METHOD FOR TREATMENT OF ELEMENTS OBTAINED BY AN ADDITIVE MANUFACTURING PROCESS

Abstract

A method for treatment of polymer elements obtained by an additive manufacturing process comprises applying to the polymer element a treating liquid in liquid form.

Claims

1. A method for treatment of polymer elements obtained by an additive manufacturing process comprising a) a heating step for heating a treating liquid to a temperature below an upper threshold temperature, wherein the upper threshold temperature is in a range of about 1° C. to about 80° C. below the melting temperature of the polymer from which the polymer elements are formed, b) a smoothing step, wherein the polymer elements are in contact with the treating liquid at a temperature above a lower threshold temperature and below the upper threshold temperature for a predetermined time period, under conditions where the treating liquid is in liquid form, c) a cooling step for cooling the polymer elements, wherein the treating liquid comprises water and at least one monovalent aliphatic alcohol, wherein the weight ratio of water to alcohol is in a range of about 98:2 to about 20:80.

2. The method of claim 1, wherein the upper threshold temperature is in a range of about 100° C. to about 190° C.

3. The method of claim 1, wherein the at least one monovalent aliphatic alcohol is selected from ethanol, propanol, isopropanol, methanol or a mixture thereof.

4. The method of claim 1, wherein the treating liquid comprises water and ethanol in a weight ratio of about 95:5 to about 30:70 and/or wherein the treating liquid is applied at a temperature in the range of about 100° C. to about 180° C. under conditions where the treating liquid is in liquid form.

5. The method of claim 1, wherein the treating liquid comprises at least one additional solvent and/or at least one plasticizer, wherein the total amount of additional solvent and/or plasticizer is up to about 20 weight-%.

6. The method of claim 5, wherein the at least one additional solvent is substituted or unsubstituted aromatic C.sub.6-C.sub.12 alcohols, polyvalent alcohols of glycerol or glycols, esters, ethers, ketones, lactones, DMSO, a salt solution, or γ-butyrolactone, or mixtures thereof, and/or wherein the plasticizer is aromatic esters, aliphatic esters, cycloaliphatic esters, or bio-based compounds.

7. The method of claim 1, wherein a plurality of polymer elements is treated in the same process.

8. The method of claim 1, wherein either in said heating step a) the treating liquid comprises and is in contact with the polymer elements to be treated during heating, or said heating step a) comprises that the treating liquid is heated at least to the lower threshold temperature, up to the upper threshold temperature or beyond, and that the polymer elements are separately heated in an aqueous solution to a temperature below the upper threshold temperature, and wherein in said step b) the treating liquid and the polymer elements are contacted for smoothing.

9. The method of claim 1, wherein said heating step a) is carried out at a temperature in the range of about 80° C. to about 170° C. for a time period of about 5 seconds to about 24 hours.

10. The method of claim 1 wherein in said smoothing step b) a temperature above the lower threshold temperature and 1° C. to 15° C. below the upper threshold temperature is maintained for a time period of about 1 second to about 20 minutes.

11. The method of claim 1 wherein in said cooling step c) the polymer elements are cooled to a temperature at least 5° C. below the upper threshold temperature.

12. The method of claim 1, wherein in said cooling step c) the treating liquid with the smoothed polymer elements are cooled for a time period of about 1 minute to about 48 hours and/or wherein the treating liquid is at least partially substituted by a cooling fluid.

13. The method of claim 1, wherein in at least one step at least one functionalizing agent is applied to the polymer elements during or after treatment with the treating liquid.

14. The method of claim 13, wherein at least one functionalizing agent is applied during or after said step c).

15. The method of claim 1, wherein during at least one of said steps a) to c) and/or during said functionalizing step d) means for impelling the treating liquid and/or the functionalizing agent are used.

16. The method of claim 13, wherein the functionalizing agent comprises at least one agent of a colorant, a dye, a pigment, a fiber, a hardening agent, a metal powder, a polymer powder, an inorganic pigment or powder, an electrostatic discharge agent, a filler, a base, a finishing agent, and/or a plasticizer.

17. The method of claim 13, wherein a colorant or dye solution is applied in said functionalizing step d).

18. The method of claim 1, wherein the polymer elements have been obtained by a sintering/melting process.

19. The method of claim 1, wherein the polymer of the polymer elements is a polyamide based polymer or copolymer, a thermoplastic elastomer, thermoplastic polyamide (TPA), thermoplastic copolyester compound (TPC), thermoplastic styrene block copolymers (TPS), acrylic polymers, acrylic ester-styrene-acrylonitrile (ASA), PMMA, POM, PC, PEI, PSU, or polybutylene-terephthalate (PBT), or a copolymer or blend thereof.

