[0001] The present invention relate to compositions for producing anti-graffiti clear coatings with excellent outdoor durability. More particularly, the present invention relates to isocyanate free, urethane-modified poly(alkoxysilane) based anti-graffiti coating compositions.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to the field of surface treatments and coatings for substrates and surfaces, and more particularly relate to treatments and coatings that possess anti-graffiti properties.
[0003] A common problem encountered with exterior surfaces that are exposed in public places, such as building walls, storage tanks, railroad cars, automobiles, trucks, cars and public rest rooms and, in open areas such as support walls for bridges, inner walls of buildings and park structures etc., is that such surfaces are often defaced and vandalized with spray paint or other marking materials by so-called graffiti artists. Graffiti damage has been an increasingly growing concern. Today most people view graffiti not as an art form but as a form of vandalism and property destruction. This is a worldwide problem and the total aggregate of the time and expense involved in the removal or covering over of the graffiti is immense. Conventionally, removal of unwanted graffiti has been performed by sandblasting the graffiti from the substrate.
[0004] Blasting often causes the removal of parts of the substrate and an increase of the substrate surface roughness. Furthermore, the original surface paints may get destroyed as well. This method is expensive and hazardous to health due to the emission of potential dust and allergic particles. No long term solutions are offered by the use of this method and the surface will likely be repainted with new graffiti damages.
[0005] At present, available technologies for removing graffiti include the application of chemical cleaners. As to the chemical cleaners usually aggressive solvents which dissolve the graffiti paint are applied. The dissolved paint compounds are subsequently washed away with water and thus may sink into the ground or soil. In the soil these paint compounds present an environmental risk.
[0006] Conventionally, 2 component system (2K) like acrylic polyols based resin with isocyanate as curing agent are used for an anti-graffiti coating. The 2 component coating system after full curing of 7 days shows pencil Hardness up to H or 2H. In market products are offered with 2-3 µ coatings with anti-graffiti and 6H hardness. However, India being a dusty area and due to repeated cleaning, such low micron coatings can be easily removed.
[0007] Hence, there is a need to develop an anti-graffiti coating with a high micron coating and longer duration of protection in outdoors.

OBJECT OF THE INVENTION
[0008] It is an object of the present invention to solve the above mentioned problems by providing an improved coating for the protection against graffiti vandalism.
[0009] It is a further object to provide such a protective coating that is applicable to most surfaces, including metal, pre-treated surfaces, organic or inorganic surfaces to provide an anti-graffiti coating with hydrophobic, oleophobic properties and with excellent resistance to dirt and dust pick up.
[0010] It is yet another object of the present invention to provide an anti-graffiti coating which is almost 100 % transparent and has an almost invisible finish with high gloss.
[0011] This object and additional objects not expressly stated will become apparent upon review of the remaining disclosure.
SUMMARY OF THE INVENTION
[0012] The inventive compositions are curable compositions, which when cured impart mark resistant properties to a surface, and which make graffiti removal much easier than known coatings which share substantial transparency. The anti-graffiti coating compositions of the present invention are one component and are hydrophobic, oleophobic, provides high scratch resistance and excellent outdoor durability.
[0013] The anti-graffiti coating composition comprises binder resin present in a range from 20% to 60% (wt./wt.); solvents present in a range from 35% to 65% (wt./wt.) and additives present in a range from 2 to 10% (wt./wt.). The binder resin comprises urethane modified poly(alkoxysilane), terminated by tri-functional alkoxy-silane, wherein the binder resin is 3-Isocyanatopropyltrimethoxysilane (IPMS). The IPMS resin has molecular weight in range of 800-2500 gm/mol.
[0014] The anti-graffiti coating composition comprises solvent wherein the solvent comprises xylene, butyl acetate, toluene, methoxy propyl acetate and ethyl acetate. Preferably, the solvent is xylene and butyl acetate. The additives used in the anti-graffiti coating compositions are silicone modified polyacrylate BYK 3700 and HALS UV stabilizer Tinuvine 292.
