EP1208147A4

EP1208147A4 - Nonionic associative thickener composition with improved viscosity retention upon tinting in architectural latex coating

Info

Publication number: EP1208147A4
Application number: EP00954049A
Authority: EP
Inventors: G Mark Zody
Original assignee: Sued Chemie Inc
Current assignee: Sued Chemie Inc
Priority date: 1999-08-13
Filing date: 2000-08-11
Publication date: 2002-10-16
Also published as: CA2384180A1; WO2001012712B1; EP1208147A1; AU772095B2; AU6639700A; MXPA02001461A; JP2003507509A; WO2001012712A1

Abstract

The present invention relates to a latex coating composition that contains at least one linear aminoplast ether copolymer having a relatively high hydrophobe content and sufficient to thicken the latex coating without the need for additional thickeners.

Description

NONIONIC ASSOCIATIVE THICKENER COMPOSITION WITH IMPROVED VISCOSITY RETENTION UPON TINTING IN ARCHITECTURAL LATEX COATING

BACKGROUND TO THE INVENTION

1. Technical Field

The present invention relates to a water soluble copolymer composition containing a linear aminoplast-ether copolymer possessing a relatively high content of the hydrophobe tristyryl phenol. Such a copolymer contains a unit of the formula:

wherein the divalent Ro , contains a divalent alkyleneoxy containing moiety, Amp is the skeletal residue of an aminoplast, as stated above, R is hydrogen, alkyl containing 1 to about 4 carbon atoms, or acyl containing 1 to about 4 carbon atoms, RO is bonded to alkylene units of Amp, and a is a number greater than 1 , preferably greater than 2. Amp includes any dimer and oligomer component of the aminoplast. Ro₂ is tristyryl phenol, that is covalently bonded to Amp through a heteroatom, p₂ is number that is equal to the free valence of Amp minus (2 + q), and q is a positive number

2. Background

Nonionic associative thickeners have been used in latex architectural coatings for nearly 20 years. They have replaced the traditional cellulosic thickeners because coatings that utilize nonionic associative thickeners exhibit improved application properties such as brush drag, flow and leveling, and water sensitivity. The term "associative thickener'^* is recognized in the art to mean a nonionic hydrophobically modified water-soluble polymer capable of interacting in aqueous solution with itself and with other species such as latex particles. Associative thickeners are widely used to enhance the performance properties of paints and coatings. The use of associative thickeners in water based compositions are described in a number of patents, including U S Patent Nos 5,574,127, 4,426,485, 4,155,892, 4,079,028, 3,035,004; 2,795,564, 2,875,166 and 3,037,952

One type of associative thickener is descπbed by the two Emmons et al. patents, U S. Pat. No. 4,079,028 and U S Pat. No 4, 155,892, patented Mar 14, 1978 and May 22, 1979, respectively. These patents descπbepolyurethane associative thickeners that contain hydrophobic groups interconnected by hydrophihc polyether groups The thickeners are nonionic

Another type of associative thickener is descπbed in US Patent Nos. 5, 627,232 and 5, 629, 373 issued on May 6, 1997 and May 13, 1997 respectively. These patents descπbe water-based coating compositions containing a water soluble linear aminoplast-ether copolymer containing aminoplast segments interlinked through ether segments Aminoplasts are defined in those patents, and herein, and m the claims, as an A-stage class of thermosetting resin based on the reaction of an amme with an aldehyde and the related acetals contaimng ammes or amides. The structural features and commercial uses of ammoplasts are also described in detail m those patents Figure 1 contains a partial list of aminoplasts.

US Patent Nos.5,627,232 and 5,629,373 describes a linear aminoplast-ether copolymer with the formula as described in Fig 2.

where the divalent RQ i contains a divalent alkyleneoxy containing moiety, Amp is the skeletal residue of an aminoplast, R is hydrogen, alkyl containing 1 to about 4 carbon atoms, or acyl containing 1 to about 4 carbon atoms, p is a positive number that is equal to the free valence of Amp minus 2, RO is bonded to alkylene units of Amp, and a is a number greater than 1.

For the purposes of this invention and the discussion of the prior art, the skeletal unit of the aminoplast is the structure of the aminoplast minus the RO — leaving groups bonded to alkylene of the alkylol or alkylol ether or ester of the aminoplast, regardless of whether any of the RO — groups are removed from the aminoplast. That skeletal unit is referred to herein and in the claims as "Amp."

The term "linear," when used herein and in the claims to characterize a polymer, relates to a polymer that is devoid of crosslinking or branching that renders the polymer solid and cured. A "wholly linear" polymer is apolymerthat is devoid of crosslinking and branching. A linear polymer may or may not be a wholly linear polymer.

