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Title:
POLYUREA COATINGS HAVING IMPROVED POT LIFE
Document Type and Number:
WIPO Patent Application WO/2004/044026
Kind Code:
A1
Abstract:
The present invention relates to a coating composition for the preparation of a polyurea coating that contains a) a polyisocyanate component, b) at least one compound corresponding to the formula (I) wherein, X represents an organic group, which has a valency of n and is inert towards isocyanate groups at a temperature of 100°C or less, R1 and R2 may be identical or different and represent organic groups, which are inert towards isocyanate groups at a temperature of 100°C or less, R3 and R4 may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at temperature of 100°C or less and n represents an integer with a value of at least 2, and c) an effective amount of a zeolite. The present invention also relates to a process for preparing aspartate based coating compositions having improved pot life.

Inventors:
BEST KURT E (US)
ZIELINSKI SANDREA L (US)
FERRI KENNETH L (US)
ERITANO RONALD G (US)
HERMANS-BLACKBURN LEONE (US)
KENDI MARGARET A (US)
Application Number:
PCT/US2003/035639
Publication Date:
May 27, 2004
Filing Date:
November 07, 2003
Export Citation:
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Assignee:
BAYER POLYMERS LLC (US)
BEST KURT E (US)
ZIELINSKI SANDREA L (US)
FERRI KENNETH L (US)
ERITANO RONALD G (US)
HERMANS-BLACKBURN LEONE (US)
KENDI MARGARET A (US)
International Classes:
C08G18/08; C08G18/38; C09D175/02; (IPC1-7): C08G18/08; C08G18/32; C08G18/38; C09D175/02
Foreign References:
EP0667362A11995-08-16
EP0573860A11993-12-15
US4341689A1982-07-27
Attorney, Agent or Firm:
Seng, Jennifer R. (100 Bayer Road Pittsburgh, PA, US)
Download PDF:
Claims:
WHAT IS CLAIMED IS
1. A coating composition for the preparation of a polyurea coating which comprises a) a polyisocyanate component, b) at least one compound corresponding to the formula wherein X represents an organic group, which has a valency of n and is inert towards isocyanate groups at a temperature of 100 ° C or less, R1 and R2 may be identical or different and represent organic groups, which are inert towards isocyanate groups at a temperature of 100 ° C or less, R3 and R4 may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100 ° C or less, and n represents an integer with a value of at least 2, and c) an effective amount of a zeolite.
2. The coating composition according to Claim 1, wherein the zeolite is an alkali metal aluminosilicate.
3. The coating composition according to Claim 1, wherein the amount of zeolite added is between 0.1 and 50 weight percent, based on the total weight percent of the coating composition.
4. The coating composition according to Claim 3, wherein the amount of zeolite added is between 2.5 and 25 weight percent, based on the total weight percent of the coating composition.
5. The coating composition according to Claim 4, wherein the amount of zeolite added is between 2.5 and 10 weight percent, based on the total weight percent of the coating composition.
6. A process for preparing a coating composition having an extended pot life, comprising the steps of mixing a) a polyisocyanate component, b) at least one compound corresponding to the formula wherein X represents an organic group, which has a valency of n and is inert towards isocyanate groups at a temperature of 100 ° C or less, R1 and R2 may be identical or different and represent organic groups, which are inert towards isocyanate groups at a temperature of 100°C or less, R3 and R4 may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100°C or less, and n represents an integer with a value of at least 2, and c) an effective amount of a zeolite.
7. The process according to Claim 6, wherein components b and c are premixed prior to being mixed with component a.
8. The process according to Claim 7, wherein the mixture comprising components b and c is degassed with nitrogen prior to being mixed with component a.
9. The process according to Claim 8, wherein component a is degassed with nitrogen prior to being mixed the mixture comprising components b and c.
10. The process according to Claim 6, wherein components a and c are premixed and degassed with nitrogen prior to being mixed with component b.
11. A method for increasing the pot life of a coating composition according to Claim 1, comprising the step of adding an effective amount of a zeolite to the coating, wherein the pot life extends after the excess water and carbon dioxide present in the coating composition is absorbed.
Description:
POLYUREA COATINGS HAVING IMPROVED POT LIFE FIELD OF THE INVENTION The present invention relates to aspartate based coating compositions, which have an improved pot life. The present invention also relates to a process for preparing aspartate based coating compositions having improved pot life.

