WO2013077805A1

WO2013077805A1 - A process for making an antimicrobial coating

Info

Publication number: WO2013077805A1
Application number: PCT/SG2011/000408
Authority: WO
Inventors: Ngai Ming Samuel CHIANG
Original assignee: Commercial Supplies (Far East) Pte. Ltd.
Priority date: 2011-11-21
Filing date: 2011-11-21
Publication date: 2013-05-30
Also published as: CN103249788B; CN103249788A

Abstract

This invention relates to a process for making an antimicrobial coating having air sanitization, self-cleansing and heat resistant properties comprising the steps of stabilizing a silane base antimicrobial agent in water with a wetting agent, a surfactant and a polyol to create a sol-gel solution, adding a photocatalyst with a particle size of less than 20nm to the sol-gel solution and followed by adding at least one metallic oxide additive to the sol-gel solution. The antimicrobial coating may be applied to air condition duct system (HVAC) or interior of automotives or on wood and textile surfaces.

Description

A PROCESS FOR MAKING AN ANTIMICROBIAL COATING

FIELD OF INVENTION

Embodiments of the present invention relate to a process for making a day and night surface antimicrobial coating which is capable of air sanitizing and self-cleansing in the light and is also heat resistant.

BACKGROUND

In the 1970s, Dow Corning invented DC5700 and DC5772 (currently AEM5700, AEM5772) as antimicrobial agents. These antimicrobial agents are capable of killing germs or microbes (i.e. single cell microorganisms) by physical rupture or electrocution. When microbes, for example bacteria, mold, mildew, algae, etc., come into contact with the antimicrobial agent, they are controlled by a complex physical and electrical phenomenon. In particular, the negatively charged cell membrane is attracted to the treated surface and then punctured by the long molecular chain in the antimicrobial agent. As it is drawn closer because of positive charge attraction, it penetrates further into the cell membrane and the cell is physically ruptured by a sword-like action and then electrocuted by a positively charged nitrogen molecule, thus destroying it. Since physical contact between the antimicrobial agents and the germs or microbes must occur before any reaction can take place, the uses of such antimicrobial agents are restrictive.

Apart from killing germs, it is desirable to have an improved antimicrobial coating which can provide additional benefits.

SUMMARY OF INVENTION

Embodiments of the present invention relate to a process for making an antimicrobial coating having air sanitization, self-cleansing and heat resistant properties comprising the steps of stabilizing a silane based antimicrobial agent in water with a wetting agent, a surfactant and a polyol to create a sol-gel solution and adding a photocatalyst with a particle size of less than 20nm to the sol-gel solution. Larger particle size is not readily responsive to visible light except UV light. Following that, at least one metallic oxide additive is added to the sol-gel solution.

In yet another embodiment, there is provided an antimicrobial coating comprising a silane based antimicrobial agent, a photocatalyst with a particle size of less than 20 nm and at least one metal oxide additive, wherein the antimicrobial coating has air sanitization, self-cleansing and heat resistant properties.

Embodiments of the present invention provide reliable, environmentally sound and effective solutions for industries to apply the antimicrobial coating on almost any kind of surfaces. Apart from the ability to remove bacteria, the provision of a photocatalyst within the antimicrobial coating renders it air sanitizing when it is exposed to visible light or UV light. The metallic oxide additives further provides for heat resistant or cigarette burn resistant properties.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows the results of a 30 minutes Light Radiation Test on blue dye tiles.

Figure 2 shows the results of a 30 minutes Light Radiation Test on blue dye fabrics.

Figure 3 shows the effect on blue dye tiles with varying sizes of a titanium dioxide photocatalyst under a 30 minutes Light Radiation Test.

Figure 4 shows the results of a 30 minutes Light Radiation Test on wood tiles using a sol-gel antimicrobial product with a titanium dioxide having a size down to 4 - 5 nm.

