 40°C a t ime period of less than 10 min is suitable. Good results are obtained when elements are treated with concentrated (30 to 65%) nitric acid at a temperature of 30 to 40°C for 10 to 20 minutes.
  • an element is treated with nitric acid such that the whole surface is in contact with nitric acid and, thus, is smoothened. If only part of an element shall be smoothened, then only this part should be in contact with nitric acid. This can be achieved by excluding that part of the element that shall remain untreated from contact with nitric acid or by protecting it from contact with nitric acid, for example, by applying a protective layer on that part of the element that shall remain untreated, for example, by applying a layer, like a wax layer or a silicone layer.
  • treating polyamide elements such as those obtained by MJF that have a grey color
  • nitric acid changes the color of the elements.
  • the color of the elements becomes black
  • the color becomes white to off-white.
  • the method of the present invention is also useful to change the color of elements, as white or off-white elements can be dyed with many different dyes, such as acid dyes, sulfur dyes, dispersion dyes and other dyes that are used for dyeing polyamide, and in many different color tones, hues, tints or shades.
  • the skilled person can find the optimal combination of conditions for changing the color of the elements. It has been found that good results are obtained when nitric acid having a concentration of 30 to 65 wt.-% is applied to an element at a temperature in the range of about 5°C to about 65°C. At lower temperatures, such as at temperatures between about 5°C and about 20°C the black color becomes very brilliant. Depending on the temperauture applied the time period can be as short as 1 to 5 seconds, for example at a temperature of 30 to 40°C, or 5 seconds or more for lower temperatures.
  • the contact time with the nitric acid is about 5 seconds to about 10 seconds or more and the contact with an aqueous solution can be in a range of at least about 1 second up to 30 minutes or more.
  • any aqueous solution as defined below can be used.
  • step b) is carried out in two or three runs, where the aqueous solution is used at different temperatures, for example in a first round at a temperature of about 20 to about 25°C and in a second round at a temperature of 50°C or above, such as 60 to 75°C, optionally in a third run the temperature can be as in the first or as in the second run.
  • Using two or three runs allows to remove the nitric acid very fast, as in every run fresh solution is applied.
  • the time periods also can differ such as a short first run (within seconds), a medium second run (within some seconds up to a few minutes) and a longer third run (within up to 60 minutes or more).
  • step b) is applied on elements obtained after step a) for 2 runs, wherein in a first run an aqueous solution, such as water, is applied for a very short time, such as 1 to 20 s, or 3 to 10 s, for example 4 to 8 s, with a temperature between room temperature and 40°C, such as 25 to 35°C, for example 28 to 33°C. This run should take away as much nitric acid as possible. Then a second run of step b) is carried out for a medium time of half a minute up to 30 min, such as 40 s to 15 min, for example 50 s to 5 min.
  • an aqueous solution such as water
  • an aqueous solution in particular water is used at the same temperature or at a temperature which is slightly higher, such as 5 to 20°C higher, than in the first run.
  • aqueous solution with a temperature of about 30 to about 50°C, such as 35 to 45°C, for example about 38 to 44°C is applied.
  • step b) it seems that it is preferable to remove nitric acid in step b) as much as possible and as fast as possible. It was found that applying an aqueous solution, in particular water in two or more runs yields good results.
  • Steps c) and d) and pre-treatment and post-treatment steps can be carried out as described below for elements that have been treated only for color change. Those elements that have been treated as described above can be dyed very easily. Acid dyes as well as dispersion dyes can be used in step c) for such elements and many color tones, hues, tints and shades can be obtained that cannot be achieved otherwise with grey elements. Moreover, it has been found that if it is the intention to change the color of elements only without necessarily smoothening the surface of elements, that instead of nitric acid concentrated formic acid can be used.
  • elements obtained by MJF that have a grey color with formic acid which has a concentration of at least 80 wt.-%, in particular 95 to 99 wt.-%, for a time period of at least about 1 minute, such as about 5 to about 60 minutes, for example 10 to 30 minutes, at a temperature in the range of about 55°C to about 65°C, and applying step b) with one or more runs as described above and in detail below, elements having a white color can be obtained.
