WO1998045348A1

WO1998045348A1 - Low voc acrylic polymer blocked isocyanate coating systems and a process for their preparation

Info

Publication number: WO1998045348A1
Application number: PCT/EP1998/002142
Authority: WO
Inventors: Scott E. Smyth
Original assignee: Cook Composites And Polymers Company; Cray Valley S.A.
Priority date: 1997-04-04
Filing date: 1998-04-06
Publication date: 1998-10-15

Abstract

Low VOC and HAPS-free coating systems are described which comprise (i) at least one blocked isocyanate, e.g. the reaction product of isophorone diisocyanate and ethanol, (ii) one or more containing acrylic polymers containing hydroxy or epoxy functionality, e.g. a polymer made from ethyl acrylate, hydroxyethyl acrylate and styrene, and (iii) water, or water and a resin, or a solvent, e.g. tripropylene glycol. These coating systems are prepared by (i) blocking the isocyanate, (ii) removing excess blocking agent, if any, and (iii) polymerizing the monomers to form the acrylic polymer in the presence of the blocked isocyanate. Urethane catalysts promote the cure of the coating systems.

Description

LOW VOC ACRYLIC POLYMER BLOCKED ISOCYANATE COATING SYSTEMS AND A PROCESS FOR THEIR PREPARATION

This invention relates to protective coating systems. In one aspect, the invention relates to coating systems that exhibit low volatile organic compound ("VOC") and/or hazardous air polluting system ("HAPS") -free emissions while in another aspect, the invention relates to the preparation of such coating systems by dispersing the reaction product of a blocked isocyanate and one or more acrylic polymers in water or water containing a resin. In another aspect of this invention, the reaction product of the blocked isocyanate and acrylic polymer is mixed with a reactive or non reactive solvent to form a high solids coating system.

The ever growing and increasingly stringent occupational and environmental regulations have caused the manufacturers and users of coating systems to develop and use systems with reduced VOC and HAPS emissions. Typically these systems comprise resins dispersed within solvents that upon cure by any mechanisms, e.g. heat, radiation, etc ., rapidly form highly crosslinked polymeric structures with the evolution of solvent and residual monomer (the VOC's and HAPS's). Ideally, as little solvent as possible is used and as much crosslinking as possible is effected to minimize the total VOC's and HAPS's. While many of the commercially available resins on the market today exhibit low VOC's and HAPS's, a demand still exists for coating systems that exhibit near zero or essentially non detectible levels of VOC's and/or HAPS's.

According to one embodiment of this invention, low VOC and/or HAPS-free coating systems comprise (i) at least one blocked isocyanate, (ii) at least one acrylic polymer, (iii) water, (iv) optionally and preferably, a urethane catalyst. In another embodiment of this invention, the systems comprise (i) at least one blocked isocyanate, (ii) at least one acrylic polymer, (iii) a solvent, (iv) at least one resin, and (v) optionally and preferably, a urethane catalyst. The coating systems of this invention are prepared by a process comprising the steps of (i) reacting by contacting an isocyanate and a blocking compound, (ii) removing excess blocking compound, if any, from the resulting blocked isocyanate, (iii) adding one or more hydroxy or epoxy functional acrylic monomers to the blocked isocyanate, and then polymerizing these monomers to form an acrylic polymer, (iv) mixing the resulting reaction product with either (a) water or water and a resin, or (b) a solvent or a solvent and a resin, and (v) optionally and preferably adding a urethane catalyst to the mixture of (iv) .

As here used, "low VOC" means vaporous emissions of volatile organic compounds as measured by ASTM 24 of less than about 419,4 kg/m (3.5 pounds per gallon, lb/gal), preferably less than about 239,7 kg/m (2 lb/gal) and more preferably less than about 59,9 kg/m (0.5 lb/gal). As here used, "HAPS-free" means vaporous emissions of hazardous air

3 polluting compounds of less than about 419,4 kg/m ,³

(3.5 lb/gal), preferably less than about 239,7 kg/m.3~ (2 lb/gal) and more preferably less than 59,9 kg/m³ (about 0.5 lb/gal) .

