WO2016064471A1

WO2016064471A1 - Tio2-latex composite binder

Info

Publication number: WO2016064471A1
Application number: PCT/US2015/046916
Authority: WO
Inventors: Josef BOROVICKA; Assim FIAZ
Original assignee: Hercules Incorporated
Priority date: 2014-10-22
Filing date: 2015-08-26
Publication date: 2016-04-28
Also published as: GB201418800D0

Abstract

An aqueous dispersion for use in a coating system comprises composite binder particles comprising polymeric particles coated with titanium dioxide pigment grains. The average particle size of the titanium dioxide pigment grains is at least 200 nm.

Description

TIO₂-LATEX COMPOSITE BINDER BACKGROUND OF THE INVENTION

[0001] The described and/or claimed inventive concept(s) relate to improved latex paint formulations and/or other coating systems, such as stains, varnishes, adhesives and inks, which contain titanium dioxide (Ti0₂) and exhibit superior light scattering properties, e.g., hiding power, at substantially lower levels of titanium dioxide loading than was previously achievable. More particularly, the present invention relates to a composite binder of Ti0₂ and a polymerizable monomer which displays high hiding power and exhibits film-forming behavior.

[0002] As a pigment, it is well known that Ti0₂ has excellent light-scattering properties and is used in a variety of applications that require white opacity and brightness. The term "white opacity" refers to a coating system, e.g., a latex paint formulation, which is not only white, but also exhibits a desirable opacity, i.e., a degree of imperviousness to light. As the price of Ti0₂ increases and/or supplies become short, coating manufacturers have been re-evaluating their respective paint formulations to optimize Ti0₂ effectiveness, i.e., optimize hiding power, as well as researching not-in-kind alternatives for achieving opacity. Ti0₂ contributes to hiding power by light scattering.

[0003] One option for manufacturers to reduce TiO₂ loading has been to incorporate air voids into their coatings, either by formulating above the Critical Pigment Volume Concentration (CPVC) or by using hollow spheres of opaque polymers. Either of these options must be balanced against maintaining other coating performance parameters. In some cases, the use of highly coated TiO₂ particles can improve light scattering efficiency whereby the particles are appropriately spaced allowing for a reduction in TiO₂ pigment loading.

[0004] A significant challenge in formulating coating systems with titanium dioxide is its propensity to aggregate and to thereby lose the hiding power per amount of titanium dioxide used in the formulation because of inefficient distribution of the pigment. This is being addressed, in part, by manufacturers attempting to adjust the surface chemistry of the titanium dioxide grains by adding additional inorganic and/or organic layers which increase compatibility for different solvents. Recently, so-called pre-composite polymers which coat the surface of the titania pigment grains and improve Ti0₂ distribution and light scattering properties have been introduced. A need still exists, however, to provide improved latex paint formulations which contain titanium dioxide (Ti0₂) for its desirable high hiding power, but at substantially lower levels of titanium dioxide loading than was previously achievable.

SUMMARY OF THE INVENTION

[0005] The described and/or claimed inventive concept(s) relate to an aqueous dispersion of titanium dioxide polymeric composite binder particles comprising polymeric particles coated with titanium dioxide pigment grains wherein the titanium dioxide pigment grains have an average particle size of at least 200 nm. The aqueous dispersion can be used as a coating composition for application to a variety of substrates.

[0006] In an alternative embodiment, the presently disclosed and/or claimed inventive concept(s) relate to a coating system (e.g., a latex paint, varnishes, stains, textile coatings, paper coatings, and inks) comprising an aqueous dispersion of titanium dioxide polymeric composite binder particles comprising polymeric particles coated with titanium dioxide pigment grains wherein the titanium dioxide pigment grains have an average particle size of at least 200 nm, and wherein the aqueous dispersion of titanium dioxide polymeric composite binder particles are deployed as an additive in a conventional latex paint or other coating compositions. The presence of the composite binder particles provides the unexpected benefit that the titanium dioxide loading in the coating system can be reduced to a value that is significantly less than an equivalent coating system that contains only free titanium dioxide and yet achieves substantially equivalent hiding power in use. In some instances the reduction in titanium dioxide loading in the coating system being evaluated (e.g., latex paint) has been observed to be as high as 40% to 60%, and even as high as 90%. Although one embodiment for reduction of titanium dioxide loading has been stated to be as high as 90%, one of ordinary skill in the art would appreciate that reduction in titanium dioxide loading according to the inventive concept(s) described and claimed herein can result in values in the range of from 87%, 85%, 80%, 75%, 70%, and even 5%, which range should be considered part of the explicit teachings of this specification. [0007] In an alternative embodiment, the inventive concept(s) relate to a method for improving the hiding power of a coating system which comprises incorporating into the coating system from about 10 wt% up to about 90 wt%, depending on the type of coating system, of a composite binder. The composite binder comprises polymeric particles coated with titanium dioxide pigment grains wherein the pigment grains have an average particle size in the range of at least 200 nm and up to 400 nm. As presently described and/or claimed herein, the titanium dioxide loading of the improved coating system can be substantially less than an equivalent coating system which contains only free titanium dioxide and still achieve substantially equivalent hiding power in use. In some instances the reduction in titanium dioxide loading in the coating systems observed has been as high as 40% to 60% and even as high as 90%.