BACKGROUND OF THE INVENTION U. S. Patent 5,126, 170, is directed to coating compositions wherein the binders are based on a two-component system of a polyisocyanate component and an isocyanate-reactive component containing partly or entirely certain secondary polyamines. Coating compositions according to U. S. Patent No. 5,126, 170 are suitable as binders in low solvent or. solvent-free coating compositions and enable the coatings to harden rapidly by a chemical cross-linking reaction which takes place either at room temperature or elevated temperature. A disadvantage of the coating compositions described in U. S. Patent No. 5,126, 170 is that even though they possess fast dry times, for some applications they do not provide adequate pot life, i. e. , the viscosity of the system increases too rapidly prior to application of the coating composition to a substrate.

It is known in the art that molecular sieves act as moisture scavengers in a wide variety of applications. Zeochem, a producer of molecular sieves, advertises in its product information available on its internet site, that specifically formulated sieves, sold under the tradename Purmole may limit any shortening of pot life in polyurethane systems. It was hypothesized that the pot life was extended as a result of water scavenging by the sieves. It was believed that the water was acting as a Lewis Acid and accordingly would accelerate the cure of the coating and shorten the pot life. Therefore, it was believed that removing the water from the coating would extend the pot life.

Molecular sieves have a unique structure and generally, greater than 99% of the adsorption occurs on the internal surface. Accordingly, the component being absorbed must physically pass through the sieves pore openings. Therefore, the sieve contains pore openings of regular and precisely defined size, allowing it to adsorb molecules selectively on the basis of size and polarity. And, it has now been discovered that a certain class of molecular sieves, preferably those based on sodium and aluminum silicate, are effective in extending the pot life of an aspartate based coating composition even after the water content of the coating composition is constant and without reducing cure time. It has also been discovered that the excess molecular sieves are also effective at continued absorption of carbon dioxide, which is also effective in extending the pot life of the aspartate based coating composition.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a longer pot life without significantly increasing the dry time of the coating composition and without altering any of the other desirable properties of the composition.

This object may be achieved with the coating compositions of the present invention, which contain the zeolites described hereinafter to increase the pot life. It is surprising that an increase in the pot life can be obtained by incorporating a zeolite based on sodium or aluminum silicate once the water has been absorbed. While zeolites are commonly used to adsorb any water present in the components before preparation of the coating compositions, the continual extension of the pot life of the coating composition after the water reduction is complete is unexpected. Further, the extension of the pot life of the coating composition by the absorption of the carbon dioxide present was also unexpected.

Accordingly, the present invention relates to a coating composition for the preparation of a polyurea coating, which contains a) a polyisocyanate component, b) at least one compound corresponding to the formula wherein

X represents an organic group, which has a valency of n and is inert towards isocyanate groups at a temperature of 100°C or less, R, and R2 may be identical or different and represent organic groups, which are inert towards isocyanate groups at a temperature of 100°C or less, R3 and R4 may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100°C or less and n represents an integer with a value of at least 2, and c) a zeolite, wherein the amount of zeolite added is an amount greater than the amount required to reduce the water content to a constant level.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, a"polyurea"is understood to mean a polymer containing urea groups and optionally other groups such as urethane groups.

The cross-linking which takes place in the process according to the present invention is based on an addition reaction between polyisocyanate component a) and the polyamines b) containing secondary amino groups, which are also known as"polyaspartic acid derivatives"or "polyaspartates."This reaction is known from previously discussed U. S.

Patent 5,126, 170 and also from DE-OS 2,158, 945, which discloses this reaction for the preparation of intermediate products which are then applied to a suitable substrate and converted at elevated temperatures into heterocyclic final products.

Examples of suitable polyisocyanates which may be used as the polyisocyanate component a) in accordance with the present invention include monomeric diisocyanates, preferably NCO prepolymers and more preferably polyisocyanate adducts. Suitable monomeric diisocyanates may be represented by the formula R (NCO) 2 in which R represents an organic group obtained by removing the isocyanate groups from an organic diisocyanate having a molecular weight of about 112 to 1,000, preferably about 140 to 400. Diisocyanates preferred for the process according to the invention are those represented by the above formula in which R represents a divalent aliphatic hydrocarbon group having 4 to 18 carbon atoms, a divalent cycloaliphatic hydrocarbon group having 5 to 15 carbon atoms, a divalent araliphatic hydrocarbon group having 7 to 15 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms.

