HK1090944A - Radiation curable coatings based on uretdione polyisocyanates - Google Patents

Description

Radiation-curable coatings based on uretdione polyisocyanates

Technical Field

The present invention relates to radiation curable coating compositions containing ethylenically unsaturated polyurethanes and substrates coated therewith.

Background

In the past, UV coatings were sold at 100% solids. Unfortunately, to achieve the desired performance properties, medium to high molecular weight acrylic functional oligomers with high viscosities have been developed. These materials are too viscous to be used alone and can only be formulated with reactive diluents, i.e. low molecular weight acrylates or methacrylates. These reactive diluents have a high risk of toxicity and are not ideal.

Recently, in order to reduce the reactive diluent content, solvents have been used to reduce the viscosity of the formulation, thereby reducing the need for large amounts of reactive diluent. In many cases, some reactive diluents are still used in order not to exceed the VOC limit and to moderate the film properties.

The market has continuously sought low viscosity oligomers to reduce the amount of reactive diluents and solvents. For example, U.S. Pat. No. 5,739,251 discloses one-component coating compositions containing ethylenically unsaturated polyisocyanates which contain allophanate groups and have i) an NCO content of 5 to 25% by weight, ii) a content of β, γ -ethylenically unsaturated ether groups introduced via allophanate groups of 0.5 to 15% by weight and iii) an allophanate group content of 1 to 30% by weight.

As another example, U.S. patent No. 5,777,024 discloses an allophanate-modified polyurethane resin formed by reacting an allophanate-modified isocyanurate with one or more hydroxy-functional olefinic compounds, which is useful in coating compositions curable by high energy radiation, including UV/visible light or electron beam radiation.

DE 2914982 discloses curable compositions comprising polyurethanes which are liquid at room temperature or solid at room temperature and can be melted at below 60 ℃ by reacting esters or polyesters containing hydroxyl end groups with difunctional and/or polyfunctional isocyanatoalkyl and/or isocyanatoaryl compounds and optionally subsequently with monofunctional isocyanatoalkyl and/or isocyanatoaryl compounds.

However, the above radiation curable coating compositions typically require large amounts of reactive diluents for coating and often provide films with insufficient toughness and/or poor softness. Thus, there is a need in the art for radiation curable coating compositions that require a relatively small amount of reactive diluent for coating and are capable of producing tough, flexible films.

Disclosure of Invention

The present invention provides a radiation curable coating composition comprising the reaction product of from about 5 to about 70 weight percent of:

i) one or more polyisocyanates in which at least 10 equivalent percent of the isocyanate groups are in the form of uretdione groups, and

ii) one or more hydroxy-functional lactone (meth) acrylates (a) having a number average molecular weight of from about 200 to about 2000 and having the formula:

CH₂＝C(R¹)-C(O)-O-R²-[O-C(O)-R³-]_n-OH

wherein n is an integer of 1 to 5,

R¹is hydrogen or a methyl group, or a mixture thereof,

R²represents an alkylene group or a substituted alkylene group having 2 to 10 carbon atoms, and which may be substituted by one or more alkyl groups having 1 to 12 carbon atoms, and

R³represents a linear or branched alkylene group of 3 to 8 carbon atoms, and which may be substituted by one or more alkyl groups having 1 to 12 carbon atoms, and

wherein the amount of component i) is substantially equal to the amount of hydroxyl equivalents of the hydroxyl-containing material in the composition, based on isocyanate equivalents.

The present invention also provides a method for preparing a coated substrate comprising coating at least a portion of a substrate with the above-described coating composition and subjecting the coated substrate to radiation.

The invention also relates to a substrate coated according to the above method.

Detailed Description

Other than in the operating examples, or where otherwise indicated, all numbers or expressions referring to components, reaction conditions, and so forth used in the specification and claims are to be understood as modified in all instances by the term "about".

In the present invention, it has now been found that the use of materials having a high level of uretdione can provide a polyurethane oligomer with low viscosity and which can provide a tough, flexible film when used in radiation curable coating compositions. Typically, the isocyanates of the present invention use a hydroxy functional acrylate as a coreactant. The resulting coating composition requires only a relatively small amount of reactive diluent for coating and is capable of producing tough, flexible films.

Acrylic functionality can be imparted to uretdiones by using hydroxy-functional acrylates according to the following structural formula:

wherein:

r is H or a methyl group, and R is H or a methyl group,

z is-C_nH_2nOH or

Wherein n is 2 to 10,

m is 2 to 8, and

p is 1 to 10.

-C_nH_2n-or-C_mH_2mThe aliphatic groups may be linear, branched or cyclic.