  • These elements can also be treated with steps c) and/or d) as described in detail below.
  • the elements can be dyed with acid dyes, sulfur dyes or other dyes such as dispersion dyes in many color tones, hues, tints, and shades.
  • step b the element obtained after application of nitric acid is treated with an aqueous solution, preferably with water.
  • the aqueous solution used in step b) can be any type of water, for example tap water, pure water, demineralized water, deionized water, distilled water etc.
  • the aqueous solution can comprise a lower amount, i.e. in an amount of up to 5 wt.-%, of further solvents that are water compatible, for example alkyl alcohols with 1 to 10 carbon atoms like ethanol or isopropanol.
  • the aqueous solution of step b) can also comprise a minor amount of an acid, like acetic acid, phosphoric acid, formic acid, or hydrogen chloride, a minor amount of a salt like an alkali, alkaline earth, or ammonium halogenide, or a minor amount of a base, like an alkali or alkaline earth hydroxide or ammoniac.
  • an acid like acetic acid, phosphoric acid, formic acid, or hydrogen chloride
  • a minor amount of a salt like an alkali, alkaline earth, or ammonium halogenide
  • a minor amount of a base like an alkali or alkaline earth hydroxide or ammoniac.
  • E-water such as distilled water, demineralized or deionized water is used as aqueous solution in step b).
  • the aqueous solution shall take up the nitric acid from the surface of the element to be treated. It has been found that the application of the aqueous solution is successful if it is carried out with a solution in liquid state, i.e. at a temperature in the range between 0 to 100°C, such as about 10 to about 65°C, for example about 20 to about 55°C. Optimal results are obtained at a temperature of 30 to 45°C. It was surprising that it is sufficient to use a solution in a temperature range which is close to room temperature and that it is not necessary to use high temperature for this treatment step. Moreover, it has been found that optimal results are obtained when the temperature range of this step is about in the same range as that one for the treatment with nitric acid.
  • the time period for application of the aqueous solution in step b) can be as short as 1 second, such as 10 or 30 seconds. However, the time period for step b) should be 1 to 5 seconds only in that cases where either step b) is repeated or where step c) and/or step d) follows.
  • a suitable time period for step b) in those cases where no further step is carried out, is at least 5 seconds, for example 30 seconds to 60 minutes, such 3 to 15 minutes. There is no upper limit for the time period except economical reasons.
  • the elements can be treated with aqueous solution for hours or even days, where the elements will not change except take up water.
  • step b) should be applied for up to about 120 minutes or more, such as up to 30 min or up to 60 minutes.
  • step b) The time period used depends on the temperature of the element and of the aqueous solution, it also depends on further steps. If a functionalizing and/or a finishing step is used, step b) can be shorter. It has been found that a high amount of nitric acid is removed already after dipping elements for just a few seconds. On the other hand, treatment with water for more than 30 min does not provide further advantage. Good results are obtained when a time period of about 30 sec to about 50 min is used, a preferred range is about 2 min to about 10 min.
  • Step b) can be carried out once or several times. For example, step b) can be carried out 2 to 5 times.
  • step b) can be carried out 2 or more times, all runs can be similar, i.e. for the same time and at the same temperature. Different runs can also be applied with different time periods and at different temperatures. For example, step b) can be carried out with 3 runs, where the first run is very short, for example only about 1 second to about 2 minutes, such as 3 to 10 seconds, at a temperature in the range of about 5 to about 40°C, such as 20 to 30°C or just room temperature. This first run can be used to remove the majority of nitric acid very fast.
  • the second run can be applied for a time period in the range of about 1 about 15 minutes, such as for about 1 to 5 minutes, either at the same temperature as the first run or at a higher temperature in the range of about 40 to about 80°C, such as about 70 to about 80°C.
