EP1353882A1

EP1353882A1 - Method for rendering surfaces resistant to soiling

Info

Publication number: EP1353882A1
Application number: EP02702249A
Authority: EP
Inventors: Harald Keller; Ekkehard Jahns; Christian Lach; Stephan Hüffer; Elmar STÖCKELMANN; Yi Thomann; Thomas Frechen
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2001-01-12
Filing date: 2002-01-10
Publication date: 2003-10-22
Also published as: WO2002055446A1; US20040047997A1; JP2004525754A

Abstract

The invention relates to a method for rendering surfaces resistant to soiling. The method is characterized in that the surfaces are coated with particles, which have an average diameter ranging from 3 nm to 5 νm and which are comprised of a material that has a surface energy of at least 20 mN/m.

Description

Process for the dirt-repellent finishing of surfaces

description

The present invention relates to a method for the dirt-repellent finishing of surfaces, characterized in that the surfaces are coated with particles which have an average diameter of 3 nm to 5 μm and consist of a material which has a surface energy of at least 20 mN / m has and is selected from organic polymers and copolymers and inorganic solid oxides, carbonates, phosphates, silicates or sulfates from groups 3 to 14 of the periodic table.

Deposits and caking in apparatus and apparatus parts for plant construction pose a serious problem in industry, especially in the chemical industry. Apparatus, container and reactor walls, boiler walls, discharge devices, fittings, pumps, filters, compressors, centrifuges, columns, dryers, centrifugal separators, washers, shredding machines, internals, fillers, heat exchangers, evaporators, condensers, nozzles, are particularly affected. Atomizers, spray dryers, crystallizers, filling systems and mixing devices. These deposits are also called deposits or fouling.

The coatings can be harmful or hinder the process in a variety of ways and lead to the need to repeatedly switch off and clean appropriate reactors or processing machines.

Measuring devices encrusted with deposits can lead to incorrect and misleading results, which can lead to operating errors.

Coverings are also disadvantageous in other applications. After wetting and evaporation, water leaves residues on surfaces, e.g. Rainwater on window panes, motor vehicles, traffic signs or billboards. Due to the wetting, flowing liquids cause friction on the surfaces to which they are exposed. This leads to friction losses, for example in ships, but also in liquids that flow through pipelines.

By wetting liquids, for example emulsions, suspensions, polymer dispersions, deposits and deposits in the interior of process engineering equipment, for example pipes, boilers, tanks, reactors, heat exchangers, evaporators, condensers. pumps, nozzles, atomizers, spray dryers, crystallizers or filling systems as well as laboratory equipment.

Electrotechnical devices and components in weathered and non-weathered areas, which are in contact with the ambient air, become dirty on their surfaces. Due to the pollution itself and especially by moistening the pollution e.g. to a certain extent, the surfaces become electrically conductive due to rain, fog or air humidity, which creates leakage currents that can impair the function of the components. Further it comes e.g. With high-voltage overhead lines and voltage conversion devices to considerable energy losses due to the contamination of the insulators. Furthermore, the soiling is often the cause of corrosion of the construction devices and the substrate for additional biological loads caused by e.g. Microorganisms, algae, lichen, moss or mussels.

By wetting (moistening) unwanted organisms, for example microorganisms, biofilms, algae, lichens, mosses or mussels, can grow on surfaces such as roofs, facades, shower cubicles, ships or heat exchangers.

Through wetting, liquids and liquid-containing substances such as milk, honey, yogurt or toothpaste sometimes get stuck on the inner surface of the packaging materials. This means that part of the packaging material cannot be used unless you want to clean it extensively. Furthermore, recycling of packaging materials is difficult because of contamination with the packaging goods. After all, the decomposition of these perishable residues is also a hygienic problem and leads to unpleasant smells near garbage cans, especially in summer.

When solid surfaces come into contact with particles, adhesion takes place. The adhesion of particles such as dirt, dust, soot, industrial powder, pollen, spores, bacteria or viruses leads to contamination of the surfaces and is undesirable in many cases.

