DESC:Technical field of the Invention
The present invention relates to a two-component polyurethane coating composition containing polyisocyanate and certain acrylic polyols as the binder. The coating composition of the present invention is suitable for use on all kind of substrates, and results in highly durable coating which is mechanically robust without compromising on aesthetic appearance.

Background of the Invention
The terms "paints" and "coatings" are often used interchangeably. However, for the most part, paints are considered to be used primarily for aesthetics, while coatings are used principally to prevent substrate deterioration or for corrosion protection.
The coatings known in prior art have the disadvantage that they are either aesthetically sound or mechanically robust but not both. Further, in term of application, prior art coatings have limited range of substrates that can be coated.
Present invention provides a new approach to overcome the difficulties associated with prior art coatings. The coating composition of the present invention, maintains the coating’s mechanical build as well as the overall appearance such as high gloss and distinctness of image along with suitable adhesion properties of the overall coating system.
Objective of the invention
Despite the developments in the field of coatings, there is a need for coating which is suitable for a variety of substrates, while still maintaining the coating’s mechanical properties as well as the overall visual appearance and adhesion strength. The present application addresses these needs.
Summary of the invention
This invention relates to a coating composition useful for coating a wide range of substrates.
In one aspect, the present invention is a two-component polyurethane coating composition.
In another aspect, the present invention is a two-component polyurethane coating composition comprising a polyisocyanate and an acrylic polyol resin.
In a related aspect, the present invention is a two-component polyurethane coating composition comprising a polyisocyanate and an acrylic polyol resin, characterized by the presence of a solution of a hydroxy-functional copolymer with acidic groups, wherein the said acrylic polyol resin is 58-62 % solid.
In a further aspect, the present invention is a two-component polyurethane coating composition comprising a polyisocyanate, an acrylic polyol resin (60% solid) and a hydroxy-functional copolymer with acidic groups along with solvent, 3-glycidoxypropyltrimethoxy silane and optionally polyester-modified polydimethylsiloxane.
In yet another aspect, the two-component polyurethane composition as per present invention, is used as a coating for a variety of substrates.
The coating composition as per present invention provides the advantage that it is suitable for a variety of substrates and still maintains the coating’s mechanical properties as well as, the overall visual appearance and adhesion strength.

Description of the invention
It should be noted that notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. For example, and without limitation, this application refers to coating compositions that comprise “an acrylic polyol”. Such references to “an acrylic polyol” is meant to encompass coating compositions comprising one acrylic polyol as well as coating compositions that comprise more than one acrylic polyol. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances.

As previously indicated, certain embodiments of the present invention are directed to “two-component” coating compositions. As used herein, the term “multi-component” means that the coating composition includes two or more components stored or packaged separately and then mixed together prior to application to a substrate. In certain embodiments of the present invention, the multi-component coating composition consists of two components.
Present invention provides a two-component polyurethane coating composition comprising a polyisocyanate, an acrylic polyol resin and a solution of a hydroxy-functional copolymer with acidic groups.
In an embodiment of the present invention, the polyisocyanate in the two-component polyurethane coating composition is an aliphatic polyisocyanate. Suitable polyisocyanates include, but are not limited to, ethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isophoronediisocyanate, cyclohexane-1,4-diisocyanate, 4,4'-dicyclohexyl methane diisocyanate, cyclopentylenediisoyanate, p-tetra-methylxylenediisocyanate (p-TMXDI) and its meta isomer (m-TMXDI), hydrogenated 2,4-toluene diisocyanate, hydrogenated 2,6-toluene diisocyanate, 1-isocyanato-1-methyl-3(4)-isocyanatomethyl-cyclohexane (IMCI), pentamethylenediisocyanate and mixtures thereof.
Preferred polyisocyanates are 1,6-hexamethylene diisocyanate (HDI), pentamethylenediisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophoronediisocyanate and (p or m) TMXDI.
In another embodiment of the present invention, the acrylic polyol resin in the two-component polyurethane coating composition is 58-62 % solid, preferably 60% solid.
In a preferred embodiment of the present invention, the acrylic polyol resin in the two-component polyurethane coating composition comprises styrene, methylmethacrylate, hydroxyethylmethacrylate, acrylic acid and butyl acrylate. Further, suitable initiators like DTBP, TBPB, DTAP may also comprise the said acrylic polyol.
In a particular embodiment of the present invention, the acrylic polyol resin in the two-component polyurethane coating composition comprises 20-30% styrene, 15-30% methylmethacrylate, 12-25% hydroxyethylmethacrylate, 0.5-2% acrylic acid and 15-35% butyl acrylate, such that total weight of the acrylic polyol resin is 100%.
In a preferred embodiment of the present invention, the acrylic polyol resin in the two-component polyurethane coating composition comprises 30% styrene, 22-23% methylmethacrylate, 16-17% hydroxyethylmethacrylate, 1.5% acrylic acid and 30% butyl acrylate, such that total weight of the acrylic polyol resin is 100%.
In yet another embodiment of the present invention, the two-component polyurethane coating composition of the present invention, further comprises solvent, polyester-modified polydimethylsiloxane and/or 3-glycidoxypropyltrimethoxy silane.
In a preferred embodiment of the present invention, the solvent in the two-component polyurethane coating composition is an acetate solvent and/or a hydrocarbon solvent. Examples of suitable solvents which can be incorporated in the polyurethane composition of the invention are acetate solvent such as n-butyl acetate, methoxypropyl acetate, t-butyl acetate, and/or butyl carbitol acetate; and/or hydrocarbon solvent, such as xylene, hexane, toluene, isooctane, pentane, benzene, trimethylbenzene, ethyldimethylbenzene or dipropylbenzene, and/or heptane.
In a particular embodiment of the present invention, the two-component polyurethane coating composition comprises
-20% polyisocyanate and 3-glycidoxypropyltrimethoxy silane; and
-30-60% acrylic polyol resin, 10-20% acetate solvent, 5-10 % hydrocarbon solvent, 2-5% solution of a hydroxy-functional copolymer with acidic groups and optionally 0.5-5% or preferably 0.5-1% polyester-modified polydimethylsiloxane, such that total weight of the coating composition is 100%. Use of polyester-modified polydimethylsiloxane assists in strong reduction in the surface tension.
Other additive ingredients for example, plasticizers, surfactants, thixotropic agents, anti-gassing agents, flow controllers, anti-oxidants, UV light absorbers and similar additives conventional in the art can be included in the compositions of the present invention.