Examples of the suitable organic diisocyanates include 1,4-tetra- methylene diisocyanate, 1, 6-hexamethylene diisocyanate, 2,2, 4-trimethyl- 1, 6-hexamethylene diisocyanate, 1, 12-dodecamethylene diisocyanate, cyclohexane-113-and-114-di isocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3-isocyanatomethyl-3, 5, 5-trimethylcyclo- hexane (isophorone diisocyanate or IPDI), bis- (4-iso-cyanatocyclo-hexyl)- methane, 2, 4'-dicyclohexylmethane diisocyanate, 1, 3-and 1,4-bis- (isocyanatomethyl)-cyclohexane, bis- (4-isocyanato-3-methyl-cyclohexyl)- methane, a, a, a', a'-tetramethyl-1, 3-and/or-1, 4-xylylene diisocyanate, 1-isocyanato-1-methyl-4 (3)-isocyanatomethyl cyclohexane, 2, 4- and/or 2, 6-hexahydrotoluylene diisocyanate, 1, 3- and/or 1, 4-phenylene

diisocyanate, 2, 4- and/or 2, 6-toluylene diisocyanate, 2, 4- and/or 4, 4'-diphenylmethane diisocyanate, 1,5-diisocyanato naphthalene and mixtures thereof. Aromatic polyisocyanates containing 3 or more isocyanate groups such as 4, 4', 4"-tri phenyl methane diisocyanate and polyphenyl polymethylene polyisocyanates obtained by phosgenating aniline/formaldehyde condensates may also be used.

In accordance with the present invention, the polyisocyanate component is preferably in the form of an NCO prepolymer or a polyisocyanate adduct, more preferably a polyisocyanate adduct. Suitable polyisocyanate adducts include those prepared from the preceding monomeric polyisocyanates and containing isocyanurate, uretdione, biuret, urethane, allophanate, iminooxadiazine dione, carbodiimide, acylurea and/or oxadiazinetrione groups. The polyisocyanates adducts, which preferably have an NCO content of 5 to 30% by weight, include : 1) Isocyanurate group-containing polyisocyanates which may be prepared as set forth in DE-PS 2,616, 416, EP-OS 3,765, EP-OS 10,589, EP-OS 47,452, US-PS 4,288, 586 and US-PS 4,324, 879.

The isocyanato-isocyanurates generally have an average NCO functionality of 3 to 4.5 and an NCO content of 5 to 30%, preferably 10 to 25% and most preferably 15 to 25% by weight.

2) Uretdione diisocyanates which may be prepared by oligomerizing a portion of the isocyanate groups of a diisocyanate in the presence of a suitable catalyst, i. e. , a trialkyl phosphine catalyst, and which may be used in a mixture with other aliphatic and/or cycloaliphatic polyisocyanates, particularly the isocyanurate group-containing polyisocyanates set forth under (1) above.

3) Biuret group-containing polyisocyanates which may be prepared according to the processes disclosed in U. S. Patent Nos.

3,124, 605; 3,358, 010; 3,644, 490; 3,862, 973; 3, 906, 126; 3,903, 127; 4,051, 165; 4,147, 714; or 4,220, 749 by using co-reactants such as water, tertiary alcohols, primary and secondary monoamines, and primary and/or

secondary diamines. These polyisocyanates preferably have an NCO content of 18 to 22% by weight.

4) Urethane group-containing polyisocyanates which may be prepared in accordance with the process disclosed in U. S. Patent No. 3,183, 112 by reacting excess quantities of polyisocyanates, preferably diisocyanates, with low molecular weight glycols and polyols having molecular weights of less than 400, such as trimethylol propane, glycerine, 1,2-dihydroxy propane and mixtures thereof. The urethane group-containing polyisocyanates have a most preferred NCO content of 12 to 20% by weight and an (average) NCO functionality of 2.5 to 3.

5) Allophanate group-containing polyisocyanates which may be prepared according to the processes disclosed in U. S. Patent Nos.

3,769, 318,4, 160,080 and 4,177, 342. The allophanate group-containing polyisocyanates have a most preferred NCO content of 12 to 21% by weight.

6) Isocyanurate and allophanate group-containing polyiso- cyanates which may be prepared in accordance with the processes set forth in U. S. Patents 5,124, 427,5, 208,334 and 5,235, 018, the disclosures of which are herein incorporated by reference, preferably polyisocyanates containing these groups in a ratio of monoisocyanurate groups to mono- allophanate groups of about 10: 1 to 1: 10, preferably about 5: 1 to 1: 7.

7) Iminooxadiazine dione and optionally isocyanurate group- containing polyisocyanates which may be prepared in the presence of special fluorine-containing catalysts as described in DE-A 19611849.

These polyisocyanates generally have an average NCO functionality of 3 to 3.5 and an NCO content of 5 to 30%, preferably 10 to 25% and most preferably 15 to 25% by weight.

8) Carbodiimide group-containing polyisocyanates which may be prepared by oligomerizing di-or polyisocyanates in the presence of known carbodiimidization catalysts as described in DE-PS 1,092, 007, US-PS 3,152, 162 and DE-OS 2,504, 400,2, 537,685 and 2,552, 350.

