WO2002051952A2

WO2002051952A2 - Water-based coating composition having carbamate-melamine cross-linking, method of preparing the same, and a cured film thereof

Info

Publication number: WO2002051952A2
Application number: PCT/US2001/042953
Authority: WO
Inventors: Swaminathan Ramesh; Paul Lessek; Wolfgang Bremser
Original assignee: Basf Corporation
Priority date: 2000-12-22
Filing date: 2001-11-19
Publication date: 2002-07-04
Also published as: CA2425948A1; BR0114923A; AU2002230412A1; MXPA03003210A; EP1356001A2; WO2002051952A3

Abstract

The present invention is directed to a curable, water-based coating composition utilized in waterborne coating systems. The coating composition is the reaction product of a water-based copolymer prepared by free-radical polymerization, and a cross-linking agent. The copolymer is the reaction product of a first block and a second block. The first block is the reaction product of a first ethylenically unsaturated monomer, acrylic acid, and a second ethylenically unsaturated monomer, methyl methacrylate, as well as the reaction product of a vinylaromatic hydrocarbon monomer, diphenylethylene. The second block is the reaction product of a plurality of ethylenically unsaturated monomers, styrene, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and carbonate-modified glycidyl methacrylate including a carbonate functional group that is subsequently converted into a carbamate functional group by ammonium hydroxie. The cross-linking agent, preferably a melamine, reacts with the carbamate functional group to establish a coating composition having urethane cross-linking from the carbamate- melamine reaction.

Description

WATER-BASED COATING COMPOSITION HAVING CARBAMATE - MELAMINE CROSS-LINKING, METHOD OF PREPARING THE SAME,

AND

A CURED FILM THEREOF

RELATED APPLICATIONS

This patent application claims priority to and all advantages of German

Application No. 10029803.6, entitled "Clearcoat Material And Its Use To Produce

Clearcoats And Multicoat Color And/Or Effect Coating Systems," which was filed

on June 16, 2000.

FIELD OF THE INVENTION

The subject invention generally relates to a curable, water-based coating

composition utilized primarily in waterborne coating systems, such as waterborne

basecoat (WBBC) systems, waterborne clearcoat (WBCC) systems, and waterborne

primer systems. More specifically, the coating composition includes a water-based

copolymer, having a carbamate functional group, and a cross-linking agent that is

reactive with the carbamate functional group and dispersible in water. The subject

invention also relates to a method of preparing the coating composition as well as a

method of preparing a cured film of the coating composition.

BACKGROUND OF THE INVENTION

Water-based coating compositions include water-based copolymers and

cross-linking agents as components. The water-based copolymers are desirable for

use in coating systems in the automotive and industrial coatings industries because these copolymers enable formulation of waterborne coating systems, such as

WBBC, WBCC, and waterborne primer systems. It is known in the art that

waterborne coating systems are ideal as compared to solventborne coating systems

because waterborne coating systems have lower content of volatile organic compounds (NOCs).

The water-based copolymers of the prior art have proven to be inadequate

for use as a component in water-based coating compositions. The water-based

copolymers of the prior art are ineffective because these copolymers are highly

viscous, as secondary dispersions, and generally have poorly defined film forming

characteristics, as primary dispersions. Furthermore, the cross-linking between

these copolymers and select conventional cross-linking agents are often particularly

susceptible to environmental acid etch.

The water-based copolymers of the prior art are also deficient because these

copolymers often incorporate additional components such as co-solvents and

increased amounts of surfactants which are both undesirable components in

waterborne coating systems. For instance, conventional water-based copolymers

typically incorporate a co-solvent to promote dispersibility of the copolymer in

water, and these co-solvents contribute to increased NOCs. Conventional water-

based copolymers also typically incorporate increased amounts of surfactants

directly into the copolymer to achieve and maintain miscibility and incorporation

of the copolymer in water, and as understood by those skilled in the art, use of

increased amounts of surfactants in the coating composition frequently contributes

to water sensitivity, humidity, and 'cratering' as well as other coating defects

detrimental to the appearance of the waterborne coating system. The free-radical polymerization methods of preparing the water-based

copolymers of the prior art are also deficient. These conventional methods are

typically highly exothermic and are therefore difficult to predict and control. The

unpredictability of these methods leads to uncontrollable and inconsistent physical

properties of the water-based copolymer and ultimately of the water-based coating

composition which includes the copolymer as a component. More specifically, the

unpredictability of these methods frequently leads to inconsistent molecular weight

distribution of the copolymer, and to incomplete conversion of monomer

components into the copolymer. Furthermore, in the preparation of conventional

water-based copolymers, distribution of the monomer components is random and

does not produce a 'tailored' polymeric architecture that is able to meet particular

needs depending on whether the copolymer is utilized in a WBBC, WBCC, or

waterborne primer system. It is understood in the art that inconsistent molecular

weights, incomplete conversion of monomer components, and even random

distribution of the monomer components affects, among other things, the stability

of the viscosity of the copolymer and can even result in 'gelling' of the copolymer

and of the water-based coating composition. Additionally, poor appearance

characteristics of the WBBC, WBCC, or waterborne primer system, such as gloss

and distinctness of image (DOI), can result from poor rheology, i.e., flow, of the

coating composition upon application that is due to the inconsistencies in the

water-based copolymer.

In sum, the prior art water-based copolymers which are components of the

water-based coating composition, as detailed above, are characterized by one or

more inadequacies. Due to the inadequacies identified in the prior art, it is desirable to provide a novel water-based copolymer and coating composition to be

utilized in WBBC, WBCC, and waterborne primer systems as well as a novel

method of preparing the coating composition and a cured film.

SUMMARY OF THE INVENTION

. A curable, water-based coating composition is disclosed. The water-based

coating composition of the subject invention is the reaction product of a water-

based copolymer (A) and at least one water-dispersible cross-linking agent (B).

The water-based copolymer (A) is prepared by free-radical polymerization and

includes a first block polymer, or first block, (A)(1) and a second block (A)(H).

The first block (A)(1) is preferably a hydrophilic block, and the second block

(A)(IT) is preferably a hydrophobic block. More specifically, the first block (A)(1)

of the copolymer (A) is the reaction product of at least one ethylenically

unsaturated monomer (A)(1)(a), and at least one vinylaromatic hydrocarbon

monomer (A)(1)(b). The second block (A)(H) of the copolymer (A) is the reaction

product of a plurality of ethylenically unsaturated monomers (A)(II)(a) different

than the ethylenically unsaturated monomer (A)(1)(a), wherein at least one of the

plurality includes at least one carbonate functional group for modification into a

carbamate functional group. The cross-linking agent (B) is reactive with the

carbamate functional group and is dispersible in water.

i the preferred water-based coating composition of the subject invention,

the at least one ethylenically unsaturated monomer (A)(1)(a) of the first block (A)(1)

is further defined as a first and second ethylenically unsaturated monomer where

the first ethylenically unsaturated monomer is preferably acrylic acid, and the second ethylenically unsaturated monomer is preferably methyl methacrylate.