The coating compositions of the present invention also may, in certain embodiments, be formulated to include one or more pigments or fillers to provide color and/or optical effects, or opacity.

In a further embodiment the two-component polyurethane coating composition of the present invention comprises a coating for variety of substrates selected from aluminium, mild steel, stainless steel, tin, galvanized iron, plastics, wood, medium density fibre board, fibre reinforced plastic, glass or copper.

The compositions can be applied by conventional means including brushing, dipping, flow coating, spraying and the like. The usual spray techniques and equipment for air spraying and either manual or automatic methods can be used. The coating compositions of the present invention may be used as a single coating, a clear top coating, a base coating in a two-layered system, or one or more layers of a multi-layered system including a clear top coating composition, colorant layer and base coating composition, or as a primer layer.
Coating composition of the present invention provides superior gloss with high gloss retention, flexibility in drying (Oven drying and Air drying), with excellent mechanical properties (Scratch resistance, Adhesion, Flexibility, Impact) and vigorous chemical properties such as acid, alkali, mild alcohol resistance, soap resistance and excellent Anti-Yellowing (QUV) along with being Anti Rust (SST) and high durability.
The coating composition of present invention has excellent performance in water immersion, Stain Mark Test (Tea, Coffee, Mustard Sauce, Red Wine, Hot Water, Olive Oil), Disinfectant wipes test and Cold & Hot Temperature test (Freeze Thaw Resistance) (-5°C for 8 Hours and 30°C for 16 Hours).
The present invention is further defined in the following examples. It should be understood that these examples are given by way of illustration only. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this invention, and can make various changes and modifications of the invention to adapt it to various uses and conditions.
Examples
Each ingredient was compounded according to the compounding amount shown in Table 1 to prepare the coating composition.
Table 1
Exp. No. Composition (Total weight being 100%)
1 20% aliphatic polyisocyanate,
30-60% acrylic polyol resin (EXP-A),
10-20% acetate solvent,
5-10% hydrocarbon solvent.
2 20% aliphatic polyisocyanate,
30-60% acrylic polyol resin (EXP-A),
10-20% acetate solvent,
5-10% hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
3 20% aliphatic polyisocyanate and 3-glycidoxypropyltrimethoxy silane,
30-60% acrylic polyol resin (EXP-A),
10-20% acetate solvent,
5-10% hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
4 20% aliphatic polyisocyanate,
30-60% acrylic polyol resin (EXP-B),
10-20% acetate solvent,
5-10% hydrocarbon solvent
5 20% aliphatic polyisocyanate,
30-60% acrylic polyol resin (EXP-B),
10-20% acetate solvent,
5-10% hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
6 20% aliphatic polyisocyanate and 3-glycidoxypropyltrimethoxy silane,
30-60% acrylic polyol resin (EXP-B),
10-20% acetate solvent,
5-10% hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
7 20% aliphatic polyisocyanate,
30-60% acrylic polyol resin (EXP-C),
10-20% acetate solvent,
5-10% hydrocarbon solvent
8 20% aliphatic polyisocyanate,
30-60% acrylic polyol resin (EXP-C),
10-20% acetate solvent,
5-10% hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
9 20% aliphatic polyisocyanate and 3-glycidoxypropyltrimethoxy silane,
30-60% acrylic polyol resin (EXP-C),
10-20% acetate solvent,
5-10% hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
* In Exp No. 3, 6 and 9, addition of 0.5-5% polyester-modified polydimethylsiloxane has also been studied.
The respective acrylic polyol resin systems as mentioned in Table 1 comprise the following components as per Table 2:
Table 2
Acrylic Polyol resin (60%Solid) Formulation
EXP-A (100%) EXP-B (100%) EXP-C (100%)
Styrene
(From Shell Chemicals) 20-30 20-30 20-30
Methyl Methacrylate
(From BASF) 20-35 20-25 15-30
HEMA
(From Wanhua Chemical) 10-20 15-25 12-25
Acrylic Acid
(From BASF) 0.1-0.2 0.1-0.2 0.5-2
Butyl Acrylate
(From Mitsubishi Chemicals) 15-30 10-30 15-35