  • the third run can be applied for a longer time period, for example up to about 120 minutes, such as for about 5 to about 30 or about 60 minutes at a temperature as in the first run or as in the second run or any other temperature, for example at 20 to 40°C, such as about 30°C. Any other combination of time periods and temperature can be used, the skilled person can find the optimal combination of conditions by routine experiments.
  • Elements obtained after step b) have a smooth surface which hardens and is mechanically strong and/or have a white or off-white color.
  • the color of the elements can be white to off-white or yellow.
  • These elements can be used as they are, they can be stored until they are used, or they can be treated further with a functionalizing solution to improve or change the properties, and/or can be treated with a finishing solution to make the surface of the element harder, glossier or more brilliant.
  • the surface of the elements after treatment according to the present invention in addition has liquid repelling properties and hinders the adhesion of liquid droplets.
  • the method of the present invention comprises at least two steps which can be carried out at room temperature or slightly above room temperature in a relatively short time and yield elements of very high quality with a smooth surface and without damage to delicate parts.
  • the use of milling, grinding, or polishing steps or other mechanical treatment steps is avoided and nevertheless a high quality finishing is obtained.
  • step b) The elements obtained after step b) can be further treated to improve their properties and/or to introduce functionality.
  • a further step b') can be added after step b), in particular for those processes where it is intended to use a dyeing step. It has been found that the application of an aqueous solution comprising a base and/or the application of an aqueous solution comprising a salt after step b) further improves the quality of the elements, in particular the surface of the elements and can have an influence on a dyeing step which follows. Without being bound by theory it is assumed that application of an aqueous solution comprising a base further supports neutralizing of any remaining acid which is still on the surface of an element to be treated.
  • Step b') can be carried out in one, two or more runs, for example 2 runs, which are both similar or different with regard to the aqueous solution used and/or to the time period applied and/or with regard to the temperature.
  • two runs can be applied with the same aqueous solution but for different time periods and/or at different temperatures.
  • step b’ Every run of step b’) can be carried out for a short time or for a longer time, time is not very critical for this step. Moreover, this step can be carried out at temperatures as convenient. It has been found that application of an aqueous solution comprising a base at room temperature yields good results. Therefore, the temperature to be applied for step b') is preferably a temperature in the range of 15 to 40°C, such as 18 to 30°C, for example 20 to 25°C.
  • the time period is not critical and can be in the range of about 1 to about 120 min. Less than 1 min might be too short to improve the results. More than 120 min is possible, but does not add any further advantage. A time period of 30 min to 90 min is useful.
  • an aqueous solution comprising a base
  • the basic solution can comprise any organic or inorganic base that is compatible with the material of the element and any agent applied, and has no deleterious properties.
  • An inorganic base like sodium or potassium hydroxide is useful.
  • the concentration of the base depends on the base used and its basicity, it can be in a range that does not destroy the element but is high enough to neutralize remaining acid and/or to increase the pH value.
  • An amount of 0.1 to 10 wt.-%, such as 1 to 8 wt.-%, for example 4 to 6 wt.-% has been found useful.
  • an aqueous solution comprising a salt can be applied in step b’). It has been found that the application of an aqueous solution comprising a salt for some time improves the quality of the surface of the element. Salts that can be applied for such an aqueous solution are inorganic or organic salts, in particular salts of alkaline and alkaline earth metals. Halogenides are particularly useful. It has been found that alkaline halogenides, such as LiCI, NaCI, CaCI 2 are particularly useful.
  • a step b) in an alternative instead of applying an aqueous solution of an alcohol, an acid or a base, a gaseous form of an alcohol, an acid and/or a base can be applied.
  • Step b”) is optional and can be carried out after step b) or, if applied, step b’) and before step c).
  • Step b”) comprises the application of water on the element obtained after step b) or step b’). It has been found that, in particular when a functionalizing agent is applied in step c), the application can be improved by before contacting the elements for a longer period of 30 minutes to 48 hours, such as 6 to 24 hours, for example 10 to 15 hours, with water.
  • step c) of the method of the present invention the elements obtained in step b) can be contacted with a functionalizing solution.
