MXPA99003659A - Pigment dispersions containing aqueous branched polymer dispersant - Google Patents

Abstract

A waterbased dispersion useful for forming aqueous coating composition containing dispersed pigment, an aqueous carrier and a branched polymer dispersant (binder);the branched polymer has a weight average molecular weight of about 5,000 - 100,000 and contains 20-80%by weight of a hydrophilic backbone and correspondingly 80-20%by weight of macromonomer side chains;wherein the backbone is of polymerized ethylenically unsaturated monomers and 2-30%by weight, based on the weight of the backbone of polymerized ethylenically unsaturated monomers having an acid-functional group;and wherein at least 10%of the acid-functional groups are neutralized with an amine or an inorganic base and is hydrophilic in comparison to the side chains;the side chains are of macromonomers of polymerized ethylenically unsaturated monomers that are polymerized into the backbone via an ethylenically unsaturated group and the macromonomers have a weight average molecular weight of about 1,000 - 30,000 and wherein the weight ratio of pigment to binder is about 1/100 - 200/100.

Description

TITLE PIGMENT DISPERSIONS CONTAINING AN AQUEOUS DISPERSANT OF BRANCHED POLYMER TECHNICAL FIELD This invention relates to improved water borne pigment dispersions containing a branched, aqueous polymer dispersant.

BACKGROUND OF THE INVENTION Water-dispersible polymers which are used as dispersants for pigments and which are used to form pigment dispersions useful in the formulation of waterborne coating compositions are known in the art. Such pigment dispersions are used in waterborne paints for the exterior for automobiles and trucks. U.S. Patent No. 5,231,131, filed July 27, 1993, issued to Chu et al. Discloses aqueous graft polymer pigment dispersants in which the side chains of the graft copolymer contain carboxyl groups which are neutralized with an inorganic base or an amine While these graft copolymers are used as dispersants for the pigments, they are REF: 29628 present relatively large amounts of ethylenically unsaturated acid monomers, polymerized in the side chains of the graft copolymer to provide dispersibility in water but the presence of these acid groups in the graft copolymer makes it water sensitive. A finished or last automotive or truck layer, exterior containing a water sensitive component is undesirable since for example, it will result in water staining and acid etching and the finish will be subject to degradation by atmospheric agents. It is necessary for a polymeric dispersant to adequately disperse the pigments and the dispersant must contain relatively small amounts of polymerized acid monomers. When the pigment dispersions formulated from such a polymer are used in the waterborne coating composition, a finish is formed which is free from the undesirable effects of water and atmospheric agents.