The isocyanate compound must have at least one functional group (NCO) preferably at least two functional groups (polyfunctional and typically referred to as a polyisocyanate) , and it must be capable of reacting with the blocking compound. Examples of suitable isocyanate compounds include tetramethylxylene isocyanate, 2,4- and 2,6-toluene diisocyanate (TDI) , 4,4 ' -diphenylmethylene diisocyanate (MDI) , polymethylene polyphenyl isocyanate (PMPPI) , dianisidine diisocyanate, metaphenylene diisocyanate, isophorone diisocyanate (IPDI) , hexamethylene diisocyanate (HDI) , urethanes, biurets, isocyanurates and mixtures of any two or more of these compounds. The preferred isocyanates are liquefied IPDI, HDI or biurets of HDI because of their low viscosity, ease of handling, and relatively low cost.

Any compound which (i) is capable of reacting with an isocyanate group (NCO) in such a manner as to effectively render the group non-reactive with the starting materials of an acrylic polymerization, (ii) is essentially non-reactive itself, after it has reacted with an isocyanate group, with the starting materials of an acrylic polymerization, and (iii) will not readily deblock (i.e. the reaction is not easily reversed) from the isocyanate group when exposed to heat or a free radical initiator (i.e. under the conditions required for acrylic polymerization) . Typically, these blocking compounds (also referred to as blocking agents) are monohydroxyl compounds and representative of these compounds are those illustrated by the formula :

R¹ (0R")_aOH

in which R' is hydrocarbyl such as alkyl, cycloalkyl, aryl, aralkyl, alkaryl, etc ., preferably containing up to 18, and more preferably containing four or less, carbon atoms ; R" is an alkylene radical, preferably of two to four carbon atoms ; and a is an integer of 0 to 18 , preferably of 0 to 2. Illustrative monohydroxyl blocking compounds include the alkanols, e.g. methanol, ethanol, isopropanol, n-butanol, 2- ethylhexanol , dodecanol, and the like ; the monoalkyl ethers of glycols and polyglycols, e.g., 2-ethoxyethanol, 2- propoxyethanol , 2-butoxyethanol, the monoethyl ethers of diethylene glycol, triethylene glycol and tripropylene glycol, and the like ; the onopropyl ethers of polyethylene glycol, polypropylene glycol and polybutylene glycol ; and the alkylene oxide adducts of substituted and unsubstituted phenols, e.g., the ethylene oxide and/or propylene oxide adducts of alkylphenols such as nonylphenol. Other blocking compounds include oximes, e.g. methyl ethyl ketoxime, acetone oxi e, cyclohexyl oxi e, and the like ; lactams, e.g. ?- caprolactam, etc. ; alkanolamines, e.g. diethylethanolamine, diethanolmethylamine, etc. ; phenols and malonic diesters. The choice of blocking compound is usually determined by the desired properties of the coating or film and the curing conditions (e.g. baking temperature) employed. The isocyanate groups are blocked by reacting by contacting, preferably in the absence of a catalyst, the isocyanate compound with a stoichio etric amount, typically with a slight excess of a stoichiometric amount, e.g. an excess of about 5 to about 30, preferably about 8 to 15, mole percent of blocking compound at a temperature and at other reaction conditions under which the blocking reaction can proceed to completion (all of which are well known in the art) . The minimum temperature for the blocking reaction is typical at least about 35, preferably at least about 60 and more preferably at least about 80°C, while the maximum temperature typically is not in excess of about 150, preferably not in excess of about 120 and more preferably not in excess of 110 °C. The pressure at which the blocking reaction is conducted can vary to convenience, but it is preferably at or slightly in excess of atmospheric pressure. The reaction is conducted with sufficient agitation to insure complete mixing of the reactants and a relatively uniform temperature throughout the reaction mass, and the exotherm from the reaction is controlled by any conventional means, e.g. metered addition of the isocyanate to the blocking agent, the use of a cooling apparatus, etc.