The coating compositions of Table 1 were evaluated for different parameters using the instruments/tests as explained below:

COATING THICKNESS GAUGE/TEST
Coating thickness gauge is the instrument used to measure the dry film thickness. Dry Coating measurement is a very crucial prospect as it defines a lot about the process, cost and quality. Apart from that, the performance can be estimated in different working environments. It is a non-destruction form of testing and can be used for on-site inspection.
SALT SPRAY TEST (SST)
Salt Spray Chamber is made as per ASTM B117 and JIS2371 which is used for conducting Natural Salt Spray Test or NSS test on Meta Surface Coatings. It is used for checking the resistance of the coating towards corrosive environment. The Salt Spray Tester generates an accelerated from of salt laden environment inside which the specimen is tested for its quality.
UV LIGHT ACCELERATED WEATHERING TEST
Polymer products usually get damaged when exposed to various environmental conditions which are formed from the atmosphere. This directly affects the actual life of the product. Hence, it is necessary to test the quality of the polymers under UV light accelerated weathering condition.
HUMIDITY CHAMBER
Humidity chamber is used for assessing the change in physical properties of materials when there is a severe change in environmental conditions like humidity.

CROSS-CUT & PULL-OFF TESTS
The cross-cut test is a method of determining the resistance of paints and coatings to separation from substrates by utilizing a tool to cut a right angle lattice pattern into the coating, penetrating all the way to the substrate.
IMPACT RESISTANCE TESTER
For tests on coatings for crack formation, breaking off, adhesion and elasticity, a bulge is formed in the sheet metal by a dropping a weight with a hemispherical end. The coating can be on the outside or on the inside of the bulge.
CONICAL BENDING MANDREL
It is an apparatus to bend coated test panels over a conical shaped mandrel in order to assess the elasticity or resistance of a coating paint or varnish to cracking, elongation and / or detachment from a metal.
The results obtained from the above investigations showed that, except for Exp. No. 9, the other compositions failed in one or more of parameters selected from Finish, Gloss, Adhesion Test, Flexibility (Conical Mandrel)-6mm, Impact, Acid resistance(0.1 N H2SO4) -24 hours, Alkali resistance(0.1 N NaOH) -24hours, Mild alcohol resistance-24hours, Soap resistance -24hours, Anti Yellowing (QUV) -500 hours, Anti Rust (SST) -Direct on MS 100 hours, Water Immersion, Stain Mark Test (Tea, Coffee, Mustard Sauce, Red Wine, Hot Water, Olive Oil) -24 hours, Disinfectant wipes test -30Days and Cold & Hot Temperature test (Freeze Thaw Resistance) (-5°C for 8 Hours and 30°C for 16 Hours)-30Cycle. Testing for these parameters was done on the basis of ASTM/IS methods as described.
To substantiate the above observations, Table 3 provides comparative results for the Exp. No. 3, 6 and 9.