9) Polyisocyanate containing acylurea groups, which may be prepared by the direct reaction of isocyanates with carboxylic acids or via a carbodiimide intermediate stage as described, e. g. , in A. H. M.

Schotman et. al. Recl. Trav. Chim. Pay-Basm 1992,111, 88-91, P.

Babusiausx et al., Liebigs Ann. Chem. 1976,487-495, German Auslegeschrift 1 230 778, DE-A 2 436 740 and the literature cited therein.

10) Polyisocyanates containing oxadiazinetrione groups and containing the reaction product of two moles of a diisocyanate and one mole of carbon dioxide.

Preferred polyisocyanate adducts are the polyisocyanates containing isocyanurate, uretdione, biuret, iminooxadiazine dione and/or allophanate groups.

The NCO prepolymers, which may also be used as the polyisocyanate component in accordance with the present invention, are prepared from the previously described monomeric polyisocyanates or polyisocyanate adducts, preferably monomeric diisocyanates, and organic compounds containing at least two isocyanate-reactive groups, preferably at least two hydroxy groups. These organic compounds include high molecular weight compounds having molecular weights of 400 to about 6,000, preferably 800 to about 3,000, and optionally low molecular weight compounds with molecular weights below 400. The molecular weights are number average molecular weights (Mn) and are determined by end group analysis (OH number). Products obtained by reacting polyiso-cyanates exclusively with low molecular weight compounds are polyiso-cyanates adducts containing urethane groups and are not considered to be NCO prepolymers.

Examples of the high molecular weight compounds are polyester polyols, polyether polyols, polyhydroxy polycarbonates, polyhydroxy polyacetals, polyhydroxy polyacrylates, polyhydroxy polyester amides and polyhydroxy polythioethers. The polyester polyols, polyether polyols and polyhydroxy polycarbonates are preferred. Further details concerning the

low molecular weight compounds and the starting materials and methods for preparing the high molecular weight polyhydroxy compounds are disclosed in U. S. Patent 4,701, 480, herein incorporated by reference.

These NCO prepolymers generally have an isocyanate content of about 0.5 to 30% by weight, preferably about 1 to 20% by weight, and are prepared in known manner by the reaction of the above mentioned starting materials at an NCO/OH equivalent ratio of about 1.05 : 1 to 10: 1 preferably about 1.1 : 1 to 3: 1. This reaction may take place in a suitable solvent which may optionally be removed by distillation after the reaction along with any unreacted volatile starting polyisocyanates still present. In accordance with the present invention NCO prepolymers also include NCO semi-prepolymers which contain unreacted starting polyisocyanates in addition to the urethane group-containing prepolymers.

Component b) contains at least one compound corresponding to the formula: wherein X represents an organic group which has a valency of n and is inert towards isocyanate groups at a temperature of 100°C or less, preferably a divalent hydrocarbon group obtained by the removal of the amino groups from an aliphatic, aromatic, aromatic aliphatic or cycloaliphatic polyamine, more preferably a diamine, R, and R2 may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 100°C or

less, such as aliphatic, aromatic, aromatic aliphatic or cycloaliphatic groups, preferably methyl or ethyl groups, R3 and R4 may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100°C or less, preferably hydrogen and n represents an integer with a value of at least 2, preferably 2 to 4 and more preferably 2.

These compounds are prepared in known manner by reacting the corresponding primary polyamines corresponding to the formula X- (-NH2) n (II) with optionally substituted maleic or fumaric acid esters corresponding to the formula R, OOC-CR3=CR4-COOR2 (III) Suitable polyamines include ethylene diamine, 1,2-diamino- propane, 1,4-diaminobutane, 1,3-diaminopentane, 1,6-diaminohexane, 2,5-diamino-2, 5-dimethylhexane, 2,2, 4-and/or 2,4, 4-trimethyl-1, 6-diamino- hexane, 1,11-diaminoundecane, 1, 12-diaminododecane, 1, 3-and/or 1, 4-cyclohexane diamine, 1-amino-3,3, 5-trimethyl-5-aminomethyl-cyclo- hexane, 2, 4- and/or 2, 6-hexahydrotoluylene diamine, 2, 4'- and/or 4, 4'-diamino-dicyclohexyl methane and 3, 3'-dialkyl-4, 4'-diaminodicyclo- hexyl methanes (such as 3, 3'-dimethyl-4, 4'-diamino-dicyclohexyl methane and 3, 3'-diethyl-4, 4'-diamino-dicyclohexyl methane.

