AU6266698A

AU6266698A - Water-based emulsion polymers which resist blocking

Info

Publication number: AU6266698A
Application number: AU62666/98A
Authority: AU
Inventors: Nicoletta Piccilrovazzi; Ute Schuster; Friedericke Stollmaier
Original assignee: Dow Chemical Co
Current assignee: Union Carbide Chemicals and Plastics Technology LLC
Priority date: 1997-02-14
Filing date: 1998-02-05
Publication date: 1998-09-08
Also published as: GB9703147D0; KR20000071020A; WO1998035994A1; EP0960133A1; ID19920A; AR011674A1; CA2281529A1; BR9808645A

Description

WATER-BASED EMULSION POLYMERS WHICH RESIST BLOCKING

This invention relates to emulsion polymers and to paints and other coatings containing emulsion polymers.

Water-based coatings and paints are well known and have been sold commercially for many years. These coatings and paints are based on emulsion polymers, which are referred to as latexes. In addition to the latex, these coatings usually contain additional ingredients such as pigments, opacifiers, coalescents and crosslinkers, among others.

Quite often, these water-based coatings and paints will contain a small quantity of an organic solvent. These solvents tend to be volatile and produce vapors when the coating or paint is applied. For environmental and safety reasons, it is desired to reduce the level of solvent and other volatile components in the water-based coatings and paints.

A problem frequently encountered with water-based coatings and paints is

"blocking". "Blocking" refers to the tendency of the coating or paint to adhere to itself or to have a tacky surface after drying. Water-based coatings and paints need to form highly coalesced films when they are dried at their particular application temperature. To achieve this high degree of coalescence, the emulsion polymer must either have a T_g below the application temperature, or else be used in conjunction with coalescing solvents. Both approaches usually lead to bad "blocking" properties of the coatings or paints. Polymers with a low T_g usually cause the coating to exhibit poor "final" blocking properties, in that the polymer will block even when completely dried. Coatings formulated with coalescing solvents dry slowly and therefore exhibit poor "early" blocking characteristics for an extended period until drying is complete. When the level of coalescing solvent is increased, this blocking problem is often worsened because the coating or paint dries more slowly. In both cases, objects coated with these coatings tend to block when the coating is applied and when the objects are stacked. This blocking often causes the coating to fail when the objects are separated.

In addition, the coating or paint must be able to resist damage caused by exposure to water and solvents such as are commonly present in household cleaners. Attempts to improve blocking resistance by blending hard components with soft components can lead to reduced resistance to water and/or solvents. It would therefore be desirable to provide an emulsion polymer which resists both early and final blocking, water spotting and spotting from common solvents such as ethanol. It would also be desirable to provide a coating or paint composition which is similarly resistant.

In one aspect, this invention is an aqueous emulsion having an aqueous phase and a dispersed polymer phase, wherein the dispersed polymer phase comprises particles of a polymer of monomer mixture including

(a) from 5.5 to 15 percent, based on the weight of all monomers, of a mixture of ethylenically unsaturated functional monomers, wherein said functional monomer mixture includes:

( 1 ) at least 0.5 percent, based on the total weight of all monomers, of at least one monomer having a carboxyl or carboxylate group

( 2 ) at least 0.8 to5 percent, based on the total weight of all monomers, of at least one monomer having a sulfonic acid, sulfonate group or sulfosuccinate group,

or both (1) and (2);

(b) from 0.5 to 10 percent, based on the weight of all monomers, of one or more ethylenically unsaturated, addition polymerizable monomer(s) containing a silicon atom to which is bound at least one hydrolyzable group, provided that the linkage between the silicon group and the ethylenic unsaturation is not hydrolyzable;

(c) from 75 to 94 percent, based on the weight of all monomers, of a nonfunctionalized vinyl aromatic monomer, a nonfunctionalized ester of acrylic or methacrylic acid, or a mixture thereof,

provided that when less than about 1.5 percent by weight of monomer (b) is present, said monomer mixture further comprises

(d) at least about 0.1 percent, based on the weight of all monomers, of a monomer having at least two ethylenically unsaturated, addition polymerizable groups. In a second aspect, this invention is an aqueous emulsion having an aqueous phase and a dispersed polymer phase, wherein the dispersed polymer phase comprises particles of a polymer of monomer mixture including

(a) from 3.5 to 15 percent, based on the weight of all monomers, of a mixture of ethylenically unsaturated functional monomers, wherein said functional monomer mixture includes:

( 2 ) at least 0.8 percent, based on the total weight of all monomers, of at least one monomer having a sulfonic acid, sulfonate or sulfosuccinate group,

or both (1) and (2);