In one embodiment of the present invention, hydroxymethyl (meth) acrylate (HEA), hydroxypropyl (meth) acrylate (HPA), trimethylolpropane di (meth) acrylate, pentaerythritol tri (meth) acrylate, gamma (a (meth) acrylic acid adduct of glycidyl (meth) acrylate) may be used, which may include two isomers:

CH₂＝CH-C(O)-O-CH₂CH(OH)CH₂-O-C(O)-C(CH₃)CH₂

and

CH₂＝CH-C(O)-O-CH(CH₂OH)CH₂-O-C(O)-C(CH₃)CH₂

or polycaprolactone hydroxyethyl (meth) acrylate (PCHEA), but any hydroxy-functional (meth) acrylate described by the structure defined above may be used.

In one embodiment of the invention, PCHEA is used alone or in combination with other hydroxy-functional (meth) acrylates to give low viscosity materials.

In a more specific embodiment of the invention, PCHEA is TONE^*M100 (poly (. epsilon. -caprolactone) ester of 2-hydroxyethyl acrylate) available from DOW Chemical Corp., Midland MI.

In another embodiment of the invention, HEA or HPA is used as the only hydroxy-functional acrylate, but in some cases these materials tend to crystallize so that the resin cannot be used alone, but must be dissolved. Solvents may be used, which are typically ester, ether or hydrocarbon solvents. Particularly useful esters also have acrylic functionality, such as hexanediol diacrylate, which will allow the solution to be 100% reacted under UV/EB conditions.

Thus in the present invention, it has now been found that polyisocyanates, which are mixtures of uretdiones and other oligomers, provide low viscosity adducts with hydroxy functional acrylates. These materials can then be cured to provide a tough, flexible film.

The present invention provides a radiation curable coating composition. The composition comprises the reaction product of i) one or more polyisocyanates wherein at least 50 equivalent percent of the isocyanate groups are in the form of uretdione groups, and ii) one or more hydroxy-functional lactone esters of (meth) acrylate.

i) The reaction product of ii) and ii) may be prepared by reacting a polyisocyanate with a hydroxy-functional lactone (meth) acrylate in a suitable vessel, optionally in the presence of a free radical polymerization stabilizer, and optionally in the presence of a reaction catalyst. The reaction is carried out at a temperature sufficient for the reaction to occur within a reasonable period of time.

As used herein, the terms "(meth) acrylic acid" and "(meth) acrylate" are meant to include both acrylic acid derivatives and methacrylic acid derivatives, e.g., the corresponding alkyl esters are commonly referred to as acrylates and (meth) acrylates, and the term "(meth) acrylate" is meant to include both.

i) The polyisocyanate(s) in (a) is present in the composition of the present invention at a level of at least 5%, in some cases at least 10%, in other cases at least 15%, in some cases at least 20% and in other cases at least 25% by weight of the reaction product of i) and ii). Also, the polyisocyanate in i) is present in an amount up to 70 weight percent, in some cases up to 60 weight percent, in other cases up to 50 weight percent, and in some cases up to 40 weight percent of the reaction product of i) and ii). The polyisocyanate can be present in any amount or range between any of the amounts described above.

In the present invention, at least 10, in some cases at least 25, in other cases at least 50, in some cases at least 55, and in other cases at least 60 equivalent percent of the isocyanate groups in the polyisocyanate are present in the form of uretdione groups.

In one embodiment of the present invention, the isocyanate i) may be of the structure R⁴(NCO)₂Of isocyanates or derivatives thereofA compound containing a uretdione group from a compound according to the structure, wherein R⁴Denotes an aliphatic hydrocarbon residue having 4 to 12 carbon atoms, an alicyclic hydrocarbon residue having 6 to 15 carbon atoms, an aromatic hydrocarbon residue having 6 to 15 carbon atoms or an araliphatic hydrocarbon residue having 7 to 15 carbon atoms.

In one embodiment of the invention, the polyisocyanate comprises DESMODUR^*N3400, a polyisocyanate available from Bayer MaterialScience, Pittsburgh, PA.

In another embodiment of the invention, isocyanate i) comprises a uretdione dimer/isocyanurate trimer of hexamethylene diisocyanate, wherein the equivalent ratio of dimer to trimer is from 20: 80 to 80: 20, in some cases from 30: 70 to 70: 30, in other cases from 60: 40 to 40: 60, in some cases from 20: 80 to 60: 40, and in other cases from 40: 60 to 80: 20.