The term "acrylic polymer" means any polymer wherein at least 50% by weight is an acrylic or methacrylic acid or ester, including mixtures of such acids and esters individually and together. The term "vinyl acetate polymer" means any polymer containing at least 50% by weight of vinyl acetate.

The symbols and designations used herein are intended to be consistently applied, especially as used in formulations and equations, unless specifically stated otherwise. Typical nonionic associative thickeners have had only limited success when used in latex coatings for the mid to neutral base formulations based on small particle size acrylics The problem aπses when colorants are added to said formulations The addition of colorant in the amounts of about 5 ounces or above results in a substantial reduction in the viscosity of the coating This reduction in viscosity leads to undesirable coating properties and has been addressed by architectural coating manufacturers in a number of ways

One method manufacturers have used is to compensate for the viscosity drop that occurs upon tinting The coating is formulated to have a very high viscosity before the colorant is added The colorant is added expecting that the viscosity of the coating drop to an acceptable level Another method that manufacturers have used is to incorporate large amounts of surfactants and solvents into the coating to control the viscosity drop upon tinting Still yet another method used by manufacturers is to incorporate other thickening agents such as cellulosics and alkai-swellable thickeners to compensate for the viscosity drop While these methods do address the viscosity problem, each of these corrective methods has problems associated with them that make their use less than ideal

The problem with formulating a pre-tmted coating with a very high viscosity is that it creates problems in the manufactuπng process The problem with additives such as surfactants and solvents, or cellulosics and alkai-swellable thickeners is that it compromises the application properties of the resulting coating The additives can also cause problems with the physical properties of the final dπed paint film For example, high levels of surfactants or the use of alkai-swellable thickeners can lead to water sensitivity or poor scrub resistance

What is needed is a nonionic associative thickener that can be used in latex coatings for the mid to neutral base formulations based on small particle size acrylics that results in minimal reduction in viscosity when the colorant is added

What is needed is a nonionic associative thickener that can be used in latex coatings of the mid to neutral base formulations based on small particle size acrylics that does not need the addition of surfactants and solvents, or other thickening agents to achieve a satisfactory viscosity when the colorant is added

What is needed is a nonionic associative thickener that can be used in latex coatings for the mid to neutral base formulations based on small particle size acrylics that maintains desirable application properties when the colorant is added without compromising the final film properties.

Summary of the Invention

The present invention relates to a water soluble copolymer composition containing a linear aminoplast-ether copolymer possessing a relatively high content of the hydrophobe tπstyryl phenol Such a copolymer contains a unit of the formula

wherein the divalent Ro, contains a divalent alkyleneoxy containing moiety, Amp is the skeletal residue of an aminoplast, as stated above, R is defined above, RO is bonded to alkylene units of Amp, and a is a number greater than 1, preferably greater than 2 Amp includes any dimer and oligomer component of the aminoplast R<,₂ ^Js tπstyryl phenol, that is covalently bonded to Amp through a heteroatom, p₂ is number that is equal to the free valence of Amp minus (2+ q), and q is a positive number The relatively high content of the hydrophobe means a copolymer that contains more than about 3 % tπstyryl phenol based on weight. In the preferred embodiment, the copolymer contains about 4% tπstyryl phenol to about 10% tπstyryl phenol based on weight when the polymer is produced usmg polyethylene oxide and a glycoluπl compound In another embodiment of the invention, the invention relates to a novel water-based coating composition that contains a linear aminoplast-ether copolymer possessing end groups characteπzed by a component of the units making up the copolymer, or a monofunctional group that effectively end-caps the copolymer, forming the end group This yields a copolymer of the formula

where each R,₎₀ is the same or different terminal group, such as hydrogen, — R^, — H, Amp bonded — (OR)_pb — Amp — (OR)_pι, tristyryl phenol, or any other mono functional organic groups, such asalkyl, cycloalkyl, aryl, alkaryl, aralkyl, alkyoxyalkyl, aroxyalkyl, cycloalkoxyalkyl, and the like, and p , is a positive number that is equal to the free valence of Amp minus 1 A particularly preferred linear aminoplast-ether copolymer comprises units of the formula:

wherein R, i ,Ro₂, and R are described above, n has a value of at least 2, x is 0 or 1 , and s+ 1 equals (i) the free valence of the

moiety and (ii) 4-x: and the average value of t/s+ t is about 0.01 to about 0.5.

In a further preferred embodiment of the invention, the linear aminoplast-ether copolymer employed in the coating composition of the invention comprises a copolymer that possesses end groups as illustrated by the following structure:

wherein each R^₀₁ is the same or different terminal group, such as hydrogen, — R^ — H, — (OR)_pι, — Amp⁰ — (OR)_p i , tristyryl phenol, or any other mono functional organic groups, such as alkyl, cycloalkyl, aryl, alkaryl, aralkyl, alkyoxyalkyl, aroxyalkyl, cycloalkoxyalkyl, and the like, and p , is a positive number that is equal to the free valence of Amp⁰ minus 1. Amp⁰ is depicted in formula V.