BRIEF DESCRIPTION OF THE INVENTION A water based pigment dispersion for the formation of an aqueous coating composition containing dispersed pigment, an aqueous carrier and a branched polymer dispersant (binder substance); the branched polymer has a weight average molecular weight of about 5,000 - 100,000 and contains 20-80% by weight of a major or longer, hydrophilic chain and correspondingly 80-20% by weight of macromonomer side chains; wherein the main chain of the branched polymer is ethylenically unsaturated monomers, polymerized and 2-30% by weight, based on the weight of the main chain, of polymerized ethylenically unsaturated monomers having an acid functional group; and wherein at least 10% of the acid functional groups are neutralized with an amine or an inorganic base and is hydrophilic in comparison to the side chains; and the side chains are macromonomers of polymerized ethylenically unsaturated monomers that are polymerized in the main chain by means of an ethylenically saturated group and the macromonomers have a weight average molecular weight of about 1,000-30,000 and wherein the weight ratio of pigment to the binder substance is about 1/100 - 200/100; DETAILED DESCRIPTION OF THE INVENTION The novel pigment dispersion is stable and in general is non-flocculated or agglomerated and is compatible with a variety of polymeric film-forming binder substances that are conventionally used in waterborne and, in particular, compatible coating compositions. with acrylic polymers that are used in waterborne coatings. The branched polymer dispersant in curing the coating composition in which it has been incorporated reacts with other film forming components of the coating composition and becomes part of the film and does not cause deterioration of the film with the Exposure to the weather as it may occur if an unreacted component of the film remains. As well, since the branched polymer is an excellent dispersant, the ratio of polymer to pigment or polymer that is dispersed is lower than that used with conventional dispersants. In addition, the branched polymers allow the use of higher molecular weight polymers having a lower viscosity as compared to linear polymers of the same composition having the same molecular weight. The acid content of the main chain of the branched polymer can be easily adjusted to maximize the dispersion properties of the polymer without increasing the molecular weight and does not decrease the performance properties of a coating composition in which a pigment dispersion has been incorporated. of this polymer. The finishes of the aqueous coatings formulated with the dispersions containing these branched polymers are hard, resistant to water and moisture. The branched polymer used to formulate the dispersion of this invention is prepared from a macromonomer that forms the side chains of the branched polymer and comprises the polymerized alpha-beta ethylenically unsaturated monomers and has an ethylenically unsaturated, terminal portion and has an average molecular weight of weight (MW) of 1,000-30,000, preferably 6,000 to 15,000. Approximately 20-80% (by weight), preferably 30-70%, of the macromonomer is copolymerized with 80-20%, preferably 70-30%, of a mixture of other alpha, beta-ethylenically unsaturated monomers forming the main chain of the branched polymer. At least 2%, preferably 2-30% by weight, more preferably 3-15%, of the alpha, beta-ethylenically unsaturated monomer of the backbone has carboxylic acid functionality and a branched polymer is formed having a MW of 5,000-100,000, preferably 5,000-40,000, which after neutralization with an amine or other neutralizing agent can be dispersed in water. All molecular weights referred to herein are determined by GPC (gel permeation chromatography) using a polystyrene standard. It has been found that improved aqueous or water borne coating compositions are obtained by using these branched polymers as dispersants for the pigments. These compositions also contain a film-forming binder usually an acrylic polymer and a curing agent. Such compositions have the advantage of providing excellent coating properties desirable for automotive finishes. The side chains of the branched polymer are hydrophobic relative to the main chain and therefore contain less than 1% by weight, preferably essentially zero percent by weight, based on the weight of the branched polymer, of functional monomers of acid, ethylenically unsaturated, polymerized which are listed below in the present. The side chains contain hydrophobic, polymerized monomers such as methacrylates and alkyl acrylates, methacrylates and cycloaliphatic acrylates and methacrylates and aryl acrylates and styrene are as listed hereinafter and may also contain up to 30% by weight, based on weight of the branched polymer, of non-hydrophobic, ethylenically unsaturated, polymerized monomers which may contain functional groups. Examples of such monomers are hydroxy ethyl acrylate, hydroxy ethyl methacrylate, acrylamide, nitro phenol acrylate, nitro phenol methacrylate, methyl phthalimido acrylate, phthalimido methacrylate, acrylamide propane sulphonic acid and mixtures thereof. The acrylic macromonomer can be prepared using a free radical initiator in a solvent with a chelate chain transfer agent of Co (II) or Co (III). The main chain of the branched polymer contains at least 2 weight percent of a functional monomer of acid (neutralized) as, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid and the like. Methacrylic and acrylic acid are preferred. Other acids that can be used are sulfonic, sulfinic, phosphoric or ethylenically saturated phosphonic acid and esters thereof; it is also possible to use styrene sulfonic acid, acrylamido methyl propane sulphonic acid, phosphonic acid or vinyl phosphoric acid and their esters and the like. The main chain of the branched polymer preferably contains 2-30% by weight of methacrylic acid or acrylic acid and, preferably, 3 to 15% by weight and has a MW of 1,000-7,000. The acid functional groups in the branched polymer are neutralized with an inorganic base or