The one or more hydroxy-functional lactone (meth) acrylates (a) generally conform to the formula:

CH₂＝C(R¹)-C(O)-O-R²-[O-C(O)-R³-]_n-OH

wherein n is an integer from 1 to 10, sometimes from 1 to 5, in other cases from 1 to 4, in some cases 2 or 3, and in other cases from 2 to 4; r¹Is hydrogen or methyl; r²Represents an alkylene group or substituted alkylene group having from 2 to 10, sometimes from 2 to 6, and in other cases from 2 to 4 carbon atoms, and which may be substituted by one or more alkyl groups having from 1 to 12, sometimes from 1 to 8, and in other cases from 1 to 6 carbon atoms, and R³Represents a straight or branched chain alkylene group of 3 to 8, sometimes 3 to 6, and in other cases 4 to 6 carbon atoms, and which may be substituted by one or more alkyl groups having 1 to 12, sometimes 1 to 8, and in other cases 1 to 6 carbon atoms.

In one embodiment of the invention, the hydroxy-functional lactone (meth) acrylate has

n＝2，

R¹Is hydrogen or a methyl group,

R²is an alkylene group having 2 to 3 carbon atoms,

and

R³is a linear alkylene group of 3 to 5 carbon atoms.

The one or more hydroxy-functional lactone (meth) acrylates generally have a number average molecular weight (Mn) of at least 200, in some cases at least 250, and in other cases at least 300. Further, the Mn of the hydroxy-functional lactone (meth) acrylate can be up to 2,000, in some cases up to 1,500, in other cases up to 1,250, and in other cases up to 1,000.

The molecular weight values described in this application can be determined by gel permeation chromatography using polystyrene or sulfonated polystyrene standards. In the case of Mn, this value can alternatively be determined by titration of the functional groups using titration methods well known in the art.

In the present invention, the equivalent ratio of isocyanate groups in i) to hydroxyl groups in ii) may be from 1: 3 to 3: 1, sometimes from 1: 2 to 2: 1, and in other cases from 1: 1.5 to 1.5: 1. In one embodiment of the invention, the amount of component i) is substantially equal to the amount of hydroxyl equivalents of the hydroxyl-containing material in the composition, based on isocyanate equivalents.

In one aspect of the invention, component ii) may further comprise one or more hydroxy-functional (meth) acrylates (b) according to the following formula:

CH₂＝C(R¹)-C(O)-O-R²-OH

wherein R is¹And R²As defined above.

(a) The weight ratio of (a) to (b) can be at least 1: 10, in some cases at least 1: 7, in other cases at least 1: 6, in some cases at least 1: 5, in other cases at least 1: 3, and in some cases at least 1: 2. Also, the weight ratio of (a) to (b) can be up to 10: 1, in some cases up to 7: 1, in other cases up to 6: 1, in some cases up to 5: 1, in other cases up to 3: 1, and in some cases up to 2: 1. (a) The weight ratio of (a) to (b) may be any value or range between any of the above values.

The radiation curable coating composition of the present invention may also optionally include a reactive diluent. The reactive diluent may be present in the composition in an amount of from 0 to 40%, sometimes 0 to 25%, in other cases 0.1 to 40%, in some cases 0.5 to 35%, in other cases 1 to 35% and in some cases 1 to 25% by weight of the composition.

Any suitable reactive diluent may be used in the compositions of the present invention. Suitable reactive diluents include, but are not limited to, alkyl mono-, di-, tri-, and tetra (meth) acrylates wherein the alkyl group is an alkyl group of 1 to 8 carbon atoms.

The radiation curable coating compositions of the present invention may also optionally include a photoinitiator. The photoinitiator may be present in the composition in an amount of from 0 to 10 weight percent, sometimes 0.1 to 10 weight percent, in other cases 0.1 to 5 weight percent, in some cases 0.5 to 5 weight percent, in other cases 0.1 to 3 weight percent, and in some cases 0.1 to 2.5 weight percent of the composition.

Any suitable photoinitiator may be used in the compositions of the present invention. Suitable photoinitiators include, but are not limited to, monoacylphosphine oxide (MAPO), bisacylphosphine oxide (BAPO), α -hydroxy ketones, Benzildimethylketals (BDK), benzophenones and derivatives thereof, non-limiting examples being diphenoxybenzophenones, halo-and amino-functional benzophenones, 2-hydroxy-2-cresol-1-propanone, fluorenone derivatives such as 2, 2-diethoxyacetophenone, anthraquinone derivatives such as 2benzyl-2-N, N-dimethylamino-1- (4-morpholinophenyl) butanone, xanthone (zanthone) derivatives such as haloacetophenone, thioxanthone derivatives such as sulfonyl chlorides of aromatic compounds, camphorquinone, acylphosphine oxides, diacylphosphine oxides, benzyl, benzimidazole, benzoin ethers such as benzoin isopropyl ether, and hydroxyalkylphenones such as 1-phenyl-2-hydroxy-2-methylpropan-1-one. Suitable photoinitiators also include, but are not limited to, those under the trade name DAROCURE^*And IRGACURE^*Photoinitiators available from Ciba Specialty Chemicals corp., Tarrytown, NY.

