COATING MATERIAL FOR PRODUCING AN ADSORBENT, POROUS, FLEXIBLE COATING FOR A HEAT EXCHANGER AND METHOD FOR PRODUCING SAID COATING MATERIAL

Abstract

A method for producing a coating material is specified, comprising the following steps: producing a mixture of hydroxyl-terminated siloxane and siloxane having at least three functional hydrides and/or silane having at least three hydrolysable groups; adding an organic solvent to the mixture; homogenizing the mixture; adding an adsorption material to the mixture; and adding a catalyst to the mixture. A coating material according to the invention, a method for coating a device, and a heat exchanger are also specified.

Claims

1. Method for producing a coating material, comprising the following steps: producing a mixture of hydroxyl-terminated siloxane and siloxane having at least three functional hydrides and/or silane having at least three hydrolysable groups; adding an organic solvent to the mixture; homogenizing the mixture; adding an adsorption material to the mixture; and adding a catalyst to the mixture.

2. Method according to claim 1, wherein the hydroxyl-terminated siloxane is produced from silanol-terminated polydimethylsiloxanes, copolymers of silanol-terminated diphenyl siloxane and dimethylsiloxane, silanol-terminated polydiphenylsiloxane, silanol-terminated methylphenylpolysiloxane, silanol-terminated polytrifluoropropylmethylsiloxane, poly(dimethylsiloxane), bis(hydroxyalkyl)-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, or a mixture of said substances.

3. Method according to claim 1, wherein the siloxane having at least three functional hydrides is formed from: hydride-terminated polydimethylsiloxanes; monodisperse, hydride-terminated polydimethylsiloxane; polymethylhydrosiloxanes, trimethylsiloxy-terminated; methylhydrosiloxane-dimethylsiloxane copolymers, trimethylsiloxy-terminated; methylhydrosiloxane-dimethylsiloxane copolymers, hydride-terminated; methylhydrosiloxane-phenylmethylsiloxane copolymers, hydride-terminated; or copolymers and/or terpolymers of hydride-terminated methylhydrosiloxane and octylmethylsiloxane; or a mixture of said substances.

4. Method according to claim 1, wherein the ratio of hydrides to hydroxyl-functionalized siloxane compounds in the mixture has a value between 0 and 4.

5. Method according to claim 1, wherein the organic solvent contains no water or is substantially anhydrous.

6. Method according to claim 1, wherein the organic solvent consists of ethanol, acetone, tetrahydrofuran (THF) or dimethylformamide (DMF), or of a mixture thereof, preferably a mixture of ethanol and acetone.

7. Method according to claim 1, wherein the adsorption material contains solid sorbents having free hydroxyl groups, silica gel, activated carbon, salt hydrates, MOFs (metal organic frameworks) and/or zeolite.

8. Method according to claim 1, wherein the adsorption material contains silica gel which is functionalized before being added to the mixture.

9. Method according to claim 1, which comprises adding a thermally conductive filler to the mixture.

10. Method according to claim 9, wherein the thermally conductive filler contains graphite, in particular graphite powder, carbon nanotubes, graphene, copper powder and/or aluminium powder.

11. Method according to claim 1 any one of the preceding claims, wherein the catalyst contains bis(2-ethylhexanoate)tin, dibutyldilauryltin, zinc octoate, iron octoate and/or metal salt.

12. Method according to claim 1 any one of the preceding claims, wherein the step of adding the adsorption material to the mixture comprises a stirring of the mixture for two minutes or more.

13. Method according to claim 1 any one of the preceding claims, wherein the step of adding the catalyst to the mixture comprises a stirring of the mixture for two minutes or more.

14. Method according to claim 1 any one of the preceding claims, wherein the proportion of the catalyst in the mixture is between 0.1 and 6 wt %, preferably between 0.1 and 5 wt %, more preferably between 0.1 and 3 wt %.

15. Method according to claim 9, wherein the proportion of the thermally conductive filler in the mixture is less than 20 wt %, preferably 7.5 wt %.