Preferred polyamines include 1,4-diaminobutane, 1,6-diamino- hexane, 2,2, 4- and 2,4, 4-trimethyl-1, 6-diamino-hexane, 1, 3- and/or 1, 4-cyclohexane diamine, 1-amino-3,3, 5-trimethyl-5-aminomethyl- cyclohexane, 2, 4- and/or 2, 6-hexahydrotoluylene diamine, 4, 4'-diamino- dicyclohexyl methane, 3, 3-dimethyl-4, 4'-diamino-dicyclohexyl methane and 3, 3-diethyl-4, 4'-diamino-dicyclohexyl methane.

Also suitable, though less preferred are the aromatic polyamines such as 2, 4- and/or 2, 6-diaminotoluene and 2, 4'- and/or 4,4'-diamino- diphenyl methane. Relatively high molecular weight polyether polyamines

containing aliphatically bound primary amino groups, for example, the products marketed under the Jeffamine trademark by Huntsman, are also suitable.

Examples of optionally substituted maleic or fumaric acid esters suitable for preparing the polyaspartates include the dimethyl, diethyl, dibutyl (e. g., di-n-butyl), diamyl, di-2-ethylhexyl esters and mixed esters based on mixtures of these and/or other alkyl groups of maleic acid and fumaric acid; and the corresponding maleic and fumaric acid esters substituted by methyl in the 2-and/or 3-position. The dimethyl, diethyl and dibutyl esters of maleic acid are preferred, while the diethyl esters are especially preferred.

The preparation of the"polyaspartic acid derivatives" corresponding to formula I from the above mentioned starting materials may be carried out, for example, at a temperature of 0 to 100°C using the starting materials in such proportions that at least 1, preferably 1, olefinic double bond is present for each primary amino group. Excess starting materials may be removed by distillation after the reaction. The reaction may be carried out solvent-free or in the presence of suitable solvents such as methanol, ethanol, propanol, n-butyl acetate, dioxane and mixtures of such solvents.

In accordance with the present invention"an effective amount of a zeolite"is understood to mean an amount greater than the amount of zeolite required to reduce the water content of the coating composition to a constant level, which may occur at a water content of 1200 ppm, or lower, such as 300ppm, 200ppm or 100ppm. The pot life continues to extend once the water content in the coating composition becomes constant. Also, the excess zeolite continues to absorb carbon dioxide, which in turn extends the pot life of the aspartate based coatings.

Preferably, the effective amount of the zeolite added is an excess of greater than 50%, preferably greater than 100%, more preferably greater than 200%, of the amount required to reduce the water content of

the coating composition to a constant level. Generally, from 0.1 to 50 weight percent, more preferably about 2.5 to 25 weight percent, and most preferably about 2.5 to 10 weight percent, based on the total weight of the coating composition, of a zeolite is added to the coating composition. In coating compositions, where appropriate, it is also preferable that the amount of zeolite added not exceed the critical pigment volume concentration of the coating composition.

Suitable zeolite have type A crystal structure and are alkali metal aluminosilicates having the chemical formula (Mx [AIO2) x (SiO2) y] zH2Oß wherein, M is sodium. Useful zeolites have a critical diameter of between 3A and 5A respectively, and do not exclusively adsorb water.

Commercially available examples of suitable zeolites include Sylosivs A-4 (GRACE Davision), Purmol@4A (Zeochem) and Molsivo 5. A (UOP). Given the small particle size of the zeolites, they readily disperse when thoroughly mixed in the coating composition.

Further, the excess zeolite continues to absorb carbon dioxide, which in turn extends the pot life of the aspartate based coatings.

The binders present in the coating compositions according to the present invention contain polyisocyanate component a), at least one secondary polyamine b) corresponding to formula I and zeolite c). While component b) may also contain other isocyanate-reactive components, such as the polyols commonly used in polyurethane coating compositions, their presence is not preferred. Components a) and b) are used in amounts sufficient to provide an equivalent ratio of isocyanate groups to isocyanate-reactive groups of about 0.8 : 1 to 20: 1, preferably about 0.8 : 1 to 3.1 and more preferably about 0.6 : 1 to 2.5 : 1.

The binders to be used according to the invention are prepared by mixing all of the individual components together or by premixing two of the components before adding the third component. For example, compound

c) may be initially blended with the component b) before the addition of the other component.

Preparation of the binders is carried out solvent-free or in the presence of the solvents conventionally used in polyurethane or polyurea coatings. It is an advantage of the process according to the invention that the quantity of solvent used may be greatly reduced when compared with that required in conventional two-component systems.