[0008] In yet another aspect, the described and/or claimed inventive concept(s) relate to a method for reducing titanium dioxide loading in a coating system selected from latex paints, stains, varnishes, adhesives, alkyd emulsion paints, paper coatings, textile coatings, and inks which comprises incorporating into the coating system from about 10 wt% up to about 90 wt% of a titanium dioxide polymeric composite binder comprising polymeric particles coated with titanium dioxide pigment grains wherein the grains have an average particle size in the range of from at least 200 nm to as high as 550 nm. The presence of the composite binder provides the benefit that the titanium dioxide loading of the coating system can be reduced to a value that is substantially less than equivalent coating systems having the same solids content and containing only free titanium dioxide and still achieve substantially equivalent hiding power in use.

[0009] In yet another aspect, the described and/or claimed inventive concept(s) relate to a method for producing the aqueous dispersion of titanium dioxide polymeric composite binder particles, comprising:

(1 ) making a stabilized aqueous emulsion comprising:

(a) a dispersed phase comprising droplets of a polymerizable monomer coated with a layer of stabilizing solid titanium dioxide pigment grains, and

(b) a continuous phase comprising an aqueous medium, wherein the titanium

dioxide pigment grains are disposed at the interface between the dispersed phase and the continuous phase; and (2) polymerizing the polymerizable monomer to form the aqueous dispersion comprising polymeric particles coated with titanium dioxide pigment grains, wherein the polymeric particles are dispersed in the aqueous medium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 is a photograph of a dry coating test card which compares a 70% Pigment Volume Concentration (PVC) matt paint formulation at 30% solids (left) with a 70% Pigment Volume Concentration (PVC) matt paint formulation at 30% solids which contained the titanium dioxide polymeric composite binder of the invention at 1 .08 wt% Ti0₂.

[0011] Fig. 2 is a photograph of a dry coating test card which compares a 70% Pigment Volume Concentration (PVC) matt paint formulation at 30% solids (left) with a 70% Pigment Volume Concentration (PVC) matt paint formulation at 30% solids which contained no dry titanium dioxide, but was compensated with an amount of calcium carbonate_.

[0012] Fig. 3 is a photograph of a wet coating test card which compares Control Formulation 1 with Recipe 2 in a wet coating.

[0013] Fig. 4 is a photograph of a dry coating test card which compares Control Formulation 1 with Recipe 2 in a dry coating.

[0014] Fig. 5 is a photograph of a wet coating test card which compares Control Formulation 1 with Recipe 3 in a wet coating.

[0015] Fig. 6 is a photograph of a dry coating test card which compares Control Formulation 1 with Recipe 3 in a dry coating.

[0016] Fig. 7 is a photograph of a wet coating test card which compares Control Formulation 1 with Recipe 4 in a wet coating.

[0017] Fig. 8 is a photograph of a dry coating test card which compares Control Formulation 1 with Recipe 4 in a dry coating.

[0018] Fig. 9 is a photograph of a wet coating test card which compares Control Formulation 1 with Recipe 5 in a wet coating.

[0019] Fig. 10 is a photograph of a dry coating test card which compares Control Formulation 1 with Recipe 5 in a dry coating.

[0020] Fig. 1 1 is a photograph of a wet coating test card which compares Control Formulation 1 with Recipe 6 in a wet coating. [0021] Fig. 12 is a photograph of a dry coating test card which compares Control Formulation 1 with Recipe 6 in a dry coating.

[0022] Fig. 13 is a graph which compares the % contrast ratio versus the wt% titanium dioxide in each of the experimental paint formulations.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Before explaining at least one embodiment of the presently disclosed and claimed inventive concept(s) in detail, it is to be understood that the presently disclosed and claimed inventive concept(s) is not limited in its application to the details of construction and the arrangement of the components or steps or

methodologies set forth in the following description or illustrated in the Figures. The presently disclosed and claimed inventive concept(s) is capable of other

embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0024] Unless otherwise defined herein, technical terms used in connection with the presently disclosed and claimed inventive concept(s) shall have the meanings that are commonly understood by those of ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0025] All patents, published patent applications, and non-patent publications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this presently disclosed and claimed inventive concept(s) pertains. All patents, published patent applications, and non-patent publications referenced in any portion of this application are herein expressly incorporated by reference in their entirety to the same extent as if each individual patent or publication was specifically and individually indicated to be incorporated by reference.