Figure 5 shows a series of wood tiles burning tests where (a) is wood tiles before burn test, (b) is 5 minutes into burn test, (c) is 10 minutes into burn test, (d) nearly 20 minutes into burn test, (e) is the end point of burn test and (f) shows no burn mark on wood coated with an antimicrobial agent with nano aluminum oxide and nano zinc oxides additives (SMP(C)).

Figure 6 shows a series of wood tiles burning tests where magnesium hydroxide in 0.2%, 035% and 0.7% is further added into an antimicrobial agent with oxides additives (SMP(C)) where (a) is wood tiles before burn test, (b) is 5 minutes into burn test, (c) is 15 minutes into burn test and (d) shows the end point of burn test.

DETAILED DESCRIPTION

According to one embodiment of the invention, there is provided a process for the making of an antimicrobial coating having air sanitization, self-cleansing and heat resistant properties.

A silane based antimicrobial agent, such as, but not limited to, AEM5700 or AEM5772 is converted into a sol-gel solution by stabilizing them in water with a wetting agent, a surfactant, and a polyol.

An example of a silane based antimicrobial agent that can be used in this process is 3- (trimethoxylsilyl)propyldimethyloctadecyl ammonium chloride, e.g. AEGIS Microbeshield, that can be represented by the formula:

CH₃

(CH₃0)₃-Si(CH₂)₃N⁺ -C₁₈H₃₇ CI^" (e.g. AEM5700 or AEM5772)

CH₃

Empirical Formula: C₂6H₅ ClN0₃Si

AEM5700 is 42% active in methanol and AEM5772 is 72% active in methanol. Generally, this can be represented by the following formula:

wherein K_\ is methyl, ethyl, propyl, or a hydroxy 1 group;

R₂ is a C] to Cio alkyl;

R₃ is an alkyl or alkoxyl group;

R4 is an alkyl or alkoxyl group;

R₅ is a C] to C]g alkyl.

After converting AEM5700 or AEM5772 into a sol-gel solution, a photocatalyst having a particle size of less than 20nm is added into the sol-gel solution. A suitable photocatalyst that may be used is titanium dioxide. The resultant sol-gel antimicrobial coating is milky or translucent due to the presence of the photocatalyst particles.

The resultant sol-gel antimicrobial coating exhibits antimicrobial properties without light or in the dark and exhibits air sanitization properties when exposed to visible or UV light. In the dark, the antimicrobial properties will continue to kill germs and when there is light, the photocatalyst will create air sanitizing and germs killing oxygen anions and hydroxy 1 ions to boost the total performance of the sol-gel antimicrobial coating.

As shown in Figure 1, blue dye tiles coated with sol-gel antimicrobial coating faded under light when half of the tile is exposed to light for a 30 minutes Light Radiation Test. The Control Tile is not coated with sol-gel antimicrobial coating so mere is no fading when the tile is exposed to the same Light Test.

Likewise, blue dye fabrics coated with sol-gel antimicrobial coating show the same results. As shown in Figure 2, SMP and WOW20 refer to blue dye stained fabrics coated with sol-gel antimicrobial coating. The Control Fabric is not coated with sol- gel antimicrobial coating so no color fading occurs even when it is exposed to the same light intensity.

Table 1 shows a durability of germs killing in an ASTM E-2149-01 Test using AEGIS Microbe Shield and the sol-gel antimicrobial coating (i.e. AEGIS + photocatalyst (WOW)) blended in different amounts of photocatalyst.

Table 1

As seen in Table 1, both AEGIS and the sol-gel antimicrobial coating give good antimicrobial properties before and after washings.

Further, the sol-gel antimicrobial coating maintains the original antimicrobial properties of separate technologies when they are applied separately. They can function as a coating with combined performance, i.e. working in the dark as AEGIS antimicrobial and with added air sanitizing (dye fading) under the reduction and oxidation process of the photocatalyst under visible light condition or UV light.