Examples of suitable solvents include xylene, butyl acetate, methyl isobutyl ketone, methoxypropyl acetate, N-methyl pyrrolidone, Solvesso solvent, petroleum hydrocarbons, iso-butanol, butyl glycol, methyl ethyl ketone, chlorobenzenes and mixtures of such solvents.

In the coating compositions to be used for the process according to the invention, the ratio by weight of the total quantity of binder components a) and b) to the quantity of solvent is about 40: 60 to 100: 0, preferably about 60: 40 to 100: 0.

The coating compositions to be used for the process according to the invention may also contain other auxiliary agents and additives conventionally used in polyurethane and polyurea coatings, in particular pigments, fillers, catalysts, levelling agents, antisettling agents, UV stabilizers and the like. Coating compositions containing pigments and/or fillers are especially suitable for the present invention due to the difficulty of removing all of the moisture from these additives.

It is also possible to incorporate other additives, which increase the pot life of compositions containing polyisocyanates and polyaspartic acid derivatives, such as the tin compounds disclosed in U. S. Patent 5,243, 012, the disclosure of which is herein incorporated by reference.

The properties of the coatings obtained by the process according to the invention may be adjusted, in particular by suitable choice of the nature and proportions of the starting components a) and b). Thus, for example, the presence of relatively high molecular weight, linear polyhydroxyl compounds in the prepolymers or semi-prepolymers of

component a) increases the elasticity of the coatings; whereas, the absence of such starting components increases the crosslinking density and hardness of the resulting coatings.

For carrying out the process according to the invention, the coating compositions to be used according to the invention are applied as one or more layers to substrates by known methods such as spraying, brush coating, immersion or flooding or by means of rollers or doctor applicators. The process according to the invention is suitable for the formation of coatings on various substrates, e. g., metals, plastics, wood, cement, concrete or glass. The process according to the invention is particularly suitable for the formation of coatings on heavy duty maintenance equipment, such as bridges and waste water facilities, and sheet steel, for example, for the manufacture of car bodies, machine trim panels, vats or containers. The substrates to be coated by the process according to the invention may be treated with suitable primers before the process according to the invention is carried out or they substrates do not have to be primed.

After the substrates exemplified above have been coated, the coatings may be cured at either ambient temperature, e. g. , by air drying or so-called forced drying, or at elevated temperature. It is of great benefit that the coatings will not thermally degrade even at the higher temperatures, which may occur in the event of a breakdown of the coatings plant.

The suppression of the viscosity increase for the coating compositions according to the invention while retaining the dry times is demonstrated in the examples that follow. All parts and percentages given are by weight unless otherwise indicated.

EXAMPLES The following materials were used in the present Examples : Polvaspartate Acid Esters (PAE's) The polyaspartate acid esters (PAE) were prepared by charging two moles of diethyl maleate to a 3-necked round bottom flask containing a mechanical stirrer, thermometer and an additional funnel. To the stirred diethyl maleate at 25°C under a nitrogen atmosphere was added a portion wise one mole of the diamines set forth below, so as to maintain a reaction temperature of 50°C or less using an ice water cooling bath, if necessary. At the completion of diamine addition the reaction temperature was maintained as determined by TLC. The crude reaction mixture was cooled to room temperature and poured into a container and sealed.

PAE A-Diamine starting material-bis-4 (4-amino-2-methyl- cyclohexyl)-methane PAE B-Diamine starting material-bis- (4-aminocyclohexyl)- methane Zeolite-UPO L Powder Xylene Methyl Ethyl Ketone Polyisocyanate 1-a biuret group containing polyisocyanate prepared by oligomerizing a portion of the isocyanate groups of 1,6- hexamethylene diisocyanate and having an NCO content of 16.6% and a viscosity of 157 cps.

Polyisocyanate 2-a HDI trimer having an equivalent weight of 182g, a viscosity of 1200 cps and an NCO content of 23% The ppm water was determined by Karl Fisher titration.

The dry times were determined according to ASTM D-5895.

The viscosity was measured using a Brookfield Viscometer.

Example 1 The molecular sieve powder identified in Table 1 was added to 2.24g of PAE-B and 2.24 g xylene and dispersed using a mechanical blade mixer. The slurry was left undisturbed overnight at room temperature. 4.47g of the aspartate/xylene (50% w/w) and 2.52g of the Polyisocyanate 1 doped with dye was added to a 4ml glass vial. The solution was briefly mixed on a rotating mixer. High throughput screening methods were used to measure the changes in bulk viscosity. An organic fluorescent probe, 4-dimethylamino-4'-nitrostilbene, DMANS, was dissolved in the isocyanate at a concentration of 2. 0x10-3 mol/l. Because both twisting and charge separation are involved in the formation of the intermolecular charge transfer states, the fluorescence emission of the probes is sensitive to both the solvent polarity and medium microviscosity.