Furthermore, the at least one vinylaromatic hydrocarbon monomer (A)(1)(b) of the

first block (A)(1) is preferably diphenylethylene. Also in the preferred

embodiment, the plurality of ethylenically unsaturated monomers (A)(II)(a) of the

second block (A)(II) that are different than the at least one ethylenically unsaturated

monomer (A)(1)(a) are styrene, 2-ethylhexyl methacrylate, cyclohexyl methacrylate,

and carbonate-modified glycidyl methacrylate having the carbonate functional

group, the preferred embodiment, the carbonate functional group of the

carbonate-modified glycidyl methacrylate is modified by an ammonia-containing

compound, preferably ammonium hydroxide, into the carbamate functional group.

Finally, the preferred water-dispersible cross-linking agent (B) that is reactive with

the carbamate functional group is hexamethoxymethyl melamine.

' A method of preparing the water-based coating composition is also

'disclosed. According to this method, the first block (A)(1) is first formed. Next, the second block (A)(II), having the at least one carbonate functional group, is

polymerized with the first block (A)(1) to establish the water-based copolymer (A).

The at least one carbonate functional group is then converted into at least one

carbamate functional group. The copolymer (A) is then combined with the water-

dispersible cross-linking agent (B) such that the cross-linking agent (B) reacts with

the carbamate functional group to form the water-based coating composition of the

subject invention.

The general object of the subject invention is to develop a water-based

coating composition for use in WBBC, WBCC, and waterborne primer systems

that utilizes carbamate - melamine cross-linking through a water-based copolymer (A), having a carbamate functional group, and a cross-linking agent (B) reactive

with the carbamate functional group. It is also a general object to introduce a

water-based coating composition that is completely solvent-free, i.e., does not

utilize any co-solvents, such that the content of NOCs is zero while maintaining the

dispersibility of the copolymer (A) in water without any co-solvents.

It is a further object of the subject invention to develop a water-based

coating composition that includes a lower cost cross-linking agent (B) reactive with

the carbamate functional group such that the WBBC, WBCC, and waterborne

primer systems prepared from the water-based coating composition of the subject

invention are resistant to environmental acid etch. It is a further object of the

subject invention to develop a water-based coating composition primarily including

a copolymer (A) that is surfactant-free, yet still fully miscible in water, such that

the WBBC, WBBC, and waterborne primer systems that utilize the copolymer (A)

in the water-based coating composition are crater resistant and do not suffer from

other surfactant-related defects .

Regarding the method of preparing the water-based coating composition, it

is an object of the subject invention to introduce a novel method that thoroughly

converts monomer components into the copolymer (A) and that is predictable and

controllable such that the structure of the copolymer (A) can be 'tailored' and

achieved. Therefore, water-based coating compositions prepared according to the

method of the subject invention maintain stable viscosities and result in cured films

in either a WBBC, a WBCC, or a waterborne primer system having ideal appearance characteristics. DETAILED DESCRIPTION OF THE INVENTION

The curable, water-based coating composition of the subject invention is

utilized in waterborne coating systems. Waterborne coating systems, such as

waterborne basecoat (WBBC) systems and waterborne clearcoat (WBCC) systems,

are used throughout automotive, industrial, and other coatings industries to coat

various substrates for aesthetic and functional purposes, such as color and

environmental resistance, respectively. Although the subject invention is directed

at WBBC and WBCC systems, it is to be understood that the subject invention may

also be utilized in other waterborne coating systems including, but not limited to

waterborne primer systems, and in other industries including, but not limited to, the

adhesive and sealant industries.

The water-based coating composition of the subject invention includes the

reaction product of a water-based copolymer (A), having at least one carbamate

functional group, and of at least one cross-linking agent (B) reactive with the

carbamate functional group to establish urethane ( — NH — CO — O — ) cross-linking

without use of an isocyanate. The water-based coating composition is prepared by

a free-radical polymerization method. In general, the method of preparing the

coating composition includes the steps of forming a first block (A)(1), polymerizing

a second block (A)(ϋ) with the first block (A)(1) to establish the water-based

copolymer (A), converting a carbonate functional group of the copolymer (A) into

a carbamate functional group, and combining the water-based copolymer (A) with

the cross-linking agent (B) to form the water-based coating composition of the

subject invention. These method steps will be discussed in greater detail below. The water-based copolymer (A) is the reaction product of the first block

(A)(1) and the second block (A)(H). In the most preferred embodiment, the first

block (A)(1) is a hydrophilic block, and the second block (A)(II) is a hydrophobic

block, and the subject invention will be described with this in mind. However, it is

to be understood that the number of blocks, as described two blocks, is not

intended to be limiting. For instance, the water-based copolymer (A) could also be

the reaction product of three blocks, e.g. a first hydrophilic block, a second

hydrophilic block, and a first hydrophobic block.

The first block (A)(1) is present in an amount from 5 to 15, preferably from

7 to 10, parts by weight based on 100 parts by weight of the coating composition.

The first block (A)(1) is the reaction product of at least one ethylenically

unsaturated monomer (A)(1)(a) and of at least one vinylaromatic hydrocarbon

monomer (A)(1)(b). More specifically, to form the first block (A)(1), the at least

one ethylenically unsaturated monomer (A)(1)(a) and at least one vinylaromatic

hydrocarbon monomer (A)(1)(b) are polymerized. This polymerization step is

conducted over time from 1 to 8, preferably from 2 to 7, and most preferably from

4 to 6, hours, and at a temperature between 50°C and 100°C. It is to be understood

that the time required to conduct this 'polymerization step' includes the time

needed for the addition of monomer components as well as any holding or cooling

time, where the addition of monomers may not be occurring. It is also to be

understood that certain ethylenically unsaturated monomers (A)(1)(a) and certain

vinylaromatic hydrocarbon monomers (A)(1)(b) require that the polymerization

step be conducted under pressure. If required, such pressure is preferably from 1.5

to 3000 bar, and more preferably from 10 to 1000 bar. The at least one ethylenically unsaturated monomer (A)(1)(a) of the first block (A)(1) is selected primarily to ensure the solubility of the copolymer (A) in

water. As such, the at least one ethylenically unsaturated monomer (A)(1)(a) is

selected to form a salt when reacted with a neutralizing agent. The neutralizing

agent will be discussed further below. In addition to the primary purpose of

ensuring the solubility of the copolymer (A) in water, the at least one ethylenically

unsaturated monomer (A)(1)(a) may also be selected to achieve an ideal minimum

film forming temperature, MFFT, for the water-based copolymer (A), and

ultimately for a cured film of the water-based coating composition utilized in either

the WBBC, WBCC, or waterborne primer system, such that the cured film is

resistant to excessive cracking, chipping, and the like. The at least one

ethylenically unsaturated monomer (A)(1)(a) may also be selected to minimize the

photo-sensitivity of the coating composition and of the cured film formed of the

coating composition. In the preferred embodiment of the subject invention, the at least one

ethylenically unsaturated monomer (A)(1)(a) is further defined as a first and second

ethylenically unsaturated monomer. The first and second ethylenically unsaturated

monomers are selected in order to balance the desired physical characteristics as

discussed above. That is, the first and second ethylenically unsaturated monomers

are selected to balance the solubility of the copolymer (A) in water as well as the

MFFT and the photosensitivity of the coating composition and of the cured film.