Another problem that arises from the formation of deposits is due to the fact that the molecular parameters, such as molecular weight or degree of crosslinking, differ significantly from the product specifications, particularly in coatings in polymerization reactors. If deposits become detached during operation, they can contaminate the product (e.g. specks in paints, inclusions in suspension beads). Unwanted filing Wrestled can in the case of reactor walls, packing or mixing elements continue to lead to an undesirable change in the residence time profile of the apparatus or impair the effectiveness of the internals or mixing elements as such. Broken coarse parts of coverings can lead to clogging of discharge and processing devices, small parts can lead to impairment of the product produced.

The deposits whose formation is to be prevented are deposits which can be caused, for example, by reactions with and on surfaces. Further reasons are the adhesion to surfaces, which can be caused by van der Waals forces, polarization effects or electrostatic double layers. Important effects are also stagnation of movement on the surface and, if necessary, reactions in the stagnant layers mentioned. Finally, there are: precipitation from solutions, evaporation residues, cracking on locally hot surfaces and microbiological activities.

The causes depend on the respective combinations of substances and can be effective alone or in combination. While the processes that give rise to the undesirable deposits have been studied fairly well (for example, AP Watkinson and DI Wilson, Experimental Thermal Fluid Sei. 1997, 14, 361 and the literature cited therein), there are few uniform concepts for preventing the above described deposits. The previously known methods have technical disadvantages.

Mechanical solutions have the disadvantage that they can cause considerable additional costs. Additional reactor internals can also significantly change the flow profile of fluids in the reactors, making an expensive new development of the process necessary. Chemical additives can lead to undesired contamination of the product; some additives pollute the environment.

For these reasons, there is an increasing search for ways to reduce the fouling tendency directly by modifying apparatus and apparatus parts for chemical plant construction.

It is known from EP-A 0 745 568 that surfaces can be made water-repellent by fluorinated and in particular perfluorinated alkylsilanes. However, these substances are comparatively expensive. WO 00/40775, WO 00/40774 and WO 00/40773 describe methods for coating surfaces, especially surfaces of reactors for the high-pressure polymerization of 1-olefins or surfaces of heat exchangers, by electroless deposition of a NiP / poly-5-tetrafluoroethylene layer or a CuP / polytetrafluoroethylene layer, by means of which the relevant metal surfaces can be modified in a non-stick manner. When using the surfaces coated according to the described method in apparatus and apparatus parts for chemical plant construction, especially reactors for

10 the high-pressure polymerization of 1-olefins, however, it is observed that the surfaces are not sufficiently mechanically stable, so that product caking is again observed after prolonged use. A renewed coating of an only partially removed NiP / polytetrafluoroethylene layer succeeds

15 not. Furthermore, it can be observed that a NiP / polytetrafluoroethylene layer which has been deposited can only be removed again with difficulty if it is no longer desired in a reactor or apparatus part. Especially in reactors with rapid product changes, in which reactions with over

20 400 ° C, a coating with NiP / polytetrafluoroethylene has not proven itself. Finally, it should be mentioned as a disadvantage that, especially when coating large-volume reactors, large amounts of immersion baths have to be used, which lead to considerable solvent waste.

25

WO 96/04123 discloses self-cleaning surfaces which can be coated with polytetrafluoroethylene and which have particularly hydrophobic properties. The structuring is achieved by etching or embossing the surface, by physical methods

30 such as sandblasting or ion etching with oxygen, for example. The distance between the elevations or depressions is more than 5 μm. Then the surface is coated with Teflon. The mechanical stability of such hydrophobized layers is, however, far too low for use in chemical apparatus.

35 construction, especially for polymerization reactors in which strong shear forces act. However, the layers applied in this way are not transparent enough for numerous applications.

Structured surfaces with hydrophobic properties are also known (EP-A 0 933 388), which are produced in such a way that the surface in question is etched, for example, elevations or grooves are produced on the surface at a distance of less than 10 μm and then coated with a layer of a hydrophobic polymer, for example polyvinylidene fluoride, the surface energy of the corresponding material being less than 20 mN / m. These layers can also contain fluorinated waxes, for example Hostaflone®. The surfaces modified in this way are hydrophobic and oleophobic. Wafer holders in semiconductor production are mentioned as applications, as well as the manufacture or coating of headlights, windshields or covers for solar cells. A disadvantage of the method, however, is that the structuring is difficult to renew after partial mechanical degradation.