The present invention further relates to a latex coating for the mid to neutral base formulations based on small particle size acrylics. The present invention improves on this type of latex coatings by reducing the drop in viscosity that normally occurs when the colorant is added to latex coating for the mid to neutral base formulations based on small particle size acrylics. The present invention also yields overall improved color acceptance compared to other compositions and competitive products.

Detailed description of the invention

This invention relates to the use of any aminoplast, including those specifically recited in FIG. 1 above, to make the copolymer of the invention. Of these aminoplasts, exceptional performing associative thickeners, for use in latex coatings for the mid to neutral base formulations based on small particle size acrylics, are obtained from the reaction of glycoluπls with alkylene oxide glycols to w uch are incorporated the tπstyryl phenol pendant moieties

The linear aminoplast-ether copolymers of formula I et seq are made by the novel condensation reaction of a polyfunctional aminoplast with a di-functional polyether (alone or with another polyol, as characteπzed with respect to formulae XII and XIII) in the presence of an acid catalyst In the pπor art, as noted above, ammoplasts are condensed with polyfunctional compounds to produce thermosetting resins or thermoset products (1 e , C-stage res ) This reaction produces a linear copolymer Thus, the copolymers of formulae I, II, III, IV, and V are either liquid or thermoplastic solids that are solvent soluble and water soluble or dispersible

The linear aminoplast-ether copolymer are made by the copolymeπzation reaction of a polyfunctional aminoplast with an ether containing two active hydrogen terminal groups, m the presence of an acid catalyst, especially a Bronsted-Lowery acid provided in catalytically effective amounts The reaction is continued until the desired molecular weight is achieved The desired molecular weight of the copolymer is dependent on the mtended use of the copolymer The molecular weight of the copolymer may range from about 12,000 to about 800,000, preferably from about 20,000 to about 100,000, and most preferably from about 30,000 to about 80,000 The aminoplast is a polymenzable resin of the general formula

(RO)-, Amp VI

wherein z is a positive number having a value of at least 2. The ether containing two active hydrogen terminal groups compπses a wide vaπety of compositions A preferred class is nonionic Illustrative of a preferred class of such ethers are polyalkylene oxides of the formula

H— Alkylene Oxide — H VII where "alkylene oxide" is a divalent moiety containing at least two alkylene oxide units in which

1. the alkylene oxide units form a linear chain and provide a terminal OH, or

2. the alkylene oxide units are bonded to a starter molecule, such as a diamine, urea, carbamate, phenoxy, amide, bis-imide, and the like, and providing a terminal OH, and/or

3. in which alkylene oxide are bonded to a terminal group that possesses a moiety that provides the active hydrogen ( — H in formula VII).

Further illustrative of such a preferred class are the water soluble or dispersible polyether compounds of the formula:

H_{x i}X ( θ )x4(Rθ5)x5(Rθ6)x6(Rθ7) 7.Rθ8)x8 XH ₂ VIII.

wherein

X is an active hydrogen functional moiety such as oxy ( — O — ), sulfidyl ( — S — ), amino ( — N<), carboxy

( — COO — ), carboxamido, silyl, phosphoryl, ureido, and the like;

R_Q4 and Ro₈ are alkyl of 2 to about 8 carbon atoms;

R^and R^are one or more alkylene oxide units, e.g., such as water soluble or dispersible ethylene oxide, propylene oxide, mixed ethylene oxide/1 ,2-propylene oxide, mixed ethylene oxide/1 ,3-propylene oxide, mixed ethylene oxide/1, 2-butylene oxide, mixed ethylene oxide/ 1,4-butylene oxide, and the like;

Rogis a divalent group such as alkyleneoxy, alkylenφolyamine, cycloalkylene polyamine, phenoxy, uriedo, carbamate, amide, and the like; xl and x2 are each equal to the free valence of X; x3, x4, x5, x6 and x7 are each 0 or 1, and one or more of x4 and x6 is 1. Specific illustrations of a limited class of polyethers encompassed by formula VIII are the Carbowax® and Pluracol® polyether diols sold by Union Carbide Chemicals & Plastics, Inc. and BASF Performance Chemicals, respectively. There are a variety of functional fluids based on alkylene oxides that are sold by Union Carbide Chemicals & Plastics, Inc. and BASF Performance Chemicals that are encompassed by formula VIII. The molecular weight of the polyether reagent may range from about 106 and lower, to about 35,000, and higher.