In terms of the total monomer composition in the first block (A)(1) of the

copolymer (A), the first and second ethylenically unsaturated monomers form from

70 to 99, preferably from 90 to 96, parts by weight based on 100 parts by weight of total monomer composition in the first block (A)(1). It is to be understood that, in

addition to the content of the first and second ethylenically unsaturated monomers,

the total monomer composition in the first block (A)(1) also includes the content of

the at least one vinylaromatic hydrocarbon monomer (A)(1)(b). As will be

discussed in greater detail below, in certain embodiments, the at least one

vinylaromatic hydrocarbon monomer (A)(1)(b) is alternatively defined as at least

one ethylenically unsaturated monomer (A)(1)(b) that is different than the at least

one ethylenically unsaturated monomer (A)(1)(a) and of the general formula

R₁R C—CR. R₄. In such embodiments, the total monomer composition in the first block (A)(1) is

defined to include the content of the at least one ethylenically unsaturated

monomer (A)(1)(b) of the general formula R₁R₂C=CR₃R₄. In the preferred

embodiment, the weight ratio of the first ethylenically unsaturated monomer to the

second ethylenically unsaturated monomer in the first block (A)(1) is from 1 : 0.5 to

1 : 5.

The first ethylenically unsaturated monomer is selected from the group of

compounds consisting of alkyl acrylic acids. The second ethylenically unsaturated

monomer is selected from the group of compounds consisting of aliphatic

acrylates, aliphatic methacrylates, cycloaliphatic acrylates, cycloaliphatic

methacrylates, and mixtures thereof of each of these compounds. It is to be

understood that each of these compounds include an alkyl radical, and in the

preferred embodiment of the subject invention, each of these compounds includes

up to 20 carbon atoms in the alkyl radical. The alkyl acrylic acids that may be selected as the first ethylenically unsaturated monomer are selected from the group consisting of acrylic acid,

methacrylic acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic

acid, and mixtures thereof. The aliphatic acrylates that may be selected as the

second ethylenically unsaturated monomer are selected from the group consisting

of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate,

ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, and mixtures thereof. The

aliphatic methacrylates that may be selected as the second ethylenically unsaturated

monomer are selected from the group consisting of methyl methacrylate, ethyl

methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate,

ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, and mixtures

thereof. The cycloaliphatic acrylate that may be selected as the second

ethylenically unsaturated monomer is cyclohexyl acrylate, and the cycloaliphatic

methacrylate that may be selected as the second ethylenically unsaturated monomer

is cyclohexyl methacrylate.

In the most preferred embodiment of the subject invention, the first

ethylenically unsaturated monomer is acrylic acid, and the second ethylenically

unsaturated monomer is methyl methacrylate. Furthermore, the weight ratio of the

acrylic acid to the methyl methacrylate in the first block (A)(1) is from 1 : 0.5 to 1 :

3 in the most preferred embodiment.

The at least one vinylaromatic hydrocarbon monomer (A)(1)(b) of the first

block (A)(1) is selected from the group consisting of α-methylstyrene,

diphenylethylene, dinapthaleneethylene, and mixtures thereof. Further, it is to be

understood that other α-alkylstyrenes may be selected as the at least one vinylaromatic hydrocarbon monomer (A)(1)(b) as well as other equivalent

compounds including, but not limited to, cis- or trans-stilbene, vinylidenebis (4- N,N-dimethylaminobenzene), vinylidenebis (4-aminobenzene), or vinylidenebis (4-

nitrobenzene). Although more than one vinylaromatic hydrocarbon monomer

(A)(1)(b) may be included in the first block (A)(1), the preferred embodiment of the

subject invention includes only one vinylaromatic hydrocarbon monomer, most

preferably diphenylethylene. In terms of the total monomer composition in the first

block (A)(1) of the copolymer (A), the vinylaromatic hydrocarbon monomer forms

from 1 to 20, preferably from 3 to 7, parts by weight based on 100 parts by weight

of total monomer composition in the first block (A)(1).

In certain embodiments, the at least one vinylaromatic hydrocarbon

monomer (A)(1)(b) of the first block (A)(1) may alternatively be defined as the at

least one ethylenically unsaturated monomer (A)(1)(b) that is different than the at

least one ethylenically unsaturated monomer (A)(1)(a) and that is of the general

formula

hi these embodiments, the radicals R_\, R , R , and Rι, each independently of

one another are hydrogen atoms or substituted or unsubstituted alkyl, cycloalkyl,

alkylcycloalkyl, cycloalkylalkyl, aryl, alkylaryl, cycloalkylaryl, arylalkyl or

arylcycloalkyl radicals, with the proviso that at least two of the variables R_1} R₂,

R , and Rj are substituted or unsubstituted aryl, arylalkyl or arylcycloalkyl radicals,

especially substituted or unsubstituted aryl radicals. Examples of suitable alkyl radicals are methyl, ethyl, propyl, isopropyl,

n-butyl, isobutyl, tert-butyl, amyl, hexyl, or 2-ethylhexyl.

Examples of suitable cycloalkyl radicals are cyclobutyl, cyclopentyl, or

cyclohexyl.

Examples of suitable alkylcycloalkyl radicals are methylenecyclohexane,

ethylenecyclohexane, or propane 1,3-diylcyclohexane.

Examples of suitable cycloalkylalkyl radicals are 2-, 3-, or 4-methyl-, -ethyl-, -propyl-, or -butylcyclohex -1-yl.

Examples of suitable aryl radicals are phenyl, naphthyl or biphenylyl,

preferably phenyl and naphthyl, and especially phenyl.

Examples of suitable alkylaryl radicals are benzyl or ethylene- or

propane-1 ,3-diylbenzene.

Examples of suitable cycloalkylaryl radicals are 2-, 3-, or

4-phenylcyclohex- 1 -yl.

Examples of suitable arylalkyl radicals are 2-, 3-, or 4-methyl-, -ethyl-,

-propyl-, or -butylphen-1-yl.

Examples of suitable arylcycloalkyl radicals are 2-, 3-, or

4-cyclohexylphen- 1 -yl.

The above-described radicals R_ls R , R₃, and R__t may be substituted. The

substituents used may comprise electron-withdrawing or electron-donating atoms

or organic radicals. Examples of suitable substituents are halogen atoms,

especially chlorine and fluorine, nitrile groups, nitro groups, partially or fully

halogenated, especially chlorinated and/or fluorinated, alkyl, cycloalkyl,

alkylcycloalkyl, cycloalkylalkyl, aryl, alkylaryl, cycloalkylaryl, arylalkyl and arylcycloalkyl radicals, including those exemplified above, especially tert-butyl;

aryloxy, alkyloxy and cycloalkyloxy radicals, especially phenoxy, naphthoxy,

methoxy, ethoxy, propoxy, butyloxy or cyclohexyloxy; arylthio, alkylthio and cycloalkylthio radicals, especially phenylthio, naphthylthio, methylthio, ethylthio,

propylthio, butylthio or cyclohexylthio; hydroxyl groups; and/or primary,

secondary and/or tertiary amino groups, especially amino, N-methylamino,

N-ethylamino, N-propylamino, N-phenylamino, N-cyclohexylamino,

N,N-dimethylamino, N,N-diethylamino, N,N-dipropylamino, N,N-diphenylamino,

N,N,-dicyclohexylamino, N-cyclo-hexyl-N-methylamino and N-ethyl-N-methylamino.