(b) from 0.5 to 10 percent, based on the weight of all monomers, of one or more ethylenically unsaturated, addition polymerizable monomers containing a silicon atom to which is bound at least one hydrolyzable group, provided that the linkage between the silicon group and the ethylenic unsaturation is not hydrolyzable;

(c) from about 75 to about 96 percent, based on the weight of all monomers, of a nonfunctionalized vinyl aromatic monomer, a nonfunctionalized ester of acrylic or methacrylic acid, or a mixture thereof;

provided that when less than 1.5 percent by weight of monomer (b) is present, said monomer mixture further comprises at least 0.1 percent, based on the weight of all monomers, of a monomer having at least two ethylenically unsaturated, addition polymerizable groups;

wherein said monomer mixture is polymerized in two stages, in which monomers which together form a polymer having a T_g of less than 25°C are polymerized in a first stage and monomer which together form a polymer having a T_g of at least 60°C are polymerized in a second stage.

In a third aspect, this invention is a coating composition comprising the aqueous emulsion of the first aspect. The emulsion of this invention surprisingly exhibits excellent resistance to both early and final blocking, even when dried at temperatures well above the T_g of the dispersed polymer particles. Moreover, this blocking resistance is not obtained at the expense of a significant loss of water and solvent resistance; this emulsion provides for adequate to excellent resistance to both water and ethanol/water mixtures.

The aqueous emulsion of this invention includes a continuous aqueous phase and a dispersed polymer phase. The dispersed polymer phase is in the form of particles of a size such that they can remain stably dispersed in the aqueous phase. A suitable size range for the particles is from 40 nm to 350 nm in diameter ("diameter" here referring to the longest dimension of the particle), preferably 50 to 120 nm.

The dispersed particles comprise a polymer which is prepared by polymerizing a mixture of monomers of at least three different types. In this context, "mixture of monomers" or "monomer mixture" means only that the polymer contains repeating units from each member of the mixture, but does not require that all the monomers must be mixed together before polymerizing, or that the monomers must all be polymerized simultaneously. As discussed further below, the monomers may be polymerized all at one time, polymerized sequentially, polymerized in groups, or any combination of these.

In the general case, the monomer mixture contains at least 5.5 weight percent, up to 15 weight percent, of an ethylenically unsaturated functional monomer. However, the level of the functional monomer may be reduced to as low as 3.5 percent or 3 percent when the emulsion polymer is prepared in a two-stage polymerization reaction as described below. For the purposes of this invention, a "functional monomer" is one which contains a highly polar group. Such functional monomers include those containing one or more ionic groups, such as sulfonate or carboxylate groups, precursors of such ionic groups, such as sulfonic acid and carboxyl groups, and other highly polar groups which, although they are not ionic in character, impart high polarity to the monomer. These groups include hydroxy, poly(oxyethylene), nitrile, and amide. Specific functional monomers useful in this invention include methacrylic acid, acrylic acid, fumaric acid, maleic acid, itaconic acid, succinic acid, hydroxyethyl methacrylate, hydroxyethyl acrylate, acrylamide, acrylonitrile, methacrylonitrile, acetoxy ethyl methacrylate, acetoxy ethyl acrylate, acetoacetoxy ethyl methacrylate, sodium styrene sulfonate, sodium 1-acrylamido-2-methylpropane sulfonate, sodium alkyl allyl sulfosuccinate (in which the alkyl group contains up to about 20 carbon atoms), and glycidyl methacrylate. Sulfonated monomers or monomers with a sulfosuccinate group, containing a long hydrocarbon chain (C₆ or higher, preferably up to C₂₀) often operate as a surfactant during the polymerization reaction; in that case, added surfactant may be minimized or unnecessary. However, when such sulfonated or sulfosuccinated monomers are used, it is preferred to also include another sulfonated monomer which does not contain a long-chain hydrocarbon group. Those monomers containing acid groups may be used in the form of their salts, preferably salts with a monovalent cation, more preferably of an alkali metal or ammonium salt. Conversely, those monomers containing acid salt groups may be used in the free acid form.

The functional monomer mixture includes one or more monomers containing at least one carboxyl or carboxylate group or one or more monomers containing at least one sulfonic acid, sulfonate or sulfosuccinate group. Preferably, monomers of both type are present. The sulfonate group is preferably in salt form, with the cation being monovalent and preferably an alkali metal or ammonium. When present, the sulfonated monomer(s) constitutes at least 0.8 percent, preferably at least 1.5 percent, more preferably at least 2 percent, up to 10 percent, preferably up to 5 percent, more preferably up to 4 percent, based on the combined weight of all monomers.