The blocked isocyanate is then used as a solvent, i.e. a reaction media, for the preparation of the acrylic polymer. Traditionally, solvents such as the glycol ethers, acetates, glycol ether acetates, ketones, and aromatic and aliphatic compounds were used, but these solvents contributed to the VOC's and/or HAPS's of the coating systems. Sufficient blocked isocyanate is used such that an equivalents ratio of isocyanate functionalities on the blocked isocyanate to the hydroxy or epoxy groups on the finished acrylic polymer product is between about 1:1 to about 4:1, preferably between about 1:1 to about 3:1, and more preferably between about 1:1 and about 1:2. The monomers used to prepare the acrylic polymer include a wide class of hydroxy or epoxy functional ethylenically unsaturated monomers, and particularly useful members of this class are the acrylic polymers which are well established for the production of coatings in the automobile industry, e.g. hydroxy or epoxy functional polymers or copolymers of one or more alkyl esters of acrylic acid or methacrylic acid, optionally together with other ethylenically unsaturated monomers. These polymers may be of either the thermoplastic type or the thermosetting, crosslinking type. Suitable hydroxy or epoxy functional polymers are obtained from monomers including acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, 2- hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, allyl alcohol, allyl alcohol propoxylate, glycidyl acrylate and glycidyl methacrylate.

The acrylic polymerization is promoted with the use of known vinyl polymerization catalysts, and these catalysts include peroxides, persulfides, perborates, percarbonates, and azo compounds or any other suitable catalyst capable of catalyzing the vinyl polymerization of the acrylic monomer, e.g. methyl methacrylate, and/or the ethylenically unsaturated monomer, e.g. styrene. Illustrative of a few such catalysts are benzoyl peroxide (BPO) , tertiarybutyl-peroxybenzoate, 2,2' -azo-bis-isobutyronitrile, lauryl peroxide, di-tertiarybutylperoxide, diisopropyl peroxide carbonate, tertiarybutylperoxy-2-ethylhexanoate, and the like. These catalysts are typically used at levels ranging from a minimum of about 0.5, preferably of about 1, to a maximum of about 10.0, preferably about 3, parts per hundred parts of monomers (pphr) .

Promoters for the vinyl polymerization can also be used in combination with vinyl polymerization peroxide catalysts to control the rate of free radical initiation. Suitable promoters for use with peroxide catalysts, e.g. BPO, include N,N-diethylaniline, N,N-dimethyl paratoluidine, other tertiary aromatic amines, and the like. The acrylic polymerization is conducted using known techniques and conditions, e.g. it is typically conducted at a temperature of at least about 50, preferably at least about 120 and more preferably at least about 150 °C and preferably at a temperature not in excess of about 200, preferably not in excess of about 175 and more preferably not in excess of 165 °C. The pressure at which the polymerization is conducted can vary to convenience, but it is preferably at or slightly in excess of atmospheric pressure. The polymerization can be performed on a batch, semi-continuous or continuous basis and depending upon the nature of the monomers, in the presence or absence of an inert atmosphere, e.g. a nitrogen blanket. In those instances in which the isocyanate is an aromatic or an amine functionality is present, the use of an inert atmosphere is preferred to promote better color since upon exposure to oxygen aromatic isocyanates tend to yellow and amines tend to darken. Prior to polymerization, the blocked isocyanate is typically and preferably stripped of any unreacted blocking agent by any conventional means, e.g. heat distillation, vacuum stripping, etc.

In one embodiment, the resulting product of the acrylic polymerization comprises acrylic polymer and blocked isocyanate which is then mixed, e.g. dissolved, dispersed, emulsified, etc., in water, optionally containing a resin. In another embodiment, the acrylic polymerization product is mixed with water and a resin. The acrylic polymerization product, water and resin can be mixed in any order, but preferably the water and resin are first mixed and then the water resin mix is added to the acrylic polymerization product.

The amount of water used to make the mixture can vary widely, but usually the minimum amount of water is at least about 10, preferably at least about 40 and more preferably at least about 60, percent by weight based on the total weight of the mixed composition, and usually the amount of water is not in excess of about 90 percent, preferably not in excess of about 80 and more preferably not in excess of about 70, weight percent. The less water that is present, the better for building film or coating thickness, and thus the less need for recoating.