Examples of ethylenically unsaturated monomers (A)(1)(b) whose use is

particularly preferred in these embodiments are diphenylethylene,

dinaphthaleneethylene, cis- or trans-stilbene, vinylidenebis

(4-N,N-dimethylamino-benzene), vinylidenebis (4-aminobenzene), and vinyl-

idenebis (4-nitrobenzene).

Also, in accordance with these embodiments, ethylenically unsaturated

monomers (A)(1)(b) may be used individually or as a mixture of at least two

monomers (A)(1)(b).

Finally, as with the preferred embodiment which includes the at least one

vinylaromatic hydrocarbon monomer (A)(1)(b), the preferred ethylenically

unsaturated monomers (A)(1)(b) in these alternative embodiments is diphenylethylene.

The subject invention will be described below only in terms of the at least

one vinylaromatic hydrocarbon monomer (A)(1)(b). In addition to the at least one ethylenically unsaturated monomer (A)(1)(a) and the at least one vinylaromatic hydrocarbon monomer (A)(1)(b), the first block

(A)(1) is also the reaction product of the neutralizing agent. That is, the

neutralizing agent is added to the at least one ethylenically unsaturated monomer

(A)(1)(a) and to the at least one vinylaromatic hydrocarbon monomer (A)(1)(b) to

form the first block (A)(1) of the water-based copolymer (A). Specifically, the

neutralizing agent is selected from the group consisting of dimethylethanolamine,

amino methyl propanol, ammonia, and mixtures thereof. It is to be understood that

other base neutralizing agents may selected including, but not limited to, sodium

hydroxide, potassium hydroxide, diethanolamine, triethanolamine, and mono-, di-,

or tri-ethylamine. In the preferred embodiment, the neutralizing agent is ammonia,

NH₃. The ammonia, NH₃, interacts with an acid group of the first ethylenically

unsaturated monomer. More specifically, in the preferred embodiment, the

ammonia, NH₃, interacts with the hydrogen atom of the -COOH group of the

acrylic acid, to form a salt of the acrylic acid, having a -COO^" group, i.e., an acid

anion group, and NH₄ ⁺. The salt of acrylic acid ensures the solubility of the

copolymer (A) in water.

Like the neutralizing agent, an initiator, also known a polymerization

promoter, is added to the at least one ethylenically unsaturated monomer (A)(1)(a)

and to the at least one vinylaromatic hydrocarbon monomer (A)(1)(b) to form the first block (A)(1) of the water-based copolymer (A). The initiator initiates the free-

radical polymerization process. The initiator is soluble in water and is selected

from the group consisting of inorganic persulfates, dialkyl peroxides,

hydroperoxides, peresters, and mixtures thereof, hi the preferred embodiment of the subject invention, the initiator is an inorganic persulfate selected from the

group consisting of ammonium persulfate, (NH₄)₂S₂O₈, potassium persulfate,

K S₂O₈, and sodium persulfate, Na S₂O₈. Most preferably, the initiator is

ammonium persulfate. However, in alternative embodiments, the free-radical

polymerization initiator may be a dialkyl peroxides such as di-tert-butyl peroxide

or dicumyl peroxide, a hydroperoxide such as cumene hydroperoxide or tert-butyl

hydroperoxide, or a perester, such as tert-butyl perbenzoate, tert-butyl perpivalate,

tert-butyl per-3,4,5,-trimethylhexanoate or tert-butyl per-2-ethylhexanoate.

The weight ratio of the initiator to the at least one vinylaromatic

hydrocarbon monomer (A)(1)(b) is preferably from 1 : 3 to 3 : 1. It is to be

understood that it is preferred to add comparatively large amounts of the initiator.

More specifically, it is preferred that the initiator be present in an amount from 0.5

to 50, more preferably from 1.0 to 20, and most preferably from 3 to 10, parts by

weight based on 100 parts by weight of total monomer composition in the first

block (A)(1). At the completion of the formation of the first block (A)(1), the first

block (A)(1) has a non- olatile content of from 20 to 40, preferably from 25 to 35,

percent non-volatile by weight. Furthermore, the completed first block (A)(1) has a

number average molecular weight, M_n, from 1,000 to 20,000, preferably from

3,000 to 10,000.

Next, monomers making up the second block (A)(IT), which have at least

one carbonate functional group, are polymerized with the first block (A)(1) to

establish the water-based copolymer (A). This polymerization step, between the

monomers making up the second block (A)(ϋ) and the first block (A)(1), is

conducted over time from 1 to 8, preferably from 5 to 6, hours, and at a temperature between 50°C and 100°C, more preferably between 80°C and 100°C.

As with the polymerization step for forming the first block (A)(1), it is to be

understood that the time required to conduct this 'polymerization step' includes the

time needed for the addition of monomer components as well as any holding or

cooling time, where the addition of monomers may not be occurring. Also, for this

polymerization step, preferably no additional free-radical initiator is required.

Instead, this polymerization step is preferably initiated by self-formation of

radicals. Also, in this polymerization step, the at least one vinylaromatic

hydrocarbon monomer (A)(1)(b) of the first block (A)(1), in the preferred

embodiment diphenylethylene, controls the polymerization of the incoming

monomers that make up the second block (A)(H). The second block (A)(H) of the

copolymer (A) is more specifically the reaction product of a plurality of

ethylenically unsaturated monomers (A)(H)(a) that can be different than the

ethylenically unsaturated monomer (A)(1)(a), and are present in an amount from 25

to 50, preferably from 32 to 43, parts by weight based on 100 parts by weight of the

coating composition.

The plurality of ethylenically unsaturated monomers (A)(II)(a) are

hydrophobic, i.e., insoluble in water, and in preparing the second block (A)(H) of

the copolymer (A), the plurality of ethylenically unsaturated monomers (A)(II)(a)

are selected to promote miscibility between the coating composition and other

components commonly utilized in WBBC, WBCC, and waterborne primer

systems. The plurality of ethylenically unsaturated monomers (A)(IT)(a) are also

selected to contribute to the MFFT for the water-based copolymer (A), and ultimately for the cured film of the water-based coating composition utilized in

either the WBBC, WBCC, or waterborne primer systems.

At least one of the ethylenically unsaturated monomers of the plurality

(A)(II)(a) includes at least one carbonate functional group. As such, the plurality of

ethylenically unsaturated monomers (A)(H)(a) are selected from the group

consisting of styrene, butyl acrylate, butyl methacrylate, 2-ethylhexyl methacrylate,

2-hydroxyethyl methacrylate, cyclohexyl methacrylate, glycidyl acrylate, glycidyl

methacrylate, carbonate-modified glycidyl acrylate, carbonate-modified glycidyl

methacrylate, and mixtures thereof, so long as the plurality of ethylenically

unsaturated monomers (A)(D)(a) that are selected are different than the

ethylenically unsaturated monomer (A)(1)(a).