  • a further advantage of the method of the present invention that in case elements shall be dyed or functionalized in another way or with at least one functionalizing agent, respectively, smoothening and dyeing or functionalizing can be done within the same process, and, thus, very efficient.
  • a further step c) is used wherein a functionalizing solution is applied to the element obtained after application of nitric acid and application of an aqueous solution.
  • a functionalizing solution is any solution that provides the surface with positive properties, such as on the appearance, color, smoothness, a hard and/or glossy surface, a deep black surface or a surface in a desired color tone, a finishing agent that provides for a specific texture of the surface, a metal that provides for a surface that can be galvanized afterwards, i.e. a priming layer for galvanization.
  • the functionalizing solution can also comprise fibers or other reinforcing agents, which can either result in a reinforced layer or in a texturized layer.
  • a plasticizer in the functionalizing solution to provide for a smooth and soft surface.
  • These functionalizing agents can be used as is known to the skilled person, i.e. in concentrations, at temperatures and in time periods that are usually used for such agents.
  • the method of the present invention allows to use such functionalizing agents and to provide functionalized surfaces in an easy way.
  • the method of the present invention is very versatile and allows the creation of different surfaces as it is desired.
  • the functionalizing solution of step c) can be an acidic aqueous solution which additionally comprise an acidic dye. It has been found that elements that have been treated with the method of the present invention can be dyed with good results with acid dyes, dispersion dyes, sulfur dyes or other dyes known for dyeing polyamide, in particular when using acid dyes. Without being bound by theory it is assumed that acid dyes are associated by the amide groups of the polyamide and thereby stay permanently on the surface without being washed away. Thus, a dyed and smooth surface with high quality is obtained.
  • acid dyes are particularly suited.
  • useful dyes are C.l. Acid Red dyes, C.l. Acid Blue dyes, C.l. Acid Yellow dyes, C.l. Acid Black dyes, C.l. Acid Orange dyes, or mixtures thereof, such as Cl Acid Red 1 , Cl Acid Red 138, Cl Acid Red 52, Cl Acid Blue 40, Nylason red N-2RBL, or mixtures thereof.
  • the acid dyes can for example be used in a concentration of 0.5 to 7.5 wt.-%.
  • an intermediate step b’) or b”) is carried out after step b) but before dyeing, wherein an element to be dyed is presoaked in a basic solution and/or a buffer or salt solution at a temperature of about 10 to 50°C, such as 35 to 45°C, for about 1 second to about 120 minutes, such as about 5 to about 90 minutes, for example about 30 to about 60 minutes.
  • the basic solution comprises a base like sodium or potassium hydroxide in an amount of 0.5 to 5 wt.-%
  • the buffer solution can comprise a buffer like sodium acetate in an amount of 0.5 to 20 wt.-%.
  • the preliminary treatment can improve the application of the dye by reducing the temperature that is necessary for dyeing.
  • a preliminary treatment element can be dyed at a temperature of least about 40 to about 140°C, for example about 60 to about 100°C, such as 70 to 85°C. Moreover, by reducing the time period necessary to dye it could be avoided that the edges of the element swell. Furthermore, it has been found that when using a intermediate step b’) and/or b”) the dyeing step can be carried out without using acetic acid for the dye solution. Whereas the results obtained for dyeing without using acetic acid are less satisfying when the dyeing step is applied directly after step b), and therefore acetic acid is used in that case, it is possible to use other dye solutions without acetic acid after pretreatment with step b’) or step b”).
  • step d) can be applied to elements obtained after step b) or after step c), i.e. elements that have been smoothened and/or functionalized.
  • step d) a finishing solution is applied that provides for hardening and further smoothening the surface and for improving color and gloss of the surface, and allows for optimal results.
  • the finishing solution can be an aqueous solution that comprises an acid, a salt, a base or an alcohol.
  • the acid can be acid as used in step b). It has been found that acetic acid is particularly useful in a finishing solution.
  • An alcohol as defined for use in step b) can be used.