DE 198 60 139 Cl discloses a process for producing an ultraphobic surface, in which surfaces are coated with Ni (OH) produced by a selected process, which is then made hydrophobic. The use of noble metal layers, for example Ag or Pt and in particular Au, is recommended as an adhesion promoter. However, the method disclosed is expensive and comparatively cumbersome.

Finally, DE-A 100 22 246 (published on ...) discloses a coating composition which contains a finely divided powder and a binder. A solvent is always required to apply a binder, which is undesirable in many cases.

So the task was

to provide a method for the dirt-repellent finishing of surfaces which avoids the disadvantages mentioned in the prior art and does not contain any binding agent, to provide dirt-repellent surfaces and to provide uses for objects with dirt-repellent surfaces.

It has now been found that this problem can be solved by coating the dirt-repellent surfaces with particles which have an average diameter of 3 nm to 5 μm and consist of a material which has a surface energy of at least 20 mN / m Has.

The method according to the invention consists of several steps.

In the first step, the dirt-repellent surface is prepared by making it sticky before the coating step so that the particles to be applied according to the invention are fixed. This can be done through several alternative steps:

A so-called primer can be applied, which functions as an adhesive. Suitable primers are, for example, polymer dispersions such as ethylene / acrylic acid copolymers which partially are quickly neutralized with ammonia or amines; a particularly preferred example is Lugalvan DC® from BASF AG; or Acronal® V 210 as a particularly preferred example of an adhesive. Hot melt adhesives and fusible polymers such as polyethylene, polypropylene, polystyrene, polyoctadecyl vinyl ether or polyvinyl chloride are also suitable. Waxes such as polyethylene waxes, polypropylene waxes, carnaύba waxes, montan waxes or paraffin waxes are also suitable as primers. The thickness of the adhesive layer to be applied is not critical for the method according to the invention and can be from 0.1 μm to 10 mm.

Alternatively, in cases where the dirt-repellent surface is made of plastics, it can also be heated for a short time to a temperature that is above the glass transition temperature of the plastic in question, or partially dissolved or swollen with a solvent.

Subsequently, the dirt-repellent surfaces are coated with particles that have an average diameter of 3 nm to 5 μm and that consist of a material that has a surface energy of at least 20 mN / m. The particles to be applied are characterized by their hydrophobic surface, their porous structure and their average diameter.

The porous structure can best be characterized by the BET surface area, measured according to DIN 66131. The particles used have a BET surface area in the range from 5 to 1000 m ² / g, preferably from 10 to 800 m ² / g and particularly preferably from 20 to 500 m ² / g.

The particles consist of a material that has a surface energy of 20 mN / m or more. Suitable materials are organic polymers such as e.g. Polyethylene, polypropylene, polyisobutylene and polystyrene and copolymers thereof with one another or with one or more further olefins such as, for example, styrene, methyl acrylate, ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, maleic anhydride or N- methylmaleimide. A preferred polyethylene or polypropylene is described for example in EP-A 0 761 696.

Other suitable materials are solid inorganic oxides, carbonates, phosphates, silicates or sulfates from groups 3 to 14 of the Periodic Table of the Elements, for example calcium oxide, silicon dioxide or aluminum oxide, calcium carbonate, calcium sulfate or calcium silicate, aluminum oxide and silicon dioxide being preferred. Silicon dioxide is particularly preferred in its modification tion as silica gel. Pyrogenic silica gels, which are commercially available, for example, as Aerosil® brands from Degussa-Hüls, are very particularly preferred. The solid inorganic oxides can be made hydrophobic thermally by heating to 400 to 800 ° C. and preferably by physisorbed or chemisorbed organic or organometallic compounds. For this purpose, the particles are reacted before the coating step with organometallic compounds which contain at least one functional group, for example alkyl-lithium compounds such as methyl lithium, n-butyl lithium or n-hexyl lithium; or silanes such as hexamethyldisilazane, octyltrimethoxysilane, trimethylchlorosilane or dichlorodimethylsilane.

The average diameter of the particles is in the range from 3 nm to 5 μm, preferably from 5 nm to 1 μm and particularly preferably in the range from 7 nm to 0.5 μm.

If desired, the dirt-proof surfaces can be coated with mixtures of particles made of two or more different materials.