Also, as discussed above, at least one of the plurality (A)(II)(a) must

introduce the carbonate functional group. Therefore, one of either carbonate-

modified glycidyl acrylate or carbonate-modified glycidyl methacrylate is to be

selected. Of course, it is understood that alternative carbonate-modified

compounds can be introduced by other chemical compounds such as epoxy group

containing compounds reacted with CO₂, and even by chemical compounds having

unsaturated bonds that are first converted to an epoxy group by known reactions

with peroxides. Once these chemical compounds have been modified to include a

carbonate functional group, the carbonate functional group can then be converted

into a carbamate functional group as will be described in greater detail below.

As also understood by those skilled in the art, the carbonate-modified

glycidyl acrylate is formed by the reaction of glycidyl acrylate, having the chemical

formula of CH^CHCOOCH CHCTbO, with CO₂, under excessive pressure and temperature conditions. Similarly, the carbonate-modified glycidyl methacrylate is

formed by the reaction of glycidyl methacrylate, having the chemical formula of

CH₂:C(CH₃)COOCH₂CHCH₂O, with CO₂, under excessive pressure and

temperature conditions, hi the most preferred embodiment, the plurality of

ethylenically unsaturated monomers (A)(IT)(a) that are selected are styrene, 2-

ethylhexyl methacrylate, cyclohexyl methacrylate, and carbonate-modified glycidyl

methacrylate which includes the carbonate functional group. For descriptive

purposes, the common chemical name for carbonate-modified glycidyl

methacrylate is 4-(hydroxymethyl)-l,3-dioxolan-2-one methacrylate and the

accepted chemical abstract chemical name is 2-propenoic acid, 2-methyl-, (2-oxo-

l,3-dioxalan-4-yl) methyl ester.

After the second block (A)(II) is polymerized with the first block (A)(1) to

establish the water-based copolymer (A), the carbonate functional group in the

second block (A)(IT) of the copolymer (A) is then modified, i.e., converted, into the

carbamate functional group. More specifically, at a temperature between 50°C and

100°C, more preferably between 50°C and 70°C, an ammonia-containing, NH₃,

compound is reacted with the carbonate functional group to convert the carbonate

functional group into the carbamate functional group. This reaction step, between

the ammonia-containing compound and the carbonate functional group, is

conducted over time from 1 to 4 hours.

The ammonia-containing compound is selected from the group consisting

of ammonia, ammonium hydroxide, and mixtures thereof. As understood by those

skilled in the art, use of either ammonia or ammonium hydroxide to convert the

carbonate functional group results in a primary carbamate functional of the general formula NH₂COO-. Additionally, a primary amine can be used to convert the

carbonate functional group. Use of the primary amine results in a secondary

carbamate functional group of the general formula NHRCOO-, where R is an alkyl

radical. However, in terms of the preferred embodiment of the subject invention,

reaction with the primary amine is not preferred because secondary carbamate

functional groups exhibit 'sluggish' reactions with the preferred cross-linking agent

(B) which will be discussed below. Although in the preferred embodiment the

carbonate functional group is converted into the carbamate functional group after

the second block (A)(II) is polymerized with the first block (A)(1), it is to be

understood that, alternatively, the carbonate functional group can be converted into

the carbamate functional group prior to polymerization of the second block (A)(II)

with the first block (A)(1).

In the preferred embodiment, ammonium hydroxide is utilized to convert

the carbonate functional group into the carbamate functional group. The ammonia,

NH₃, group of the ammonium hydroxide can form a primary carbamate functional

group having a primary hydroxyl (-OH) group which is shown schematically

below.

Alternatively, the ammonia, NH , group of the ammonium hydroxide can form a

primary carbamate functional group having a secondary hydroxyl (-OH) group

which is shown schematically below.

The water-based coating composition is also the reaction product of the at

least one cross-linking agent (B) that is reactive with the carbamate functional

group and that is dispersible in water. It is to be understood that dispersibility in

water indicates that the cross-linking agent (B) can be mixed into water to produce

a homogenous mixture of the cross-linking agent (B) and the water with no phase

separation between the two components. The water-based copolymer (A) is

combined with the cross-linking agent (B) to form the coating composition of the

subject invention. More specifically, small amounts, from 0.1 to 3 parts by weight

based on 100 parts by weight of the total coating composition, of an anionic

surfactant are added with the copolymer (A) and the cross-linking agent (B) to

guarantee the dispersibility of the cross-linking agent (B) in water. Preferably, a

sulfonate-based surfactant is selected as the anionic surfactant.

The cross-linking agent (B) is selected from the group consisting of water-

dispersible aminoplasts, water-dispersible polymers having acrylamide groups, and

water-dispersible polymers having methylol or alkoxymethyl groups, and mixtures

thereof. Furthermore, the cross-linking agent (B) is present in an amount from .1 to 10, preferably from .05 to 5, and most preferably from 1 to 3, parts by weight based on 100 parts by weight of the coating composition.

It is to be understood that the water-dispersible aminoplasts include urea

resins and melamine fonnaldehyde resins. The melamine formaldehyde resins of

the preferred embodiment include either a methylol group, CH OH, an

alkoxymethyl group, or both. The alkoxymethyl group is of the general formula —

CH OR_l5 where R₁ is an alkyl chain having from 1 to 20 carbon atoms. As

understood by those skilled in the art, the methylol groups and the alkoxymethyl

groups are reactive with the carbamate functional group.

Possible cross-linking agents include, but are not limited to, monomeric and

polymeric melamine formaldehyde resins, including both partially and fully

alkylated melamines such as methylated melamines, butylated melamines, and

methylated/butylated melamines. Other cross-linking agents (B) that are urea

resins include methylol ureas such as urea formaldehyde resins, and alkoxy ureas

such as butylated urea formaldehyde resin.

The preferred embodiment of the subject invention includes

hexamethoxymethyl melamine (HMMM). HMMM is commercially available from

Monsanto under its Resimene Amino Crosslinker Resins. HMMM is shown in the

following chemical representation.

Upon addition of the cross-linking agent (B) to the copolymer (A), the alkoxymethyl groups of the HMMM, specifically the CH OCH₃ group, reacts with the carbamate functional group in the second block (A)QI) of the copolymer (A) to establish a urethane ( — NH — CO — O — ) linkage without use of an isocyanate. The urethane linkage between the copolymer (A) and the cross-linking agent (B) is from the carbamate - melamine reaction and is ideal for resistance to environmental acid etch. Overall, the copolymer (A) has a number-average molecular weight, M_n, of from 5,000 to 2,000,000. Additionally, the coating composition of the subject invention has a non-volatile content of from 20 to 60, preferably from 30 to 50,

percent non- volatile by weight, and an average volume particle size of # 200 nm.

The cured film of the water-based coating composition of the subject invention is prepared by applying the water-based coating composition to the substrate. More specifically, the water-based coating composition can be sprayed onto the substrate by air-atomized or bell-applied spray application, and other equivalent processes. Once applied to the substrate, the coating composition is cured to form the cured film. Although cross-linking may occur prior to the curing step, the cross-linking agent (B) completely reacts with the at least one carbamate functional group during the curing step to form the cured film of the water-based coating composition including the urethane cross-linking. Preferably, the reaction between the cross-linking agent (B) and the carbamate functional group occurs at a temperature between 100°C and 175°C, and more preferably at a temperature between 110°C and 130°C from 20 to 30 minutes. It is to be understood that all of the preceding chemical representations are

merely two-dimensional chemical representations and that the structure of these

chemical representations may be other than as indicated.