  • a salt like sodium chloride or a base like sodium hydroxyde in a minor amount can be useful.
  • the base can be an organic or anorganic base. Examples are alkaline, alkaline earth or ammonium hydroxides or a misxture, among others.
  • the finishing solution is for example an acidic aqueous solution comprising acetic acid, which is applied for at least 5 minutes, such as for a period in the range of 5 min to 24 hours.
  • a time period of about 60 to about 90 min has been found useful. Below 5 min the effect might not be sufficient.
  • An application for more than 90 min can be done but does not provide further advantage.
  • the temperature for this step can be in the range of about 20 to about 40°C, such as room temperature or slightly above. This is a specific advantage of the method of the present invention that the temperature used does not have to exceed more than 40°C to obtain optimal results. These are very gentle conditions to avoid any damage to the elements.
  • An acidic aqueous solution that can be applied as finishing solution in step d) is for example an aqueous solution which comprises an organic acid, like acetic acid in a concentration in the range of 0.1 to 50 wt.-%, such as 1 to 20 wt.-%.
  • the acidic aqueous solution comprises 5 to 15 wt.-% acetic acid.
  • a basic aqueous solution that can be applied as finishing solution in step d) is for example an aqueous solution which comprises an anorganic or organic base in a concentration in the range of 0.1 to 50 wt.-%, such as 1 to 20 wt.-%.
  • the basic aqueous solution has a pK b -value of at least 4.
  • Another option is to use an alcoholic solution as finishing solution.
  • an alcoholic solution any aqueous solution comprising an alcohol, such as a Ci-Ci 0 -alcohol, for example ethanol, isopropanol, or butanol, further improves the quality and the appearance of the surface.
  • the post-treatment with the alcoholic solution results in a hard, glossy and white or off-white surface.
  • the alcoholic solution comprises an alcohol in an amount of about 1 to about 10 wt.-%. It can all comprise a mixture of alcohols wherein the total amount of alcohols is in the range of about 1 to about 10 wt.-%, for example 2 to 8, in particular 3 to 7 wt.-%. Optimal results have been obtained with an amount of alcohol in the range of about 4 to about 6 wt.-%.
  • a finishing step d) in an alternative instead of applying an aqueous solution of an alcohol, an acid or a base, a gaseous form of an alcohol, an acid and/or a base can be applied.
  • the element is taken out of the device and dried. Any remaining liquid should be removed and the element can be dried as is known to the skilled person, for example by just leaving the element in open air, or by heating, using an air stream or any other means that is usually used for drying elements or components. It is also possible to apply a vacuum chamber for drying, with or without heating. Moreover, when applying a vacuum chamber for the drying step at the same time or before drying a finishing agent in gaseous form can be introduced, such as ethanol or ammoniac.
  • a functionalizing solution is applied which comprises a colorant, a fiber, a hardening agent, a metallizing agent, a plasticizer, a filler, a finishing agent, after functionalizing the surface, a finishing solution is applied which comprises an alcohol for increasing hardness, gloss and/or improving the quality of the color.
  • each of the optional steps can be carried out for a time period of a few seconds up to many hours.
  • the specific time period useful in a specific sequence of steps can be find out by the skilled person using routine experiments. Examples are outlined below.
  • the temperature that is used for steps c) and d) depends on the agent used. It is one advantage of the method of the present invention that for most treatments a temperature close to room temperature can be used, such as a temperature in the range of 20 to 50°C, for example 30 to 40°C. However, for some applications, a higher temperature might be suitable. It has been found that for dyeing a surface a temperature in the range of about 60 to about 100°C is suitable, although it is also possible to use a temperature in the range of up 120°C.
  • a dye composition comprising high concentrated acetic acid and a dye can be used for dyeing within a short period at higher temperature or at a temperature of 70 to 80°C when using a longer time period.
  • a post-treatment with an aqueous solution having a temperature in the range of 70 to 85°C allows to get a surface with high quality in a short time.