While ordinary tap water is usually suitable for making the mixture, water of high hardness is usually undesirable. Some cations, particularly iron, if present in the mixing water may cause a decrease in stability of the mixture (particularly if the mixture is an emulsion) and/or adversely affect the physical and/or chemical stability of the coating. Deionized or distilled water is preferred. In the making of the mixture, the resin is typically first neutralized with a neutralizing agent to the extent that the resin contains one or more functionalities which would otherwise ionize upon mixing with water. If the functionality is acid in nature, then an appropriate amount of a suitable base, e.g. an amine, is added to and well mixed with the polymer before mixing the polymer with water. For example, if the acrylic polymer contained an amine functionality, then a neutralizing amount (e.g. stoechiometric or a slight stoichiometric excess) of a suitable acid, e.g. lactic acid, is first added to and well mixed with the polymer before the polymer is mixed with the water. Usually, the polymer is added to the water, and the addition is done slowly with high shear agitation.

If an emulsion is desired, then agitation is continued until an emulsion, usually milky in appearance, is formed. As here used, "high shear" means sufficient shear to form a stable emulsion from the materials at hand. The actual shear necessary to create an emulsion will be dependent upon such variables as the nature and concentrations of the various components, the blade and container configurations, and similar such considerations familiar to those skilled in the art.

In another embodiment, the acrylic polymerization product is mixed in any suitable solvent to produce a high (e.g. 838,8 kg/m or more or 7 or more lb/gal of resin) solids coating system. "Suitable solvents" are those that will reduce the viscosity of the acrylic polymerization product to that needed for a particular application, e.g. spraying, dipping, electrodeposition, etc. The solvent can be either reactive, e.g. it will react with either the acrylic polymer or the deblocked isocyanate during the cure, or non-reactive, i.e. it will not react with either the acrylic polymer or the deblocked isocyanate during the cure. Representative solvents include methyl ethyl ketone, methyl amyl ketone, butyl acetate, tripropylene glycol, diethylene glycol, glycerine, hydroxy or epoxy functional monomers such as hydroxypropyl acrylate, and the like.

The amount of solvent used to make the mixture can vary widely, but usually the minimum amount of solvent is at least about 10, preferably at least about 30 and more preferably at least about 50, percent by weight based on the total weight of the mixed composition, and usually the amount of solvent is not in excess of about 90 percent, preferably not in excess of about 70 and more preferably not in excess of about 65, weight percent. The less solvent that is present, the better for building film or coating thickness, and thus the less need for recoating.

The optional resin (s) used in practice of this invention include any of those well known in the coating industry, e.g. the polyesters, polyethers, alkyds, etc., such as those described in "Surface Coatings" by S. Paul (Wiley- Interscience, New York, 1985) , "Polyesters and their Applications", Bjorksten Research Laboratories (Reinhold, New York, 1956), "Polyethers" by N.G. Gaylord (ed.) (Part 1, Wiley-Interscience, New York, 1963), and "Alkyd Resins" by CR. Martens (Reinhold, New York, 1961) . Typically, these resins readily react with one or both of the acrylic polymer and deblocked isocyanate during the cure of the coating system. The amount, if any, and nature of the resin used in the coating systems of this invention can vary to convenience, and these considerations are usually determined by the desired properties of the coating.

During the cure of the coating system, the isocyanate is deblocked and the blocking agent is either or both emitted as a gas or remains in the coating. Depending upon the blocking agent, the end use of the coating and many other factors, the released blocking agent can serve various purposes. In those instances in which flexibility is a desirable property of the coating, some blocking agents can act as a plasticizer. Other blocking agents, e.g. glycol ethers, have a leveling effect, i.e. they promote the smooth flow of the coating during cure.

Since the cure of the coating systems (regardless whether solvent or aqueous based) involves the formation of urethane linkages (NCOO) , the cure process is promoted by catalysts that promote the formation of urethane bonds and, preferably, also promote the deblocking of the isocyanate. Representative catalysts include (a) tertiary amines such as N,N-dimethylcyclohexylamine, (b) tertiary phosphines such as trialkylphosphines, (c) strong bases such as alkali and alkaline earth metal hydroxides and phenoxides, (d) acidic metal salts of strong acids such as ferric chloride, (e) organo-tin compounds such as dibutyl tin dilaurate, and (f) cyclic amines such as 1, 5-diazabicyclo(5.5.0)undec-5-ene. Other commonly used catalysts for making polyurethanes are described in USP 4,280,979 and 4,598,103 both of which are here incorporated by reference. These catalysts can be used alone or in combination with one another, and are used in a catalytic amount, e.g. between about 0.1 and 2, preferably between about 0.5 and 1, weight percent based on the total weight of the acrylic polymerization product.