The following examples, illustrating the formation of the first block (A)(1),

the formation of an initial form of the copolymer (A), the formation of the

complete copolymer (A), the formation of the coating composition, and of the

cured film of the coating composition, as presented herein, are intended to illustrate

and not limit the invention.

EXAMPLES: Example 1:

The first block (A)(1) of the copolymer (A) was prepared by adding and

reacting the following parts, by weight, unless otherwise indicated.

Table 1

Per the above table, Table 1, 1051.3 grams of de-ionized water were added

to a reaction flask. The reaction flask, preferably a steel reactor, was equipped with

a stirrer and a reflux condenser. The reaction flask, including the water, was

heated via a conventional heat supply to a temperature of 90°C. Next, three feed

streams from three independent feed vessels were fed into the water in the reaction

flask over approximately 4 to 5 hours to form the first block (A)(1) of the copolymer (A). More specifically, the first feed stream included 203.6 grams of

acrylic acid, 366.9 grams of methyl methacrylate, and 29.9 grams of

diphenylethylene. The second feed stream included 198.3 grams of the

neutralizing agent ammoma, and the third feed stream included 105.0 grams of

water and 45.1 grams of the initiator ammonium persulfate. During the addition of

the three feed streams into the reaction flask containing water, satisfactory reflux

was achieved. Further, after the addition of the three feed streams, the temperature

of the reaction flask increased from 90°C to 94°C - 96°C thus indicating an

exotherm, and then the temperature of the reaction flask returned to 90°C. The

batch was maintained at 90°C for an additional two hours. After this, the heat

supply was removed from the reaction flask and the first block (A)(1), formed by

the polymerization of the acrylic acid, the methyl methacrylate, and the

diphenylethylene, as well as by the ammonia and the ammonium persulfate, was

allowed to cool. The percent non- volatile of the first block (A)(1) was determined

to be 32.9%. Example 2:

Next, an initial form of the copolymer (A) was formed by polymerizing the

second block (A)(II) with the first block (A)(1) prepared in Example 1 above. This

polymerization step included the following parts, by weight, unless otherwise

indicated.

Table 2

Per the above table, Table 2, 1032.4 grams of water were added to a

reaction flask. The reaction flask, including the water, was heated via a conventional heat supply to a temperature of 90°C for approximately 30 minutes.

Next, 181.5 grams of the first block (A)(1), from Example 1, was added to the

reaction flask including the water. Following the complete addition of first block

(A)(1), a feed stream of the second block (A)(II) was added to the reaction flask.

More specifically, the second block (A)(II) feed stream included 157.9 grams of

styrene, 177.6 grams of 2-ethylhexyl methacrylate, 198.8 grams of cyclohexyl

methacrylate, and 126.6 grams of carbonate-modified glycidyl methacrylate. This

feed stream was added to the reaction flask, including the water and the first block

(A)(1), over approximately 5 to 6 hours, and the temperature of the reaction flask

fluctuated between 90°C and 94°C throughout the addition of the second block

(A)(I_) feed stream. The polymerization of the second block (A)(H) with the first

block (A)(1) completed the formation of the initial form of copolymer (A) of the

subject invention.

Example 3: In Example 3, the carbonate functional group of the initial form of

copolymer (A) was converted into the carbamate functional group according to the

following parts, by weight, unless otherwise indicated.

Table 3

Per the above table, Table 3, 200.0 grams of the initial form of copolymer

(A), from Example 2 above, and 1.0 gram of de-ionized water were added into a

reaction flask. The reaction flask, including the water, was heated via a

conventional heating supply to a temperature of 60°C. Next, 15.2 grams of

ammonium hydroxide were added into the reaction flask over approximately 1 to 2

hours. During this addition, the temperature in the reaction flask fluctuated

between 60°C and 80°C. After the addition of the 15.2 grams of ammonium

hydroxide, the extent of the carbonate-to-carbamate conversion was verified by a

known method, specifically infrared (DR.) spectroscopy. It was determined that

some carbonate functionality remained. As such, an additional 5.0 grams of

ammomum hydroxide were added into the reaction flask at 60°C over

approximately 0.5 hours to complete the conversion of the carbonate functional

group to the carbamate functional group. The completed copolymer (A) of Example 3, including both the first block

(A)(1) and the second block (A)(II), and including the carbamate functional group

converted from the carbonate functional group had a percent non-volatile of 41.3%.

Furthermore, the initial physical property integrity of the copolymer (A) was

evaluated by verifying resistance to a strong solvent, i.e., resistance to MEK double

rubs, of a 2 mil thickness drawdown under air dry conditions. The result of the

initial physical property integrity is included in Table 2. As understood by those

skilled in the art, the MEK double rub method is an acceptable method for initial

verification of the integrity of an air-dried or oven-cured film.

Example 4:

In Example 4, the completed copolymer (A) and the cross-linking agent (B)

were added to form the coating composition of the subject invention. The coating

composition as depicted in this example is merely a preliminary 'scale-up'

intended to equal coating compositions utilized in WBBC, WBCC, and waterborne

primer systems that may include other components such as pigments, flow

additives, catalysts, UN-resistance packages, and the like. The coating

composition was prepared according to the following parts, by weight, unless

otherwise indicated.

Table 4

Per the above table, Table 4, the coating composition (Sample A) was

formed by the addition, at room temperature, of 200 grams of the copolymer (A)

and 3.0 grams of the cross-linking agent hexamethoxymethyl melamine (HMMM).

More specifically, the copolymer (A) was first added into a container, and then the

cross-linking agent (B) was added into the container, including the copolymer (A),

under mixing. Additionally, a small amount of anionic surfactant, specifically 1.0

gram, was incorporated to guarantee the dispersibility of the HMMM in water.

After the addition, under mixing, of the cross-linking agent, Sample A was

evaluated for stability. For instant stability, i.e., immediately after the addition of

the cross-linking agent (B), Sample A did not show any significant increase in viscosity. For stability after a 24 hour time period, the result was the same, no significant viscosity increase.

Furthermore, Sample A was spray applied to a substrate, specifically ACT

e-coated panels, and then cured to form the cured film of the subject invention.

The 'sprayabihty' of Sample A was evaluated as acceptable primarily because the

sample had a workable spray viscosity. As for the curing step, Sample A was

cured in a conventional oven at 250°F for 30 minutes, and then the cured film of

coating composition was evaluated for appearance and initial physical property

integrity.

The general appearance of the cured film was uniform and acceptable.

Sample A had a slight 'peel.' Finally, the initial physical property integrity of the

cured film of Sample A was evaluated after the cure of 250°F for 30 minutes. The

results of the initial physical property integrity of the cured film of Sample A was

acceptable and is included above in Table 4.

The invention has been described in an illustrative manner, and it is to be

understood that the terminology which has been used is intended to be in the nature

of words of description rather than of limitation. Obviously, many modifications and

variations of the present invention are possible in light of the above teachings, and

the invention may be practiced otherwise than as specifically described.