The composition of the present invention may further comprise a solvent or a mixture of solvents. The solvent may be present in an amount of about 5 to about 95 weight percent, sometimes about 10 to about 85 weight percent, in other cases about 15 to about 75 weight percent, in some cases about 20 to about 70 weight percent, and in other cases about 25 to about 65 weight percent, based on the weight of the composition.

Non-limiting examples of suitable solvents that may be used in the curable coating composition include ether or hydrocarbon solvents, ester hydrocarbon solvents, non-limiting examples of which are butyl acetate, and those having acrylic functionality, non-limiting examples of which are hexanediol diacrylate, acetone, butanone, tetrahydrofuran, dioxane, acetonitrile, dipropylene glycol dimethyl ether, and 1-methyl-2-pyrrolidone.

In one embodiment of the present invention, a radiation curable composition comprises:

from about 15 to about 60 weight percent, sometimes from about 20 to about 55 weight percent, and in other cases from about 25 to about 50 weight percent of the reaction product of i) and ii);

from about 10 to about 25 weight percent, sometimes from about 12.5 to about 22.5 weight percent, and in other cases from about 15 to about 20 weight percent of a reactive diluent selected from the group consisting of alkyl mono-, di-, tri-, and tetra (meth) acrylates wherein alkyl is an alkyl of 1 to 8 carbon atoms;

about 3 to about 7 weight percent, sometimes about 3.5 to about 6.5 weight percent, and in other cases about 4 to about 6 weight percent of one or more photoinitiators as described above, and

about 0 to about 70 weight percent, sometimes about 20 to about 65 weight percent, in other cases about 40 to 65 weight percent, and in some cases about 50 to about 60 weight percent of a solvent or solvent mixture.

The composition of the present invention may further comprise other additives commonly used in coating compositions. Suitable additives include, but are not limited to, light stabilizers, UV absorbers, antioxidants, fillers, anti-settling agents, defoamers, wetting agents, flow control agents, thixotropic agents, reactive diluents, plasticizers, solvents, thickeners, pigments, dyes, matting agents, and combinations thereof.

The present invention also provides a method for preparing a coated substrate comprising coating at least a portion of a substrate with the above-described coating composition and subjecting the coated substrate to radiation for a time sufficient to cure the composition.

The coating composition can be used to coat any kind of substrate, such as wood, plastic, leather, paper, textiles, glass, ceramics, plaster, masonry, metal and concrete. It can be applied by standard methods such as spraying, knife coating, flow coating, dip coating, roll coating. The coating composition may be clear or pigmented.

After evaporation of any inert solvent used, the coating may be crosslinked by high energy radiation such as UV light, electron beam or gamma-ray, by heating to elevated temperatures in the presence of peroxides or azo compounds, or by curing with a metal salt of a drying acid (siccativacid) and optionally (hydro) peroxides at elevated temperatures or at room temperature or below. Photoinitiators are added to the coating composition when the coating is crosslinked by UV radiation.

When curing the coating composition at elevated temperatures, the curing must be carried out in the presence of from 0.1 to 10% by weight, sometimes from 0.1 to 5% by weight, based on the weight of the composition, of an initiator such as a peroxide or azo compound. The temperatures required to cure the coating composition at elevated temperatures are from 80 ℃ to 240 ℃ and sometimes from 120 ℃ to 160 ℃.

Suitable initiators include, but are not limited to, known free radical initiators, for example, aliphatic azo compounds such as azobisisobutyronitrile, azo-bis-2-methylpentanonitrile, 1 '-azo-bis-1-cyclohexanecarbonitrile, and alkyl 2, 2' -azo-bis-isobutyrate; symmetrical diacyl peroxides such as acetyl, propionyl or butyryl peroxide, benzoyl peroxide substituted with bromine, nitro, methyl or methoxy, and lauryl peroxide; symmetric peroxydicarbonates such as diethyl, diisopropyl, dicyclohexyl and dibenzoyl peroxydicarbonate; tert-butyl peroxy-2-ethylhexanoate and tert-butyl perbenzoate; hydroperoxides such as tert-butyl hydroperoxide and cumene hydroperoxide; and dialkyl peroxides such as dicumyl peroxide, t-butyl cumyl peroxide or di-t-butyl peroxide.