[0026] All of the articles and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the articles and methods of the presently disclosed and claimed inventive concept(s) have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the articles and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the presently disclosed and claimed inventive concept(s). All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the presently disclosed and claimed inventive concept(s) as defined by the appended claims.

[0027] As utilized in accordance with the present disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings:

[0028] The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one." The use of the term "or" in the claims is used to mean "and/or" unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or." Throughout this application, the term "about" is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects. For example but not by way of limitation, when the term "about" is utilized, the designated value may vary by plus or minus twelve percent, or eleven percent, or ten percent, or nine percent, or eight percent, or seven percent, or six percent, or five percent, or four percent, or three percent, or two percent, or one percent. The use of the term "at least one" will be understood to include one as well as any quantity more than one, including but not limited to, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, etc. The term "at least one" may extend up to 100 or 1000 or more, depending on the term to which it is attached; in addition, the quantities of 100/1000 are not to be considered limiting, as higher limits may also produce satisfactory results. In addition, the use of the term "at least one of X, Y and Z" will be understood to include X alone, Y alone, and Z alone, as well as any combination of X, Y and Z. The use of ordinal number terminology (i.e., "first," "second," "third," "fourth," etc.) is solely for the purpose of differentiating between two or more items and is not meant to imply any sequence or order or importance to one item over another or any order of addition unless otherwise expressly indicated.

[0029] As used in this specification and claim(s), the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as

"contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0030] The term "or combinations thereof" as used herein refers to all

permutations and combinations of the listed items preceding the term. For example, "A, B, C, or combinations thereof" is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AAB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0031] As used herein, the term "substantially" means that the subsequently described event or circumstance completely occurs or that the subsequently described event or circumstance occurs to a great extent or degree. For example, the term "substantially" means that the subsequently described event or circumstance occurs at least 90% of the time, or at least 95% of the time, or at least 98% of the time.

[0032] For purposes of the following detailed description, other than in any operating examples, or where otherwise indicated, numbers that express, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". The numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties to be obtained in carrying out the invention.

[0033] The terms "latex" and "emulsion" are used herein interchangeably to describe the inventive concept(s) and mean a stable dispersion or formulation of polymer particles and/or microparticles in an aqueous medium, such as, for example, a latex paint.

[0034] The term "titanium dioxide pigment grains" as used herein means small particles of titanium dioxide pigment which have the specified average particle size in the range of from 200 nm up to 550 nm. The titanium dioxide pigment grains can be sourced from rutile, ilmenite, or anatase ores, and the pigment grains may or may not be surface modified. [0035] Average particle size is measured by laser diffraction (Fraunhofer diffraction) using a Malvern Mastersizer and refers to the volume distributed median particle diameter (equivalent spherical diameter corresponding to 50% of the volume of all the particles, read on the cumulative distribution curve relating volume % to the diameter of the particles - often referred to as the "D(v,0.5)" value).

[0036] The aqueous dispersions of titanium dioxide polymeric binder particles as described and/or claimed herein are typically derived from aqueous dispersions comprising droplets of a polymerizable monomer that have been coated with a layer of stabilized solid Ti0₂ pigment particles. The coated areas of the Ti0₂ pigment particles over the droplets can be varied from at least 5% to100% of the total droplets areas. In one non-limiting embodiment, the coated areas of the Ti0₂ pigment particles over the droplets can be varied from 10% to100% of the total droplets areas. In another non- limiting embodiment, the coated areas of the Ti0₂ pigment particles over the droplets can be varied from 20% to100% of the total droplets areas. In yet another non-limiting embodiment, the coated areas of the Ti0₂ pigment particles over the droplets can be varied from 30% to100% of the total droplets areas.

[0037] The aqueous dispersions can typically be formed from an oil-in-water Pickering emulsion, meaning an emulsion that utilizes solid Ti0₂ particles, the Ti0₂ pigment grains, as a stabilizer to stabilize a polymerizable monomer in a dispersed phase, the monomer being in the form of droplets that are dispersed throughout a continuous phase comprising an aqueous medium.

[0038] In certain embodiments, the polymerizable monomer may be a

polymerizable, ethylenically unsaturated monomer. Suitable polymerizable, ethylenically unsaturated monomers can include any of the vinyl monomers known in the art. Examples of useful ethylenically unsaturated carboxylic acid functional group- containing monomers can include, but are not limited to, (meth)acrylic acid, beta- carboxyethyl acrylate, acry-loxypropionic acid, crotonic acid, fumaric acid, monoalkyl esters of fumaric acid, maleic acid, monoalkyl esters of maleic acid, itaconic acid, monoalkyl esters of itaconic acid and mixtures thereof. As used herein,

"(meth)acrylic" and terms derived therefrom are intended to include both acrylic and methacrylic.