When the cross-linking of the polymer matrix increases, the intramolecular charge transfer probe increases its fluorescent intensity. The fluorescence experiment was the method used for monitoring the potlife of the composition. A fluorescent intensity ratio method was used to eliminate the effect of intensity variations arising due to external factors, such as lamp intensity, optical alignment and temperature variation. Wavelengths were selected that represent the lowest and highest intensity changes.

Low high intensity change (LHIC) curves were obtained by dividing the intensities at a given wavelength in the longer wavelength region by the intensities of a given wavelength in the shorter wavelength region at all times the potlife was monitored. The ratios were normalized as follows: NormalizedLHICratio = 1 - R Ro where R is the LHIC ratio at any degree of the cure and Ro is the initial LHIC ratio. A calibration curve was drafted by measuring the viscosity every 15 minutes for 2 hours. The viscosity was measured at 25 C using a cone and plate viscometer. A regression analysis was used to calculate the change in bulk viscosity.

Three commercially available molecular sieves were added to aspartate based coating compositions, at varying amounts, as detailed above. As illustrated in Table 1, certain molecular sieves increase the pot life of aspartate based coatings, regardless of the water content.

Table1 Control NA 2500 34 min Control NA 2600 SylosivA-4 2. 5 200 56 min 64. 71 Svlosiv A-4 2. 5 200 SV-------------------59 min 73. 53 Sylosiv A-4 5 200 59 min 73. 53 Sylosiv A-4 5 300 Sylosiv A-4 10 200 64 min 88. 24 Svlosiv A-4 10 300 Purmol 4A 2. 5 1000 57 min 67. 65 Purmol 4A 2. 5 1200 Purmol 4A 5 300 59 min 73. 53 Purmol 4A 5 300 Purmol 4A 10 400 74 min 117. 65 Purmol 4A 10 500 UOP 5A 2. 5 100 69 min 102. 94 UOP 5A 2. 5 200 UOP 5A 5 100 70 min 105. 88 UOP 5A 5 200 UOP 5A 10 100 >80 min >135. 29 UOP 5A 10 200 Example 2 The coating composition having the formula described in Table 2 were prepared and then tested to determine the effect on the pot life if the carbon dioxide present in the coating components was removed prior to preparing the coating and/or with a molecular sieve. Samples A-F were prepared by mixing the components listed in Table 2 as described below.

As noted below some of the components were degassed by bubbling nitrogen for 8 hours at room temperature under a vacuum before preparing the coating composition.

The coating compositions were prepared by first mixing PAE A, PAE B, UOP L Powder and the MEK (Component 1) at medium speed in the quantities specified in Table 2, this mixture was then pulled under a vacuum and then sat overnight and then the specified amount of Polyisocyanate 2 was added.

Some of the components were degassed as discussed herein, Component 1 of Samples B and C was first pulled under a vacuum and then was degassed for 8 hours under vacuum at room temperature by nitrogen prior to being added to Polyisocyanate 2. Polyisocyanate 2 of Sample D was degassed as discussed above prior to being mixed with Component 1. In Samples E and F both Component 1 and Polyisocyanate 2 were degassed as discussed above prior to being combined. The viscosity of the samples was measured until the viscosity of the coating passed 1000cps.

Table 2: Coating Composition Components A (wt. %) B (wt. %) C (wt. %) D (wt. %) E (wt. %) F (wt. %) Control PAE A 23. 61 23.61 23.03 23.61 23.61 23.03 PAE B 23.61 23.61 23.03 23.61 23.61 23.03 UOP L Powder 0 0 2. 44 0 0 2.44 Methyl ethyl 19.44 19.44 18.97 19.44 19.44 18.97 ketone Polyisocyanate 2 33. 34 33.34 32.53 33.34 33.34 32.53 Table 3: Physical Properties of Samples A-H Time (min) Viscosity Viscosity Viscosity Viscosity Viscosity Viscosity of A of B of C of D of E of F (cps) (cps) (cps) (cps) (cps) (cps) 0 52. 5 50 50 50 47. 5 47.5 5 67.5 57.5 57.5 60 55 57. 5 10 85 73. 5 75 75 65 72. 5 15 110 91.5 87.5 102.5 77.5 92.5 20 142. 5 117.5 113.5 130 90 120 25 182. 5 147.5 145 172.5 107.5 155 30 245 185.6 180 230 132.5 222.5 35 300 233 228 280 152.5 270 40 385 287.5 292.5 362.5 192.5 340 45 480 363 350 467.5 235 420 50 560 436.5 430 562 285 490 55 664 574 524 674 342.5 590 60 810 628 630 832 425 720 65 970 760 860 1038 470 880 70 1190 934 922 550 1070 75--1070 1034 670 80 -- -- -- -- 950 -- 90 -- -- -- -- 1080 00 Circular Drytime STT (min) 20 20 25 20 30 20 SD (min) 60 50 50 45 60 35 HD (min) 85 70 60 60 70 55 Temp (°C) 23 23 23 23 23 23 RH (%) 50 50 50 50 50 50 Karl Fisher Water 1074 230 190 1074 230 190 (ppm)