[0015] The anti-graffiti coating composition are cured on initiation by moisture at ambient temperature. The curing at ambient temperature takes place in less than 60 minutes upon exposure to moisture. The coating composition has contact angle of more than 100°. Preferably, the coating has a contact angle of 118.5°. The coating has a transparency of at least 99%. The coating of cured composition can have thickness up to 20µ.
[0016] The present invention also discloses a method of imparting anti-graffiti properties, dirt and particulate repellence, and combinations thereof, to a surface comprising the steps of: applying a film coating of a composition to a surface to inhibit graffiti marks or particulate build; and exposing the film coating to conditions appropriate to initiate cure of the composition; wherein the composition comprises urethane modified poly(alkoxysilane)in a range of 20% to 60% (wt./wt.).
DESCRIPTION OF FIGURES
[0017] Figure 1: shows the structure of urethane-modified poly(alkoxysialne) IPMS resin (Formula I) of the present invention.
[0018] Figure 2: shows the structure of IPMS-based silane-urethane hybrid cross linker containing urethane groups, terminated by tri-functional alkoxy-silane structures.
[0019] Figure 3: shows schematic illustration of moisture curing in IPMS based resin of the present invention.
[0020] Figure 4: shows hydrophobicity test using 10 µl water drop volume at dose rate of 600 µl onto surface treated with 1 K anti-graffiti coating composition (A) and surface treated with 2K conventional PU coating composition (B).
DESCRIPTION OF THE INVENTION
[0021] The invention according to its various aspects is particularly pointed out and distinctly claimed in the appended claims read in view of this specification and appropriate equivalents.
[0022] It is to be noted, as used in the specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound includes a mixture of two or more compounds. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. The expression of various quantities in the terms of “% w/w” or “%” means the percentage by weight, relative to the weight of the total composition unless otherwise specified.
[0023] For the purpose of the present invention, the term "graffiti" designates undesirable marks (for example: inscriptions, drawings, messages, tags or others) made in ink, in paint, or in chalk, to which may be added, in an expanded definition, posters, stickers, and contaminations such as soiling due to atmospheric or biological pollution, bird droppings, insect carcasses.
[0024] For the purpose of the present invention, the term “one-component coating (1K)”, also known as one package coating or one pack coating, refers to a coating comprising one component that is stored in one package and cures into a film when the package is opened for use.
[0025] The invention is a one component (1K) anti-graffiti coating that provides a protective outer layer, the coating provides a surface possessing high surface tension and high chemical resistance against the solvents within the spray paint and other marking materials, such that the spray paint and like marking materials will not adequately adhere to the coating and is easily removed, such as by wiping within an hour or so of application. The anti-graffiti coating of the invention remains effective for a significantly greater number of cleanings than known anti-graffiti coatings, is resistant to scratch, degradation by weather and dirt or removal by fire or chemical attack, and does not significantly alter the appearance of the surface to which it is applied, the anti-graffiti coating being essentially transparent and possessing a high gloss or flat finish. The coating may be applied using conventional techniques, such as brushing, spraying, rolling, immersing, etc.
[0026] The surfaces to be protected can be of any kind and in particular porous (bricks, cement, concrete or wood) or non-porous. In particular, nonporous solid surfaces, painted or unpainted, made of glass, or of organic polymers or of metal, are intended, in particular metal surfaces, painted or unpainted, of public transport vehicles such as the train, metro, tram, bus, etc.
[0027] The coating is a solvent born coating and one component composition ready for use, intended to be applied to the surface to be protected.
[0028] The 1K anti-graffiti coating composition of the present invention comprise of film forming binder or resin or mixture of binders, solvent and additives.
[0029] The binder or resin in the anti-graffiti coating of the present invention primarily consists of urethane-modified poly(alkoxysilane). The polyalkoxy silanes have two or more alkoxy groups bonded to the silicon atom. The polyalkoxy silane are modified by incorporation of urethane group.