20. (canceled)

21. (canceled)

22. A device for treatment of polymer elements obtained by an additive manufacturing process comprising a chamber with a lid, at least one container for receiving the polymer elements and the treating liquid, and means for temperature control.

Description

EXAMPLE 1

[0158] Elements were smoothed with the method of the present invention. Elements first were treated at a temperature below a lower threshold temperature, where time is not critical. Only when this temperature is exceeded a noticeable reaction does take place at all. Below the lower threshold temperature, no smoothing or change of the surface occurs neither in a few minutes nor over a period of some hours. This means that the elements can remain in the treating liquid or another pre-treatment liquid like water or an aqueuos solution for any time period. This allows high flexibility for the process. The lower threshold temperature depends on the treating liquid and on the type of elements to be treated. Thus, the lower threshold temperature can vary depending e.g. on elements produced with different manufacturing processes such as SLS and MJF. It can generally be assumed that this lower threshold temperature is at least about 5° C. and up to about 50° C. or more below the upper threshold temperature.

[0159] The “lower threshold temperature” may not necessarily be an exact temperature value but can be a temperature range comparable to the melting range of a polymer. Thus a lower threshold temperature of x° C. may include temperature values between (x−1)° C. and (x+1)° C. The same may apply to the upper threshold temperature. As smoothing beyond the lower threshold temperature starts slowly, this is not critical as long as any pre-treatment that should not start smoothing is carried out well below the lower threshold temperature. When polyamide elements are treated and the treating liquid is a water-alcohol-mixture with a ratio of water to alcohol of about 60:40 to about 40:60, the lower threshold temperature is usually higher than 100° C. and lower than 145° C.

[0160] Until the lower threshold temperature is reached, the heating rate plays no significant or direct role for the element quality. The actual smoothing process starts slowly as soon as the lower threshold temperature is reached. This temperature can be maintained for some time or alternatively or additionally, one or more temperature holding cycles can be set up for heating the treating liquid and optionally the elements to about the lower threshold temperature. These holding cycles or alternatively a delayed heating rate can be of advantage to saturate the elements with water by using an aqueous medium such as water, or a water-alcohol-mixture. In other words the elements can be pre-treated with water or an aqueous liquid or the treating liquid before the smoothing step as such starts, which means the elements can be contacted with an aqueous medium at a lower temperature and can be heated slowly or can be hold at a temperature below the lower threshold temperature for any useful time period. Smoothing begins when the treating liquid is heated to a temperature higher than the lower threshold temperature. Different approaches for heating are possible.

[0161] In one approach the treating liquid with the elements therein is heated very quickly from the lower threshold temperature to the upper threshold temperature. The heating rate should preferably be high to very high. Temperature should be controlled as precisely as possible. In addition to the generally known heating characteristic, it is preferable to control and detect possible energetic fluctuations in the process chamber through evaporation and to provide means to counteract these in a process-enhancing way, for example by providing circulation or impelling means. Once the upper threshold temperature or a temperature close to it, such as 1 to 5° C. below the upper threshold temperature has been reached, this temperature can be maintained for a short period of time, such as some seconds up to about a few minutes. The temperature regimen can be adapted to achieve optimal results for example by using a predetermined heating rate until a desired temperature like 1 to 5° C. below the upper threshold temperature has been reached, holding this temperature for some seconds or up to about 2 minutes, and then cooling with a predetermined cooling rate. Heating rate and holding time can be adapted for optimal results and the cooling rate can also be adapted accordingly. For example means can be provided to allow for a shorter or longer holding time and adaptation of temperature ranges, by fast or slow temperature increase and/or decrease. In general it is preferred to have a fast temperature increase to the predetermined smoothing temperature and a fast decrease of temperature down to the lower threshold temperature to stop smoothing as fast as possible. Time periods for increase and decrease in the range of less than 5 minutes, preferably of less than 2 minutes are preferred.

[0162] The smoothing step is followed by a cooling step, where the temperature inside the process chamber is lowered. This can be done with any means known in the art and can be done as quickly as possible and/or in a controlled manner, at least until the lower threshold temperature has been reached, preferably by means of active cooling media. Examples for active cooling means are pipe cooling lines arranged within the process chamber or cold exchangers. A further possibility to rapidly lower the temperature can be achieved by selectively discharging process gas within the process chamber, preferably into a third chamber. By selectively discharging process steam in a deliberately arranged gas area above the actual treating liquid within the process chamber, further steam is generated from the liquid, which leads to a cooling of the treating liquid.