In addition, the sol-gel antimicrobial coating can vary from being hydrophobic to hydrophilic depending on the ratio of AEGIS and photocatalyst present in the coating. When there is a high AEGIS and low photocatalyst ratio, the sol-gel antimicrobial coating is hydrophobic. When there is a low AEGIS and high photocatalyst ratio, the sol-gel antimicrobial coating is hydrophilic. When the ratio between AEGIS and photocatalyst is the same, the sol-gel antimicrobial will exhibit both hydrophobic and hydrophilic properties.

By varying the particle size of the photocatalyst in the sol-gel antimicrobial coating, for example from 10-15 nm to 4-5 nm size, an improvement of sol-gel antimicrobial coating can be seen.

As shown in Figure 3, three blue dye tiles are coated with sol-gel antimicrobial coating, namely, SMP(A), SMP(B) and SMP(C), and half of each tile is exposed to light for a 30 minutes Light Radiation Test.

Both SMP(A) and SMP(B) are coated with a sol-gel antimicrobial coating with a titanium dioxide having a size of 10 to 15 nm (6% Active) in two purchase lots and formulations give similar photocatalyst color fading action.

SMP(C) coated with a sol-gel antimicrobial coating with a titanium dioxide having a size of 4 to 5 nm (5% Active) gives a stronger photocatalyst color fading action as evidence in the stronger fading of methyl blue dye. This is due to a better spreading or coverage of finer size nano powder on the ceramic tile or non-penetrable surfaces.

SMP(C) is next coated on a wood tile as seen in Figure 4. Some of SMP(C) have sunk into the wood surface and the remaining SMP(C), less than 5% on the surface of the wood tile, shows photocatalyst action. It can be seen that photocatalyst action on wood is not as strong as on ceramics. To overcome this, the photocatalyst levels can be adjusted to intensify the photocatalyst action to compensate for the drop due to wood absorption of the nano photocatalyst that needs to be exposed to light for effectiveness. To make the sol-gel antimicrobial coating flame retardant, at least one metallic oxide additive, such as, but not limited to, nano aluminium oxide (A1₂0₃), zinc oxide (ZnO) and magnesium oxide (MgO) or magnesium hydroxide (Mg(OH)₂) is added to the sol-gel antimicrobial coating. Preferably, nano aluminium oxide is used. The final coating is a non-tacky and non-powdery surface that is resistant to cigarette burn as shown in Figure 5.

The addition of A1₂0₃ (2% Active) and ZnO (1% Active) into SMP(C) renders the coating heat resistant or cigarette burn resistant as compared with an unmodified SMP(C) coating which burned as the treated or Blank Wood Tile in the above Cigarette Burning Tests. The ratio of titanium dioxide and metallic oxides is 66% versus 34% approximately. (2/3 versus 1/3).

The coating causes the cigarette to self-extinguish around 3 minutes into the Burn Test. Hence, there is no burning between 5 minutes to the end point of the modified SMP(C) containing the two oxides.

The nano particle size of Al₂O₃ is around 20 to 30 ran and ZnO is around 30 nm to 100 nm. Other synergistic metal oxides such as, but not limited, to magnesium oxide or magnesium hydroxide can also be added. The nano particle used for Cigarette Light Resistant properties can be between 20 nm to 150 nm range. The finer the nano particles, the better is the coverage. These are inert metallic oxides that are green to the environment and will not burn to give off toxic substances as compared to brominates, bromides or fluorinated chemicals.

In another embodiment of this invention, nano magnesium hydroxide (Mg(OH)₂), commonly found in antacid drugs, can be added into the nano Α1₂Ο₃ and nano ZnO to neutralize acidic burn by-products. Figure 6 shows a Burn Test in which an additional nano Mg(OH)₂ is added in percentages of 0.2%, 0.35% and 0.7% into modified SMP(C) with Al₂O₃ (2%) and ZnO (1%) in three additional tests. Again,no burn marks can be seen on the wood tiles coated with these modified SMP(C). Although ceramic and wood surfaces are mainly discussed above, it should be understood that the new antimicrobial coating works with similar effects on cellulosic surfaces such like cotton textiles or even synthetic materials.