an amine. In this way, the main chain is relatively hydrophilic in comparison to the side chains and the branched polymer keeps the pigments well dispersed in the resulting coating composition. Of course, the relative hydrophobicity or hydrophilicity could be further adjusted by varying the percentage of functional acid and / or hydroxy monomers against more hydrophobic monomers such as 2-ethylhexyl methacrylate. In a preferred embodiment, the branched polymer contains in total (including both the backbone chain and the macromonomer arms) about 0 to 40, preferably 5 to 40, and most preferably 10 to 30, percent by weight of monomers functional hydroxy acrylics such as, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, 4-hydroxybutyl acrylate and the like. These hydroxy groups can be used for the crosslinking in addition to the acid groups. Hydroxy groups are not necessary when the acid groups are the only crosslinking functionality in the copolymer. Hydroxy groups are necessary when the crosslinking agent of the coating composition is melamine or blocked organic polyisocyanate. As indicated above, the branched polymer comprises side chains of macromonomers attached to a polymer backbone. Each macromonomer ideally contains a terminal, ethylenically unsaturated, individual group which is polymerized in the main chain of the branched polymer and typically contains polymerized styrene monomers, esters and / or nitriles and / or methacrylic or acrylic acid amides or mixtures of these monomers . Other polymerized ethylenically unsaturated monomers may be present in the macromonomer and the backbone, for example (but are not limited to), acrylic and methacrylic acid esters of straight or branched chain monoalcohols of 1 to 20 carbon atoms. Alkyl acrylates and methacrylates having 1-12 carbon atoms in the alkyl group can be used as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethyl hexyl acrylate, nonyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, lauryl methacrylate and the like can be used. Cycloaliphatic acrylates such as trimethylcyclohexyl acrylate, t-butyl cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl methacrylate, 2-ethylhexyl methacrylate, and the like can be used. Also, aryl acrylates and methacrylates such as benzyl acrylate and benzyl methacrylate can be used. Ethylenically unsaturated monomers containing the hydroxy functionality include hydroxy alkyl acrylates and hydroxy alkyl methacrylates, wherein the alkyl has 1 to 12 carbon atoms. Suitable monomers include hydroxy ethyl acrylate, hydroxy propyl acrylate, hydroxy isopropyl acrylate, hydroxy butyl acrylate, hydroxy ethyl methacrylate, hydroxy propyl methacrylate, hydroxy isopropyl methacrylate, hydroxy butyl methacrylate and the like, and mixtures thereof. same. Other suitable olefinically unsaturated monomers include: acrylamide and methacrylamide and derivatives such as alkoxy methyl (meth) acrylamide monomers, such as methacrylamide, N-oxobutoxymethyl methacrylamide and N-methylol methacrylamide; maleic, itaconic and fumaric anhydride and their halves and diesters; vinyl aromatics such as styrene alpha methyl styrene and vinyl toluene; and polyethylene glycol monoacrylates and monomethacrylates. The above monomers can also be used in the main chain of the branched polymer. The branched polymer can be prepared by polymerizing the ethylenically unsaturated monomers in the presence of macromonomers each having a terminal ethylene unsaturation. The resulting branched polymer can be imagined as being composed of a main chain having a plurality of "arms" of macromonomers attached thereto. In the present composition, both the macromonomer arms and the backbone can have reactive functionality capable of reacting with a crosslinking compound or polymer, although it is optional to have such relative functionality alone or essentially alone or substantially only in the backbone. It should be understood that the backbone or macromonomers referred to as having functionality may be part of a mixture of macromonomers of which a portion does not have any functionality or varying amounts of functionality. It is also understood that, when preparing any main chain or macromonomer, there is a normal distribution of functionality. To ensure that the resulting macromonomer has only one ethylenically unsaturated terminal group which will polymerize with the monomers of the main chain to form the branched polymer, the macromonomer is polymerized using a catalytic chain transfer agent. Typically, in the first step of the process for preparing the macromonomer, the monomers are mixed with an inert organic solvent which is water miscible or water dispersible and a cobalt chain transfer agent and is usually heated to the temperature of reflux of the reaction mixture. In the subsequent steps, the additional monomers and the cobalt catalyst and the conventional polymerization catalyst are added and the polymerization is continued until a macromonomer of the desired molecular weight is formed. Preferred cobalt chain transfer agents or catalysts are described in U.S. Patent No. 4,680,352 issued to Janus icz et al. And U.S. Patent No. 4,722,984 issued to Janowicz. More preferred are pentacyanocobaltate (II), diaquabis (borondifluorodimethyl-glioximate) cobaltate (II) and diaquabis (borondifluorophenylglyoximate) cobaltate (II). The cobalt (II) versions of these catalysts are also preferred. Typically, these chain transfer agents are used in concentrations of about 5-1000 ppm based on the monomers used. The macromonomer is preferably formed in a solvent or mixture of solvents using a free radical initiator and a chelate chain transfer agent of Co (II) or (III). Examples of solvents are aromatic, aliphatic, ketone, glycol ethers, acetates, alcohols, such as, for example, methyl ethyl ketone, isopropyl alcohol, n-butyl glycol ether, n-butyl diethylene glycol ether, propylene glycol methyl ether acetate , methyl ether of propylene glycol and N-butanol. The initiators peroxy- and azo- (0.5-5% by weight in monomer) can be used in the synthesis of macromonomers in the