Table 3
Parameters Exp-3 Exp-6 Exp-9
Finish
(IS:101 (Part 3/Sec-4-1987) OK OK OK
Gloss
(IS:101 (Part 4/Sec-4-1989) Not Ok Not Ok OK
Adhesion Test Result
(ASTM D3359-93) Passes on, MS, Tin,
Wood, FRP Passes on, MS,SS, Tin, FRP Passes on, MS,
Tin,
FRP,SS,GI, Al, ABS,
Glass,
Plated Substrate & Other Substrate
Flexibility (Conical Mandrel )-6mm
(ASTM D522-93a) PASS PASS PASS
Impact
(IS:101 (Part 5/Sec-3-1999) PASS PASS PASS
Acid resistance(0.1 N H2SO4) -24Hours
(ASTM D1308 – 02) PASS PASS PASS
Alkali resistance(0.1 N NaOH) -24 Hours
(ASTM D1308 – 02) PASS PASS PASS
Mild alcohol resistance-24 Hours
(ASTM D1308 – 02) FAIL FAIL PASS
Soap resistance -24 Hours
(ASTM D1308 – 02) FAIL FAIL PASS
Anti Yellowing (QUV) -500Hours
(ASTM G154) FAIL FAIL PASS
Anti Rust (SST) -Direct on MS 100Hours
(ASTM B117-73) FAIL FAIL PASS
Water Immersion
(IS:101 (Part 7/Sec-1-1989) FAIL FAIL PASS
Stain Mark Test (Tea, Coffee, Mustard Sauce, Red Wine, Hot Water, Olive Oil) -24Hours
(ASTM D3023-88) FAIL FAIL PASS
Disinfectant wipes test -30Days
(ASTM E2414-05) FAIL FAIL PASS
Cold & Hot Temperature test (Freeze Thaw Resistance) (-5°C for 8 Hours and 30°C for 16 Hours)-30Cycle
(ASTM D6944) FAIL FAIL PASS

Further for comparative study, following ingredients were compounded according to the compounding amount shown in Table 4 to prepare the coating composition, wherein commercially available resins ‘Idecryl 1069’ and ‘Synocure 867’ were used instead of Acrylic polyol resin of the present invention.
Table 4
Exp. No. Composition (Total weight being 100%)
I 20% aliphatic polyisocyanate,
30-60% Idecryl-1069,
10-15% acetate solvent,
5-10 % hydrocarbon solvent
II 20% aliphatic polyisocyanate,
30-60% Idecryl-1069,
10-15% acetate solvent,
5-10 % hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
III 20% aliphatic polyisocyanate,
2-5% 3-glycidoxypropyltrimethoxy silane,
30-60% Idecryl-1069,
10-15% acetate solvent,
5-10 % hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
IV 20% aliphatic polyisocyanate,
30-60% Synocure 867,
10-15% acetate solvent,
5-10 % hydrocarbon solvent
V 20% aliphatic polyisocyanate,
30-60% Synocure 867,
10-15% acetate solvent,
5-10 % hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
VI 20% aliphatic polyisocyanate,
2-5% 3-glycidoxypropyltrimethoxy silane,
30-60% Synocure 867,
10-15% acetate solvent,
5-10 % hydrocarbon solvent,
2-5% solution of a hydroxy-functional copolymer with acidic groups
* In Exp No. III and VI, addition of 0.5-5% polyester-modified polydimethylsiloxane has also been studied.
Composition I-VI (comparative) were also subject to the same abovementioned investigations, wherein all experiments failed in one or more of parameters selected from Finish, Gloss, Adhesion Test, Flexibility (Conical Mandrel)-6mm, Impact, Acid resistance(0.1 N H2SO4) -24 hours, Alkali resistance(0.1 N NaOH) -24hours, Mild alcohol resistance-24hours, Soap resistance -24hours, Anti Yellowing (QUV) -500 hours, Anti Rust (SST) -Direct on MS 100 hours, Water Immersion, Stain Mark Test (Tea, Coffee, Mustard Sauce, Red Wine, Hot Water, Olive Oil) -24 hours, Disinfectant wipes test -30Days and Cold & Hot Temperature test (Freeze Thaw Resistance) (-5°C for 8 Hours and 30°C for 16 Hours)-30 Cycle.
It is evident from Table 3 and 4, that it is the coating composition of Exp. No. 9 (as per present invention), which passes in all the test parameters (on all the surfaces) in comparison to the coating compositions of comparative examples 3, 6 and III, VI.
The coating composition as per present invention provides the advantage that it is suitable for a variety of substrates and still maintains the coating’s mechanical properties as well as, the overall visual appearance and adhesion strength.