The coating composition according to the invention can also be cured at room temperature in the presence of a drier and optionally (hydro) peroxides. Suitable siccatives are known and include metal salts of acids such as flax oil fatty acid, tall oil fatty acid and soybean oil fatty acid, preferably cobalt or vanadium salts; resin acids such as abietic acid and naphthenic acid; acetic acid; isooctanoic acid; and inorganic acids such as hydrochloric acid and sulfuric acid. Cobalt and vanadium compounds which are soluble in the coating composition and act as siccatives are particularly suitable and include the salts of the above acids. The siccatives are generally used in the form of organic solutions in such amounts that the metal content is from 0.0005 to 1.0% by weight, preferably from 0.001 to 0.5% by weight, based on the weight of the ethylenically unsaturated polyurethane.

Examples of (hydro) peroxides include di-tert-butyl peroxide, benzoyl peroxide, cyclohexanone peroxide, methyl ethyl ketone peroxide, acetylacetone peroxide, dinonyl peroxide, di- (4-tert-butylcyclohexyl) -peroxydicarbonate, tert-butyl hydroperoxide, cumene hydroperoxide, 2, 5-dimethyl-hexane-2, 5-hydroperoxide and diisopropylbenzene-hydroperoxide. The (hydro) peroxides are preferably used in amounts of 1 to 10% by weight, based on the weight of the ethylenically unsaturated polyurethane.

In a particular embodiment, the resin is mixed with one or more photoinitiators and optionally diluted with a solvent. The formulation was applied to a substrate to form a wet film having a thickness of 1 to 15 mils. The wet film is then exposed to radiation for a period of time sufficient to cure the film.

In the process of the present invention, the radiation may be UV radiation, visible light, electron beam radiation or a combination thereof.

In many cases, the wavelength of the radiation is at least 300 nm. In some cases, the radiation has a wavelength of about 320 to about 450 nm.

The resulting coating film is a tough, flexible film. By way of non-limiting example, the pendulum hardness of the film coating provided by the present invention is at least 30 seconds, in some cases at least 33 seconds, and in other cases at least 35 seconds. The pendulum hardness of the cured coating film can be measured using ASTM D4366-95 (test method A), a standard test method for testing the hardness of organic coatings by the pendulum damping test using a Koenig hardness tester.

The invention also provides a substrate coated according to the above method.

The invention is further described with reference to the following examples. The following examples are merely illustrative of the present invention and are not intended to be limiting thereof. All percentages are by weight unless otherwise indicated.

Examples

Raw materials

Uretdione ═ DESMODUR^*N3400 polyisocyanate, available from Bayer MaterialScience, Pittsburgh, Pa. The uretdione dimer/isocyanurate trimer ratio was 60/40 equivalents/equivalent. Isocyanate equivalent weight 193.

PCHEA＝TONE^*M100 (poly (. epsilon. -caprolactone) ester of 2-hydroxyethyl acrylate), available from DOW ChemicalCorp., Midland MI. Hydroxyl equivalent weight 344.

HEA ═ hydroxyethyl acrylate. Hydroxyl equivalent weight 116.

HPA ═ hydroxypropyl acrylate. Hydroxyl equivalent weight 130.

Example 1

Uretdione adducts of PCHEA were prepared.

To a three liter round bottom flask equipped with stirrer, heater, dropping funnel and oxygen inlet was added 719 grams (3.7 equivalents) of Desmodur N3400 polyisocyanate, 1281 grams (3.7 equivalents) of PCHEA and 10 grams of butylated hydroxytoluene stabilizer. The mixture was stirred until homogeneous at which point 2 grams of dibutyltin dilaurate catalyst was added. The reaction mixture was then heated to 60 ℃ and held at that temperature for six hours, at which time no isocyanate was observed in the infrared absorption spectrum. The viscosity was 5175 mPasec and the density was 9.4 lbs/gal.

Example 2

Uretdione adducts of PCHEA were prepared.

To a two liter round bottom flask equipped with stirrer, heater, dropping funnel and oxygen inlet was added 360 grams (1.86 equivalents) of Desmodur N3400 polyisocyanate, 641 grams (1.86 equivalents) of PCHEA and 5 grams of butylated hydroxytoluene stabilizer. The mixture was stirred until homogeneous at which point 1 gram of dibutyltin dilaurate catalyst was added. The reaction mixture was then heated to 60 ℃ and held at that temperature for six hours, at which time no isocyanate was observed in the infrared absorption spectrum. The viscosity was 6094 mPasec and the density was 9.4 lbs/gal.