presence of 2-5,000 ppm (in total monomer) or chelates of Co (II) in the range of temperature between 70-160 ° C, more preferably initiators of the azo- type, such as, for example, 2,2'-azobis (2,4-dimethylpentane nitrile), 2,2'-azobis (2-methylpropane nitrile) , 2, 2'-azobis (2-methylbutane nitrile), 1, 1'-azo (cyclohexane carbonitrile) and 4,4'-azobis (-cianopentanoic acid). After the macromonomer is formed as described above, the solvent is optionally removed and the monomers of the backbone are added to the macromonomer together with the additional solvent and the polymerization catalyst. Any of the azo-type catalysts mentioned above can be used as can other suitable catalysts such as peroxides and hydroperoxides. Typical of such catalysts are tertiary di-butyl peroxide, di-cumyl peroxide, tertiary amyl peroxide, eumenal hydroperoxide, di (n-propyl) peroxydicarbonate, peresters such as amyl peroxyacetate, and the like. Commercially available peroxy initiators include, for example, t-butyl peroxide or Triganox® B from AKZO, t-butyl peracetate or Triganox® FC50 from AKZO, t-butyl perbenzoate or Triganox® from AKZO, and perpivalate from t-butyl or Triganox® 25 C-75 from AKZO. The polymerization is continued at or below the reflux temperature of the reaction mixture until a branched polymer of the desired molecular weight is formed. Typical solvents that can be used to form the macromonomer or branched polymer are ketones such as methyl ethyl ketone, isobutyl ketone, ethyl amyl ketone, acetone, alcohols such as methanol, ethanol, isopropanol, esters such as ethyl acetate, glycols such such as ethylene glycol, propylene glycol, ethers such as tetrahydrofuran, ethylene glycol mono butyl ether and the like. In the synthesis of the macromonomer and / or the branched polymer, small amounts of the alpha-beta unsaturated, difunctional compounds can be used, such as, for example, ethylene glycol dimethacrylate or hexane diol diacrylate. After the branched polymer is formed, it is neutralized with an amine or an inorganic base such as ammonium hydroxide or sodium hydroxide and then water is added to form a dispersion. Typical amines that can be used include AMP (2-amino-2-methyl-1-propanol), dimethyl-AMP, amino methyl propanol, amino ethyl propanol, dimethyl ethanol amine, triethylamine and the like. A preferred amine is amino methyl propanol and the preferred inorganic base is ammonium hydroxide. The conversion to a water dispersion can be carried out preferably by removing 30 to 60% of the solvent followed by mixing with an organic amine or ammonia and dilution with water, or by mixing with a solution of water and amine after the elimination of the solvent. Alternatively, the branched polymer solution, after removal, can be slowly stirred in a solution of water and the amine. The degree of neutralization of the dispersion can be from 10 to 150% of the total amount of acid groups, preferably 40-100%. The final pH of the dispersion can therefore be about 4-10, preferably 7-9. The solvents can be removed eventually. The waterborne dispersion of the total branched polymer should be characterized by an acid value of from 5 to about 150 (mg KOH / g resin solids), more preferably from 10 to about 70, and even more preferably from 15 to about 35, and a hydroxyl number of from about 0 to about 250 (mg KOH / g resin solids), more preferably from 40 to 150. Branched polymers, particularly useful include the following: a branched polymer that has a polymerized acrylate backbone or methacrylate monomers, styrene monomers, methacrylic or acrylic acid monomers, and hydroxy-functional acrylate or methacrylate monomers, and side chains of a macromonomer having a weight average molecular weight of about 2,000 -30,000 and containing about 50% by weight, based on the weight of the main chain, of methacrylate monomers or alkyl acrylate polymers bristles, hydroxy-functional acrylate or methacrylate monomers and 2-30% by weight, based on the weight of the main chain, methacrylic acid or polymerized acrylic acid. a branched polymer having the above main chain of side chains comprising polymerized methyl methacrylate, butyl acrylate, methacrylic acid, styrene, and hydroxyethyl acrylate. a branched polymer having the above main chain and macromonomers comprising polymerized 2-ethylhexyl acrylate, butyl methacrylate and hydroxyethyl methacrylate. a branched polymer having the above main chain and macromonomers of isobutyl methacrylate, 2-ethylhexyl methacrylate and hydroxy ethyl methacrylate. The branched polymer is used as a dispersion resin to disperse a wide variety of pigments that are commonly used in waterborne coating compositions. The typical pigments that are used are metal oxides such as titanium dioxide, iron oxides of various colors, zinc oxide, carbon black, filler pigments such as talc, cao.lin, barite, carbonates, silicates and a wide variety of colored, organic pigments such as quinacridones, copper phthalocyanines, perylenes, azo pigments, indantrone blue, carbazoles such as carbazole violet, isoindolinones, isoindolones, thioindigo reds, benzimilazolinones and the like. To form the water borne pigment dispersion of this invention, the branched polymer is neutralized and water is added to form a dispersion with constant mixing and then the dispersion and the pigment to be dispersed is added to a suitable mixing flask such as a grinder, sand mill, ball mill, two roll mill and the like and then mix for about 1- 150 minutes to form a dispersion having a deformation load of about 0-1,000 Pa (Pascal), a viscosity with low shear stress (20 sec-1) of approximately 100-10,000 m.Pas (milliPascal seconds) and a viscosity with high shear stress (1,000 sec-1) of approximately 10-1,000 m.Pas measured in a Rotvfisco viscometer. An alternative method for forming a pigment dispersion is to add pigment to a solvent solution of the branched polymer before it is neutralized and dispersed in water and forming a dispersion by one of the aforementioned dispersion methods for a pigment dispersion. Then, the amine or base and water neutralizing agent is added