Abbreviations:
HEMA : Hydroxyethylmethacrylate
MS : Mild Steel
SS : Stainless Steel
FRP : Fibre Reinforced Plastic
GI : Galvanized Iron
ABS : Acrylonitrile Butadiene Styrene
DTBP : Di-tert-butyl peroxide
TBPB : Tert.Butylperoxybenzoate
DTAP : Di(tert.-amyl)peroxide

General Preparation Method:

1) ACRYLIC POLYOL RESIN (Prepared by using Styrene, Methyl Methacrylate, HEMA, Acrylic Acid, and/or Butyl Acrylate):
Charged solvent in the glass reactor. Monomer and catalyst/ initiator like DTBP, TBPB, DTAP are added in a 5 litre glass beaker to prepare monomer mixture. 5 litre glass beaker is attached with peristaltic pump for uniform addition of monomer mixture. In glass reactor, to 1st neck is attached stirrer & to 2nd neck attach thermometer pocket, in 3rd neck peristaltic pump & to 4th one is attached dean & stark & glass condenser to reflux the solvent. Close the 5th hole of glass reactor and start stirring.
Start heating up to 135~140°C. Maintain temperature and add monomer mixture in 4~6hr. After complete monomer addition, hold reaction for 2~3hr at 135~140°C. After achieving the conversion, cool the reaction mass to room temp. Discharge the material through filter. Check the filtered sample for clarity.

2) TWO-COMPONENT POLYURETHANE COATING COMPOSITION:

Component A: Take acrylic polyol resin as prepared above in clean container under slow speed mixing. Add n-butyl acetate (BASF,
Her shine precision technology), methoxypropyl acetate, xylene and solution of a hydroxy-functional copolymer with acidic groups (Byk), slowly under stirring and mix for 10 minutes. Adjust viscosity by using n-butyl acetate. Do the filtration with 5 micron Cuno Filter for 3 hours. Check all quality parameters and transfer to packing section.

Component B: Mix hexamethylene diisocyanates (HDI) (Covestro chemicals) and 3-Glycidoxypropyltrimethoxy silane (Evonik) and then pack immediately with nitrogen punching.

,CLAIMS:A two-component polyurethane composition comprising:
- a polyisocyanate,
- an acrylic polyol resin; and
- a solution of a hydroxy-functional copolymer with acidic groups;
wherein the said acrylic polyol resin is 58-62 % solid.

2. The two-component polyurethane composition as claimed in claim 1, wherein the polyisocyanate is an aliphatic polyisocyanate.

3. The two-component polyurethane composition as claimed in claim 1, wherein the acrylic polyol resin comprises styrene, methylmethacrylate, hydroxyethylmethacrylate, acrylic acid and butyl acrylate.

4. The two-component polyurethane composition as claimed in claim 3, wherein the acrylic polyol resin is 60% solid and comprises 20-30% styrene, 15-30% methylmethacrylate, 12-25% hydroxyethylmethacrylate, 0.5-2% acrylic acid and 15-35% butyl acrylate, such that total weight of the acrylic polyol resin is 100%.

5. The two-component polyurethane composition as claimed in claim 3, wherein the acrylic polyol resin comprises 30% styrene, 22-23% methylmethacrylate, 16-17% hydroxyethylmethacrylate, 1.5% acrylic acid and 30 % butyl acrylate, such that total weight of the acrylic polyol resin is 100%.

6. The two-component polyurethane composition as claimed in claim 1, wherein the said coating composition further comprises solvent, polyester-modified polydimethylsiloxane and/or 3-glycidoxypropyltrimethoxy silane.

7. The two-component polyurethane composition as claimed in claim 6, wherein the solvent is an acetate solvent and/or a hydrocarbon solvent.

8. The two-component polyurethane composition as claimed in claim 1, 6 and 7, wherein the said coating composition comprises-
- 20% polyisocyanate and 3-glycidoxypropyltrimethoxy silane; and
- 30-60% acrylic polyol resin, 10-20% acetate solvent, 5-10 % hydrocarbon solvent, 2-5% solution of a hydroxy-functional copolymer with acidic groups and optionally 0.5-5% polyester-modified polydimethylsiloxane, such that total weight is 80%.

9. The two-component polyurethane composition as claimed in claim 1-8, wherein the aliphatic polyisocyanate comprises hexamethylene diisocyanate, pentamethylenediisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophoronediisocyanate and/or (m or p) TMXDI; acetate solvent comprises n-butyl acetate, methoxypropyl acetate or a mixture thereof and hydrocarbon solvent comprises o-, m-, or p- xylene or mixture thereof.

10. The two-component polyurethane coating composition as claimed in claim 1-9, wherein the said composition comprises a coating for substrates selected from aluminium, mild steel, stainless steel, tin, galvanized iron, plastics, wood, medium density fibre board, fibre reinforced plastic, glass or copper.