The mixing ratios can be selected in a wide range, but care must be taken to ensure that the particles made of the material which has a surface energy of more than 20 mN / m are present to more than 50% by weight of the particles, preferably more than 75% by weight .-%.

The particles described above are applied to the dirt-repellent surface. This application is also referred to as coating. Coating is done without liquid dispersants. In one embodiment of the method according to the invention, a workpiece to be coated is dusted with the particles described above. This method is particularly suitable for flat surfaces, such as foils.

In another embodiment of the present invention, which is particularly suitable for the inner surfaces of apparatus or containers, the apparatus or the container is completely or partially filled with the particles, sufficient convection is provided and then the non-firmly adhering particles are removed.

The coating step can be repeated if desired.

With the method according to the invention, the dirt-repellent surfaces are coated with a particle layer whose thickness is in the range from 3 nm to 10 μm. Preferred the thickness does not bear more than 1 μm. The thickness of the particle layer is particularly preferably in the range from 5 nm to 0.3 μm.

After coating, the layer is allowed to age before the objects with the surfaces coated according to the invention are used. This aging can last from 20 minutes to about 10 hours, preferably 1 to 3 hours. The aging can be carried out at room temperature or at a slightly elevated temperature; however, the temperature should be so high that particles 10 or primers begin to sinter. It has been shown that a temperature in the range from 20 to 50 ° C. is sufficient in many cases.

The choice of materials for the dirt-repellent 15 surfaces is not critical. For example, polymers such as polyethylene, polypropylene, polystyrene, polyester, plexiglass, polyamides, polycarbonates or polyurethanes are suitable, as well as metals and alloys such as silver, palladium, platinum, steels, copper, nickel and paper, cardboard, textiles, stone, ceramics, be - 20 ton, porcelain, glass or wood. Transparent materials such as glass, plexiglass and polycarbonates from the Makrolon® brands are particularly suitable.

Another object of the present invention are surfaces which have been made dirt-repellent by the method described above. They can be cleaned extremely easily by simply rinsing them with water, for example; unlike surfaces described in the prior art, no addition of surfactants is necessary. Furthermore, the surfaces according to the invention are highly transparent.

The surfaces have proven to be particularly dirt-repellent to the following media: water, coffee, honey, glycerin, 32% by weight aqueous hydrochloric acid, 5% by weight aqueous sodium hydroxide solution, 35 30% by weight aqueous solution of polyacrylic acid, 30% by weight aqueous solution of a copolymer consisting of vinyl pyrolidone and vinyl imidazole, aqueous polymer dispersion Acronal® 290 D (BASF AG), aqueous polymer dispersion Styronal® D 808 (BASF AG).

40 Another object of the present invention are pipes or pipelines with surfaces which are made dirt-repellent by the method described above. They are particularly suitable for pumping through solutions because the dirt-repellent surfaces prevent them from

45 wrestle and therefore the flow contradiction and remains low. Pipes made of glass, plexiglass or are particularly preferred o α. ω

H α.

- *

O

Do not allow water to wet and protect it from rotting for a particularly long time.

Another object of the present invention relates to textile fabrics and leather, the surface of which is finished by the process according to the invention. They are particularly water and dirt repellent. The high transparency of the surfaces coated according to the invention also ensures that colors and prints are particularly effective.

Another object of the present invention are filter materials and separation membranes, for example for chlor-alkali electrolysis, with surfaces equipped according to the invention.

Another object of the present invention are papers, cardboard and cardboard with surfaces equipped according to the invention. They prevent wet soaking and reduce pollution. As a special case of papers, banknotes and official documents are to be mentioned, for the coating of which the method according to the invention is particularly suitable. The high transparency of the surfaces coated according to the invention also ensures that colors and prints are particularly effective.

working examples

example 1

A glass plate was coated with a doctor blade with a doctor blade gap of 50 μm with an aqueous dispersion of a copolymer consisting of ethylene and acrylic acid (Lugalvan® DC, BASF AG) and dried in room air for 15 minutes.

Then the coated side of the glass plate was dusted with a powder consisting of a hydrophobized silicon dioxide pigment with a BET surface area of 220 m ² / g (DIN 66131), by distributing the particles through a sieve over the surface, and for 2 hours Stored at 20 ° C. The coated side was then blown off with compressed air. An optically completely transparent layer was obtained which showed no clouding when viewed in the backlight.