with mixing to form an aqueous pigment dispersion. The water borne coatings in which the pigment dispersions of the present invention are used contain a binder substance of an acrylic based polymer and a crosslinking agent such as melamine resin or a blocked polyisocyanate in an aqueous carrier. These acrylic polymers form stable solutions or dispersions in water, typically as a dispersed polymer having an average particle size diameter of 10 nm to 1 miter, preferably 20 to 400 nm. These coating compositions contain about 10-70%, more typically 15-50% by weight of binder, and about 30-90%, more typically 50-85% by weight, of an aqueous carrier. The carrier is at least 50% water, preferably 75 to 95% water. Suitable water borne coatings are prepared by mixing other useful components according to normal paint formulation techniques. To form a composition which will crosslink under cooking or baking temperatures, raised from about 60-180 ° C for about 5-60 minutes, about 10 to 40%, preferably 15 to 30% by weight, is preferred, based on to the weight of the binder substance, of a melamine formaldehyde crosslinking agent, alkylated, water dispersible, soluble in water having 1-4 carbon atoms in the alkylated group. These crosslinking agents are generally partially alkylated melamine formaldehyde compounds and can be monomeric or polymeric as described above. These coating compositions containing a melamine crosslinking agent may contain about 0.1 to 1.0% by weight, based on the weight of a binder, a strong acid catalyst or a salt thereof at low cure temperatures and time. Paratoluenesulfonic acid is a preferred catalyst or its ammonium salt. Other catalysts that may be used are dodecylbenzenesulfonic acid, phosphoric acid and amine or ammonium salts of these acids. Other film forming polymers can also be used in these coating compositions such as acrylourethanes, polyesters and polyester urethanes, polyethers and polyether urethanes which are compatible with the branched polymer dispersion. Although the dispersion of this invention is aqueous, a solvent, preferably minimal amounts, may be used to facilitate the formulation and application of the coating compositions formulated with the dispersions of the present invention. An organic solvent is used which is compatible with the components of the composition. In addition, the coating composition utilizing the dispersion of the present invention may contain a variety of other optional ingredients, including fillers, plasticizers, antioxidants, surfactants and flow control agents. To improve the weathering of a finish produced from such coating compositions, an ultraviolet light stabilizer or a combination of ultraviolet light stabilizers in the amount of about 0.1-5% by weight, based on the weight of the binder substance. The stabilizer can be added, for example, to a dispersion of this invention which contains pigments or can be added directly to the coating composition. Such stabilizers include ultraviolet light absorbers or eliminators, protectors, attenuators and stabilized amine light stabilizers, specific. An antioxidant may also be added, at about 0.1-5% by weight, based on the weight of the binder substance. Typical ultraviolet light stabilizers that are useful include benzophenones, triazoles, triazines, benzoates, hindered amines and mixtures thereof. Specific examples of ultraviolet light stabilizers are described in U.S. Patent No. 4,591,533, the entire disclosure of which is incorporated herein by reference. Such a coating composition also includes conventional formulation additives such as flow control agents, for example, "Resiflow" S (polybutyl acrylate), BYK 320 and 325 (high molecular weight polyacrylates).; rheology control agents, such as fumed silica and thickeners such as the Acrilsol copolymers from Rohm & Haas. The pigment dispersions of the present invention can be used in a pigmented color coating or base coat on which a clear coat is applied to provide a clear coat / color coating finish, also, small amounts of dispersion can be added. of pigment to the clear coating to provide special color or aesthetic effects such as color addition. The coating compositions formulated with the dispersion of this invention have excellent adhesion to a variety of metallic and non-metallic substrates, such as pre-painted substrates, cold-rolled steel, phosphatized steel, and steel coated with conventional primers by electrodeposition. This coating composition can be used to coat plastic substrates such as polyester reinforced glass fiber, reaction injection molded urethanes and partially crystalline polyamides. The coating compositions formulated with the dispersion of this invention can be applied by conventional techniques such as spraying, electrostatic spraying, dip coating, brush application, spray painting and the like. The preferred techniques are spray and electrostatic spray. In OEM applications, the composition is typically baked at 100-150 ° C for approximately 15-30 minutes to form a coating of approximately 0.1-3.0 mils in thickness. When the composition is used as a clear coating, it is applied over the color coating which can be dried to a stick-free state and cured or preferably dried instantaneously for a short period before the clear coating is applied. The color coating / clear coating finish is then baked as mentioned above to provide a dry and cured finish. The present invention is also applicable to unbaked finishing systems, as will be readily appreciated by those skilled in the art. It is usual to apply a clear, top coat on the base coat by means of a "wet on wet" application, that is, the top coat is applied to the base coat without fully curing or drying the base coat. The coated substrate is then heated for a predetermined period of time to allow simultaneous cure of the base and clear coatings. The following Examples illustrate the invention. All parts and percentages are on a weight basis unless otherwise indicated. All molecular weights described herein were determined by GPC (gel permeation chromatography) using a polystyrene standard.