In another embodiment of this invention, the mixture of acrylic polymerization product and (i) water, or (ii) water and a resin, or (iii) solvent, or (iv) solvent and a resin, can contain one or more a,b-ethylenically unsaturated monomers which can crosslink with the deblocked isocyanate and/or acrylic polymer or self-polymerize through thermally or ultraviolet light induced free radical polymerization during cure. The presence of such monomers provide a high solids, dual-curing coating system. If present, the concentration of these monomers is usually less than about 30, preferably less than about 10 and more preferably less than about 5, weight percent based upon the total weight of the mixture, and the vinyl crosslinking is promoted with one or more free radical initiators, e.g. a catalytic amount of a peroxide. Illustrative monomers include the mono-, di- and trifunctional acrylic and methacrylic esters, glycidyl acrylates and methacrylates, N-vinyl-2-pyrrolidone, N-methacrylamide, the hydroxyalkyl esters of acrylic and methacrylic acid, and aromatic vinyl and divinyl compounds, e.g. styrene. If these monomers are present at all, then unsaturated monomers with relatively low volatility under process conditions, such as the polyfunctional acrylic and methacrylic esters, are preferred. Illustrative free radical initiators include benzoyl peroxide, tertiarybutylperoxybenzoate, 2, 2 ' -azo-bis- isobutyronitrile, lauryl peroxide, di-tertiarybutylperoxide, diisopropyl peroxide carbonate, tertiarybutylperoxide-2- ethylhexanoate, and the like.

The coating systems of this invention can be applied to a wide array of substrates, e.g. metal, plastic, ceramic, wood, etc. , in any conventional manner, e.g. electrodeposition, spraying, drawing, dipping, powder coatings, and the like. Cure can be effected under ambient conditions or promoted with heat, light, etc.

The following examples are illustrative of certain embodiments of this invention. Unless indicated to the contrary, all parts and percentages are by weight.

Example 1

Preparation of a Blocked Isocyanate

Isophorone diisocyanate (IPDI, 500 g) is placed in an addition funnel which is attached to a one liter resin kettle charged with anhydrous ethanol (285 g) . The temperature of the resin kettle is gradually increased to 80°C at which time the addition of the IPDI to the ethanol begins. The IPDI is added to the ethanol at a constant rate, and the addition is completed at the end of five hours. At that time, the temperature of the resin kettle is 120 °C and the reaction product is clear and of low viscosity. One hour after, the last of the IPDI is added to the resin kettle, a sample of the reaction product is analyzed for free isocyanate using ASTM D 1638. The percent of free isocyanate is usually less than 0.5 weight percent (based on the total weight of the reaction product) .

The blocked isocyanate is then tested for the stability or propensity of the ethanol to deblock from the isocyanate, i.e. the propensity of the urethane linkage formed by the reaction of the isocyanate and ethanol to break. Three

1-gram samples of the product are placed in an oven preheated to 165 "C. Another three 1-gram samples are mixed with two weight percent (based on the weight of the blocked isocyanate) of dicumyl peroxide and placed in the same oven. One sample without the peroxide and one sample with the peroxide are removed at 1, 3.5 and 6.5 hours after placement in the oven, and these samples are then cooled and measured for free isocyanate by both Fourier Transform Infrared Spectroscopy

(FTIR) and ASTM D 1638. For each sample, deblocking of the ethanol from the isocyanate is not detected.

Upon cooling to room temperature, the reaction product is measured to comprise 89 weight percent of non- volatile material with a viscosity of 50 Pa.s (500 poise) and a water-clear color. The free isocyanate is measured at less than one weight percent.