[0030] In an embodiment of the present invention the polyalkoxy silane –urethane hybrid cross linker is 3-Isocyanatopropyltrimethoxysilane (IPMS). IPMS has the structural formula (I) as shown in Figure 1. IPMS based silane-urethane hybrid crosslinker contains urethane groups, terminated by tri-functional alkoxy-silane structures. IPMS is obtained with any kind of isocyanate-reactive groups (R-group) preferably with the hydroxyl groups of diols, polyols or oligomeric diols to build a urethane linked but alkoxy-silane functional non-isocyanate cross linker/binder as shown in Figure 2.
[0031] The R-group in the diols (HO-R-OH) are linear or branched alkyl groups. The choice of R-group in the diols will primarily determine the properties of the cross linker and hence will also significantly influence the attributes of the coating. For example, the longer the backbone of the cross linker the more it acts as a flexibiliser in the coating. In contrast, a branched and short R-group will result in higher hardness. In the present invention, the R group is preferably between C4-C10. It is also possible in principle to use diols with additional functionalities incorporated, such as fluorinated compounds, to create coatings which are even more multifunctional.
[0032] In the present invention the urethane linkages are imparted by formulating the composition with IPMS-based cross-linkers, the beneficial properties of aliphatic polyurethanes such as high chemical resistance, good adhesion and excellent mechanical properties, are retained.
[0033] IPMS owns the bi-functionality of a reactive isocyanate group and a hydrolysable alkoxy group. The presence of the trimethoxy group makes IPMS to hydrolyze rapidly and bond with inorganic materials tightly. Alkoxy groups of isocyanate silanes can hydrolyze to form a reactive silanol group and offer superior adhesion to a wide range of inorganic substrates. IPMS binder resin provides higher crosslinking density, and at the same time, provides highly flexible clear coat, and also allows the formation of hard SiO2-like areas solidly integrated into the coating matrix—comparable to quartz. The urethane modified polyalkoxy silane (IPMS) of the present invention is obtained from Evonik Resource Efficiency GmbH (Trade name VESTANAT). The molecular weight of the modified resin is in range from 800 to 2500 gm/mol. The urethane-modified poly(alkoxysilane) is in the range of 20% to 60% wt./wt. of the coating composition.
[0034] Although it is preferred to employ only a single modified organofunctional silane in the process for the manufacture of the anti-graffiti resin, a mixture of one or more modified organofunctional silane or non-organofunctional silanols, e.g. modified triethoxy silane is also contemplated.
Solvent
[0035] The anti-graffiti coating composition contain solvents. Suitable solvents include aliphatic, cycloaliphatic and aromatic hydrocarbons, alcohols, ketones, esters, and mixtures of the above. Examples of suitable solvents are white spirit, cyclohexane, toluene, xylene, methoxy propyl acetate and naphtha solvent, esters such as methoxypropylacetate, n-butyl acetate and 2-ethoxyethylacetate; octamethyltrisiloxane, and mixtures thereof. The solvents typically constitute 35% to 65% wt. based on the total weight of the coating composition. The solvents preferable for use in the present invention are xylene and butyl acetate. Xylene and butyl acetate help to reduce the viscosity, adjust the polarity and these evaporates from the film once the coating gets cured properly.
Additives
[0036] The composition according to the invention preferably comprises further additives selected from the group of, rheology additives, and UV stabilizers. The additives are used in the range of 2% to 10% wt. /wt. of the coating composition. The additives preferably used are BYK 3700 and Tinuvine 292. BYK 3700 is a solution of silicone modified poly-acrylate (OH-functional), this helps to reduce the surface tension, wetting the substrate and boost the hydrophobicity and oleo-phobicity. Byk 3700 is Trade product from BYK –Chemie GmbH.
[0037] UV stabilizers are preferably known products based on hindered phenolic systems or benzotriazoles. Light stabilizers used may be, for example, those known as HALS amines. Stabilizers used may, for example, be the products known to those skilled in the art or product combinations composed, for example, of Tinuvin® stabilizers (BASF), for example Tinuvin® 1130, Tinuvin® 292 or else Tinuvin® 400, preferably Tinuvin® 292. The amount in which they are used is determined by the degree of stabilization required.