Example 3 The coating compositions having the formula outlined in Table 4 were prepared as in Example 2. However, instead of degassing either Component 1 and/or Polyisocyanate 2 with nitrogen prior to preparing the coating composition, Component 1 and/or Polyisocyanate 2 was sparged with C02 for eight hours at room temperature until near saturation as discussed below.

In Samples H and 1, Component 1 was sparged with COs to near saturation prior to being added to Polyisocyanate 2. Polyisocyanate 2 of Sample J was sparged with COs prior to being added to Component 1.

Both Component 1 and Polyisocyanate 2 were sparged with C02 prior to being mixed in Samples K, L and N. In Sample M, the UOP L Powder was added to Polyisocyanate 2 instead of being mixed in Component 1 and Polyisocyanate 2 was sparged with CO2. In Sample N Polyisocyanate 2 was sparged with C02 and the molecular sieve was added to the Polyisocyanate 2 prior to being added with Component 1 as in Sample M.

The physical properties of the coating compositions are outlined in Table 5 below.

Sample H shows the effect of sparging Component 1 with C02.

Viscosity increases and pot life is reduced even at relatively equal water levels. Sample I shows the effect of adding a molecular sieve to Component 1, and the pot life is extended. In Sample J only Polyisocyanate 2 was sparged with CO2. The PAE was as manufactured and no molecular sieve was added. This sample along with K suggests that CO2 levels are more problematic on the isocyanate side of the coating composition. Samples L-N show that addition of UOP L Powder corrects the problem and pot life is again increased.

Table 4 Coating Composition Formulation Raw Materials (normalized to 100 by weight) Components Sample G Sample H Sample I Sample J Sample K Sample L Sample N Sample M PAE A 23.61 23.61 22.55 23.61 23.61 22.55 22.85 22.85 PAE-B 23.61 23.61 22.55 23.61 23.61 22.55 22.85 22.85 UOP L Powder 0 0 4.51 0 0 4.51 3.23 3.23 Methyl ethyl 19.44 19.44 18.56 19.44 19.44 18.56 18.81 18.81 ketone Polyisocyanate 2 33.34 33.34 31.84 33.34 33.34 31.84 32.26 32.26 Table 5: Physical Properties of Samples G-M Time (min) Viscosity Viscosity Viscosity Viscosity Viscosity Viscosity Viscosity Viscosity of G ofH of I (cps) of J (cps) of K (cps) of L (cps) of M of N (cps) (cps) (cps) (cps) 0 40 43 48 44 44 45 46 50 5 46 50 48 54 50 47 45 51 10 54 57 48 67 57 48 47 58 15 63 67 50 82 66 50 50 61 20 77 79 51 104 78 51 51 65 25 91 94 52 124 94 53 55 67 30 110 112 54 156 122 55 65 73 35 127 133 58 199 156 57 61 77 40 151 167 58 238 187 60 63 82 45 176 189 59 294 220 62 64 88 50 202 218 63 346 254 65 68 91 55 232 258 64 481 332 68 69 99 60 268 304 65 508 385 74 72 103 Table 5: Physical Properties of Samples G-M Time (min) Viscosity Viscosity Viscosity Viscosity Viscosity Viscosity Viscosity Viscosity of G of H of I (cps) of J (cps) of K (cps) of L (cps) of M of N (cps) (cps) (cps) (cps) 65 315 354 70 626 428 70 73 112 70 349 424 67 688 510 88 76 122 75 397 470 72 754 566 73 78 130 80 457 494 71 850 644 76 79 139 85 458 572 72 970 852 76 74 152 90 470 648 75 1060 1000 80 82 162 Garner Circular Drytime STT (min) 25 25 30 30 30 25 25 30 SD (min) 55 60 b70 65 60 65 55 75 HD (min) 65 70 85 75 65 75 60 95 Temp (°C) 23 23 23 23 23 23 23 23 RH (%) 50 50 50 50 50 50 50 50 Karl Fisher Water (ppm) 672 185 125 672 180 125 -- --

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.