Example 2

Solution Preparation of an Acrylic Polymer

The blocked isocyanate (179 g) prepared in

Example 1 is charged to one liter reactor equipped with reflux, nitrogen sparger, two addition funnels, a mechanical agitator and a temperature controller. The temperature of the reactor is raised over 75 minutes from ambient to 150 " C to strip excess ethanol by distillation from the blocked isocyanate. Sixty minutes after reaching 150 °C, initiator (dicumyl peroxide (2.3 g) dissolved in styrene (20 g) ) is added to the reactor at a rate of about 1 drop every 10-15 seconds. After 15 minutes of initiator addition, monomer solution is added at a rate of about 1 or 2 drops per second. The monomer solution consists of styrene (68 g) , ethyl acrylate (130 g) and hydroxyethyl acrylate (22 g) . After 1.5 hours, the initiator addition is complete and the contents of the reactor become a viscous solution ; after 2.5 hours, the addition of monomer is complete at which time a second charge of initiator (0.26 g) is added and the temperature held at 150 °C for an additional 60 minutes. The reaction product is then allowed to cool, and it is recovered from the reactor and measured to have a non-volatile material content of 98 weight percent. The resin is water-white clear, and it is determined by gel permeation chromatography (GPC) to have a weight average molecular weight (M ) of 43,000 and a number average molecular weight (M ) of 13,500 for a polydispersity (M_w/M_n) of approximately three.

The cure properties of the resin are then determined. Propylene glycol t-butyl ether is used to reduce the viscosity of the resin. Films are prepared which are approximately 38.1 μm (1.5 mil) thick upon drying in an oven at 196°C (385°F) for 20 minutes. The first film is prepared without the benefit of a catalyst and comprises approximately 60 weight percent of the acrylic polymer of this example and approximately 40 weight percent blocked isocyanate. This film is simply a dried, uncrosslinked resin and it demonstrates deterioration after only 10 double rubs with methyl ethyl ketone (ASTM D 4752-87) .

The second film is virtually identical in composition to the first film except it is cured with approximately one weight percent of dibutyl tin diacetate (DBTDA) . This film does not exhibit any deterioration after more than 100 double rubs with MEK. The third film is modified with about 20 weight percent (based on the weight of the mix) of an epoxy resin (which has an hydroxy equivalent weight of 200) , and the crosslinking is promoted with less than one percent DBTDA. After less than 10 double rubs with MEK, the film exhibits deterioration. However, a similar film in which the crosslinker level is increased by fifty weight percent demonstrates no deterioration after more than 100 double rubs with MEK.

Example 3

Example 2 is repeated except that the amount of initiator is increased to two weight percent ; the monomer solution contains 24 g of styrene, 44.5 g of ethyl acrylate, 7.2 g of hydroxy ethylacrylate and 12 g of dimethylaminoethyl methacrylate (DMAEMA) ; and the weight ratio of acrylic monomer to blocked isocyanate is adjusted to 1:1. The resulting acrylic polymer is measured to have a M-^ of 42,500, a M_n of 12,700 for a polydispersity of 3.35. The acrylic polymer is neutralized with 1.1 weight percent lactic acid, and the acrylic polymerization product (blocked isocyanate and neutralized acrylic polymer) is then used to prepare a water dispersion of approximately 70 weight percent water based upon the weight of the dispersion.

Example 4

The procedure of Example 2 is repeated. Excess ethanol (12 g recovered from 222 g of blocked isocyanate heated from room temperature to 155 °C over one hour and then held at 155 "C for an additional hour) is stripped from the blocked isocyanate prior to the addition of di-t-amyl peroxide (2.58 g in 10 g of styrene) as the catalyst, and the monomer solution contains 43.64 g of styrene, 99.46 g of ethyl acrylate, 16.1 g of hydroxyethyl acrylate and 26.82 g of DMAEMA. The reaction product is measured to have a non- volatile material (NVM) content of 98 weight percent, the resin is clear, and it is determined by gel permeation chromatography (GPC) to have a weight average molecular weight

(KL.) of 42,700 and a number average molecular weight (M_n) of 13,400 for a polydispersity (IL./M_) of approximately 3.1.