16. Coating material, preferably produced by a method according to claim 1, consisting of: 2 to 40 wt % hydroxyl-terminated siloxane, less than 20 wt % siloxane having at least three functional hydrides, and/or less than 10 wt % silane having at least three hydrolysable groups, 10 to 70 wt % of an organic solvent, 5 to 85 wt % of an adsorption material, 0.1 to 6 wt %, preferably between 0.1 and 5 wt %, more preferably between 0.1 and 3 wt % of a catalyst, and optionally less than 20 wt %, preferably 7.5 wt % of a thermally conductive filler, the remainder being unavoidable impurities.

17. Coating material according to claim 16, wherein the hydroxyl-terminated siloxane is produced from silanol-terminated polydimethylsiloxanes, copolymers of silanol-terminated diphenylsiloxane and dimethylsiloxane, silanol-terminated polydiphenylsiloxane, silanol-terminated methylphenylpolysiloxane, silanol-terminated polytrifluoropropylmethylsiloxane, poly(dimethylsiloxane), bis(hydroxyalkyl)-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, or a mixture of said substances.

18. Coating material according to claim 16, wherein the siloxane having at least three functional hydrides is formed from: hydride-terminated polydimethylsiloxanes; monodisperse, hydride-terminated polydimethylsiloxane; polymethylhydrosiloxanes, trimethylsiloxy-terminated; methylhydrosiloxane-dimethylsiloxane copolymers, trimethylsiloxy-terminated; methylhydrosiloxane-dimethylsiloxane copolymers, hydride-terminated; methylhydrosiloxane-phenylmethylsiloxane copolymers, hydride-terminated; or copolymers and/or terpolymers of hydride-terminated methylhydrosiloxane and octylmethylsiloxane; or a mixture of said substances.

19. Coating material according to claim 16, wherein the ratio of hydrides to hydroxyl-functionalized siloxane compounds in the mixture has a value between 0 and 4.

20. Coating material according to claim 16, wherein the organic solvent contains no water or is substantially anhydrous.

21. Coating material according to claim 16, wherein the organic solvent consists of ethanol, acetone, tetrahydrofuran (THF) or dimethylformamide (DMF), or of a mixture thereof, preferably a mixture of ethanol and acetone.

22. Coating material according to claim 16, wherein the adsorption material contains silica gel, activated carbon, salt hydrates, MOFs and/or zeolite.

23. Coating material according to claim 16, wherein the adsorption material contains silica gel, which is functionalized before being added to the mixture.

24. Coating material according to claim 16, wherein the thermally conductive filler contains graphite, in particular graphite powder, carbon nanotubes, graphene, copper powder and/or aluminium powder.

25. Coating material according to claim 16, wherein the catalyst contains bis(2-ethylhexanoate)tin, dibutyldilauryltin, zinc octoate, iron octoate and/or metal salt.

26. Method for coating a device, in particular a heat exchanger, comprising the following steps: providing a coating material produced by a method according to claim 1; applying the coating material to the device in order to form a coating; drying the coating; and curing the coating.

27. Method according to claim 26, wherein the application of the coating material takes place by means of spraying, dip-coating or pouring.

28. Method according to claim 26, wherein the drying of the coating takes place at room temperature for one hour or longer.

29. Method according to claim 26, wherein the curing of the coating takes place at a temperature between 50° C. and 100° C., preferably at 80° C., for 24 hours or longer.

30. Method according to claim 26, wherein, after the curing, a post-curing step is carried out at a temperature between 60° C. and 150° C. for 3 to 48 hours, preferably at 90° C. for 3 hours under vacuum; or at room temperature for 2 weeks.

31. Method according to claim 26, wherein the curing steps are carried out at a temperature between 40° C. and 110° C.

32. Method according to claim 26, wherein the thickness of the coating is between 0.05 mm and 2.0 mm.

33. Heat exchanger having a coating made of a coating material produced by a method according to claim 1.

34. Method for coating a device, comprising the following steps: providing a coating material according to claim 16; applying the coating material to the device in order to form a coating; drying the coating; and curing the coating.

35. Heat exchanger having a coating formed of a coating material according to claim 16.

36. Heat exchanger coated by the method according to claim 26.

Description

[0086] In the figures:

[0087] FIG. 1 shows adsorption curves of a coating material according to the invention compared to a reference adsorption material.