  • Contacting an element with hot water for a short time surprisingly yields elements with exact contours, whereas it was found that using an aqueous solution with a temperature in the range of about 50 to about 70°C for a longer time can result in elements where the edges are swollen, i.e. the contours are not as accurate.
  • the method of the present invention can be improved by a pre-treatment step which can be carried out before step a), wherein the pre- treatment step comprises impregnating an element for a period of at least 1 minute, for example about 1 minute to about 24 hours or more in an aqueous pre-treatment solution that comprises tap water or E-water and optionally a base, an acid, a buffer, or an alcohol, at a temperature of about 20 to about 50°C.
  • an aqueous pre-treatment solution that comprises tap water or E-water and optionally a base, an acid, a buffer, or an alcohol, at a temperature of about 20 to about 50°C.
  • time and/or temperature of the treatment with nitric acid can be lowered which avoids damage for the elements, without being bound by theory, it is assumed that by impregnating or presoaking elements allows a faster smoothening action and thereby avoids damage in deeper parts of the element.
  • Elements can be pretreated for even longer time. At least 1 minute is useful to allow soaking of the element
  • ultrasonic energy can be used to improve contacting elements with a liquid or solution applied in one of steps b), c), or d).
  • Ultrasonic energy can be used for example in a range between 25 and 135 kHz. Although the use of ultrasonic energy in step a) in most cases does not add an advantage, it can be used in cases where ultrasonic energy provides for desired surface properties. It is useful to use ultrasonic energy after a solution has been applied in anyone of steps b) and c) or d), if applicable, and has been in contact with the element for some minutes, such as 10 minutes.
  • Sources for ultrasonic energy are known to the skilled person as are methods for using it, for example an ultrasonic bath. Ultrasonic energy can for example be used to support removal of nitric acid in step b) or for dyeing in step c).
  • the method of the present invention smoothens the surface of elements that have been obtained by an additive manufacturing process using building material in powder form, where the elements have a roughness R a of the surface of the elements before treatment in the range of 2.5 to 20 pm.
  • the elements can be smoothened to reduce the roughness by up to about 7 pm, such as about 2 to 5 pm, such that the roughness after treatment is in the range of 0.5 to 13, for example 0,5 to 7 pm, or in particular 1 to 3 pm.
  • This smoothening effect can be obtained without mechanical pre- treatment.
  • the method of the present invention creates elements with a surface that is liquid repelling and shows an excellent beading effect. This is particularly useful when elements are prepared that are used in processes where the surface of these elements is in contact with fluids because it enhances the flow of fluids. Without being bound by theory it is assumed that by processing elements with the method of the present invention a surface is created which avoids or at least makes it very difficult for a droplet to keep in contact with the surface. This effect is particularly obtained when a finishing solution has been used in a last step.
  • the method of the present invention has further advantages as the steps can be carried out easily and can be automatized.
  • the elements have high quality and can be used in every field where 3D printed elements are applied.
  • the elements can be used for devices in many fields, on earth, in the sea and in the space.
  • a method for treatment of polyamide comprising elements obtained by an additive manufacturing process comprising
  • step b) applying an aqueous solution on the element obtained in step a) for a period of at least 1 sec at a temperature in the range from about 0°C to about 100°C;
  • step b) optionally applying a functionalizing solution comprising at least one functionalizing agent on at least a portion of the element obtained in step b) for a period of at least 5 min at a temperature of at least about 20°C and/or
  • finishing solution comprising an acid, salt or an alcohol.
  • step a) nitric acid with a concentration of 40 to 85 weight-% is used.
  • step a) nitric acid is applied for about 1 second to about 30 min, optionally for about 1 to 5 seconds, or for about 2 to about 45 min, optionally about 3 to about 30 minutes, and/or at a temperature in the range from about 20 to about 50°C.
  • the aqueous solution of step b) comprises tap water, pure water, demineralized water, distilled water, or deionized water; and optionally a C1-C10 alcohol, a salt, an inorganic or organic base, a buffer, and/or an inorganic or organic acid having a pK a -value of at least 4.