Example 5

The blocked isocyanate prepared in Example 1 is charged to a 500 ml reactor equipped with a reflux condenser, dean-stark trap, mechanical agitator, nitrogen inlet and temperature controller. The temperature of the reactor is raised to 155 °C with an increased flow of nitrogen to remove any excess ethanol. After approximately one hour at 155 ^-"-C, both initiator solution (7.7 g dicumyl peroxide and 15 g butyl acrylate) and monomer solution (95 g butyl acrylate, 74 g methyl methacrylate, 29 g 2-hydroxyethyl acrylate and 18 g acrylic acid) are added. The initiator solution is added at a rate of approximately one drop every 12-15 seconds. After 2.5 hours, both the initiator and monomer addition are completed. The finished resin, e.g. acrylic polymerization product, is measured to have a non-volatile content of 98 percent and an acid value of 35 mg KOH/gm resin. The finished resin is then neutralized with dimethylethanol amine and dispersed in water to a non-volatile content of 30.2%. Films are then prepared with and without the use of a cure catalyst to evaluate the cure response of the aqueous dispersion.

Example 6

The basic procedure of Example 1 is repeated except 1.73 moles of IPDI is reacted with 2.76 moles of propylene glycol monopropyl ether and 0.87 moles of anhydrous ethanol. The resulting blocked isocyanate is a viscous, slightly yellow solution at room temperature void of free isocyanate.

Example 7

Preparation of a Methanol Blocked Diisocyanate

Trimethylhexamethylene diisocyanate (trimethyl

HDI, 227 g) is placed in an addition funnel which is attached to a one liter round bottom flask equipped with agitation, reflux condenser, temperature controller, and nitrogen purge and charged with anhydrous methanol (73 g) . The temperature of the flask contents is increased to approximately 70°C. The trimethyl HDI is added to the methanol at a constant rate over a time period of one hour. At the end of that time period, the addition funnel is rinsed with anhydrous methanol and the reflux condenser is replaced with a distillation column. The temperature of the reactants is gradually increased to 120°C over a period of one hour and maintained at that temperature for an additional one hour. A sample of the reaction product is analyzed for free isocyanate using ASTM D 1638. The free isocyanate is less than 0.1 weight-percent and the amount of non-volatile material in the product is at least 98 weight- percent (based on the total weight of the reaction product) .

Example 8

Preparation of an Acrylic Polvol

The blocked diisocyanate (200 g) prepared in Example 7 and 26 g methyl amyl ketone (2-heptanone) are charged to one liter round bottom flask equipped with agitation, nitrogen purge, reflux condenser, temperature controller and two addition funnels. The round bottom flask is heated to a temperature of 155-160°C and then a mixture of 156 g 2-hydroxyethyl acrylate, 147 g styrene and 156 g ethyl acrylate is added at a constant rate from one addition funnel and 29 g di-t-amyl peroxide is added at a constant rate from the other addition funnel at a constant weight ratio of 10:1 over a six-hour time period. When those additions to the reactor flask are completed, the temperature is maintained at 5 160°C for one hour. Then 2.9 g di-t-amyl peroxide is added and the reaction conditions are maintained for an additional one hour. The reactor flask is then permitted to cool to approximately 100 °C, at which time the product is discharged. The product obtained according to this Example is a clear 0 homogeneous solution having a non-volatile material (NVM) content of 90 weight-percent with a viscosity of 58,2 Pa.s (582 poise) at 25°C, and it is determined by gel permeation chromatography (GPC) to have a weight average molecular weight (M^ of 6323 and a number average molecular weight (M ) of 5 2881 for a polydispersity (M^M^ of approximately 2.2.

Although the invention is described in considerable detailed by the preceding examples and description, this detailed is for the purpose of illustration only. Many variations and modifications can be made by one 0 skilled in the art without departing from the spirit and scope of the invention as it is described in the following claims.

Claims

1 - A low volatile organic compound (VOC) and hazardous air polluting system (HAPS) -free acrylic polymer blocked isocyanate coating system comprising : A. A blocked isocyanate, and B. An acrylic polymer.

2 - The coating system of Claim 1 further comprising a urethane catalyst.

3 - The coating system of Claim 2 further comprising water.

4 - The coating system of Claim 2 further comprising a solvent.

5 - The coating system of Claim 3 further comprising a resin.

6 - The coating system of Claim 4 further comprising a resin.