[0038] Suitable pigments for colouring in the case of coating systems are particularly inorganic pigments such as metal oxides or spinel pigments. For improvement of corrosion protection, it is also possible to use the typical anticorrosion pigments, for example zinc phosphate.
Application of 1K anti-graffiti coating compositions
[0039] The invention also provides a process for coating a substrate selected from the materials metal, glass, ceramic and plastic, wherein a coating composition of the invention is applied to the substrate, is cross-linked by physical drying, by reactive self-crosslinking or reactive foreign crosslinking. The coating may be applied using conventional techniques, such as brushing, spraying, rolling, immersing, etc. The coating is applied in very thin layer for protection.
[0040] The coating composition is then dried, for example by evaporation. Drying time will vary depending on temperature, humidity and air circulation. In wet and cold periods, the drying will be longer. In general, coating formation is rapid (usually from a few minutes to a few hours), when the coating composition is applied at a temperature of between 5° C and 35° C, preferably between 10° C and 25° C. The drying operation can be carried out at a temperature between 5° C and 35° C and preferably at room temperature (about 27° C). In general, the coating is dry to the touch in less than 60 minutes, preferably between 40 minutes to 50 minutes under normal temperature and humidity conditions. Advantageously, the coating of the invention has a matt or satin surface appearance.
[0041] The 1k anti –graffiti coating of the present invention can build thickness of 15-20 µ while providing much longer duration of protection. In 48 hours of air drying product the coating film can achieve pencil hardness of 6H.
[0042] Urethane-modified poly(alkoxysilanes) prepared by the non-hydrolytic process have a higher tendency to migrate and are oriented toward the air at the surface of the coating compositions. By contact with atmospheric water or rain, a silica network is formed. There are two possible reaction mechanisms by which the IPMS-based cross-linkers shown in figure 2 can react via their alkoxy groups in coating systems. One reaction is a combination of hydrolysis and condensation to form siloxane linkages (Si-O-Si) as illustrated in Figure 3. The other crosslinking mechanism is a trans-esterification reaction which occurs only if a hydroxyl group, for example that of an acrylic or other polyol, is present. Each of these mechanisms can be accelerated by using appropriate catalysts. This highly cross-linked silica network in the top layer of the coating agent film prevents contaminants from entering the surface and allow easy cleaning of the graffiti.
[0043] In addition, it has been found that the coating effectively withstands mechanical aggression such as shocks, scratches, and abrasions. In addition, such a coating is of low cost and isocyanate free. It can be prepared with products that are readily available commercially and by methods that are easy to implement.
Example 1:
Process for the preparation of 1K anti-graffiti coating composition
[0044] The components of the coating composition as illustrated in Table 1 are taken in predefined amount in the defined sequence in a mixer container. All the components in the mixer container are mixed at a speed of 300 – 500 RPM for 15 to 20 minutes. The mixing takes place at ambient room temperature and pressure.
Table 1: 1K Anti-graffiti coating composition
Components % (wt. /wt.)
Polymethoxysilane (PMS) modified resin 20-60%
Xylene 10-30%
Butyl Acetate 25-35%
Additive 2-10%

Example 2:
Different formulations for the 1K anti-graffiti coating composition
[0045] Different formulations of the coating composition are prepared by the process as illustrated in Example 1. The compositions of different formulations are illustrated in Table 2.
Table 2: Formulations of 1K anti-graffiti coating compositions
Components Formulation 1
(wt. /wt.) Formulation 2
(wt. /wt.) Formulation 3
(wt. /wt.)
Polymethoxysilane (PMS) modified resin 20% 40% 60%
Xylene 37% 25% 15%
Butyl Acetate 35% 30% 19%
Rheology additives (BYK 3700) 6% 3% 4%
UV stabilizer (Tinuvin® 292) 2% 2% 2%

[0046] The formulation 2 is found to be the best in properties and meeting the specification PCN 127.