EXAMPLE 1 A branched polymer was prepared first by preparing a macromonomer and then by polymerizing the macromonomer with monomers forming the main chain of the branched polymer. A pigment dispersion was then prepared from the branched polymer.

Preparation of the macromonomer A 5% macromonomer of IBMA (isobutyl methacrylate), 20% HEMA (hydroethyl methacrylate) and 75% 2EHMA (2-ethylhexyl methacrylate), for use in a preparation of a branched polymer is Prepared as follows: To a 2-liter flask equipped with a stirrer, condenser, heating jacket or mulch, nitrogen inlet, thermocouple and an addition orifice were added 15.25 g of isobutyl methacrylate monomer, 228.94 g of methacrylate monomer of 2-ethyl hexyl, 61.07 g of hydroxy ethyl methacrylate monomer and 251.3 g of propylene glycol monomethyl ether. The mixture was stirred and heated to reflux (128-135 ° C) under nitrogen. This was then added, as a shot, a premix of a solution of 0.5 g of initiator Vazo® 88 [1,1 azobis (cyanocyclohexane)], 13.8 of monomethyl ether propylene glycol and 26.1 g of a solution of 0.17% bis (boron difluoro diphenyl flioximato) cobaltate (II) in ethyl acetate. This was followed by the addition of a premix of a solution of 22.87 g of isobutyl methacrylate monomer, 343.42 g of 2-ethylhexyl methacrylate monomer, 91.61 g of hydroxyethyl methacrylate monomer, 2 g of Vazo® 88 initiator. , 10.0 g of ethyl acetate, 70.6 g of propylene glycol monomethyl ether over 240 minutes while maintaining reflux temperature (116-122 ° C). After a sustained period of 30 minutes, a premixed solution of 0.4 of Vazo® 88 initiator, 4.95 g of ethyl acetate and 18 g of propylene glycol monomethyl ether is added over 60 minutes, while maintaining reflux. The batch was then refluxed for an additional 60 minutes at which time a mixture of 0.3 g of t-butyl peroctoate and 33.35 g of ethyl acetate was added as an individual addition and then the reaction mixture was cooled. The macromonomer thus prepared has a number average molecular weight of 6988 as determined by the GPC. The heavy solids are 62.3% and viscosity of Gardner S. The percentage of terminal vinyl unsaturation is greater than 95 as determined by the thermogravimetric analysis. Preparation of the branched polymer To a 2 liter flask equipped with a stirrer, condenser, heating jacket or mulch, nitrogen inlet, thermocouple and an addition orifice were added 542.7 g of the macromonomer prepared above and 91.7 g of hexanol and the temperature was refluxed (100 ° C) under nitrogen. This was followed by the addition of a premixed solution of 158.4 g of methyl methacrylate monomer (MMA), 73.9 g of styrene monomer (STY), 21.1 g of hydroxy ethyl acrylate monomer (HEA), 118.3 g of monomer of butyl acrylate (BA), 50.7 g of methacrylic acid monomer (MAA), 4.67 g of initiator Vazo® 88 and 54.9 of butyl acetate for 180 minutes maintaining the temperature at 98-102 ° C. Following a sustained period of 60 minutes at the same temperature and then the reaction mixture was cooled to 90 ° C over a period of 30 minutes and kept at that temperature for 270 minutes and then cooled to room temperature. The branched polymer has a number average molecular weight of 11,960 and a weight average molecular weight of 23,030. The heavy solids are 64.4 and the Gardner Holdt viscosity is R. The ratio of the main chain to the macromonomer arms is approximately 55/45. The composition of the main chain is MMA / STY / BA / HEA / MAA in a weight ratio of 37.5 / 17.5 / 28/5/12. Preparation of the waterborne dispersion of the branched polymer To a 2 liter flask equipped with a stirrer, condenser, jacket or heating mantle, nitrogen inlet, thermocouple and an addition orifice were added 500 g of the branched polymer, prepared above and the temperature was raised to distill 97.5 g of solvent. The batch was cooled to less than 80 ° C at which time 23 g of a 95% solution of 2-amino-2-methyl-1-propanol and water were added to neutralize the acid functionality of the branched polymer. The batch was stirred for 10 minutes, at which time 853.6 g of deionized water was slowly added over 60 minutes with good agitation and the resulting dispersion was cooled to room temperature. A stable, white dispersion of the branched polymer having a total solids weight of 24.7%, viscosity of Gardner A3, pH 8.7 and a particle size of 56 nanometers was obtained as determined by the near-electric light scattering. Preparation of a white, aqueous pigment dispersion A mixture of 97.2 g of branched polymer dispersion, prepared above, 62.8 g of deionized water and 240.0 g of titanium dioxide pigment Ti Pure R-960 was milled in a grinder for 2 hours at 500 RPM. The resulting dispersion has a deformation load of 0.49 Pa, a viscosity with low shear stress (20 sec-1) of 74 m.Pas and a viscosity with high shear stress (1000 sec-1) of 40 m.Pas as measured in a Rotvisco viscometer. As a comparison, a similar dispersion was prepared using a linear polymer having the same monomeric constituents in about the same amount except that the methacrylic acid content was 10% and the polymer had a weight average molecular weight of 10,000. The deformation load of this dispersion was 1.25 Pa, viscosity with low shear stress (20 sec-1) 92 m.Pas and viscosity with high shear stress (1000 sec-1) 38 m.Pas. A linear polymer of lower molecular weight was used for comparison since this polymer provided an optimum balance of acid content ratio to molecular weight. If a linear polymer having a weight average molecular weight of 23,000 which is the molecular weight of the branched polymer was used, the viscosity of the linear polymer would have been too high to form a useful pigment dispersion.