Example 3

Preparation of PCHEA and uretdione adducts of HEA.

To a two liter round bottom flask equipped with stirrer, heater, dropping funnel and oxygen inlet tube were added 405 grams (2.1 equivalents) of Desmodur N3400 polyisocyanate, 530 grams (1.54 equivalents) of PCHEA, 65 grams (0.56 equivalents) of HEA and 5 grams of butylated hydroxytoluene stabilizer. The mixture was stirred until homogeneous at which point 1 gram of dibutyltin dilaurate catalyst was added. The reaction mixture was then heated to 60 ℃ and held at that temperature for six hours, at which time no isocyanate was observed in the infrared absorption spectrum. The viscosity was 5720 mPasec and the density was 9.47 lbs/gal.

Example 4

Preparation of PCHEA and uretdione adducts of HEA.

To a two liter round bottom flask equipped with stirrer, heater, dropping funnel and oxygen inlet was added 419 grams (2.17 equivalents) of Desmodur N3400 polyisocyanate, 497 grams (1.45 equivalents) of PCHEA, 84 grams (0.72 equivalents) of HEA and 5 grams of butylated hydroxytoluene stabilizer. The mixture was stirred until homogeneous at which point 1 gram of dibutyltin dilaurate catalyst was added. The reaction mixture was then heated to 60 ℃ and held at that temperature for six hours, at which time no isocyanate was observed in the infrared absorption spectrum. The viscosity was 6310 mPasec and the density was 9.48 lbs/gal.

Example 5

Preparation of PCHEA and uretdione adducts of HEA.

To a five liter round bottom flask equipped with stirrer, heater, dropping funnel and oxygen inlet was added 1938 grams (10 equivalents) of Desmodur N3400 polyisocyanate, 2073 grams (6 equivalents) of PCHEA, 466 grams (4 equivalents) of HEA and 22 grams of butylated hydroxytoluene stabilizer. The mixture was stirred until homogeneous at which point 1 gram of dibutyltin dilaurate catalyst was added. The reaction mixture was then heated to 60 ℃ and held at that temperature for six hours, at which time no isocyanate was observed in the infrared absorption spectrum. The viscosity was 7300 mPasec and the density was 9.46 lbs/gal.

Example 6

Preparation of PCHEA and uretdione adducts of HEA.

To a five liter round bottom flask equipped with a stirrer, heater, dropping funnel and oxygen inlet tube was added 215.4 grams (1.12 equivalents) of Desmodur N3400 polyisocyanate, 230.3 grams (0.67 equivalents) of PCHEA, 52 grams (0.45 equivalents) of HEA and 2.5 grams of butylated hydroxytoluene stabilizer. The mixture was stirred until homogeneous at which point 0.25 grams of dibutyltin dilaurate catalyst was added. The reaction mixture was then heated to 60 ℃ and held at that temperature for six hours, at which time no isocyanate was observed in the infrared absorption spectrum. The viscosity was 5860 mPasec.

Example 7

Uretdione adducts of PCHEA and HPA were prepared.

To a five liter round bottom flask equipped with a stirrer, heater, dropping funnel and oxygen introduction tube was added 213 grams (1.1 equivalents) Desmodur N3400 polyisocyanate, 227.5 grams (0.66 equivalents) PCHEA, 57.4 grams (0.44 equivalents) HPA and 2.5 grams butylated hydroxytoluene stabilizer. The mixture was stirred until homogeneous at which point 0.25 grams of dibutyltin dilaurate catalyst was added. The reaction mixture was then heated to 60 ℃ and held at that temperature for six hours, at which time no isocyanate was observed in the infrared absorption spectrum. The viscosity was 7150 mPasec.

Example 8

Preparation of PCHEA and uretdione adducts of HEA.

To a two liter round bottom flask equipped with stirrer, heater, dropping funnel and oxygen inlet was added 565 grams (2.93 equivalents) of Desmodur N3400 polyisocyanate, 144 grams (0.42 equivalents) of PCHEA, 291 grams (2.5 equivalents) of HEA and 5 grams of butylated hydroxytoluene stabilizer. The mixture was stirred until homogeneous at which point 0.1 grams of dibutyltin dilaurate catalyst was added. The reaction mixture was then heated to 60 ℃ and held at that temperature for six hours, at which time no isocyanate was observed in the infrared absorption spectrum. The viscosity was 13,600 mPasec and the density was 9.48 lbs/gal.