When a monomer containing a carboxyl or carboxylate group is present, it constitutes at least 0.5 percent, preferably at least 1.5 percent, more preferably at least 2.5 percent, up to 10 percent, preferably up to 5 percent of the total weight of all monomers.

The second type of monomer is one or more ethylenically unsaturated monomer(s) containing a silicon atom to which is bound at least one hydrolyzable group. In those monomers, the ethylenic unsaturation is bound to the silicon atom through a linkage which is not itself hydrolyzable. The monomer(s) of this type constitute at least about 0.5 percent, preferably from about 1.6 percent, more preferably at least about 2 percent, up to 10 percent, preferably up to 7 percent, more preferably up to 4 percent of the weight of all monomers.

The monomers of the second type have at least one, preferably at least two, and more preferably three hydrolyzable groups bound to the silicon atom. Suitable such hydrolyzable groups include aceto (-C(H)=O) and halogen groups, and groups of the form -O-R, wherein R is branched-, straight-chain or cyclic hydrocarbyl, or a hydrocarbyl group which is substituted with ether, hydroxyl or other inert substituents. Examples of such hydrolyzable groups include aceto groups and those in which the R group corresponds to methyl, ethyl, propyl, 1 -methylethyl or 1-methyl-2-methoxyethyl. Illustrative monomers of the second type include methacryloxypropyl trimethoxy silane, vinyl tris(1-methoxypropyl-2-oxy) silane, vinyl triethoxy silane, vinyl trimethoxysilane, γ-methacryloxy propyl trimethoxy silane, or vinyl triacetoxysilane.

When less than 1.5 percent of the monomer of the second type is used, then the monomer mixture must also contain at least 0.1 percent of a monomer having at least two ethylenically unsaturated, addition polymerizable groups. In other cases, this last type of monomer is optional, but not required. This type of monomer may constitute up to 5 percent of the monomer mixture, preferably up to 1.5 percent. Examples of such monomers include divinylbenzene and ethylene glycol di methacrylate. Preferably, this monomer contains at least two ethylenically unsaturated groups of significantly differing reactivity, such as allyl methacrylate or allyl acrylate. When the monomer contains ethylenically unsaturated groups of differing reactivity, it is possible to provide a polymer which can be post- crosslinked, because the more reactive monomer will polymerize as the polymer is prepared, but the less reactive unsaturated group will remain unreacted and available for reaction at a later time, such as during the curing of the polymer.

The third type of monomer is one or more nonfunctionalized vinyl aromatic monomer(s), acrylic esters or methacrylic esters. By "nonfunctionalized", it is meant that the monomer contains (1) no groups which cause the monomer to be highly polar (as defined above), (2) no groups other than a polymerizable group which react during the course of polymerization, and (3) no silicon atoms having hydrolyzable substituents. Suitable such monomers include styrene, α-methyl styrene, vinyl toluene, vinyl naphthalene, any of which can be inertly-substituted, such as with alkyl or alkoxyl groups; acrylic and methacrylic esters in which the ester group is C,-C₂₀ alkyl, preferably C₂-C₈ alkyl, such as butyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate, 1-ethylhexyl acrylate, methyl and methacrylate.

The monomer or monomers of the third type can be selected to provide desirable properties to the polymer. In particular, the monomers can be selected so that the dispersed polymer particles have a T_g within a desired range, or so that the polymer particles will form a film at a desired temperature. For example, when the third type of monomer is largely selected from "hard monomers" like styrene and/or methyl methacrylate and/or tertiary-butyl methacrylate, the T_g and the minimum film formation temperature (MFFT) of the resulting polymer tend to be high, such as, for example above 35°C, preferably above 60°C. On the other hand, when the third type of monomer is largely selected from "soft monomers" like n-butyl acrylate and/or n-hexyl acrylate and/or n-heptyl acrylate and/or 2-ethyl hexyl acrylate, then the T_g and MFFT tend to be lower, such as below 35°C, preferably below 15°C, more preferably less than or equal to 6°C. By selecting the third type of monomer properly, the T_g and MFFT of the polymer particles may be adjusted to a desired value.

The MFFT is measured by casting a 150 μm film of the emulsion on a heating plate that has a temperature gradient. The film is dried and the minimum temperature at which a coherent film is formed is recorded as the MFFT.