Claims

CLAIMSWhat is claimed is:

1. A curable, water-based coating composition comprising the reaction

product of:

(A) a water-based copolymer prepared by free-radical polymerization,

said copolymer comprising the reaction product of;

(I) a first block comprising the reaction product of;

(a) at least one ethylenically unsaturated monomer, and

(b) at least one vinylaromatic hydrocarbon monomer;

and

(II) a second block comprising the reaction product of;

(a) a plurality of ethylenically unsaturated monomers

different than (A)(1)(a), wherein at least one of said plurality includes at least one

carbonate functional group for modification into a carbamate functional group; and

(B) at least one cross-linking agent reactive with said carbamate

functional group and dispersible in water.

2. A coating composition as set forth in claim 1 wherein said at least

one cross-linking agent (B) is selected from the group consisting of water-

water-dispersible polymers having methylol or alkoxymethyl groups, and mixtures thereof.

3. A coating composition as set forth in claim 2 wherein said water- dispersible aminoplasts are selected from the group of melamine formaldehyde resins having a methylol group, an alkoxymethyl group, or both, which are reactive

with said carbamate functional group.

4. A coating composition as set forth in claim 1 further including an

ammonia-containing compound reactive with said ethylenically unsaturated

monomer of said plurality (A)(II)(a) that includes said carbonate functional group,

said ammoma containing compound modifying said carbonate functional group

into said carbamate functional group.

5. A coating composition as set forth in claim 4 wherein said

ethylenically unsaturated monomer of said plurality (A)(Tf)(a) that includes said

carbonate functional group is selected from the group consisting of carbonate-

modified glycidyl acrylate, carbonate-modified glycidyl methacrylate, and mixtures

thereof.

6. A coating composition as set forth in claim 4 wherein said

ammoma-containing compound is selected from the group consisting of ammonia,

ammonium hydroxide, and mixtures thereof.

7. A coating composition as set forth in claim 1 wherein said first

block (A)(1) is present in an amount from 5 to 15 parts by weight based on 100

parts by weight of said coating composition.

8. A coating composition as set forth in claim 1 wherein said second

block (A)(D) is present in an amount from 25 to 50 parts by weight based on 100

parts by weight of said coating composition.

9. A coating composition as set forth in claim 1 wherein said at least

one cross-linking agent is present in an amount from 0.1 to 10 parts by weight

based on 100 parts by weight of said coating composition.

10. A coating composition as set forth in claim 1 wherein said first

block (A)(1) further comprises the reaction product of a neutralizing agent.

11. A coating composition as set forth in claim 10 wherein said

amino methyl propanol, ammonia, and mixtures thereof.

12. A coating composition as set forth in claim 1 wherein said first

block (A)(1) further comprises the reaction product of an initiator.

13. A coating composition as set forth in claim 12 wherein said initiator

is selected from the group consisting of inorganic persulfates, dialkyl peroxides,

hydroperoxides, peresters, and mixtures thereof.

14. A coating composition as set forth in claim 12 wherein the weight

ratio of said initiator to said at least one vinylaromatic hydrocarbon monomer

1 : 3 to 3 : 1.

15. A coating composition as set forth in claim 1 wherein said at least

one ethylenically unsaturated monomer (A)(1)(a) is further defined as a first and

second ethylenically unsaturated monomer.

16. A coating composition as set forth in claim 15 wherein said first

ethylenically unsaturated monomer is acrylic acid.

17. A coating composition as set forth in claim 16 wherein said second

ethylenically unsaturated monomer is methyl methacrylate.

18. A coating composition as set forth in claim 15 wherein said first

ethylenically unsaturated monomer is selected from the group of compounds

consisting of alkyl acrylic acids, and said second ethylenically unsaturated monomer is selected from the group of compounds consisting of aliphatic

acrylates, aliphatic methacrylates, cycloaliphatic acrylates, cycloaliphatic

methacrylates, and mixtures thereof, wherein each of said first and second

ethylenically unsaturated monomers include up to 20 carbon atoms in the alkyl

radical.

19. A coating composition as set forth in claim 18 wherein the weight

ratio of said first ethylenically unsaturated monomer to said second ethylenically

unsaturated monomer is from 1 : 0.5 to .1 : 5.

20. A coating composition as set forth in claim 1 wherein said at least

one ethylenically unsaturated monomer (A)(1)(a) is selected from the group of

compounds consisting of aliphatic acrylates, aliphatic methacrylates, cycloaliphatic

acrylates, cycloaliphatic methacrylates, alkyl acrylic acids, and mixtures thereof,

each of said compounds having up to 20 carbon atoms in the alkyl radical.

21. A coating composition as set forth in claim 20 wherein said

aliphatic acrylates are selected from the group consisting of methyl acrylate, ethyl

acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, ethylhexyl acrylate, stearyl

acrylate, lauryl acrylate, and mixtures thereof.

22. A coating composition as set forth in claim 20 wherein said

aliphatic methacrylates are selected from the group consisting of methyl

methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl

methacrylate, ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate,

and mixtures thereof.

23. A coating composition as set forth in claim 20 wherein said

cycloaliphatic acrylate is further defined as cyclohexyl acrylate.

24. A coating composition as set forth in claim 20 wherein said

cycloaliphatic methacrylate is further defined as cyclohexyl methacrylate.

25. A coating composition as set forth in claim 20 wherein said alkyl

acrylic acids are selected from the group consisting of acrylic acid, methacrylic

acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and

mixtures thereof.

26. A coating composition as set forth in claim 1 wherein said at least

one vinylaromatic hydrocarbon monomer (A)(1)(b) is selected from the group

consisting of α-methylstyrene, diphenylethylene, dinapthaleneethylene, and

mixtures thereof.

27. A coating composition as set forth in claim 1 wherein said plurality

of ethylemcally unsaturated monomers (A)(_I)(a) are selected from the group

methacrylate, carbonate-modified glycidyl acrylate, carbonate-modified glycidyl

methacrylate, and mixtures thereof, such that said plurality of ethylenically

unsaturated monomers (A)(ϋ)(a) are different than (A)(1)(a) and at least one of said

plurality (A)(IT)(a) includes said carbonate functional group.

28. A coating composition as set forth in claim 1 further comprising the

reaction product of an anionic surfactant.

29. A coating composition as set forth in claim 1 wherein said first

block (A)(1) has a molecular weight of from 1,000 to 20,000.

30. A coating composition as set forth in claim 1 having a non- volatile content of from 20 to 60 percent non- volatile by weight.

31. A coating composition as set forth in claim 1 having an average

particle size of less than or equal to 200 nm.

32. A coating composition as set forth in claim 1 wherein said

copolymer (A) ha a molecular weight of from 5,000 to 2,000,000.

33. A method of preparing a curable, water-based coating composition,

said method comprising the steps of:

(A) forming a first block;

(B) polymerizing a second block having at least one carbonate

functional group with the first block to establish a water-based copolymer;

(C) converting the at least one carbonate functional group in the second

block of the water-based copolymer into at least one carbamate functional group;

and

(D) combining the water-based copolymer with at least one cross-

linking agent that is reactive with the carbamate functional group and dispersible in

water.