Example 3:
Performance analysis with respect to 2K PU system
[0047] Different substrates mild steel (MS), galvanized iron (GI) and glass were taken and coated with 2K PU system and 1K anti-graffiti coating compositions of formulation 2 of the present invention. As illustrated in Table 3, it was observed that formulation 2 of the present invention showed good adhesion on all three substrates and showed better performance than conventional 2K PU system in pencil hardness and PU thinner spot test.
Table 3: Comparison of 2K PU system with 1K anti-graffiti coating composition
Parameter Conventional 2K Pu System 1K Anti-Graffiti Clear Coat (Formulation 2)
Adhesion
On MS Passes 5B Passes 5B
On GI Passes 4B (selective Resins) Passes 5B
On Glass failed Passes 5B
Pencil Harness Passes H to 2H after 7days passes 6H after 48 hours
PU thinner Spot Test Film gets Soft within 15-20mins No change in Gloss or Hardness even after 24 hours of Dipping

Example 4:
Hydrophobicity test
[0048] The hydrophobicity test was carried out in accordance with ASTM F22-13. It was observed that contact angle for 1K anti-graffiti coating is more than 100°. Preferably, the contact angle value for 1K anti-graffiti coating is 118.50 and for 2K conventional PU coating is 85.40 at water drop volume of 10 micro lit and dose rate of 600 micro lit/min as shown in Figure 4. This clearly illustrates that the coating composition of the present invention provides better water repellence than convention 2K PU coating systems. Thus, the present coating composition provides advantages like decreased dirt retention, self-clean ability, improved moisture and corrosion resistance, as well as extended life expectancy of the coating and substrate.
Example 5:
Performance analysis of the 1K anti-graffiti coating composition
[0049] The formulation 2 as shown in Example 2 is tested for various short and long term tests, the results are illustrated in Table 4 below.
Table 4: Performance analysis result of the 1K anti-graffiti coating composition (Formulation 2) under short and long term tests.
S.No. Characteristics 1K Anti-Graffiti Clear coat (Formulation 2) Test method
1 • Drying time at 27± 2 °C
1. Surface dry/touch dry 40 mins. - 50 mins. IS 101-86 (Part 3/ Sec. 1)
2.Hard Dry 24 hrs.
3.Recoating Time Within 10 mins
2 Finish Smooth IS : 101-87 (Part 3/ Sec. 4)
3 Gloss at 60 Direct on Aluminium - 70-80, on Original coated surface gloss is higher IS: 101-88 (Part 4/Sec. 4)
4 Flexibility & adhesion Passes IS: 101-88 (Part 5/Sec. 2)
5 Impact resistance test,100 cm with 2 kg on steel , 0.5 mm thick cured panels Passes ASTM-D-2794
6 Adhesion test ( Cross cut tape test) Passes with 5B ASTM-D-3359
7 Consistency/efflux time at 27± 2.0 °C
12 sec IS :101-89 (Part 1 Sec. 5)
8 Protection against corrosion under conditions of condensation.( 500 hrs) Passes - total system of ETCH Primer+ PUPS+ PU topcoat + Anti-Graffiti clear coat IS: 101.88 (Part 6 ISec.1))
9 Solvent MEK Rub Test Passes ASTM 0-5402-93
100 DS
10 Resistance to (a) 30 %,w/v (a)citric acid for 3 hrs. Passes
10 Resistance to (b) 5% ,v/v ammonia for 20 minutes
Passes 24 hrs.
(c) Resistance to lubricating oil for 24 hrs.
(d) Resistance to solvents for 20 Minutes. Passes 24 hrs.