EXAMPLE 2 A white pigment dispersion was prepared as in Example 1 except that the following branched polymer was used in place of the branched polymer used in Example 1: the ratio of the main chain to the macromonomer arms was 50/50 and the The main chain composition was MMA / STY / BA / HEA / MAA in a weight ratio of 45/10/13/20/12 and the weight average molecular weight was 20,500. The resulting dispersion has a deformation load of 0.49 Pa, a viscosity with low shear stress (20 sec-1) of 72 m.Pas and a viscosity with high shear stress (1000 sec-1) of 35 m.Pas.

EXAMPLE 3 A white pigment dispersion was prepared as in Example 1 except that the following branched polymer was used in place of the branched polymer used in Example 1: the ratio of the main chain to the macromonomer arms was 60/40 and the The main chain composition was MMA / STY / BA / HEA / AA (AA which is acrylic acid) in a weight ratio of 23/20 / 32.6 / 15 / 9.4 and the weight average molecular weight was 20,500. The resulting dispersion has a deformation load of 0.16 Pa, a viscosity with low shear stress (20 sec-1) of 58 m.Pas and a viscosity with high shear stress (1000 sec-1) of 38 m.Pas.

EXAMPLE 4 A white pigment dispersion was prepared as in Example 1 except that the following branched polymer was used in place of the branched polymer used in Example 1: the ratio of the main chain to the macromonomer arms was 40/60 and the The main chain composition was MMA / STY / BA / HEA / AA in a weight ratio of 37/20/8/25/10 and the weight average molecular weight was 24,500. The resulting dispersion has a deformation load of 0.275 Pa, a viscosity with low shear stress (20 sec-1) of 76 m.Pas and a viscosity with high shear stress (1000 sec-1) of 51 m.Pas.

EXAMPLE 5 A red pigment dispersion was prepared by charging the following constituents in a minimolino distributor apparatus and mixing for 10 minutes: 35 g of Red Irgazine DPP pigment and 28.34 g of water dispersion of the branched polymer of Example 4 which has been neutralized with 2-amino-2-methyl-1-propanol. The resulting dispersion has a deformation load of 0.09 pa, a viscosity with low shear stress (20 sec-1) of 18.6 m.Pas and a viscosity with high shear stress (1000 sec-1) of 10.5 m.Pas. A similar dispersion made as above using a linear polymer having the same constituents except 10% methacrylic acid instead of acrylic acid has a deformation load of 1.04 Pa, a viscosity with low shear stress (20 sec-1) of 66 m .Pas and a viscosity with high shear stress (1000 sec-1) of 22 m.Pas.

EXAMPLE 6 A red pigment dispersion was prepared as in Example 5 except that the following branched polymer was used instead of the branched polymer used in Example 5: the ratio of the main chain to the macromonomer arms was 60/40 and the The main chain composition was MMA / STY / BA / HEA / MAA in a weight ratio of 38.6 / 20/8/25 / 8.4 and the weight average molecular weight was 27.840. The resulting dispersion has a deformation load of 0.22 Pa, a viscosity with low shear stress (20 sec-1) of 26 m.Pas and a viscosity with high shear stress (1000 sec-1) of 12 m.Pas.

EXAMPLE 7 A red pigment dispersion was prepared by charging the following constituents in a minimolino distributor apparatus and mixing for 90 minutes: 15 g of Violet NRT-201-D pigment and 12.15 g of water dispersion of the branched polymer of Example 6 which it has been neutralized with 2-amino-2-methyl-1-propanol. The resulting dispersion has a deformation load of 0.0 Pa, a viscosity with low shear stress (20 sec-1) of 3.8 m.Pas and a viscosity with high shear stress (1000 sec-1) of 4.4 m.Pas. A similar dispersion made as above using a linear polymer having the same constituents except 10% methacrylic acid has a deformation load of 0.0 Pa, a viscosity with low shear stress (20 sec-1) of 10.5 m.Pas and a viscosity with high shear (1000 sec-1) of 4.5 m. Pas.

EXAMPLE 8 A red pigment dispersion was prepared by charging the following constituents in a minimolino distributor apparatus and mixing for 90 minutes: 15 g of Violet NRT-201-D pigment and 60.73 g of water dispersion of a branched polymer similar to Example 1 , except that the branched polymer has a ratio of the main chain to the 50/50 macromonomer arms and the main chain composition is MMA / STY / BA / HEA / MMA in a ratio of 45/10/30/50 / 10 and a weight average molecular weight of 20,470 and neutralized with 2-amino-2-methyl-1-propanol. The resulting dispersion has a deformation load of 1.3 Pa, a viscosity with low shear stress (20 sec-1) of 26.8 m.Pas and a viscosity with high shear stress (1000 sec-1) of 17.2 m.Pas. A similar dispersion made as above using a linear polymer having the same constituents and having a weight average molecular weight of 10,000 has a deformation load of 8.94 Pa, a viscosity with low shear stress (20 sec-1) of 299 m .Pas and a viscosity with high shear stress (1000 sec-1) of 75 m.Pas. The various modifications, alterations, additions or substitutions of the components of the compositions of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention is not limited to the illustrative embodiments set forth herein, but preferably the invention is defined by the following claims.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following claims is claimed as property.

Claims (6)