In the prior art. as noted above, aminoplasts are condensed with polyfunctional compounds to produce thermosetting resins or thermoset products (i.e., C-stage resin). The above method produces a linear copolymer. Thus, the copolymers of formulae I, II, III, IV, and V are either liquid or thermoplastic solids that are solvent soluble and water soluble or dispersible.

Aminoplast reagents include, but are not restricted to, aldehyde reaction products of melamines, ureas, benzoguanamines, glycolurils, and the like, to produce the array of aminoplasts, including but not limited to those described in FIG. 1 above. While any of these can be used to make associative thickeners, the glycolurils, such as those of formula IX

H₃co- -OCH,

where R and x are defined above, have shown appropriate hydrolyric stability, when reacted with the polyether compounds, such as those encompassed by formula VIII, to meet commercial criteria for associative thickener-containing coating compositions. However, the reaction products of such aminoplasts with, e.g., thiols and NH groups from amides and carbamates, encompassed by formula VIII, are much more hydrolytically stable than aminoplast ether linkages. The use of such reactants allow for the production of most hydrolytically stable aminoplast-based copolymers.

Suitable polyethers include polyalkylene polyethers. The preferred polyethers are water soluble. The most preferred polyethers are the alkylene polyethers where the predominant alkylene groups are ethylene. The most desirable polyethers are polyethylene oxide diols that possess molecular weights from about 1,000 to about 35,000.

Illustrative of the desirable polyethylene oxide diols are those of the formula:

HO— (— CH₂CH₂O)_x , , CH₂CH₂OH X.

wherein xl 1 has a value of about 20 to about 800, preferably from about 50 to about 500, and most preferably from about 100 to about 300.

A further desirable embodiment of the invention is the modification of the linear aminoplast-ether copolymers used in making the coatings of the invention by including a minor mole proportion of the following unit structure in the repeating structure of the copolymer:

— Amp— R₁₅— XL

wherein R_]5is the residue of a diol possessing greater hydrophobicity than R_Q,, thereby providing for a linear copolymer containing the structure

Amp- ^"Roι ^•Amp R₁₅

J x29 x30 XII

wherein x29 has a value that is greater than x30. Preferably, x30/x29 is less than about 1 , preferably less than about 0.33. Illustrative of such R₁₅ groups are H(0CH₂CH wherein x31 has a value of about 8 to about 20, x32 has a value of about 8 to about 23, x33 and x34 have values of 0 to about 8. The linear copolymer of formula XII may be modified to possess the terminal groups of formulae II and V, discussed above.

The linear aminoplast-ether copolymers of this invention, contains a hydrophobe pendant group. Acceptable hydrophobe groups include aliphatic to alkyl phenol to tristyryl phenol. The most preferred hydrophobic pendant group is tristyryl phenol. Tristyryl phenol extends from aminoplast component of the linear backbone of the aminoplast-ether copolymer. Tristyryl phenol groups are typically bonded to the backbone through ether or ester groups, as illustrated in formula II. The presence of tristyryl phenol enhances the performance of the resulting aminoplast-ether copolymer as an associative thickener in architectural coating compositions for the mid to neutral base formulations based on small particle size acrylics where the level of colorant added is in large amounts for about the 5 to 16 oz per gallon range.

This invention relates to the use of any aminoplast, including those specifically recited in FIG. 1 above, to make the copolymer of the invention. Of these aminoplasts, exceptional performing associative thickeners are obtained from the reaction of glycolurils with alkylene oxide glycols to which are incorporated tristyryl phenol pendant moieties at a relatively high concentration. The relatively high concentration of tristyryl phenol means about 3% or greater based on weight. In the preferred embodiment the concentration of tristyrl phenol is at a concentration of about 4% to about 10% based on weight. The production of the aminoplast-ether copolymers are made by solvent or melt polymerization. The typical preparation of an aminoplast-, such as glycoluril-, based associative thickener involves dissolving the aminoplast (e.g., glycoluril), a polyether compounds within the scope of formula IX (such as a Carbowax© polyether sold by Union Carbide Chemical and Plastics, Inc., Danbury, Conn.), with or without the addition of a more hydrophobic polyol within the scope of formula XI,with the addition of ethoxylated tristyryl phenol (such as Soprophor BSU), in a stripping solvent, such as alkylated benzene (e.g., toluene or xylenes). Prior to the combination of these reagent, each may be dried by azeotropic distillation with toluene, xylenes, or a mixture of them, or by any other drying procedure. Total concentration of the reagents in the solvent may be maintained from about 10 to about 60 weight %. The temperature of the mixture may be brought to about 60°- 140° C, preferably to about 80°- 120° C. An acid catalyst, such as a sulfonic acid catalyst, is then added. The reaction mixture is placed under reduced pressure to bring about a steady distillation of the toluene/xylenes which azeotropes the alcohol byproduct that must be removed in order for the reaction to proceed. Fresh solvent is constantly added to maintain a constant level. The reaction is allowed to proceed until a given high viscosity is achieved as measured by Gardner bubble tubes or until viscosity increase ceases. Such viscosity increase indicates an increase in the molecular weight of the copolymer.