The emulsion of this invention is conveniently prepared by polymerizing the monomer mixture just described in an emulsion polymerization in an aqueous phase. Such polymerization methods are well known and are described, for example, in Emulsions:

Theory and Practice, by P. Becher Reinhold, New York (1959), High Polymer Latices, by D. C. Blackley, Pamerton Publishing Co., New York (1966); and Emulsion Polymer Technology, by Robert D. Athey, Jr. Marcel Dekker, Inc., New York (1991).

In general, the emulsion polymerization process includes mixing the monomers into a continuous aqueous phase under agitation sufficient to disperse the monomers into fine droplets. Unless one or more of the monomers has surface active characteristics, one or more surfactants are present in order to form micelles as reaction loci and to form a stable emulsion having discrete particles of desirable size. A free radical initiator or redox catalyst is usually employed to provide an acceptable rate of polymerization and a high conversion of monomers to polymer.

The monomers may be added to the aqueous phase all at once in a batchwise operation, or all of a portion may be added continuously or in increments as the polymerization proceeds. The different monomers may be added at different times during the polymerization, or at varying relative rates at different times, or at the same relative rates throughout the polymerization.

Seed polymer particles may be added at the start of the polymerization in order to help control the nucleation of particles and the size of the final polymer particles. The weight of the seed particles is preferably no greater than 2.0 percent of that of the monomer mixture; in such a case, the composition of the seed particles is ignored when calculating the amounts of the various monomer types in the monomer mixture. In an illustrative polymerization process, water, surfactant and optional seed particles are initially charged to a suitable reactor and heated to the desired polymerization temperature. The desired polymerization temperature depends on the particular catalyst and monomers employed, and typically ranges from 30°C to 100°C, preferably from 50°C to 100°C, more preferably from 60°C to 100°C. The initial charge to the reactor may include all or a portion of the monomer mixture. After the initial charge is heated to the desired temperature, one or more streams is fed to the reactor. One of those streams contains the free radical initiator (or redox catalyst). The monomer mixture may be added in one or more separate streams. Additional surfactant may also be added, either as a separate stream or mixed with the catalyst or one or more of the monomers. When the monomers are not added together as a single mixture, they can be added as two or more separate streams, which may be added simultaneously, sequentially, or staggered with respect to each other. Following the addition of all streams, the reactor contents are typically heated for a period to complete polymerization. Often, this post addition heating is conducted at a higher temperature.

Alternatively, a two-stage polymerization process can be used. This two- stage process has the advantage of requiring a smaller amount of the functional monomer. In the two-stage process, monomers selected from one or more of the types previously described, which together from a polymer having a T_g of 25°C or less, are polymerized in a first stage. The monomers polymerized in the first stage may or may not contain a functional monomer, and may or may not contain the monomer containing a silicon atom having hydrolyzable substituents; all that is required is that the first stage monomers polymerize to form a polymer having the requisite T_g. The monomers polymerized in the first stage can be mixed and polymerized, or may be fed into the reaction mixture as separate streams. One or more of the monomers polymerized in the first stage may be added as part of the initial charge to the reactor, with the remaining monomers in the first stage added as a stream. Once the first stage monomers are added, they are polymerized to a conversion of at least 70 weight percent, preferably at least 80 weight percent, and then the second stage monomers are added. The second stage monomers are selected from the types described before, and are chosen so that they form a polymer having a T_g of at least 60°C. The second stage monomers may or may not contain a functional monomer, and may or may not contain the monomer containing a silicon atom having hydrolyzable substituents; all that is required is that the second stage monomers polymerize to form a polymer having the requisite T_g. The functional monomers and the monomer containing the silicon atom having hydrolyzable substituents may be added in either the first stage, the second stage, or both.

In this invention, all references to Tg are those obtained by differential scanning calorimetry (DSC) on a dried latex sample made by pouring one drop of latex into an aluminum crucible and drying for 12 to 20 hours at room temperature in a desiccator. The samples are evaluated using a Mettler DSC 30 calorimeter, scanning at a rate of 10°C/minute over a range of -40 °C to 110°C.

In some cases, it may be difficult to measure the separate T 's of the polymer using DSC. In those cases, the T_g of the polymer formed in each stage can be determined by polymerizing the monomer or monomer mixture alone in a single stage polymerization process, and measuring the T_g of the resulting polymer in the manner just described. For example, the T_g of a styrene/2-ethylhexyl acrylate mixture can be determined by polymerizing that mixture in a single-stage polymerization, and measuring the T_g of the resulting polymer. To the extent that the T_g is affected by the selection of reaction conditions such as temperature and free radical initiator, those conditions should be kept constant when T_g is determined in this way.