1. A water-based pigment dispersion useful for forming the aqueous coating composition, which consists of a dispersed pigment, an aqueous carrier and a branched polymer dispersant; characterized in that the branched polymer has a weight average molecular weight of about 5,000 - 100,000 and comprises 20-80% by weight of a hydrophilic backbone and correspondingly 80-20% by weight of side chains of macromonomers; wherein the main chain consists of 70-98% by weight, based on the weight of the main chain, of ethylenically unsaturated monomers, polymerized free of any carboxylic acid functionality and 2-30% by weight, based on the weight of the main chain of polymerized ethylenically unsaturated monomers having a carboxylic acid functional group; and wherein at least 10% of the carboxylic acid functional groups are neutralized with an amine or an inorganic base and is hydrophilic in comparison to the side chains; the side chains consist of macromonomers of polymerized ethylenically unsaturated monomers which are polymerized in the main chain by means of an ethylenically unsaturated group and the macromonomers have a weight average molecular weight of about 1,000-30,000 and wherein the monomers of the main chain and macromonomers that do not contain carboxylic functionality are selected from the group consisting of alkyl acrylates, alkyl methacrylates, cycloaliphatic acrylates, cycloaliphatic methacrylates, aryl acrylates, aryl methacrylates, styrene, styrene alkyl, acrylonitrile, hydroxy alkyl acrylates, methacrylates hydroxy alkyl and mixtures thereof; and wherein the ethylenically unsaturated monomers containing carboxyl functionality of the main chain are selected from the group consisting of acrylic acid and methacrylic acid, wherein the aforementioned alkyl, cycloaliphatic and aryl groups each have 1 to 12 carbon atoms; and wherein the weight ratio of pigment to dispersant is 1 / 100-200 / 100; and wherein the branched polymer contains 5-40% by weight of monomer having hydroxyl functionality.

2. The dispersion according to claim 1, characterized in that the main chain of the branched polymer comprises 3-15% by weight of monomers having a carboxylic acid functionality or a salt thereof.

3. The dispersion according to claim 1, characterized in that the main chain of the branched polymer contains 3-15% by weight of a functional carboxylic acid monomer or a salt thereof and wherein the polymer has a weight average molecular weight of 5,000 at 40,000, an acid value of 5-150.

4. The dispersion according to claim 3, characterized in that the branched polymer has a hydroxyl number of 40-150, an acid value of 10-70 and a weight average molecular weight of 5,000-40,000.

5. A process for preparing the dispersion according to claim 1, wherein the polymer is a branched polymer comprising a polymeric backbone having a plurality of polymerized macromonomers in the main chain having carboxylic functionality, the method is characterized in that comprises (a) preparing macromonomers, in an organic solvent, by polymerizing the ethylenically unsaturated monomers using a catalytic chain transfer agent containing cobalt, to form a macromonomer having an ethylenically unsaturated, terminal bond; (b) forming, in an organic solvent, the branched polymer by polymerization, in the presence of the macromonomers prepared in step (a), 70-98% by weight, based on the weight of the main chain, of ethylenically monomers unsaturated carboxylic acid groups and 2 to 30% by weight, based on the weight of the main chain, of monomers selected from the group of acrylic acid and methacrylic acid, whereby the macromonomers are incorporated into the main chain by polymerizing the ethylenically unsaturated bond terminal with the ethylenically unsaturated monomers of the main chain, whereby a branched polymer is formed with a molecular weight of 5,000-100,000, which is neutralized with an amine and dispersed in water by inverting the polymer in a carrier liquid, aqueous to form a dispersion; and (c) dispersing the pigment in the branched polymer dispersion to form a pigment dispersion.

6. A process for preparing the dispersion according to claim 1, wherein the polymer is a branched polymer comprising a polymeric backbone having a plurality of polymerized macromonomers in the main chain having carboxylic functionality, the method is characterized in that comprises (a) preparing macromonomers, in an organic solvent, by polymerizing the ethylenically unsaturated monomers using a catalytic chain transfer agent containing cobalt, to form a macromonomer having an ethylenically unsaturated, terminal bond; (b) forming, in an organic solvent, the branched polymer by polymerization, in the presence of the macromonomers prepared in step (a), of 70-98% by weight, based on the weight of the main chain, of monomers ethylenically unsaturated free of carboxylic acid groups and 2 to 30% by weight, based on the weight of the main chain, of monomers selected from the group of acrylic acid and methacrylic acid, whereby the macromonomers are incorporated into the main chain when polymerizing the ethylenically unsaturated bond, terminal with the ethylenically unsaturated monomers of the main chain, whereby a branched polymer with a molecular weight of 5,000-100,000 is formed, which is neutralized with an amine and dispersed in water by inverting the polymer in a carrier liquid, aqueous to form a dispersion; (c) dispersing the pigment in the branched polymer composition of organic solvent formed in (b) above, (d) adding water and an amine to the composition formed in (c) above wherein the polymer is neutralized with an amine and Invests in water to form a pigment dispersion. SUMMARY OF THE INVENTION A water-based dispersion useful for forming an aqueous, dispersed pigment-containing coating composition, an aqueous carrier and a branched polymer dispersant (binding substance); the branched polymer has a weight average molecular weight of about 5,000-100,000 and contains 20-80% by weight of a hydrophilic backbone and correspondingly 80-20% by weight of macromonomer side chains; wherein the main chain is ethylenically unsaturated monomers, polymerized and 2-30% by weight, based on the weight of the main chain of polymerized ethylenically unsaturated monomers having an acid functional group; and wherein at least 10% of the acid functional groups are neutralized with an amine or an inorganic base and is hydrophilic in comparison to the side chains, the side chains are of macromonomers of polymerized ethylenically unsaturated monomers that are polymerized in the chain by the ethylenically unsaturated group and the macromonomers have a weight average molecular weight of about 1,000-30,000 and wherein the weight ratio of the pigment to the binder is about 1/100 - 200/100.