Formulation, curing procedure and testing

The resin was mixed with 5phr (by weight) of photoinitiator DAROCURE^*4265(Ciba specialty Chemicals Corp., Tarrytown, N.Y.) and 1phr (by weight) of photoinitiator IRGACURE^*184(Ciba Specialty Chemicals corp.,). The formulation was mixed until homogeneous and diluted to 85% solids with butyl acetate. The formulations were formed into thin films on double-sided cold rolled steel panels for MEK double rub evaluation and glass panels for bob hardness evaluation using a 4 mil wet film thickness draw bar. Flash all plates for 30 seconds after draw and at H&S Autoshot 400A low-intensity UVA lamp (H)&SAutoshot, Georgetown, ON) was cured for two minutes with a 10 inch lamp spacing.

MEK double rubs were performed using a two pound bullnose hammer covered with several layers of cheesecloth. Cheesecloth was saturated with MEK. An MEK soaked hammer was placed on the coated surface such that the hammer was at a 90 ° angle to the surface. Without applying downward pressure, the hammer was pushed back and forth over an approximately 4 "long area of the coating. One forward and one backward operation is counted as one double rub. After every twenty-five double rubs, the cloth was soaked with MEK. The end point is the time when the hammer breaks through the substrate to the surface of the board.

Pendulum hardness was determined using ASTM D4366-95 (test method A), a standard test method for determining organic coating hardness by the pendulum damping test using a Koenig hardness tester.

EXAMPLES coating	A	B	C	D	E	F	G
								Example resins	1	2	3	4	5	6	8
Component (equivalent ratio) uretdione PCHEAHEA	1.01.00.0	1.01.00.0	3.02.20.8	3.02.01.0	3.01.81.2	3.01.81.2	7.01.06.0
								Performance MEK double friction pendulum hardness (sec)	4236	4531	3542	3041	3038	3536	10043

The data demonstrate that the radiation curable coating compositions of the present invention have desirable viscosities and can provide tough, flexible films without the need for excessive amounts of reactive diluents.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (24)

1. A radiation curable coating composition comprising the reaction product of about 5 to about 70 weight percent of

i) One or more polyisocyanates in which at least 10 equivalent percent of the isocyanate groups are in the form of uretdione groups, and

ii) one or more hydroxy-functional lactone (meth) acrylates (a) having a number average molecular weight of from about 200 to about 2000 and having the formula:

CH₂＝C(R¹)-C(O)-O-R²-[O-C(O)-R³-]_n-OH

wherein n is an integer of 1 to 5,

R¹is hydrogen or a methyl group,

R²represents an alkylene group or a substituted alkylene group having 2 to 10 carbon atoms, and which may be substituted by one or more alkyl groups having 1 to 12 carbon atoms, and

R³represents a linear or branched alkylene group of 3 to 8 carbon atoms, and which may be substituted by one or more alkyl groups having 1 to 12 carbon atoms, and

wherein the amount of component i) is substantially equal to the amount of hydroxyl equivalents of the hydroxyl-containing material in the composition, based on isocyanate equivalents.

2. The composition according to claim 1, wherein ii) further comprises one or more hydroxy-functional (meth) acrylates (b) according to the formula:

CH₂＝C(R¹)-C(O)-O-R²-OH

wherein R is¹And R²As defined above.

3. The composition according to claim 1 further comprising from 0 to about 40 weight percent of one or more reactive diluents selected from the group consisting of alkyl mono-, di-, tri-, and tetra (meth) acrylates wherein the alkyl group is an alkyl group of from 1 to 8 carbon atoms.

4. The composition of claim 1 further comprising from about 0.1 to about 10 weight percent of one or more photoinitiators.

5. The composition of claim 1 further comprising from about 5 to about 95 weight percent of a solvent or solvent mixture, based on the weight of the composition.

6. The composition of claim 2 wherein the weight ratio of (a) to (b) is from about 1: 10 to about 10: 1.

7. The composition of claim 1, comprising:

about 15 to about 60 weight percent of the reaction product of i) and ii),

from about 10 to about 25 weight percent of a reactive diluent selected from the group consisting of alkyl mono-, di-, tri-, and tetra (meth) acrylates wherein the alkyl group is an alkyl group of 1 to 8 carbon atoms,

about 3 to about 7 weight percent of one or more photoinitiators, and

about 40 to about 70 weight percent of a solvent or solvent mixture.

8. The composition of claim 1 wherein said isocyanate i) may be of the structure R⁴(NCO)₂Or a compound containing uretdione groups derived from a compound of said structure, wherein R⁴Denotes an aliphatic hydrocarbon residue having 4 to 12 carbon atoms, an alicyclic hydrocarbon residue having 6 to 15 carbon atoms, an aromatic hydrocarbon residue having 6 to 15 carbon atoms or an araliphatic hydrocarbon residue having 7 to 15 carbon atoms.