A convenient way to estimate the T_g of a polymer formed from a particular monomer mixture is through the Fox equation:

1/T_gAN = wA T_gA + wB/T_gB = . . . +wN/T_gN

wherein A, B and N represent individual monomers in the mixture containing N monomers, wA, wB and wN represent the weight fractions of monomers A, B and N, respectively, T AN represents the T_g of the polymer formed, and T_gA, T_gB and T_gN represent the T_g of homopolymers of monomers A, B and N, respectively. See T.G. Fox, Bull. Am. Physics Soc, vol. 1(3), page 123 (1956). By using the Fox equation, it is possible to screen combinations of monomers to estimate which combinations will provide a polymer having the required T_g.

The amount of monomers added and polymerized is selected so that the resulting polymer emulsion has a desired solids content, and the copolymer particles have a desired size. Preferably, the resulting emulsion has a solids content from 10 to 70 percent by weight, more preferably from 25 to 55 percent by weight, and the copolymer particles have a volume average diameter from 40 nm to 350 nm, preferably from 50 to 120 nm. Any surfactant which stabilizes the monomer mixture as discrete droplets and the subsequent copolymer as discrete particles in the aqueous phase can be used. The surfactant may be of the nonionic, anionic or amphoteric type. Exemplary surfactants include alkali metal alkyl carboxylates, polyoxyethylene alkyl phenols, linear alkyl sulfonates, alkyl aryl sulfonates, alkylated sulfosuccinates, C₆-C₂₀ amine oxides, N,N-bis(carboxyl alkyl) and C₆-C₂₀ alkyl amines. SIPONATETM A246L brand surfactant (available from Rhone- Poulenc), sodium dodecyl benzene sulfonate, sodium lauryl sulfate, disodium dodecyldiphenylether disulfone, N-octadecyl disodium sulfosuccinate, dioctyl sodium sulfosuccinate, N,N-bis-carboxyethyl lauramine, and sulfonated alkylated phenyl ethers such as DOWFAX^* 2EP and DOWFAX^* 2A1 (Trademark of The Dow Chemical Company and both are available from The Dow Chemical Company), are all suitable surfactants. The surfactant is advantageously used in an amount from 0.1 to 2 percent, preferably from 0.1 to 0.5 percent, based on the weight of the monomer mixture.

Suitable free radical initiators include peroxy compounds such as peroxydisulfates (commonly known as persulfates), perphosphates, t-butyl hydroperoxide, cumene hydroperoxide and hydrogen peroxide. Ammonium persulfate, sodium persulfate and potassium persulfate are preferred initiators. Redox catalysts, which are activated in the water phase through a water-soluble reducing agent, can also be used. The free radical initiator is advantageously used in an amount from 0.01 to 5 percent, preferably 0.1 to 2 percent, based on the weight of the monomers. If desired, an amount of initiator or catalyst in excess of the foregoing amounts may be added after the addition of the monomer streams, in order to finish off the polymerization.

When the monomer mixture contains a monomer having free acid groups, and in particular free carboxyl groups, it is preferred to stabilize the resulting polymer emulsion by adjusting the pH to above 5.0. This can be done by adding a fugitive base like ammonia, dimethylamine, diethyl amine, aminopropanol, ammonium hydroxide or 2-amino- 2-methyl-1-propanol, or through the addition of an alkali such as sodium hydroxide, potassium hydroxide or sodium, potassium or ammonium carbonate. This base may be added toward the end of the addition of the monomer stream(s), after all the monomer addition has been completed, or after the polymerization reaction is finished.

Other ingredients can also be used during the polymerization process as desired, such as chain transfer agents, buffers, or preservatives. Following the polymerization, the resulting emulsion may be steam-stripped or otherwise treated to remove impurities and unreacted monomers.

The emulsion of this invention can be formulated into a variety of paints and coatings. The coatings can be formulated for use in a wide variety of applications, and the selection of the emulsion of this invention for use in the coating does not require any special ingredients or formulating techniques. Accordingly, those ingredients and paint and coating formulations which are well understood in the art may be used to formulate paints and coatings with the emulsion of this invention.

The latex can be formulated in clear and pigmented coatings and paints. The pigmented formulation, for example, will generally contain a filler, opacifying agent or pigment, such as calcium carbonate, talc, silica, aluminum hydroxide, glass powder, titanium dioxide, zinc phosphate, red oxide, carbon black, Hansa Yellow, Benzidine Yellow, Phthalocyanine Blue, or Quinacridone Red. These are generally used in amounts sufficient to provide the coating with a pigment volume concentration of 15 to 80 percent.