34. A method as set forth in claim 33 wherein the at least one cross-

linking agent (B) is selected from the group consisting of water-dispersible

aminoplasts, water-dispersible polymers having acrylamide groups, and water-

dispersible polymers having methylol or alkoxymethyl groups, and mixtures

thereof.

35. A method as set forth in claim 34 wherein the water-dispersible

aminoplasts are selected from the group of melamine formaldehyde resins having a

methylol group, an alkoxymethyl group, or both, which are reactive with the

carbamate functional group.

36. A method as set forth in claim 33 wherein the step of (C) converting

the at least one carbonate functional group in the second block of the water-based

copolymer into the at least one carbamate functional group is further defined as

reacting an ammoma—containing compound selected from the group consisting of ammonia, ammomum hydroxide, and mixtures thereof, with the carbonate

functional group to convert the carbonate functional group into the carbamate

functional group.

37. A method as set forth in claim 33 wherein the steps of (A) - (C) are

conducted at a temperature between 50°C and 100°C.

38. A method as set forth in claim 33 wherein the step of (A) forming

the first block is further defined as polymerizing at least one ethylenically

unsaturated monomer and at least one vinylaromatic hydrocarbon monomer to

form the first block of the water-based copolymer.

39. A method as set forth in claim 38 wherein the step of polymerizing

the at least one ethylenically unsaturated monomer and the at least one

vinylaromatic hydrocarbon monomer is conducted over time from 1 to 8 hours.

40. A method as set forth in claim 38 wherein the step of (A) forming

the first block further includes the step of adding a neutralizing agent selected from the group consisting of dimethylethanolamine, amino methyl propanol, ammonia,

and mixtures thereof, to the at least one ethylenically unsaturated monomer and the

at least one vinylaromatic hydrocarbon monomer to form the first block of the

water-based copolymer.

41. A method as set forth in claim 38 wherein the step of (A) forming

the first block further includes the step of adding an initiator selected from the

group consisting of inorganic persulfates, dialkyl peroxides, hydroperoxides,

peresters, and mixtures thereof, to the at least one ethylenically unsaturated

monomer and the at least one vinylaromatic hydrocarbon monomer to form the first block of the water-based copolymer.

42. A method as set forth in claim 38 wherein the at least one

ethylenically unsaturated monomer is selected from the group of compounds

consisting of aliphatic acrylates, aliphatic methacrylates, cycloaliphatic acrylates,

cycloaliphatic methacrylates, alkyl acrylic acids, and mixtures thereof, each of the

compounds having up to 20 carbon atoms in the alkyl radical.

43. A method as set forth in claim 38 wherein the at least vinyl aromatic

hydrocarbon monomer is selected from the group consisting of α-methylstyrene,

diphenylethylene, dinapthaleneethylene, and mixtures thereof.

44. A method as set forth in claim 33 wherein the step of (B)

polymerizing the second block having at least one carbonate functional group with

the first block is further defined as polymerizing a plurality of ethylenically

unsaturated monomers with the first block, wherein at least one of the plurality

includes the carbonate functional group that is converted into the carbamate

functional group, to form the second block of the water-based copolymer.

45. A method as set forth in claim 44 wherein the step of polymerizing the plurality of ethylenically unsaturated monomers with the first block is

conducted over time from 1 to 8 hours.

46. A method as set forth in claim 44 wherein the plurality of

ethylenically unsaturated monomers are selected from the group consisting of

styrene, butyl acrylate, butyl methacrylate, 2-ethylhexyl methacrylate, 2-

hydroxyethyl methacrylate, cyclohexyl methacrylate, glycidyl acrylate, glycidyl ' methacrylate, carbonate-modified glycidyl acrylate, carbonate-modified glycidyl

methacrylate, and mixtures thereof, such that at least one of the plurality includes

the carbonate functional group.

47. A method as set forth in claim 34 wherein the step of (D) combining the water-based copolymer with the at least one cross-linking agent further includes the step of reacting the methylol and the alkoxymethyl groups of the melamine formaldehyde resins with the at least one carbamate functional group.

48. A method as set forth in claim 33 wherein the step of (C) converting the at least one carbonate functional group in the second block of the water-based copolymer into the at least one carbamate functional group is conducted over time from 1 to 4 hours.

49. A method as set forth in claim 33 wherein the step of (D) combining the water-based copolymer with at least one cross-linking agent further includes the step of adding an anionic surfactant to guarantee the dispersibility of the cross- linking agent in water.

50. A method of preparing a cured film of a water-based coating composition, said method comprising the steps of:

(A) forming a first block;

(B) polymerizing a second block having at least one carbonate

functional group with the first block to establish a water-based copolymer;

(C) converting the at least one carbonate functional group in the second

and

(D) combining the water-based copolymer with at least one cross-

linking agent that is dispersible in water and reactive with the carbamate functional

group to form the water-based coating composition;

(E) applying the water-based coating composition to a substrate; and

(F) curing the water-based coating composition to form the cured film.

51. A method as set forth in claim 50 wherein the step of (E) applying

the water-based coating composition to the substrate is further defined as spraying

the water-based coating composition on to the substrate.

52. A method as set forth in claim 50 wherein the step of (F) curing the

water-based coating composition is further defined as reacting the cross-linking

agent with the at least one carbamate functional group to form the cured film of the

water-based coating composition.

53. A method as set forth in claim 52 wherein the cross-linking agent is

a water-dispersible aminoplast selected from the group of melamine formaldehyde

resins having a methylol group, an alkoxymethyl group, or both, which are reactive

with the carbamate functional group.

54. A method as set forth in claim 53 wherein the step of reacting the cross-linking agent with the at least one carbamate functional group is further defined as reacting the methylol and alkoxymethyl groups of the melamine formaldehyde resins with the at least one carbamate functional group.

55. A method as set forth in claim 52 wherein the step of reacting the cross-linking agent with the at least one carbamate functional group is conducted at a temperature between 100°C and 175°C.

56. A curable, water-based coating composition comprising the reaction

product of:

(A) a water-based copolymer prepared by free-radical polymerization,

said copolymer comprising the reaction product of;

(I) a first block comprising the reaction product of;

(a) at least one ethylenically unsaturated monomer, and

(b) at least one ethylenically unsaturated monomer

different than (A)(1)(a) and of the general formula

^Rl _κ ^R3

\ /

/^C-\

R₂ R₄

wherein the radicals each independently of one

another are hydrogen atoms or substituted or unsubstituted

alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl, aryl,

alkylaryl, cycloalkylaryl, arylalkyl or arylcycloalkyl radicals,

with the proviso that at least two of the variables R_l5 R₂, R₃,

and R_ι are substituted or unsubstituted aryl, arylalkyl or

arylcycloalkyl radicals, especially substituted or

unsubstituted aryl radicals; and

(II) a second block comprising the reaction product of;

(a) a plurality of ethylenically unsaturated monomers

different than (A)(1)(a) and (A)(1)(b), wherein at least one of said plurality includes

at least one carbonate functional group for modification into a carbamate functional

group; and (B) at least one cross-linking agent reactive with said carbamate functional group and dispersible in water.