7 - The coating system of any of Claims 1 to 6 in which the blocked isocyanate is the reaction product of an isocyanate compound having at least two isocyanate functionalities and a blocking agent.

8 - The coating system of Claim 7 in which the blocking agent is selected from the group consisting of monohydroxyl compounds, oxi es, lactams, alkanolamines, phenols, malonic diesters and mixtures of two or more of these blocking agents.

9 - The coating system of Claim 8 in which the acrylic polymer is prepared from at least one of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, allyl alcohol, allyl alcohol propoxylate, glycidyl acrylate and glycidyl methacrylate.

10 - The coating system of Claim 9 in which the urethane catalyst is at least one of

A. Tertiary amines, B. Tertiary phosphines, C. Strong bases, D. Acidic metal salts of strong acids,

E. Organo-tin compounds, and

F. Cyclic amines.

11 - The coating system of Claims 9 or 10 in which 5 the isocyanate functionalities on the blocked isocyanate and hydroxy or epoxy groups on the acrylic polymer are present in an equivalents ratio of between about 1:1 to about 4:1.

12 - The coating system of any of Claims 3, 5, 9, 10, 11 in which the water comprises between about 10 and about

10 90 weight percent.

13 - The coating system of any of Claims 4, 6, 9, 10 in which the solvent is at least one of methyl ethyl ketone, methyl amyl ketone, butyl acetate, tripropylene glycol, diethylene glycol, glycerine, glycidyl acrylate, glycidyl

15 methacrylate, hydroxypropyl acrylate, hydroxy ethyl acrylate and hydroxy ethyl methacrylate.

14 - The coating system of Claim 13 in which the solvent comprises between about 10 and about 90 weight percent.

20 15 - The coating system of any of Claims 1 to 14 which contains one or more ╬▒, ╬▓-ethylenically unsaturated monomers which can crosslink through thermally or ultra violet light induced free radical polymerization during cure.

16 - A process for preparing a low VOC and HAPS-free

25 acrylic polymer blocked isocyanate coating system, the process comprising the steps of :

A. Reacting by contacting an isocyanate and a blocking agent to form a blocked isocyanate,

B. Adding at least one hydroxy or epoxy functional 30 acrylic monomer, optionally together with other ethylenically unsaturated monomers to the blocked isocyanate, and

C. Polymerization of the monomers to form an acrylic polymer.

35 17 - The process of Claim 16 in which the isocyanate is contacted with an excess of a stoichiometric amount of the blocking agent.

18 - The process of Claim 17 comprising the further step of removing excess blocking agent from the blocked isocyanate prior to adding the acrylic monomer to the blocked isocyanate.

19 - The process of any of Claims 16 to 18 in which the isocyanate compound and blocking agent are contacted at a temperature between about 35 and about 150┬░C.

20 - The process of any of Claims 16 to 19 in which the polymerization of the acrylic monomer is initiated with a vinyl polymerization catalyst and the polymerization is conducted at a temperature between about 50 and about 200┬░C.

21 - The process of any of Claims 16 to 20 in which the isocyanate compound has at least two isocyanate functionalities.

22 - The process of any of Claims 16 to 21 in which the blocking agent is selected from the group consisting of monohydroxyl compounds, oximes, lactams, alkanolamines, phenols, malonic diesters and mixtures of two or more of these agents.

23 - The process of any of Claims 16 to 22 in which the monomers of step B are at least one of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, allyl alcohol, allyl alcohol propoxylate, glycidyl acrylate and glycidyl methacrylate.

24 - The process of any of Claims 16 to 23 comprising the further step of mixing a resin with the product of the acrylic polymerization step.

25 - The process of Claim 24 comprising the further step of adding a urethane catalyst to the mixture of water and the product of the acrylic polymerization step.

26 - The process of Claim 25 comprising the further step of adding a resin to the mixture of water and the product of the acrylic polymerization step.

27 - The process of Claim 18 or 23 comprising the further step of adding a solvent to the product of the acrylic polymerization step.

28 - The process of Claim 27 comprising the further step of adding a urethane catalyst to the mixture of solvent and the product of the acrylic polymerization step.

29. - The process of making a coating, the process comprising the step of curing the coating system of Claim 1, 5, 6 or 13.