In addition, the formulation may contain inorganic dispersants such as sodium hexametaphosphate or sodium tripolyphosphate, organic dispersants such as the polycarboxylic acid polymers (for example, Nopcoperse™ 44c, from Summopco Co., Ltd. and Orotan™ 681 , from Rohm & Haas); wetting agents; thickeners such as polyvinyl alcohols, polyurethanes such as Acrylsol RM8, from Rohm & Haas, and cellulosic derivatives; crosslinking agents such as water soluble polyvalent metal salts, aziridine compounds, water-soluble epoxy or melamine resins, or water dispersible blocked isocyanates; surfactants; matting agents and defoamers. Solvents such as alcohols, glycol ethers, hydroxy-tertiary amines, ketoximes, active methylene compounds and lactams may also be added. However, it is an advantage of this invention that the use of coalescing type solvents are not necessary in order to obtain good early and final blocking properties.

The following examples are provided to illustrate the invention, but are not intended to limit its scope. All parts and percentages are by weight unless otherwise indicated. Examples 1. 1a and 2-15

A. Preparation of the Latexes

The following general procedure was used to make latex Examples 1 , 1 a and 2 to 15. The composition of the monomer mixture used in each Example is given in Table I. In each case, a latex with approximately 42.5 percent solids was obtained.

A stainless steel reaction vessel is charged with 81 parts of deionized water and 0.42 part of sodium C₁₀.₁₂ alkyl allyl sulfosuccinate and heated to 80°C. Then, 10 percent of the total charge of styrene (when used), 2-ethyl hexyl acrylate and methyl methacrylate (when used) are fed to the reactor over 20 minutes. Following the addition of the monomer stream, the contents of the reaction vessel were held at 80°C while feeding 0.12 part potassium persulfate dissolved in 5.25 parts water for 30 minutes to form seed polymer particles. Three streams were then fed to the vessel, all starting at the same time. The first stream contained the reminder of the styrene, 2-ethyl hexyl acrylate and methacrylic acid and methacryl oxypropyl trimethoxy silane, and was added to the reactor over 170 minutes. The second stream consisted of the sodium p-styrenesulfonate, the rest of the sodium alkyl(C₁₀.₁₂) allyl sulfosuccinate and 28 parts of water. It was added over 180 minutes. The third stream contained 0.35 parts of potassium persulfate and 15.75 parts water, and was added over 190 minutes. After the streams were completed, the reaction temperature was held at 80°C for an additional 120 minutes to complete polymerization. The monomer compositions used are given in the following table.

All amounts provided are parts by weight. The monomers used in making the in situ seed particles are included, since the seeds constitute in excess of 5 percent of the mass of the final polymer.

TABLE I

*Also contains 0.6 parts by weight allyl methacrylate;

¹ 2-ethylhexyl acrylate;

² Methyl methacrylate; ³ Methacrylic acid;

⁴ Sodium styrene sulfonate;

⁵ Sodium alkyl (C_{1( 2})allyl sulfosuccinate;

⁶ γ-methacryloxy propyl trimethoxysilane (commercially available from DOW Corning as Z- 6030.

B. Evaluation of the Latexes

Multiple films were prepared from each of Latex Example Nos. 1-15. The films were cast on a black plastic foil commercially available from Leneta Company (Leneta foil) at a wet thickness of 150 μm. The resulting films were evaluated for hot-blocking resistance, water spot resistance and ethanol/water spot resistance as follows.

For hot-blocking resistance testing, duplicate film samples were dried for one day and others for one week at ambient temperature (approximately 21 °C) in a room held at a constant relative humidity of 50 percent. Two duplicate films were blocked at 50°C for two hours under a weight of 4 kg/cm², and then peeled apart. The films were then visually inspected for damage and rated on a scale of from 0 (complete destruction) to 5 (no damage). The results of this blocking test are as reported in Table II. The values reported include a composite rating of the samples cured for 1 day and those cured for one week.

For water spot resistance testing, a drop of water was applied to a film sample and covered with a watch glass. The time required for the film to visibly whiten was rated on a scale of (-) (whitening in less than one hour), (0) (whitening occurred after more than one hour but less than four hours, and (+) (no more than barely observable whitening after four hours). The results of this water spot resistance test are as reported in Table II.

For ethanol/water spot resistance testing, a filter paper soaked in a 50/50 ethanol/water mixture was placed onto the film, covered with a watch glass and visually inspected after four hours. The results were evaluated on a +/- scale, with (+) indicating no more than barely observable whitening after four hours, which faded within 30 minutes after the filter paper was removed and (-) indicating easily visible whitening which required greater than 30 minutes to fade. The results of this testing are also reported in Table II.

