DE102005000905A1 - Hydrophilic antibacterial coating, useful for applying on e.g. heat exchangers, comprises maleic acid-functional silica nano-particle and water-insoluble active substances based on chloro bisphenol or octenidine - Google Patents

Abstract

The The invention relates to an antibacterial coating for heat exchangers and drip pans in air conditioners. The layer contains 75 to 99 wt .-% maleic acid functional Silica nanoparticles and 1 to 25 wt .-% water-insoluble active ingredients based on chlorobisphenols or octenidine. The production the maleate functional Nanoparticles are made by sol / gel technology by adding maleic anhydride reacted with aminosilanes and with other silanes to stable sols is condensed. The layers show a high antibacterial Effect both opposite gram positive as well as gram negative bacteria.

Description

The The invention relates to a hydrophilic antibacterial coating based on functional silica nanoparticles as a binder, in particular for the coating of heat exchangers or drip pans in air conditioners.

It It is known that a colonization of surfaces with microorganisms significant material damage caused. Such biofilms are formed on almost all materials, such as metal, plastic, textiles or wood. Of Furthermore, such biofilms are also a serious health hazard, there often pathogenic germs are contained in concentrated form and become uncontrolled can spread. Examples of this are bacteria in water supply facilities, sanitary facilities as well as air conditioners.

It is state of the art, the formation of such biofilms by special Lacquers, usually very toxic tin or lead compounds contain, suppress. The inevitable release of these compounds from the coatings often causes Allergies and represents a significant environmental risk, so this Connections may be used only very limited.

It is furthermore known that an antibacterial effect is achieved by incorporation of biologically active substances in thin layers based on silica nanoparticles (sol / gel technology) (H. Böttcher, J. Prakt. Chem. 2000, 322 (5 ) DE 4 041 574 , 4 234 030, 198 33 479). In addition to organic compounds, heavy metal compounds such as copper compounds ( EP 459,003 , J. Sol-Gel Sci Tech. 26, 1213 (2003) or silver in combination with perfluoroalkyl compounds ( DE 102 19 127 ) or in combination with quaternary nitrogen compounds or phenols ( DE 199 35 230 ).

To avoid biofilm formation on heat exchangers in air conditioning systems, which usually leads to a significant odor nuisance, numerous methods are proposed. In US Pat. No. 6,170,564 a coating of silver oxide, zinc oxide and water glass is proposed. A doping of paints with colloidal silica particles and silver nitrate is in US 5,203,402 proposed. Furthermore, a coating with Teflon, to which cationic silanes are added, should effectively suppress biofilm formation. All of these known methods have the disadvantage that the corrosion resistance of the heat exchangers is considerably impaired by local element formation due to the presence of silver. Although a coating with Teflon in combination with quaternary silanes provides a good corrosion protection and suppresses the bacterial colonization, but impairs the required good wetting of the heat exchanger surfaces and thus a good heat exchange.

aim and object of the present invention is the development of a new hydrophilic antibacterial protective layer that is transparent is and contains no silver or silver compounds. The layer should be a good one Adhere to metals such as aluminum, by Water be well wetted and characterized by a high moisture stability.

According to the invention Task solved with a protective layer consisting of 75 to 99 wt .-% maleinsärefunktionelle Silica nanoparticles and 1 to 25 wt .-% water-insoluble active ingredients based on chlorobisphenols or octenidine.

The Preparation of maleic acid functional Nanoparticles according to the invention as a binder for the act antibacterial agents, using sol / gel technology.

The reaction of maleic anhydride with aminoalkyltrialkoxysilanes is carried out in the absence of moisture in the presence of polar solvents such as acetone, methyl ethyl ketone or acetonitrile at a temperature of 15 to 50 ° C. Suitable aminoalkyltriethoxysilanes are compounds such as
3-aminopropyltriethoxysilane
3-aminopropyltrimethoxysilane
N- (2-aminoethyl) -3-aminopropyltrimethoxysilane

After completion of the 1st reaction stage, dilution is carried out with further solvents such as acetone, ethanol, isopropanol or methoxypropanol and addition of water, preferably in stoichiometric amounts based on the silanes used. Thereafter, the cocondensation with other silanes to form stable sols. The molar ratio of maleic anhydride amino silane adduct to comonomers is 1: 1 to 1:20, preferably 1: 3 to 1: 5. Suitable comonomers are, for example
tetraethoxysilane
methyltriethoxysilane
3-glycidoxypropyltrimethoxysilane
3-glycidoxypropyl triethoxysilane
3- (trihydroxysilyl) -1-propanesulfonic acid
as well as mixtures of these.

When water Antibacterial agents are 1 to 25% by weight of chlorobisphenols such as triclosan or octenidine in the layers. Depending on Application and desired Layer thickness is their concentration is preferably 2.5 to 10%. The application of the antibacterial coating can be achieved by conventional coating technologies, such as dipping, flood or spray painting done. After air drying the layer is cured at 110 to 130 ° C for 15 to 60 minutes. Because the new binder contains reactive double bonds, it is also possible according to the invention by means of radical initiators or UV initiators curing to realize lower temperatures. To achieve a good Antibacterial effect is usually a dry film thickness from 0.5 to 1 μm sufficient.