9. The composition of claim 1 wherein the isocyanate i) is a uretdione dimer/isocyanurate trimer of hexamethylene diisocyanate wherein the equivalent ratio of dimer to trimer is from 20: 80 to 80: 20.

10. The composition of claim 1 wherein the hydroxy-functional lactone (meth) acrylate has

n＝2，

R¹Is hydrogen or a methyl group,

R²is an alkylene group having 2 to 3 carbon atoms,

R³is a linear alkylene group of 3 to 5 carbon atoms.

11. A method for preparing a coated substrate comprising coating at least a portion of a substrate with a coating composition and subjecting the coated substrate to radiation for a time sufficient to cure the composition, wherein the coating composition comprises:

about 5 to about 70 weight percent of the reaction product of:

i) one or more polyisocyanates in which at least 50 equivalent percent of the isocyanate groups are in the form of uretdione groups, and

ii) one or more hydroxy-functional lactone (meth) acrylates (a) having a number average molecular weight of from about 200 to about 2000 and having the formula:

CH₂＝C(R¹)-C(O)-O-R²-[O-C(O)R³-]_n-OH

wherein

n is an integer of 1 to 5 and,

R¹is hydrogen or a methyl group,

R²represents an alkylene group or a substituted alkylene group having 2 to 10 carbon atoms, and which may be substituted by one or more alkyl groups having 1 to 12 carbon atoms, and

R³represents a linear or branched alkylene group of 3 to 8 carbon atoms, and which may be substituted by one or more alkyl groups having 1 to 12 carbon atoms, and

wherein the amount of component i) is substantially equal to the amount of hydroxyl equivalents of the hydroxyl-containing material in the composition, based on isocyanate equivalents.

12. The method according to claim 11, wherein ii) further comprises one or more hydroxy-functional (meth) acrylates (b) according to the following formula:

CH₂＝C(R¹)-C(O)-O-R²-OH

wherein R is¹And R²As defined above.

13. The method according to claim 11, wherein the coating composition further comprises from 0 to about 40 weight percent of one or more reactive diluents selected from the group consisting of alkyl mono-, di-, tri-, and tetra (meth) acrylates wherein the alkyl group is an alkyl group of from 1 to 8 carbon atoms.

14. The method of claim 11, wherein the coating composition further comprises from about 0.1 to about 10 weight percent of one or more photoinitiators.

15. The method of claim 11, wherein the coating composition further comprises about 5 to about 95 weight percent of a solvent or solvent mixture, based on the weight of the composition.

16. The process according to claim 12, wherein the weight ratio of (a) to (b) is from about 1: 10 to about 10: 1.

17. The method according to claim 11, wherein the coating composition comprises:

about 15 to about 60 weight percent of the reaction product of i) and ii),

from about 10 to about 40 weight percent of a reactive diluent selected from the group consisting of alkyl mono-, di-, tri-, and tetra (meth) acrylates wherein the alkyl group is an alkyl group of 1 to 8 carbon atoms,

about 3 to about 7 weight percent of one or more photoinitiators, and

about 40 to about 70 weight percent of a solvent or solvent mixture.

18. The process of claim 11 wherein the isocyanate i) may be of the structure R⁴(NCO)₂Or compounds derived from said structural compounds containing uretdione groups, in which R⁴Denotes a residue of an aliphatic hydrocarbon having 4 to 12 carbon atoms, a residue of an alicyclic hydrocarbon having 6 to 15 carbon atoms, a residue of an aromatic hydrocarbon having 6 to 15 carbon atoms or a residue of an araliphatic hydrocarbon having 7 to 15 carbon atoms.

19. The process according to claim 11 wherein the isocyanate i) is a uretdione dimer/isocyanurate trimer of hexamethylene diisocyanate, wherein the equivalent ratio of dimer to trimer is from 50: 50 to 70: 30.

20. The method according to claim 11, wherein the hydroxy-functional lactone (meth) acrylate has

n＝2，

R¹Is hydrogen or a methyl group,

R²is an alkylene group having 2 to 3 carbon atoms,

R³is a linear alkylene group of 3 to 5 carbon atoms.

21. The method according to claim 11, wherein the radiation is selected from the group consisting of UV radiation, visible light and electron beam radiation.

22. The method of claim 21, wherein the radiation has a wavelength of at least 300 nm.

23. The method of claim 21, wherein the radiation has a wavelength of about 320 to about 450 nm.

24. A substrate coated according to the method of claim 11.