Figure 1 shows a scanning electron micrograph of the layer produced according to the example. Example 2

A glass plate was coated as described in Example 2. In a departure from example 2, the glass plate was stored at 40 ° C. for 2 hours after the powder coating. The coated glass plate was also completely optically transparent and showed no cloudiness when viewed in the backlight.

Comparative example:

A glass plate was coated as described in Example 2. In a departure from example 2, the glass plate was stored at 80 ° C. for 2 hours after the powder coating. The coated glass plate was not completely transparent optically. When viewed against the light, it showed a slight cloudiness.

Wettability tests:

The coated glass plates described in Examples 1 and 2 were mounted on a flat table and inclined at 2 ° to the horizontal. Then the following liquids were applied in succession in a defined amount and in the form of drops:

- water (30 mg)

Coffee (30 mg)

Honey (59 mg)

Glycerin (49 mg)

32% by weight aqueous hydrochloric acid (41 mg) - 5% by weight aqueous sodium hydroxide solution (45 mg)

30% by weight aqueous solution of polyacrylic acid (47 mg)

30 wt .-% aqueous solution of a copoly eren consisting of

Vinylpyrolidone and vinylimidazole (35 mg) aqueous polymer dispersion Acronal 290 D (BASF AG, 58 mg) - aqueous polymer dispersion Styronal D 808 (BASF AG, 46 mg)

All liquids beaded off from the coated glass plates from Examples 1 and 2 at an inclination angle of 2 ° and left no residue.

In a comparative experiment, the liquids listed above were applied to a glass plate which was only coated with the copolymer consisting of ethylene and acrylic acid, but not with a hydrophobized silicon dioxide pigment. The angle of inclination of the glass plate was also 2 ° to the horizontal. Wetting occurred in all cases; with the ecxeption of Water left all liquids residue on the glass plate.

The static contact angle of the coated glass plates from Examples 1 and 2 with water is greater than 160 °.

Dirt removal test:

The coated glass plates from Examples 1 and 2 were soiled with 100 mg / cm ² carbon black powder (Printex V from Degussa-Huls AG, average particle diameter of the primary particles: 25 nm) and then washed off with water. The soot powder is removed by the droplets of water so that the original clean surface is restored without the use of cleaning agents.

Claims

Pa t en t an e rü ehe

1. Process for the dirt-repellent finishing of surfaces, characterized in that the surfaces are coated with particles which have an average diameter of 3 nm to 5 μm and consist of a material which has a surface energy of at least 20 mN / m and is selected from organic polymers and copolymers and solid inorganic oxides, carbonates, phosphates, silicates or sulfates of groups 3 to 14 of the periodic table.

2. The method according to claim 1, characterized in that the particles have an average diameter of 7 nm to 0.5 μm.

3. The method according to claims 1 or 2, characterized in that the particles have a porous structure.

4. The method according to claims 1 to 3, characterized in that one makes the dirt-repellent surface to be tacky before coating.

5. The method according to claims 1 to 4, characterized in that the dirt-repellent surface to be coated is coated with a primer selected from adhesives, hot-melt adhesives and polymer dispersions, and then coated with particles.

6. The method according to claims 1 to 4, characterized in that the dirt-repellent plastic surface to be heated to a temperature above the glass temperature or dissolved or swollen with a solvent and then coated with particles.

7. Dirt-repellent surfaces with high transparency, obtainable by the process according to claims 1 to 6.

8. Pipes or pipelines with dirt-repellent surfaces according to claim 7.

9. vessels and packaging with dirt-repellent surfaces according to claim 7.

10. Non-icing or pollution-prone motor vehicles with dirt-repellent surfaces according to claim 7.

11. Use of apparatus or apparatus parts, in particular sight glasses, with dirt-repellent surfaces according to claim 7 in plants.

12. Sanitary facilities, fittings, swimming pools, shower cubicles, catheters and medical vessels with dirt-repellent surfaces according to claim 7.

13. Wooden objects with dirt-repellent surfaces according to claim 7.

14. Textile fabric and leather with dirt-repellent surfaces according to claim 7.

15. Filter materials and separation membranes with dirt-repellent surfaces according to claim 7.

16. Papers, cardboard and cardboard boxes with dirt-repellent surfaces according to claim 7.