  • step b) an aqueous solution having a temperature of about 20 to about 50°C is applied on the element for a time period of about 10 to about 240 minutes and thereafter the element is dried.
  • the aqueous solution of step b) comprises a C1- C10 alcohol and/or about 0.1 to about 5 wt.-% of a salt, wherein optionally the salt is a alkali or alkaline earth halogenide, and/or about 0.1 to about 5 wt.-% of an anorganic or organic acid having a pK a -value of at least 4 and/or about 0.1 to about 5 wt.-% of an anorganic or organic base having a pK b -value of at least 4.
  • step b’ comprises that an aqueous solution comprising a base and/or an aqueous solution comprising a salt is applied in one, two or more runs to an element obtained after step b).
  • step b’ at least one run with an aqueous solution comprising a base and at least one run with an aqueous solution comprising a salt is applied.
  • step b”) comprises that water is applied in one, two or more runs to an element obtained after step b) or step b’) for 30 minutes to 48 hours.
  • a functionalizing solution of step c) which comprises at least one functionalizing agent selected from a colorant, a dye, a fiber, a hardening agent, a metallizing agent, a filler, a base, a finishing agent, and/or a plasticizer.
  • step d) a finishing solution of step d) is applied, wherein the finishing solution comprises an acid, a salt, wherein optionally the salt is a alkali or alkali earth halogenide, a base, a buffer and/or a C1-C10 alcohol.
  • step c) a functionalizing solution having a temperature of about 20 to about 90°C is applied on the element for a time period of about 10 to about 120 minutes and thereafter the element is dried.
  • step d) the functionalizing solution is a solution which comprises at least one acidic dye, wherein optionally the acidic aqueous solution comprises acetic acid in an amount of 1 to 99 wt.-%.
  • step d) the finishing solution is aqueous acetic acid with a concentration of 0.1 to 99 wt.-%.
  • step b) after application of the aqueous solution and/or in step c) after application of the functionalizing solution, and/or in step d) ultrasonic energy, optionally in the range of about 25 to about 135 kHz, is applied.
  • Acid Red dyes C.l. Acid Blue dyes, C.l. Acid Yellow dyes, C.l. Acid Black dyes, C.l. Acid Orange dyes, or mixtures thereof, wherein optionally the dye is at least one of Cl Acid Red 1 , Cl Acid Red 138, Cl Acid Red 52, Cl Acid Blue 40, Nylason red N-2RBL, or mixtures thereof; wherein optionally the acid dye has a concentration of 0.1 to 7.5 wt.- %.
  • step d) is applied for post- treating an element obtained in step c) by applying an aqueous solution at a temperature in the range from about 20 to about 40°C for a time period of about 5 min to about 120 min, wherein optionally the aqueous solution comprises an alcohol in an amount of about 2 to about 10 wt.-%; wherein optionally the alcohol is ethanol or isopropanol.
  • polyamide is polyamide 6, polyamide 6.6, polyamide 1 1 , polyamide 12 or a powder blend comprising polyamide.
  • element has been obtained by a sintering/melting process, such as a multi-jet fusion process or a binder- jetting process.
  • step b) demineralized, deionized or distilled water is used as aqueous solution and/or wherein in step c) a finishing solution comprising acetic acid is used.
  • step c) a colorant or dye solution is applied having a temperature in the range of about 60 to about 90°C, wherein the temperature is maintained over the treatment period or is increased continuously or incrementally.
  • step c) the functionalizing solution is a dye solution comprising 30 to 99% acetic acid.
  • a pre-treatment step is carried out before step a), wherein the pre-treatment step comprises impregnating an element for a period of 1 minute to 24 hours in an aqueous pre-treatment solution that comprises E-water and optionally a base, an acid, a buffer, a salt, or an alcohol, at a temperature of about 20 to about 50°C.
  • step a) nitric acid is applied on the element for a period of 1 second to 5 seconds at a temperature in the range from about 5°C to about 40°C.
  • step a) nitric acid is applied on the element for a period of 1 second to 10 minutes at a temperature in the range from about 5°C to about 40°C.