The coating according to the invention is characterized by a high antibacterial effect against both gram positive as well as gram negative bacteria. Furthermore it inhibits colonization of the coated surfaces Green algae. Good adhesion is achieved on glass, plastics and metals. The coated surfaces are well wettable by water and thus do not affect the water drainage behavior in coated heat exchangers. In addition to heat exchangers the coating according to the invention is suitable also for antibacterial equipment of sanitary equipment, Filters, textiles and water collecting trays.

example 1

Synthesis of maleate functional Nanoparticles A

In a stirrable flask 25 ml of acetonitrile are placed at room temperature and dissolved therein 4.9 g of maleic anhydride. Thereafter, with stirring, the addition of 11.6 ml of aminopropyltriethoxysilane. After completion of the addition, the stirring is continued at 35 ° C for 2 h. The mixture is then mixed with 180 ml of methoxypropanol, 50 ml of 0.1 N trifluoroacetic acid and 55.7 ml of tetraethoxysilane and stirred at 50 ° C for 8 h. A stable sol with the following characteristics is obtained:
pH: 2.8
Solids content: 9.5%
Viscosity: 3.6 mPas

Example 2

Synthesis of maleinsäurefunktionellen Nanoparticles B

The procedure of Example 1 is repeated, wherein 4.9 g of maleic anhydride are presented in 25 ml of acetone. After reaction with 11.6 ml of aminopropyltriethoxysilane, the mixture is mixed with 180 ml of isopropanol, 50 ml of 0.1 N nitric acid, 33.6 ml of tetraethoxysilane and 11 ml of glycidyltrimethoxy silane and stirred at 50 ° C for 8 h. A stable sol with the following characteristics is obtained:
PH value: 3.1
Solids content: 10.7%
Viscosity: 3.5 mPas

Example 3

Synthesis of maleinsäurefunktionellen Nanoparticles C

The procedure of Example 1 is repeated, wherein 4.9 g of maleic anhydride in acetonitrile are initially charged and reacted with 11.6 ml of N- (2-aminoethyl) -3-aminopropyltrimethoxysilane. Thereafter, the reaction mixture is mixed with 180 ml of methoxypropanol, 50 ml of 1 M trifluoroacetic acid and 55.7 ml of tetraethoxysilane and stirred at 50 ° C for 8 h. A yellow, stable sol with the following characteristics is obtained:
pH: 2.5
Solids content: 13.5%
Viscosity: 4.4 mPas

Example 4

coating of aluminum specimens

100 g of the sol from Example 1 are ethanolic with stirring 9.5 ml octenidine (Octenidine concentration 100g / liter). The emotion is Continued for 30 minutes. Thereafter, a dip coating with 1 mm made of strong aluminum specimens. After drying at room temperature, the layer is cured at 120 ° C. for 30 minutes. It a dry film thickness of 1.6 microns is obtained. The wettability of the Layer is characterized by contact angle determination. The determination the biological activity takes place according to the following method:

test organisms

• Pseudomonas putida (gram negative bacteria) Bacillus subtilis (gram positive bacteria)

medium

• Standardnähragar
• Incubation period: 14 days
• Incubation temperature: 30 ° C

test conditions

The Aluminum specimens were placed in 100 ml Erlenmeyer flasks and then with 80 ml standard nutrient broth filled. For inoculation was 1 ml suspension from a bacterial pre-culture. At the end of the incubation period, the aluminum bodies became three times Wash gently in phosphate buffer pH 7 to remove loose organisms from the carrier to wash. Thereafter, 1 minute in 40 ml of fresh phosphate buffer at 2400 Stirred / min. The cell suspension thus obtained was examined under the microscope a counting chamber after Neubauer examined their concentration. The antibacterial Effect is reported in percent relative to the total germ count of uncoated specimens. The Results are summarized in Table 1 and show the coating of Example 4 a good antibacterial effect both in gram positive as well as gram negative bacteria.

Example 5

Analogously to Example 4, an aluminum test specimen is coated with the following composition:
100 g of sol from Example 2
0.8 g octenidine

It will have a good antibacterial effect both in gram positive as well also gram negative bacteria achieved (see Table 1)

Example 6

Analogously to Example 4, an aluminum test specimen is coated with the following composition:
100 g sol from example 3
0.6 g Triclosan

It will have a very good antibacterial effect both in gram positive as well as gram negative bacteria achieved (see Table 1).

Example 7

Analogously to Example 4 aluminum test specimens are coated with the following composition:
100 g sol from example 3
1.3 g octenidine

To Drying and curing the test specimen is in one with dest. Water filled Beaker hanged, wherein by means of magnetic stirrer at 22 ° C a constant flow is produced. It becomes the antibacterial after 2 weeks of water contact Effect determined in comparison to specimens that do not contact water to have. The results in Table 1 show high water resistance the layer off. The antibacterial effect is retained.

Table 1 Antibacterial action - layer wetting

Claims (6)

Hydrophilic antibacterial coating, characterized in that the coating a) 75 to 99 wt .-% of maleate functional silica nanoparticles b) 1 to 25 wt .-% of water-insoluble active ingredients based on chlorobisphenol or octenidine contains. Hydrophilic antibacterial coating according to claim 1, characterized in that the maleic acid-functional silica nanoparticles by sol / gel technology prepared by reacting maleic anhydride with aminoalkyltrialkoxysilane is reacted and after hydrolysis with tetraalkoxysilane, alkyltrialkoxysilane or Dialkyldialkoxysilane in solvents be condensed. Hydrophilic antibacterial coating according to claim 2, characterized in that the molar ratio of maleic anhydride aminosilane adduct to comonomers 1: 1 to 1: 20. Hydrophilic antibacterial coating according to claims 1 to 3, characterized in that the coating is preferably 3 to 10 wt .-% octenidine. Hydrophilic antibacterial coating according to claims 1 to 3, characterized in that the coating is preferably 1 contains up to 5 wt .-% triclosan. Hydrophilic antibacterial coating according to claims 1 to 5, characterized in that these heat exchangers and / or water collecting trays of air conditioners is applied.