TABLE II

As can be seen from the data in Table II, each of these latexes has excellent early and final blocking resistance and good to excellent resistance to water and ethanol spotting.

C. Evaluation of Coating Formulations.

C1. Clear Coatings

Clear Coating Formulations 1 to 9 and 11 to 15 were made from each of Latex Examples 1 to 9 and 11 to 15, respectively, by blending the following components at room temperature: TABLE

^aA defoamer commercially available from Henkel; ^ba nonionic tenside commercially available from Air Products; ^ca wetting agent commercially available from Byk Chemie; ^da polyurethane thickener commercially available from Rohm & Haas as 30% solution; ^ea matting agent commercially available from W.R. Grace & Co.

Each of Clear Coating Formulations 1 to 9 and 11 to 15 was tested for blocking under four sets of conditions. The results are as reported in Table III below. Under Condition 1 , 150 μm (wet thickness) films are applied to Leneta foil and dried for two hours at approximately room temperature. Samples of the films were blocked (Condition 1 A) for 1 hour at 50°C under a weight of 0.5 metric ton/square meter and other samples were blocked (Condition 1 B) for 24 hours at room temperature and under a weight of 1 metric ton/square meter. The films were then separated and evaluated as described above.

Under Condition 2, 150 μm (wet thickness) films were applied to Leneta foil and dried for 48 hours at approximately room temperature. Some samples of the films were blocked (Condition 2A) for 24 hours at 50°C under a weight of 1 metric ton/square meter and other samples were blocked (Condition 2B) for 24 hours at room temperature and under a weight of 1 metric ton/square meter. The films were then separated and evaluated as described above.

Under Condition 3, 100 μm (wet thickness) films were applied to Leneta foil and dried for 48 hours at approximately room temperature. Samples of the films were blocked for 12 hours at 35°C under a weight of 2 metric ton/square meter. The films were then separated and evaluated as described above. Under Condition 4, two coatings of 150 μm (wet thickness) films were applied to beech wood and dried for 48 hours at approximately room temperature. Samples of the films were blocked (Condition 4A) for 2 hours at 50°C under a weight of 2.7 metric ton/square meter and other samples were blocked (Condition 4B) for 24 hours at room temperature and under a weight of 2.7 metric ton/square meter. The films were then separated and evaluated as described above.

Water/ethanol resistance was evaluated for all coatings by applying a 150 μm (wet thickness) film of the coating on samples of beech wood and drying at ambient conditions for 30 minutes, followed by application of a second 150 μm film and drying under ambient conditions. Resistance to spotting by an ethanol/water mixture was evaluated on multiple samples which were dried for two hours after application of the second film, and on other samples which were dried for 24 hours after application of the second film. The samples were evaluated by applying to each of them a filter paper soaked in a 50/50 ethanol/water mixture. The filter paper was removed from various samples after 15 minutes, 30 minutes and 2 hours. The films were then visually examined 24 hours after the filter paper was removed.

The films are tested for water spotting resistance in the same manner, except that the filter paper is removed from various samples after 30 minutes, 1 hour and 2 hours.

The results of the ethanol/water spotting and water spotting tests were rated on a scale from 0 to 5, with 5 being best. These results are as reported in Table IV below.

TABLE IV

TABLE V

Values reported for 30 minute/1 hour/2 hour exposure time. ²Values reported for 15 minute/30 minute/1 hour exposure time.

C2. Pigmented Coatings

Examples 1 and 1 B were evaluated in a pigmented coating designed for architectural gloss paint applications in the following formulation:

TABLE VI

Orotan 681 is an anionic dispersant commercially available from Rohm & Haas; "Triton X100 is a nonionic surfactant commercially available from Union Carbide; ^cAcrysol RM 1020 is a polyurethane thickener commercially available from Rohm & Haas; Tiona RCL-535 is titanium dioxide commercially available from SCM Chemicals.

The pigmented coatings were prepared by mixing the first four ingredients and grinding them together for 20 minutes, and then adding the remaining ingredients in the order listed, with slow stirring.

The pigmented coatings were tested for blocking resistance at ambient and at elevated temperature, 20° gloss and water, ethanol and hand cream resistance according to the following test conditions:

23°C Blocking resistance:

150 μm wet thickness films were applied to Leneta foil. Some samples were dried for 1 day and others were dried for 7 days at a temperature of 23°C and 50 percent relative humidity. Identically dried films are blocked for 24 hours at 23°C and 50 percent relative humidity under a load of 4 kg/ 25 cm². The films were then pulled apart and the force required to pull them apart was rated on a scale of 0 to 5, with 5 meaning that no force was required to separate the samples and 0 meaning that the films cannot be separated. 50°C Blocking resistance (Hot Blocking Resistance):

150 μm wet thickness films were applied to Leneta foil. Some samples were dried for 1 day and others were dried for 7 days at a temperature of 23°C and 50 percent relative humidity.