[0039] Examples of other useful ethylenically unsaturated monomers can include, but are not limited to, alkyl esters of (meth)acrylic acids, such as, for example, ethyl (meth)acrylate, methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxy butyl (meth)acrylate, isobornyl (meth)acrylate, and lauryl (meth)acrylate; vinyl aromatics, such as styrene and vinyl toluene; (meth)acrylamides, such as N- butoxymethyl acrylamide; acrylonitriles; dialkyl esters of maleic and fumaric acids; vinyl and vinylidene halides; N-vinyl pyrrolidone, vinyl acetate; vinyl ethers; allyl ethers; allyl alcohols; derivatives thereof and mixtures thereof.

[0040] The ethylenically unsaturated monomers can also include ethylenically unsaturated, beta-hydroxy ester functional monomers, such as those derived from the reaction of an ethylenically unsaturated acid functional monomer, such as a monocarboxylic acid, for example, acrylic acid, and an epoxy compound which does not participate in the free radical initiated polymerization with the unsaturated acid monomer. Examples of such epoxy compounds are glycidyl ethers and esters.

Suitable glycidyl ethers include glycidyl ethers of alcohols and phenols, such as butyl glycidyl ether, octyl glycidyl ether, phenyl glycidyl ether and the like.

[0041] Suitable glycidyl esters include those which are commercially available from Shell Chemical Company under the trade name CARDURA™ E including CARDURA™ E10, CARDURA™ E10P and CARDURA™ E 10S and from Exxon Chemical Company under the trade name GLYDEXX N-10. Alternatively, the beta- hydroxy ester functional monomers can be prepared from an ethylenically

unsaturated, epoxy functional monomer, for example glycidyl (meth)acrylate and allyl glycidyl ether, and a saturated carboxylic acid, such as a saturated monocarboxylic acid, for example isostearic acid.

[0042] The polymerizable monomer is typically present in the aqueous dispersions that lead to the formation of the composite binder of the presently described and/or claimed inventive concept(s) in an amount ranging from 5 wt% to 50 wt%, such as 5 wt% to 40 wt%, based on the total weight of the dispersion. However, higher or lower concentrations of the polymerizable monomer can be used depending on the specific application and application conditions and can still achieve satisfactory results.

[0043] According to the presently described and/or claimed inventive concept(s), the Ti0₂ pigment grains are disposed at the interface of the dispersed phase and the continuous phase as a layer, i.e., forming a coating on the surface of the monomer droplets that is sufficiently continuous enough to prevent coalescence of the droplets within the aqueous medium. The average particle size of the Ti0₂ pigment grains is at least about 200 nm, although the size can range from 200 nm up to and including 400 nm with satisfactory results in terms of light scattering and hiding power.

Particles sizes larger than 400 nm, e.g., up to 550 nm can also be used. In a preferred embodiment, the rutile form of Ti0₂ pigment grains are in the size range of 200-350 nm.

[0044] The shape (or morphology) of the Ti0₂ pigment grains can vary from generally spherical morphologies to particles that are cubic, platy, or acicular (elongated or fibrous).

[0045] The Ti0₂ pigment grains are present in the described and/or claimed aqueous dispersion comprising the inventive concept(s) in an amount ranging from 0.1 to 30 wt%, 0.1 to 15 wt%, and 0.1 to 10 wt% based on the total weight of the dispersion. Stated differently, the ratio of titania pigment to polymer in the aqueous dispersion can be from 0.1 -1 :30; 0.1 -1 :15; and 0.1 -1 .0:10.

[0046] Although the inventive concept(s) are described in terms of Ti0₂ pigment, the inventive concept(s) may be applied to any white pigment that can be deployed in a paint formulation. Such white pigments include barytes, clays, magnesium silicate, lithopone, zinc oxide, antimony oxide, zinc sulfide, and the like.

[0047] The aqueous dispersions giving rise to the inventive concept(s) described and/or claimed herein can be prepared, for example, according to a "suspension polymerization" technique wherein the polymerizable monomers, and any optional polymers, are added to an aqueous medium containing a suspension of the Ti0₂ pigment grains. The mixture is agitated under shearing forces to reduce the size of the monomer droplets. During this time an equilibrium is reached, and the size of the monomer droplets is stabilized by the action of the Ti0₂ pigment grains in coating the surface of the droplets. Polymerization is completed to form an aqueous suspension of polymer particles coated with a layer of the Ti0₂ pigment grains, i.e., the composite binder particles of the presently described and/or claimed inventive concept(s).

Average size of the polymer particles can range from 800 nm to 40 microns.

[0048] In one non-limiting embodiment, a method for producing the aqueous dispersion of titanium dioxide polymeric composite binder particles comprises:

(1 ) making a stabilized aqueous emulsion comprising:

(a) a dispersed phase comprising droplets of a polymerizable monomer coated with a layer of stabilizing solid titanium dioxide pigment grains, and (b) a continuous phase comprising an aqueous medium, wherein the titanium dioxide pigment grains are disposed at the interface between the dispersed phase and the continuous phase; and

(2) polymerizing the polymerizable monomer to form the aqueous dispersion

comprising polymeric particles coated with titanium dioxide pigment grains, wherein the polymeric particles are dispersed in the aqueous medium.