i) Acetone
ii) Toluene
Solvent MEK Rub Test
11 Mass in Kg/10 litres 9.35 IS :101-87 (Part 11 Sec. 7)
12 Flash Point More than 27 IS: 101-87 (Part 1 Sec. 6)
13 Keeping property/shelf life 1 year Shelf Life/ Aging test PCN 127 Appendix -II
14 Anti-Graffiti test Passes the test ASTM D-6578
Contact Angle for Hydrophobicity test 118.5 °
15 Identification of base material/resin Poly methoxy Silane Modified Resin By FTIR METHOD. ( as per PCN 127& Appendix- v)
16 Coverage ( Spreading capacity) , min., at microns DFT, by spray, dipping, wiping method
50-52 sqr.m./lit at 5-8 micron DFT As per PCN 127 Appendix-I
17
Dry Film Thickness per coat, min., b wipe/spray Spray 5-10 micron As per Appendix-I
18 Pencil hardness 6H ASTM D 3363
19 % vol. solid 30-35% As per PCN 127 Appendix-I
20 Durability tests
(i)Accelerated weathering test at 4 hrs. QUV and 4 hrs. Passes 1000 Hrs QUV As per Appendix-IV
& ASTM-G-53
Condensations
Alternatively, temp. 50°C(750 hrs)
(ii) Xenon test for2000hrs. Passes 2000 hrs DIN – 53387

[0050] It was observed that the anti-graffiti coating compositions exhibited good anti-graffiti properties, are easily cleanable, provides good scratch resistance, solvent resistance, hydrophobic and oleophobic properties and have excellent outdoor durability.
[0051] It is contemplated that equivalents and substitutions for elements set forth above may be obvious to those of ordinary skill in the art, and therefore the true scope and definition of the invention is to be as set forth in the following claims.

Claims:We claim:
1. An anti-graffiti coating composition comprising:
binder resin present in a range from 20% to 60% (wt./wt.);
solvents present in a range from 35% to 65% (wt./wt.); and additives present in a range from 2 to 10% (wt./wt.).
2. The anti-graffiti coating composition as claimed in claim 1, wherein the coating composition is one component coating system.
3. The anti-graffiti coating composition as claimed in claim 1 to 2, wherein the binder resin comprises urethane modified poly(alkoxysilane), terminated by tri-functional alkoxy-silane.
4. The anti-graffiti coating composition as claimed in claim 1 to 3, wherein the binder resin is 3-Isocyanatopropyltrimethoxysilane (IPMS).
5. The anti-graffiti coating composition as claimed in claim 1 to 4, wherein the IPMS resin has molecular weight in range of 800-2500 gm/mol.
6. The anti-graffiti coating composition as claimed in claim 1, wherein the solvent comprises xylene, butyl acetate, toluene, methoxy propyl acetate and ethyl acetate.
7. The anti-graffiti coating composition as claimed in claim 6, wherein the solvent is xylene and butyl acetate.
8. The anti-graffiti coating composition as claimed in claim 1, wherein the additives are rheology additive BYk 3700 and UV stabilizer Tinuvine 292.
9. The anti-graffiti coating composition as claimed in claim 1 to 8, wherein moisture initiates cure of the composition at ambient temperature.
10. The anti-graffiti coating composition as claimed in claim 1 to 9, wherein the composition cures at ambient temperature in less than 60 minutes upon exposure to moisture.
11. The anti-graffiti coating composition as claimed in claim 1 to 10, wherein the thin coating of cured composition is graffiti repellent under ASTM D-6578.
12. The anti-graffiti coating composition as claimed in claim 1 to 11, wherein the coating has contact angle of more than 100°.
13. The anti-graffiti coating composition as claimed in claim 12, wherein the coating has a contact angle of 118.5°.
14. The anti-graffiti coating composition as claimed in claim 1 to 12, wherein coating has a transparency of at least 99%.
15. The anti-graffiti coating composition as claimed in claim 1 to 14, wherein the coating of cured composition can have thickness up to 20µ.
16. A method of imparting anti-graffiti properties, dirt and particulate repellence, and combinations thereof, to a surface comprising the steps of:
applying a film coating of the coating composition to a surface to inhibit graffiti marks or particulate build; and
exposing the film coating to conditions appropriate to initiate cure of the composition;
wherein the composition comprises urethane modified poly(alkoxysilane)in a range of 20% to 60% (wt./wt.).
17. The method as claimed in claim 16, wherein moisture initiates cure of the composition at ambient temperature.
18. The method as claimed in claim 16, wherein curing takes place in less than 60 minutes upon exposure to moisture.