[0163] Typical heating rates from the lower threshold temperature to the upper threshold temperature are about 1° C./min up to about 60° C./min, such as about 5° C./min to about 20° C./min. Cooling rates can be in the same range, but can also be slower or faster.

[0164] In an alternative design, the treating liquid, for example an ethanol-water mixture, is not heated each time from about room temperature to the lower threshold temperature, but pumped after the smoothing step into a second chamber, where it can be kept at about the same temperature and can be used again for the next charge of elements to be smoothed. In another approach the ethanol-water mixture is heated separately to a temperature higher than the lower threshold temperature, such as to the upper threshold temperature or beyond within a second chamber. The temperature of the treating liquid in this approach at most should be such that when the treating liquid is contacted with the elements to be smoothed the temperature drops during pumping from the second chamber into the process chamber and/or by the contact with the elements down to about the upper threshold temperature. In the process chamber, this temperature can either be maintained as a function of the initial temperature and the thermal mass of the process chamber wall and the elements, or it can be adjusted to the optimum upper threshold temperature by active heating or cooling. After a predetermined treatment period at the preferred smoothing process parameters or within the preferred smoothing process parameter ranges, the temperature of the treating liquid is brought below the lower threshold temperature again by the cooling options already described. The treating liquid can then be pumped back into a second chamber.

[0165] In another approach, the treating liquid 5 from the reservoir 25 is not cooled to or below the lower threshold temperature but, preferably in a second chamber, is maintained at a temperature, that is suitable for smoothing, such as slightly above or at the upper threshold temperature. When the treating liquid 5 at a temperature of about the upper threshold temperature or slightly below or above is fed into the process chamber 1, its temperature will be slightly lowered by the lower temperature and the thermal mass of the process chamber 1 and the polymer elements 4 arranged within the process chamber 1. This approach allows fast heating of the polymer elements 4, in shorter time than by heating the elements 4 directly in the treating liquid 5. Thus, in those cases where fast heating and smoothing is required, this approach is suitable. Heating treating liquid 5 and elements 4 together usually requires more time as the heating device 8 can only bring in a certain heating power.

[0166] In an alternative process, the smoothing process can be stopped slower so that the surface of the elements is in a transition phase where the surface is still soft. This is useful if a functionalizing step is carried out following the smoothing step or when a second smoothing step follows. This improves finishing of the surface while maintaining the exact geometric contours. Another way to stop the smoothing process is to introduce liquid nitrogen into the pressure vessel. This can be advantageous when the inlet pressure is kept as low as possible by introducing compressed air and/or process gas.

[0167] In an additional step of the method of the present invention or as part of one or more of the steps dyes and/or fillers can be added to the element surface during the process. For this purpose, the alcohol-water mixture is mixed directly with the dye and/or fillers. Dyeing with dispersion, metal complex or acid dyestuffs or sulphur dyestuffs can also be carried out either directly after smoothing or in the process chamber using an additional colour tank (23). Colouring directly after the smoothing process can have advantages in colouring, because the surface still has a certain softness due to the ethanol content, whereby certain dyestuffs or fillers can better and in a shorter time period penetrate the surface under certain circumstances.

[0168] In addition to alcohols, substances that increase the polarity of water are able to whiten MJF and HSS components on the surface without being bound to any theory. It is assumed that an increasing polarity of the liquid increasingly displaces the relatively nonpolar carbon black within the mentioned components to the inside, namely at a temperature above the crystallinity range of the polymer. Suitable materials for the white coloration are e.g. tap water or mineral water. However, the temperature must be raised significantly in the range of the crystallinity temperature. If salts are added to the water or water, a white colouring can already occur at temperatures of approx. 140° C. It has been found that generally by treating elements with a salt solution, for example an aqueous solution of a salt like NaCl and/or Na.sub.2CO.sub.3, for example at a concentration of approx. 1% to approx. 20 weight-%, the surface of the elements can become light grey to whitish. This is achieved for elements obtained by additive manufacturing when they contain carbon black, independent from a treatment with a water-alcohol-mixture for smoothing as described above. For the whitening action a salt solution can be used together with the above mentioned additives such as benzyl alcohol, glycerine, glycols or plasticizers, which are used in small quantities.