[0049] The stabilized aqueous emulsion may include other materials, for example, but not by way of limitation, catalysts and/or initiators. The catalyst and/or initiators that can be soluble in the particular monomer or monomers polymerized within the droplets can be used in the presently disclosed and/or claimed inventive concept(s). Typical initiators for polymerization are the peroxide and azo initiators such as 2, 2' azobis (2, 4-dimethyl valeronitriles), lauroyl peroxide, benzoyl peroxide, and the like. Also suitable are water soluble initiators, such as ammonium peroxydisulfate, potassium peroxydisulfate, and hydrogen peroxide.

[0050] The aqueous medium can exclusively be water. However, in some cases, it can be desirable to also include a minor amount of inert organic solvent in the continuous phase. In certain embodiments, the amount of organic solvent present is less than 20 weight percent, such as less than 10 weight percent, or, in some cases, less than 5 weight percent, or, in yet other cases, less than 2 weight percent based on total weight of the emulsion. Examples of suitable organic solvents which can be incorporated for this purpose include, but are not limited to, propylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monobutyl ether, n-butanol, and benzyl alcohol, as well as mixtures thereof.

[0051] The aqueous dispersions of the composite binder described herein can represent the primary film-forming component of a coating composition (i.e., an aqueous dispersion of the presently disclosed and/or claimed composite binder can be a coating composition/system by itself), or, alternatively, the aqueous dispersion can represent one of the components in a more complex or conventional coating composition. For example, in addition to the aqueous dispersion of the present invention, such coating compositions also can include a resinous binder system comprising one or more film-forming polymers which may or may not include reactive functional groups, and/or, if appropriate, a crosslinking agent having functional groups reactive with those of the film-forming polymer. [0052] The coating compositions made possible by the presently disclosed and/or claimed inventive concept(s) can be used in a variety of applications, such as, for example, in automotive coatings, automotive refinish coatings, industrial field applied coatings, architectural coatings, coil coatings, opaque stains, paper and textile coatings, inks, and aerospace coatings.

[0053] The aqueous dispersion of the composite binder made by the presently described and/or claimed inventive concept(s) can be applied to any suitable substrate by any of the conventional coating techniques known to those skilled in the art. Suitable substrates include cellulosic-containing materials, including paper, paperboard, cardboard, plywood and pressed fiber boards, hardwood, softwood, wood veneer, particleboard, chipboard, oriented strand board, and fiberboard as well as metallic substrates and silicatic substrates, such as glass, porcelain and ceramics. Other substrates include textile substrates, polymer substrates, leathers, and foams.

[0054] After application of the above-described aqueous dispersions of the composite binder, or the above-described coating compositions comprising the composite binder as an additive, to the substrate, the dispersion/composition is allowed to coalesce. Typically, the film thickness will be in the range of from 0.01 to 20 mils (about 0.25 to 508 mm), such as 0.01 to 5 mils (0.25 to 127 mm), or, in some cases, 0.1 to 2 mils (2.54 to 50.8 mm) in thickness. The term "mil" is used herein to mean a unit of length or thickness equal to 0.001 of an inch or 0.0254 mm.

[0055] The film is formed on the surface of the substrate by driving diluent, i.e., water and/or other solvent that may be present, out of the dispersion or coating composition by heating or by a drying period in ambient air. Other solvents that can be used may include, for example in architectural paints, ester alcohols, glycol ethers, and low VOC coalescents (higher boiling point esters). In some cases, the heating will only be for a short period of time, sufficient to ensure that any subsequently applied coatings can be applied to the film without dissolving the composition.

Suitable drying conditions will depend on the particular composition, but, in general, a drying time of from about 1 to 5 minutes at a temperature of about 68 °F to 250 °F (20°C to 121 °C) will be adequate. More than one coat of the aqueous dispersions of the composite binder, or the coating composition comprising the composite binder, may be applied to develop an optimum appearance. Between coats, the previously applied coat may be flashed, that is, exposed to ambient conditions for about 1 to 20 minutes. [0056] The following examples illustrate the presently disclosed and/or claimed inventive concept(s), parts and percentages being by weight, unless otherwise indicated. Each example is provided by way of explanation of the presently disclosed and claimed inventive concept(s), not limitation of the presently disclosed and claimed inventive concept(s). In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the presently disclosed and claimed inventive concept(s) without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the presently disclosed and claimed inventive concept(s) covers such modifications and variations as come within the scope of the appended claims and their equivalents.