  • step a) formic acid is applied on the element instead of nitric acid, for a period of up to 40 minutes at a temperature of 55 to 65°C.
  • the elements were pretreated by impregnating them in an aqueous/ethanolic solution comprising 5% ethanol and 95% E-water for 24 h, and then drying the elements for 90 minutes.
  • step 4 4.) removing the elements from basic solution of step 3) and immersing them in a solution comprising 5% ethanol and 95% E-water for 30 minutes
  • the application of a liquid workingat x°C“ means that the liquid has the temperature when it is applied and that the temperature of the liquid is maintained by heating means, such as a heating bath for the indicated time period.
  • Steps 1 ) to 5) can be carried out easily and can be automatised.
  • the elements obtained have clear contours, edges no or mininal rounding of edges, no waviness.
  • the surface has high quality, it is smooth, firm and white. The roughness could be reduced significantly:
  • the elements were not pretreated.
  • Nylosan red N-2RBL (4 wt.-% Nylosan red N-2RBL, 86 wt.-% E-Wasser, 10 wt.-% acetic acid 99%) for 90 minutes
  • the elements were immersed in the nylosan solution at 30°C, the solution was heated to 90°C with a heating rate of 2°C/min, then maintained at 90°C for 60 minutes, after 90 minutes the elements were cooled to room temperature (about 25°C) at a rate of 5°C/min
  • the surface is smooth, firm and has a red uniform coloring

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Abstract

L'invention concerne un procédé de traitement de polyamide contenant des éléments obtenus par un procédé de fabrication additive qui comprend a) l'application sur l'élément d'acide nitrique pendant une période allant jusqu'à environ 45 min à une température comprise entre environ 0 °C et environ 65 °C ; b) l'application d'une solution aqueuse sur l'élément obtenu à l'étape a) pendant une période d'au moins 1 s à une température comprise entre environ 0 °C et environ 100 °C ; c) l'application éventuelle d'une solution de fonctionnalisation comprenant au moins un agent de fonctionnalisation sur au moins une partie de l'élément obtenu à l'étape b) pendant une période d'au moins 5 min à une température d'au moins environ 20 °C ; d) l'application facultative d'une solution de finition comprenant un acide, une base, un sel ou un alcool.
PCT/EP2019/057795 2018-03-27 2019-03-27 Procédé de traitement d'éléments obtenus par un procédé de fabrication additive WO2019185756A1 (fr)

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WO2021081507A1 (fr) * 2019-10-24 2021-04-29 Postprocess Technologies, Inc. Finition de pièces de fabrication additive avec lissage et couleur
WO2022093262A1 (fr) * 2020-10-30 2022-05-05 Hewlett-Packard Development Company, L.P. Impression tridimensionnelle
DE102021104659A1 (de) 2021-02-26 2022-09-01 Dyemansion Gmbh Verfahren zur selektiven räumlichen auftrennung von verbundmaterialien/kompositmaterialien in additiv gefertigten formteilen

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WO2011145960A1 (fr) * 2010-05-21 2011-11-24 Mbm Technology Społka Cywilna Procédé et dispositif d'uniformisation d'éléments fabriqués par la technique sls par strate
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WO2021081507A1 (fr) * 2019-10-24 2021-04-29 Postprocess Technologies, Inc. Finition de pièces de fabrication additive avec lissage et couleur
WO2022093262A1 (fr) * 2020-10-30 2022-05-05 Hewlett-Packard Development Company, L.P. Impression tridimensionnelle
DE102021104659A1 (de) 2021-02-26 2022-09-01 Dyemansion Gmbh Verfahren zur selektiven räumlichen auftrennung von verbundmaterialien/kompositmaterialien in additiv gefertigten formteilen
WO2022180186A1 (fr) 2021-02-26 2022-09-01 Dyemansion Gmbh Procédé de séparation spatialement sélective de matériaux composites/matériaux composites dans des moulages fabriqués de manière additive

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