SPECIFIC ILLUSTRATION OF SOLVENT PROCESS The following is an illustration of the sequential steps involved in preparing the aminoplast- ether copolymer.

1. Polyether polyol, ethoxylated tristyryl phenol, and azeotroping solvent (e.g., toluene) are added to an appropriately sized container that accommodates a heater, temperature reading device, a nitrogen inlet, and a Dean Stark water trap and condenser. 2. The mixture of step 1 is heated to reflux to dry the mixture by azeotropic distillation. When water removal ceases, the mixture is cooled to about 100° C, and the water trap is removed. A distillation column and receiving vessel are installed in the container.

3. Glycoluril (e.g., Powderlink 1 174) is added and allowed to melt.

4. The catalyst is added and vacuum is applied. The pressure is reduced to a level that causes a steady distillation of solvent at about 100° C. The solvent is continually replenished from a pressure equalizing add funnel.

5. As the reaction proceeds, samples are removed and cooled to room temperature, and the Gardner bubble viscosity is measured.

6. When the proper viscosity is reached, the heat is removed and the mixture is cooled in a waterbath. When the temperature has been reduced to below 75° C, an amine neutralizing agent is added. When the temperature is reduced to below 65° C, the polymer solution is poured out onto trays to air dry.

7. The dried polymer is cut into strips and redissolved in water or water/cosolvent mixture.

Polymerization in the melt involves the admixture of the same reagents in the absence of a solvent with a heavy duty laboratory mixer (such as an Universal Sigma Blade Mixer, sold by Baker Perkins Guittard S A, Paris, France) at a temperature sufficient to generate leaving groups and remove the reaction condensation products. The removal of volatile byproducts by vacuum is necessary in order to shift the reaction to the right and prevent an equilibrium reaction from occurring that impedes the reaction before the desired degree of polymerization is achieved. Catalysts useable for effecting the copolymerization reaction includes the standard Brδonsted-Lowery acid catalysts typically used for the condensation of aminoplast resins. Such acid catalysts include mineral acids (e.g., HC1, H₂S0₄, H₃PO₄, and the like), aryl sulfonic and alkylated aryl sulfonic acids, such as benzene sulfonic acid, p-toluene sulfonic acid, 1 -naphthalene sulfonic acid, 2-naphthalene sulfonic acid, naphthalene- 1,5-disulfonic acid, naphthalene-2,7-disulfonic acid, 1,3,6-naphthalene trisulfonic acid, naphtholsulfonic acid, dinonylnaphthalene disulfonic acid, dodecylbenzene sulfonic acid, oxalic acid, maleic acid, hexamic acid, alkyl phosphate ester, phthalic acid, and copolymerized acrylic acid. Of these catalysts, the sulfonic acid catalysts are the most effective and efficient for making the copolymers of the invention and dodecylbenzene sulfonic acid is the most preferred sulfonic acid catalyst.

Glycolurils are marketed by Cytec Industries as Cymel 1170, 1171, 1175 and Powderlink 1174. The Cymel versions are either mixed methylolated species and typically contain a relatively high dimer or oligomer content of up to about 20 weight percent. Powderlink 1174 is a purer form that is solely the methyl ester of the formula:

H,

with about 3-5 weight percent of a dimer-oligomer of the monomer form. The purer the monomeric form of the aminoplast, the better it is in forming the copolymers of the invention. In about 5-7 weight percent ofPowderlink 1174, x is 0, and such monomer form is trifunctional. The dimer-oligomer forms provide greater amounts of methoxy per molecule. For example, the dimer contains 6 methoxy functional groups. Such tri- and hexa- functionality does not alter this invention. The glycoluril ether linkage is much more resistant to hydrolysis than other aminoplast ether bonds. The higher dimer-oligomer content of the less pure glycolurils is not as favored as the lower dimer-oligomer content of Powder link 1 174. ' Further reduction of oligomers can be effected by recrystallization.