EAMPLES

Example 1 : Preparation of Titanium Dioxide Polymeric Composite Binder

Particles According to One Embodiment

Reagents:

Emulsion

Polymerization Initiator

e g Ammonium persulfate (APS)

40 g Water [0057] A particle stabilized aqueous emulsion of the polymerizable monomers was prepared by adding the above three combined monomers to a suspension of titanium dioxide pigment grains in water which was pre-dispersed by agitation with the finest Silverson generator at maximum speed for 10 minutes. Emulsification was maintained for 5 minutes, and the emulsion temperature was maintained < 30 °C by conducting the procedure in an ice bath. Polymerization was carried out at about 90 °C by feeding the aqueous emulsion and the polymerization initiator in parallel into a 1 L reactor containing 185 g of water. The emulsion feed time was about 4 hours, and the initiator feed lasted for about 5 hours. The resulting aqueous dispersion was then kept at about 90 °C for an additional one hour. The aqueous dispersion was subsequently cooled to about 30 °C and passed through an 80 mesh sieve.

[0058] In each of the experimental formulations, i.e., Recipes, which follow and that are shown in Table 1 , water and dispersant were pre-mixed before adding the combined pigments, and the dispersion was then mixed at 5000 rpm on a Dispermat mixer for 30 minutes. Then the polymeric composite binder and defoamer were incorporated into the dispersions and mixing was continued for a further 30 minutes. Next, pH was checked, a desired weight of rheology modifier was added, and the pH of each dispersion was adjusted to 8.5. Mixing was then continued at 1000 rpm for an additional 5 minutes to incorporate the rheology modifier uniformly into the compositions/dispersions.

Table 1

(1 ) Jaypol™ C-986: defoamer, available from Ashland Inc.

(2) Jaypol™ S40: dispersant, available from Ashland Inc.

(3) Snowcal® 60: calcium carbonate, available from Omya.

(4) Omnicarb: calcium carbonate, available from Omya. [0059] With respect to each experimental formulation, titanium dioxide, calcium carbonate and talc were weighed accurately and combined into a suitable container. Into a 150 ml plastic container the deionised water and dispersant were weighed accurately, and pre-mixed for 30 seconds at 1000 rpm. The pigment was then loaded with mixing at 1000 rpm until fully wetted, then mixed for an additional 30 minutes at 5000 rpm. The additional components for each experimental formulation were then weighed accurately into a suitable syringe and added to the dispersed base phase. Next, the defoamer, (Jaypol™ C-986), and the unthickened paint base were added and mixed for a further 30 minutes at 5000 rpm.

[0060] Initially the unthickened paint bases were coated onto a Sheen Instruments Ltd. "black and white chequered" card with K-bar no. 8. All the coatings were drawn with the Control Formulation 1 on the left for direct comparison, and the visual characteristics as a wet film were recorded. These cards were then dried at 1 10° C for 15 minutes, and re-inspected.

[0061] Referring now to the figures, Fig. 1 is a photograph of a dry coating test card which compares a 70% Pigment Volume Concentration (PVC) matt paint formulation at 30% solids (left) with a 70% Pigment Volume Concentration (PVC) matt paint formulation at 30 % solids which contained the titanium dioxide polymeric composite binder of the invention at 1 .08 wt% Ti0_2.

[0062] Fig. 2 is a photograph of a dry coating test card which compares a 70% Pigment Volume Concentration (PVC) matt paint formulation at 30% solids (left) with a 70% Pigment Volume Concentration (PVC) matt paint formulation at 30% solids which contained no dry titanium dioxide, but was compensated with calcium_.

[0063] Fig. 3 is a photograph of a test card which is used to show a wet coating comparison, (using a K-bar no. 8 card), of a standard paint (Control Formulation 1 ) vs. the formulation designated "Recipe 2" according to the inventive concepts. When the card was initially coated, Control Formulation 1 gave a whiter/greater hiding coverage when compared to Recipe 2. Recipe 2 showed a slight degree of transparency, despite containing the same pigment loading and approximately the same Ti0₂ concentration.

[0064] On drying, (1 10°C for 10 minutes), as shown in Fig. 4, Control Formulation 1 at the indicated coat weight dried with a lower degree of "hiding" and was observed as not as white as the dry coating that resulted from Recipe 2. The effect is significant, and may indicate that there is a potential optical/physical interaction that occurs between the wet and dry coated films.

[0065] Figs. 5-8 illustrate the same comparison for Control Formulation 1 vs. Recipes 3 and 4 on wet and dry test cards.

[0066] Figs. 9-1 2 illustrate wet and dry coating comparisons between Control Formulation 1 and Recipes 5, 6 and 7 which contained no separate dry Ti0₂ pigment addition. The only Ti0₂ present and active in contributing to hiding/whiteness of the resulting wet and dry films is from 1 .08% of the inventive Ti0₂-polymeric composite binder that was incorporated into each of the experimental Recipes.