The antimicrobial coating may be applied to an air condition duct system (HVAC) or the interior of automotives or on wood surface or the like.

In an air condition duct system (HVAC), the ducting surface may be coated internally with the improved antimicrobial coating according to this invention. The surface is self-sanitizing. When air passes through the ducts when the light is on, the air will be cleansed by the oxygen anions and hydroxyl ions generated by the photocatalyst in the antimicrobial coating and this improves the air quality. In the dark, the antimicrobial coating kills germs on physical contact and hence, the hygiene level can be maintained at a high level for a longer period of time as compared with an air condition duct system without any coating or with just ordinary basic protective paint against corrosion.

In another embodiment, the new antimicrobial coating may be sprayed or applied to the interior of automotives to protect the surfaces as well as to sanitize the interior of the automotives.

In yet another embodiment, the new antimicrobial coating may be applied to wood surface to render it hydrophobic, anti-fungal, antibacterial, burn resistant and air sanitizing and self-cleaning during the day time while maintaining the wood having antimicrobial properties during the night.

While the above-described process may be a stand alone process, it will be appreciated by persons skilled in the art that the above-described process of obtaining an antimicrobial coating may be combined with other processes.

Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the invention. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the disclosed embodiments of the invention. The embodiments and features described above should be considered exemplary, with the invention being defined by the appended claims.

Claims

1. A process for making an antimicrobial coating having air sanitization, self- cleansing and heat resistant properties comprising the steps of:

(a) stabilizing a silane based antimicrobial agent in water with a wetting agent, a surfactant and a polyol to create a sol-gel solution;

(b) adding a photocatalyst with a particle size of less than 20nm to the sol-gel solution obtained in step (a); and

(c) adding at least one metallic oxide additive to the sol-gel solution obtained in step (b).

2. A process according to claim 1, wherein the silane based antimicrobial agent is 3-(trimethoxysilyl)propyldimethoxyoctadecyl ammounium chloride.

3. A process according to claim 1, wherein the photocatalyst has a particle size between 10 to 15 nm.

4. A process according to claim 1, wherein the photocatalyst has a particle size between 4 to 5 nm.

5. A process according to claim 1, wherein the photocatalyst is titanium dioxide.

6. A process according to claim 1, wherein the metallic oxide additive has a particle size between 20 nm to 150 nm.

7. A process according to claim 1 wherein the at least one metallic oxide additive is chosen from one of nano aluminium oxide, nano zinc oxide, nano magnesium oxide and nano magnesium hydroxide.

8. A process according to claim 7, wherein the at least one metallic oxide is nano aluminium oxide. An antimicrobial coating made in accordance with claim 1, wherein the antimicrobial coating can vary from being hydrophobic to hydrophilic.

An antimicrobial coating comprising:

a silane based antimicrobial agent;

a photocatalyst with a particle size of less than 20 nm; and

at least one metal oxide additive,

wherein the antimicrobial coating has air sanitization, self-cleansing and heat resistant properties.

An antimicrobial coating according to claim 10, wherein the silane based antimicrobial agent is 3-(trimethoxysilyl)propyldimethoxyoctadecyl ammounium chloride.

An antimicrobial coating according to claim 10, wherein the photocatalyst has a particle size between 10 to 15 nm.

An antimicrobial coating according to claim 10, wherein the photocatalyst is titanium dioxide.

An antimicrobial coating according to claim 10, wherein the metallic oxide additive has a particle size between 20 nm to 150 nm.

An antimicrobial coating according to claim 10 wherein the at least one metallic oxide additive is chosen from one of nano aluminium oxide, nano zinc oxide, nano magnesium oxide and nano magnesium hydroxide.

An antimicrobial coating according to claim 15, wherein the at least one metallic oxide is nano aluminium oxide.