'Powderlink 1 174 is called a "resin" and "crosslinker" by Cytec, and has been sold under the Cymel® name (i.e., Cymel 1174). Its empirical structure is C _]2H₂₂N₄0₆. Its chemical name is Imidazo [4,5-D] imidazole-2,5 ( 1 H,3H)-dione, tetrahydro- 1 ,3 ,4,6-tetrakis (methoxymethyl)-. CAS 17464-88-9. It is also known by the following names: (i) Glycoluril, 1 ,3,4,6 tetrakis methoxymethyl, (ii) Glycoluril, tetrakis methoxymethyl, (iii) Glycoluril, N,N,N,N tetrakis methoxymethyl, (iv) Glyoxal diuriene, tetrakis methoxymethyl, and (v) Tetramethoxytetramethylol acetylenediurea. The favored name is (i) and such skeletal structure is called glycoluril.

The ratio of aminoplast resin to the difunctional polyether is not critical. Typically, either the aminoplast resin or the difunctional polyether may be used in molar excess or stoichiometrically equivalent amounts in making the linear copolymer of the invention. In characterizing stoichiometry of the aminoplast resin, the resin is treated as being difunctional since linearity, according to the invention, is achieved when the aminoplast resin functions as a difunctional monomer even though the resin has the capability ofhigher functionality, e.g. , tri- and tetrafunctionality, as the case may be. Thus, more than one mole of a polyether diol to one mole of, e.g., a glycoluril such as Powderlink 1174, represents a stoichiometric excess of the polyether to the glycoluril. Using this characterization, one may use between 1 -2 moles of one of these reagents to 1 mole of the other. Either the polyether or the aminoplast may be in excess. However, it is more typical to use a mole amount ofone reagent of about 1-1.75 to 1 ofthe other reagent. Typically, one employs a molar excess ofthe aminoplast resin because one may incorporate more hydrophobicity into the copolymer this way. This is especially the case when the copolymer is dimeric to oligomeric (e.g., possessing less than about 15 repeating units). When making higher polymeric structures, one uses a greater proportion ofthe polyether reagent, up to a 1 : 1 mole ratio . In general, it is desirable to use a molar excess of aminoplast of about 1.001-2.0 moles to 1 mole ofthe difunctional polyether. The amount of ethoxylated tristyryl phenol should not exceed about 2.0 moles, nor be less than about 0.4 mole per mole of reacted aminoplast resin in the copolymer ofthe invention. Usually, the amount of ethoxylated tristyryl phenol ranges from about 0.7 mole to about 1.5 mole per mole of reacted aminoplast.

Waterbome coatings may be defined as coatings that contain water as the major volatile component and utilize water to dilute the coating to application consistency. These coatings consist mainly of resinous binder, pigments, water, and organic solvent. The type of pigmentation and the method of incorporation of the pigment vary widely.

Waterbome coatings can be made by dispersing, emulsifying or emulsion polymerizing the resin binder by use of added surfactants. This technique leads to opaque liquids. Because some hard resins are difficult or impossible to disperse directly into water, the resin sometimes can be dissolved in a water- immiscible solvent, and the resulting solution dispersed by the use of added surfactants. In this case, the solvent aids subsequent film coalescence. Surface activity or water dispersability also can be introduced into resin molecules by chemical modification ofthe resin by introducing functional polar groups such as the carboxyl group.

Some very finely dispersed resins appear as clear or slightly hazy liquids; they frequently are described as soluble, solubilized, colloidal dispersions, micro-emulsions, hydrosols, etc. These resins contain built-in functional groups that confer water ' 'solubility' ' upon the resin, and, normally, external added surfactants are not used.

Waterbome resin binders can be classified as anionic, cationic, or non-ionic. Anionic dispersions are characterized by negative charges on the resin or by negative charges on the surfactant associated with the resin. Cationic dispersions have a positive charge on the resin or on the surfactant associated with the resin. Nonionic dispersions are those that have been dispersed by addition of nonionic surfactants or that contain a built-in hydrophilic segment such as polyethylene oxide which is part ofthe main chain of a relatively hydrophobic resin molecule.

The coating compositions may be ofthe thermosetting or thermoplastic varieties. The resin used in forming the coating may be insoluble in water, and the conversion of such a resin into a waterbome system typically involves com erting the resin into an emulsion or dispersion hi the context of this invention, the waterbome composition contains the aminoplast-ether copolymer associative thickener ofthe invention

The aqueous polymer dispersions may be prepared according to well known emulsion polymeπzation procedures using one or more emulsifiers of an anionic, cationic, or nonionic type Mixtures of two or more non-neutralizing emulsifiers regardless of type may be used The amount of emulsifier may range from about 0 1 to 10% by weight or sometimes even more, based on the weight ofthe total monomer charge In general, the molecular weight of these emulsion polymers is high, e g , from about 100,000 to 10,000,000 number average molecular weight, most commonly above 500,000