[0067] The Figures illustrate that with respect to the wet film test cards, despite the total pigment solids for Recipes 5, 6 and 7 being the same, as the Ti0₂ level decreased, transparency of the wet film increased, suggesting that on wet application the hiding capacity of the system was lower than the control.

[0068] However, according to the inventive concepts described and/or claimed herein, the hiding capacity of the coatings derived from Recipes 5, 6 and 7 increased when cured. This shows that on a dry film representation test card that a potential 64% reduction in normally added Ti0₂ could be attained while maintaining a slightly improved "dry" hiding capacity. Thus, the coating system with the titanium dioxide polymeric composite binder could produce desirable results with < 6% formulated Ti0₂ and achieve a "dry" hiding capacity that is substantially equivalent to currently available commercial paint formulations.

[0069] Recipe 5, as illustrated by Figs. 9 and 10, show the formulation with dry Ti0₂ pigment removed and compensated by addition of calcium carbonate and talc (equal loading). In a wet coating, almost complete transparency was found, compared to Control Formulation 1 , i.e., a standard paint formulation. The Figs, also show that the Ti0₂ not only contributes to dry hiding capacity, but also has a significant impact on the wet film.

[0070] On drying, as seen in Fig. 1 0, Recipe 5 with no added Ti0₂ pigment, also showed a significant decrease in hiding capacity. This is interpreted to mean that the Ti0₂ level at approximately 1 wt% was insufficient to behave as a sole source of Ti0₂ in this example.

[0071] Figs. 1 1 and 12, however, illustrate that the degree of whiteness, and potentially, "hiding" in the wet film can be compensated by decreasing the lower grade talc, and increasing the whiter grade of calcium carbonate. However, the apparent transparency of the wet film remains.

Example 2: Contrast Ratio

[0072] To further illustrate the inventive concept(s) described and/or claimed herein, a master batch of a high pigment volume concentration (PVC) paint grind was made, using a high speed disperser with a "Cowles" mixing blade. The pigment composition of the grind consisted of commercially available calcium carbonate and Kaolin clay. No titanium dioxide was added to the grind. After completion of the grind, an aliquot sample was letdown with a commercially available vinyl acrylic emulsion. Texanol at 9.72 wt% based on the vinyl acrylic solids was used as a coalescent. Then 5.99 wt% titanium dioxide was post added from a commercially acquired high solids slurry. The paint was bulked to its final volume (1 gallon) with water. The theoretical formulation constants for this experimental paint formulation, designated as the Control, were: 70.4% PVC and 34.2% volume solids.

[0073] A second paint formulation was prepared using the same master paint grind, i.e., the master batch of high pigment volume concentration (PVC) paint. The vinyl acrylic emulsion was replaced with a polymeric composite polymer according to the inventive concept(s) (Designated ENC 262/265) at the same wt% polymer solid level. The paint formulation was letdown in the exact same manner as the Control with the following changes: no titanium dioxide slurry addition increased the level of the grind paste to compensate for removal of the titanium dioxide slurry to maintain 70.4% PVC.

[0074] A third series of paint formulations were prepared that were similar to the previous paint formulation, but without increasing the grind as compensation for removal of the titanium dioxide. A ladder study of titanium dioxide was evaluated from 0.76 wt% to 5.26 wt%; addition via commercially available titanium dioxide slurry.

[0075] All of the paint formulations were applied to a Leneta form 1 B black and white application card using a 3.0 mil wet film thickness Bird blade applicator. The applications were dried for 24 hours in a 70% humidity room set at 25°C. After drying, the percent reflectance of the paint over both the white and black sections of the application card panels was measured with a BYK Spectro-Guide 45/0 spectrophotometer. Contrast ratios were determined by dividing the reflectance values of the black by the white. A higher the contrast ratio indicates better hiding.

[0076] Referring now to Fig. 1 3, the graph (x-axis) shows the % contrast ratio versus the wt% titanium dioxide in each of the experimental paint formulations. At equal PVC (70.4%), the Control has a slightly higher contrast ratio compared to the ENC262/265 polymeric composite binder formulation. The level of titanium dioxide in the control is 5.99 wt% versus 0.76 wt% for the ENC262/265 polymeric composite binder formulation. In this example PVC of the ENC 262/265 paint was maintained by using a higher loading of grind, thus a higher pigment level.

[0077] A final evaluation was conducted to demonstrate how much titanium dioxide can be removed from the formulation without having to compensate for the amount of titanium dioxide removed. Graph (x-axis) shows a linear response as titanium dioxide is increased in this experiment and equal hiding to the Control is achieved at roughly 50% lower titanium dioxide level.

Claims

What is claimed is:

1 . An aqueous dispersion of titanium dioxide polymeric composite binder particles comprising polymeric particles coated with titanium dioxide pigment grains, wherein the average particle size of the titanium dioxide pigment grains is at least 200 nm.

2. The aqueous dispersion of claim 1 , wherein the polymeric particles are prepared by polymerizing a polymerizable, ethylenically unsaturated monomer.