[0088] In order to produce a coating material according to the invention, 2 to 40 wt % hydroxyl-terminated siloxane and less than 20 wt % siloxane having at least three functional hydrides, and also less than 10 wt % silane having at least three hydrolysable groups are mixed with one another in a first step. Here and also below, the proportions by weight always relate to the total mass of the end product. The hydroxyl-terminated siloxane is a monomer which is provided for forming a silicon-containing, porous matrix. The hydride-terminated siloxane and the silane provided with hydrolysable groups serve as a hardening agent or crosslinker for the hydroxyl-terminated siloxane.

[0089] In order to achieve an optimal crosslinking of the matrix-forming components, the amounts of the monomer and of the hardening agent are selected such that the ratio of hydrides to hydroxyl-functionalized siloxane compounds has a value between 0 and 4. A value between 1.5 and 2.5 is particularly preferred.

[0090] In a further step, between 10 and 70 wt %, preferably between 40 and 50 wt %, of an anhydrous, organic solvent are added to the mixture. The mixture is homogenized, for example by means of mechanical stirring. The homogenization of the mixture is facilitated as a result of using an anhydrous organic solvent.

[0091] Thereafter, an adsorption material is added to the mixture, as well as optionally a thermally conductive filler. The mixture is then mixed until a homogeneous mass is achieved. A mechanical stirring process for two minutes is usually sufficient for this.

[0092] Finally, a catalyst is added to the mixture with vigorous stirring for approximately one to two minutes. The coating material thus produced can then be bottled or applied directly to a heat exchanger.

[0093] The application of the coating material to a heat exchanger may take place by means of spraying, dip-coating, pouring, or another method. After being applied in the desired thickness, a drying step is carried out at room temperature. During this, approximately 30% of the organic solvent evaporates. Approximately one hour is usually sufficient for the drying step in order to achieve the desired solvent evaporation.

[0094] In order to achieve the final curing and bubble formation in the interior of the coating, a curing step is carried out at low temperature, in the range between 50° C. and 100° C., preferably 80° C., for 24 hours. Low curing temperatures encourage the formation of small bubbles and therefore coatings with small pore diameters and high density. High curing temperatures encourage the formation of large bubbles and therefore porous coatings with large pore diameters and low density.

[0095] A post-curing in the temperature range between 60° C. and 150° C. may be carried out for 6 to 48 hours in order to ensure a complete outgassing of all non-reacting compounds. Alternatively, albeit less effectively, storage at room temperature for 2 weeks may also be carried out for post-curing purposes as an inexpensive alternative.

[0096] FIG. 1 shows measured adsorption curves of an above-described coating according to the invention containing SAPO-34 as the adsorption material compared to that of pure SAPO-34 powder. In each case, the adsorption capacity in wt % is plotted against temperature. The adsorptive used was water at a pressure of 11 mbar. The coating exhibits an excellent adsorbability with an adsorption curve very similar to that of pure SAPO-34. The maximum adsorption capacity in the coating is 25.2 wt %. This value is achieved with a coating containing 80 wt % SAPO-34 as the adsorption material in the coating material, and is approximately 20% lower than the maximum adsorption capacity of pure SAPO-34 powder (31.7 wt %). This proves the excellent adsorption properties that can be achieved with the coating material according the invention.

[0097] The substantially matching course of the adsorption curves in FIG. 1 additionally shows that the crosslinking of the silanol-siloxane matrix does not significantly influence the adsorption capacity of the coating material, but instead primarily stabilizes the structure in the coating so that high efficiencies can be achieved when using the coating material on heat exchangers. These properties can also be achieved with the other adsorption materials (not shown here), which proves the high degree of flexibility of the coating material according to the present invention.

[0098] The coating material according to the invention is suitable for a wide range of uses in a large temperature range and can be used for example in the field of dehumidification, air conditioning or adsorption of water vapor. The adsorption material can be suitably selected depending on the field of application.

[0099] In addition, although the coating material is hydrophilic to water vapor, it is hydrophobic to water in the liquid phase. Thanks to these properties, the coating material according to the invention is optimally suited to systems in which water condensation may occur, since both corrosion problems and biofouling problems can be prevented.