The water insoluble resm may be any of those known in the art, and may be a conventional natural or synthetic polymer latex emulsified with one of a nonionic, cationic or anionic surfactant The primary resins are based on homopolymeπzed and copolymeπzed olefinic monomers such as vmyl acetate, vmyl chloπde, styrene, butadiene, vinyhdene chloride, acrylonitπle, methacrylonitπle, acrylic acid, methacrylic acid, alkyl acrylates, alkyl methacrylates, acrylamide, methacrylamide, hydroxyethyl methacrylate ("HEMA"), glycidyl methacrylate, dihydroxypropyl methacrylate, homopolymers of C₂-C₄₀ alpha-olefins such as ethylene, isobutylene, octene, nonene, and styrene, and the like, copolymers of one or more of these hydrocarbons with one or more esters, mtπles or amides of acrylic acid or of methacrylic acid or with vmyl esters, such as vmyl acetate and vinyl chlonde, or with vmyhdene chloπde, and diene polymers, such as copolymers of butadiene with one or more of styrene, vmyl toluene, acrylomtπle, methacrylonitπle, and esters of acrylic acid or methacrylic acid, and the like It is also quite common to include a small amount, such as 0 1 to 5% or more, of an acid monomer m the monomer mixture used for making the copolymers mentioned above by emulsion polymerization Acids used include acrylic, methacrylic, itacomc, crotomc, maleic, fumaπc, and the like

The vinyl acetate copolymers are well-known and include copolymers such as vmyl acetate/butyl acrylate/2-ethylhexyl acrylate, vinyl acetate/butyl maleate, vmyl acetate/ethylene, vmyl acetate/vmyl chloπde^/butyl acrylate and vmyl acetate/vinyl chloπde/ethylene Other waterbome systems involve reactive copolymers that are crosslinked by the presence of complementary functional groups in the system. For example, a copolymer of acrylic ester/glycidylmethacrylate can be emulsified and crosslinked by the presence of a melamine-formaldehyde resin similarly emulsified in the system. In another system, a copolymer of HEMA and another acrylate, hydroxyl terminated polyesters, polyethers, or polyurethanes, can be emulsified and crosslinked by the presence of either an aminoplast resin, a polyisocyanate or blocked polyisocyanate.

The term ' 'acrylic polymer" means any polymer wherein at least 50% by weight is an acrylic or methacrylic acid or ester, including mixtures of such acids and esters individually and together. The term "vinyl acetate polymer" means any polymer containing at least 50% by weight of vinyl acetate.

Small particle size (about 0.1-0.15 micron) acrylic and other latices are thickened effectively, and flow and leveling improved, by thickeners ofthe invention. The use of this invention for producing architectural coatings for the mid to neutral base formulations based on small particle size acrylics where the level of colorant added is in large amounts for about the 5 to 16 oz per gallon range eliminates the need to incorporate other thickener systems, such as cellulosics and alkai-swellable thickeners or large amounts of surfactants.

The amount ofthe aminoplast-ether copolymer described herein that is employed in the coating composition ofthe invention is not critical. That amount will vary based on the resin system used, the water concentration, the amount of fillers and the choice of fillers, the presence or absence of thixotropic agents, and the like. In that respect, the amount ofthe aminoplast-ether copolymer in the composition is sufficient to thicken the composition. However, in general, the amount ofthe copolymer will range from about 0.1 weight percent to about 15 weight percent, preferably from about 0.5 weight percent to about 10 weight percent, and most preferably from about 1 weight percent to about 8 weight percent, ofthe weight ofthe coating composition, exclusive of fillers, pigments and like additives.

The following is an illustrative formulation for an architectural coating based on small particle size acrylic. Optiflo H600 is the aminoplast-ether copolymer described above. EXAMPLE

1 ) Water, propylene glycol, Tamol 731 , foamaster VL, Kathon LX are added to a high speed disperser tank equipped with a cowls high speed agitator blade Agitation is begun followed by the addition of the R-900 dry TιO2 pigment The mixture is ground at high speed (-2,000 rpm) for 20 to 30 minutes or until the Tι02 is well dispersed (usually determined using a hegman grind gauge of greater than 6)

2) Once the gπnd is complete the speed or shear is decreased and the gπnd paste is transferred to another tank equipped with a mixing blade (usually a slow speed paddle blade) The SG-10M and OP62 are added and mixed for approximately 10 minutes The remaining ingredients can be added (water, Optiflo L 100 and Optiflo H600) A defoamer (Foamaster VL) is usually added so as to remove any enframed air

3) Quality Control checks usually consist of viscosity (Stormer & ICI), pH, weight per gallon (WPG), hiding power and color acceptance