3. The aqueous dispersion of claim 2, wherein the polymerizable, ethylenically unsaturated monomer is selected from the group consisting of (meth)acrylic acid, alkyl esters of (meth)acrylic acid, beta-carboxyethyl acrylate, acry-loxypropionic acid, crotonic acid, fumaric acid, monoalkyi esters of fumaric acid, maleic acid, monoalkyi esters of maleic acid, itaconic acid, monoalkyi esters of itaconic acid, styrene, and combinations thereof.

4. The aqueous dispersion of claim 2, wherein the polymerizable, ethylenically unsaturated monomer is selected from the group consisting of ethylenically unsaturated, beta-hydroxy ester functional monomers derived from the reaction of a monocarboxylic acid and an epoxy compound.

5. A composite binder for a coating system comprising polymeric particles coated with titanium dioxide pigment grains having an average particle size of at least 200 nm, wherein the titanium dioxide loading of the coating system containing the composite binder is at least 10% less than an equivalent coating system containing only free titanium dioxide.

6. The composite binder of claim 5, wherein the coating system is selected from the group consisting of latex paints, alkyd emulsion paints, varnishes, adhesives, inks, textile coatings, paper coatings, and combinations thereof.

7. The composite binder of claim 5, wherein the coating system is a latex paint.

8. The composite binder of claim 5, wherein the polymeric particles are prepared by polymerizing a polymerizable, ethylenically unsaturated monomer selected from the group consisting of (meth)acrylic acid, alkyl esters of (meth)acrylic acid, beta- carboxyethyl acrylate, acry-loxypropionic acid, crotonic acid, fumaric acid, monoalkyi esters of fumaric acid, maleic acid, monoalkyl esters of maleic acid, itaconic acid, monoalkyl esters of itaconic acid, styrene, and combinations thereof.

9. The composite binder particles of claim 8, wherein the polymerizable, ethylenically unsaturated monomer is selected from the group consisting of ethylenically unsaturated, beta-hydroxy ester functional monomers derived from the reaction of a monocarboxylic acid and an epoxy compound.

10. A method for improving the hiding power of a coating system comprising incorporating into the coating system from about 10 wt% to about 90 wt% of a composite binder comprising polymeric particles coated with titanium dioxide pigment grains, wherein the average particle size of the titanium dioxide pigment grains is at least 200 nm and the titanium dioxide loading of the coating system containing the composite binder is at least 10% less than an equivalent coating system containing free titanium dioxide.

1 1 . The method of claim 10, wherein the coating system is selected from the group consisting of latex paints, alkyd emulsion paints, varnishes, adhesives, inks, textile coatings, paper coatings, and combinations thereof.

12. The method of claim 10, wherein the coating system is a latex paint.

13. A method for reducing titanium dioxide loading in a coating system comprising incorporating into the coating system from about 10 wt% to 90 wt% of a composite binder comprising polymeric particles coated with titanium dioxide pigment grains, wherein the average particle size of the titanium dioxide pigment grains is at least 200 nm and the titanium dioxide loading of the coating system containing the composite binder is less than an equivalent coating system containing free titanium dioxide.

14. The method of claim 13, wherein the coating system is selected from the group consisting of latex paints, alkyd emulsion paints, varnishes, adhesives, inks, textile coatings, paper coatings, and combinations thereof.

15. The method of claim 13, wherein the coating system is a latex paint.

16. A method for producing the aqueous dispersion of titanium dioxide polymeric composite binder particles of any one of claims 1 -4, comprising:

(1 ) making a stabilized aqueous emulsion comprising:

(a) a dispersed phase comprising droplets of a polymerizable monomer coated with titanium dioxide pigment grains, and

(b) a continuous phase comprising an aqueous medium, wherein the titanium dioxide pigment grains are disposed at the interface between the dispersed phase and the continuous phase; and

(2) polymerizing the polymerizable monomer to form the aqueous dispersion

comprising polymeric particles coated with titanium dioxide particles, wherein the polymeric particles are dispersed in the aqueous medium.

17. The method of claim 16, wherein the polymerizable monomer comprises a polymerizable, ethylenically unsaturated monomer.

18. The method of claim 17, wherein the polymerizable, ethylenically unsaturated monomer is selected from the group consisting of (meth)acrylic acid, alkyl esters of (meth)acrylic acid, beta-carboxyethyl acrylate, acry-loxypropionic acid, crotonic acid, fumaric acid, monoalkyl esters of fumaric acid, maleic acid, monoalkyl esters of maleic acid, itaconic acid, monoalkyl esters of itaconic acid, styrene, and

combinations thereof.

19. The method of claim 17, wherein the polymerizable, ethylenically unsaturated monomer is selected from the group consisting of ethylenically unsaturated, beta- hydroxy ester functional monomers derived from the reaction of a monocarboxylic acid and an epoxy compound.