SEMI-GLOSS SG-10M

GRIND POUNDS GALLONS

WATER 11.13 1 34

PROPYLENE GLYCOL 65 00 7 51

TAMOL 731 12.88 1 40 FOAMASTER VL 1 00 0.13 KATHON LX 1.80 0.22 TI-PURE R-900 253 00 7.60

GRIND TιO2 @ 1300 rpm FOR 30 MINUTES

R E C O R D M A X I M U M G R I N D TEMPERATURE

LET DOWN 5 GALLON PAIL - 3F

BLADE WATER 88 10.56

RHOPLEX SG-10 465.5 52.78 ROPAQUE OP-62 27.96 3.25 TEXANOL 24.32 3.07

SUB TOTAL:

950.62 87.87

MIX AT LOW SPEED 30 MINUTES RECORD WPG : 10.82 RECORD pH:

PREMIX:

WATER 72.20 8.67

L100 28.35 3.28

H600 0.50 0.06

FOAMASTER VL 1.00 0.13

TOTAL:

1,052.67 100.00

PVC%: 27.26 VS%: 34.10

Paint Examples

Evaluation in a Neutral Base Latex Paint Formuation:

The 17.5% solution from example 1 was evaluated in a semi-gloss neutral base formuation which contained Rhopex SG- 10M acrylic latex. The paints were tinted with 12 oz of F Colorant (red iron oxide) from CreaNova (888).

Loading Initial Stormer Stormer after tinting •KU

(Dry lbs/lOOgal) (KU) (KU)

Example 1 0.525 108 98 10

Acrysol RM825 0.525 102 82 20 Evaluation in a deep Base Latex Paint Formulation:

The 17.5% solution from example 1 was evaluated in a semi-gloss neutral base formulation which contained Rhopex SG-20M acrylic latex. The paints were tinted with 8 oz of F Colorant (red iron oxide) from CreaNova (888).

Loading Initial Stormer Stormer after tinting *KU

(Dry lbs/lOOgal) (KU) (KU)

Example 1 0.44 11 1 91 20

Acrysol RM825 0.44 110 64 246

7?

Claims

We claim:

1. A latex coating based on small particle size acrylics with improved viscosity retention, comprising: a) at least one pigment, water,

b) at least one dispersant, c) at least one defoamer,

d) at least one aminoplast ether copolymer sufficient to thicken the latex coating without the need for additional non-aminoplast ether copolymer thickeners.

2. The latex coating of claim 1, wherein the aminoplast ether copolymer has a relatively high hydrophobe content.

3. The latex coating of claim of claim 2, wherein the hydrophobe content is about 3 to about 10% weight content.

4. The latex coating of claim of claim 2, wherein the hydrophobe is tristyryl phenol.

5. The latex coating of claim 2, wherein the amount of aminoplast ether copolymer is from about 0.1 weight percent to about 15 weight percent.

6. The latex coating of claim 2, wherein the aminoplast ether copolymer has a molecular weight of about 12,000 to about 800,000.

7. The latex coating of claim 5, wherein the hydrophobe is tristyryl phenol.

8. A method for making a latex coating with improved viscosity retention having the following steps:

(a) admixing water, a dispersant, a defoamer, propylene glycol, and Kathon LX;

(b) admixing in additional desired additives and pigments;

(c) adding a premix to the container; and

(d) optionally adding a defoamer to remove entrained air.

9. The method for making a latex coating of claim 8, wherein the premix comprises water and aminoplast ether copolymer.

10. The method for making a latex coating of claim 9, wherein the aminoplast ether copolymer contains a relatively high hydrophobe content.

11. The method for making a latex coating of claim 9, wherein the hydrophobe is tristyryl phenol.

12. The method of making a latex coating of claim 9, wherein the hydrophobe content is greater than about 3% by weight.

13. The method for making a latex coating of claim 8, wherein the dispersant comprises Tamol

731.

14. The method for making a latex coating of claim 8, wherein the defoamer comprises foamaster VL.

15. The method for making a latex coating of claim 8, wherein the pigments comprise TiO₂.

16. The method of making a latex coating of claim 9, wherein the aminoplast ether copolymer contains a relatively high hydrophobe content.

17 The method of making a latex coating of claim 16, wherein the hydrophobe is aliphatic, alkyl phenol, tristyryl phenol, or combinations thereof.

18. A method for making a small particle size acrylic latex coating with an improved viscosity retention having the following steps:

(a) admixing water, a dispersant. a defoamer. propylene glycol, and Kathon LX;

(b) admixing in additional desired additives and pigments;

(c) adding a premix to the container; and

(d) optionally adding a defoamer to remove entrained air.

19. The method for making a small particle size acrylic latex coating of claim 18, wherein the premix comprises water, Optiflo LI 00, and Optiflo H600.

20. The method for making a small particle size acrylic latex coating of claim 18, wherein the pigments comprise TiO₂

21. The method for making a small particle size acrylic latex coating of claim 19, wherein the pigments comprise TiO₂