Identically dried films were blocked for 1 , 3 or 5 hours at 50°C/50 percent relative humidity under a load of 4 kg/25 cm². The films were then pulled apart and the force required to pull them apart was rated on a scale of 0 to 5, with 5 meaning that no force was required to pull them apart and 0 meaning that the samples cannot be pulled apart. The amount of surface damage was also evaluated, and reported as a percentage of the total surface area.

20° Gloss:

The paints were applied with a drawdown bar (150 μm wet film thickness) on glass, dried for 1 day at 23°C and 50 percent relative humidity and evaluated for 20° gloss using a Byk Glossmeter.

Water/Ethanol/Hand cream resistance:

The pigmented coatings were applied on glass with a drawdown bar (150 μm wet film thickness), dried for 7 days at a temperature of 23°C and 50 percent relative humidity and evaluated for water resistance by applying a drop of water on the dried film for either 5 minutes or 30 minutes. The film was evaluated for softening and formation of blisters 10 minutes after the water was removed, and rated on a scale of 0 to 2, with 2 meaning no film softening, 1 indicating slight film softening, 0 indicating severe film softening. The coatings were tested for ethanol and hand cream resistance in the same manner.

TABLE VII

Examples 16 to 19

Latex Example 16 was prepared in the same manner as Latex Examples 1 ■ 15, using the following monomer mixture: TABLE VIII

Latex Example 16 had an MFFT of 15°C. The formulation of Latex Example No. 17 can be adjusted (Example No. 17) by substituting 5 parts by weight of methyl methacrylate for an equal amount of the 2-ethyl hexyl acrylate. In this manner, the MFFT can be further increased to 32°C. By substituting another 5 parts by weight of methyl methacrylate for an equal amount of the 2-ethyl hexyl acrylate, the MFFT can be increased to 60°C (Example 18) and by substituting yet another 5 parts by weight of methyl methacrylate for an equal amount of the 2-ethyl hexyl acrylate, the MFFT can be increased to 80°C (Example 19).

Coatings were prepared from blends of Latex Examples 17 and 18 with Latex Example 1. The same coating formulation was used as described with respect to Examples 1-15, except that a 1 :1 (by weight) blend of c

TABLE IX

Examples 20 to 22

Example 20 was prepared by charging a stainless reaction vessel with 49 parts of deionized water, 0.17 part of sodium alkyl(C₎₀_₁₂) allyl sulfosuccinate, 0.92 part of itaconic acid and 0.09 part of sodium hydroxide (10 percent), followed by heating to 82°C. Then, a stream containing 0.12 part of sodium alkyl(C₎₀.₁₂) allyl sulfosuccinate in 2.6 parts water and a second stream containing 2.3 parts styrene, 0.15 part MPTS, 2.1 parts butyl acrylate and 0.33 part 2-HEMA were added over 20 minutes. A second stream of 0.18 part of potassium persulfate dissolved in 7.5 parts of water was started 15 minutes after the start of the monomers and was fed to the reactor over 30 minutes, to form in situ seed particles. After this initial seeding step monomer streams containing 44.56 parts styrene, 38.9 parts butyl acrylate, 6.17 parts HEMA, 1.43 parts sodium alkyl(C_1(H2) allyl sulfosuccinate and 2.85 parts MPTS and a stream containing 0.18 part of initiator in 7.5 parts of water were added continuously to the reactor over 200 minutes. To assure good conversion, an additional 0.2 part of potassium persulfate in 5 parts of water were added over a 30 minute period after the end of the monomer addition. The reaction temperature was then held at 82°C for an additional 90 minutes to complete polymerization.

Example 21 was prepared in essentially the same manner, except that the styrene level was decreased by 1 weight percent and the MPTS level was increased by the same amount.

Example 22 was prepared in essentially the same manner as Example 20 except no MPTS was added to the reactor during the initial seeding step. Instead, all the MPTS was added to the reactor over 60 minutes as a separate stream after the seeding step.

The resulting latex Examples 20 to 22 were evaluated for hot-blocking resistance, water and ethanol spotting resistance and MFFT in the same manner as Examples 1 to 9 and 11 to 15. All are rated "+" in both water and ethanol spotting resistance, and all had an MFFT of 24°C. Example 20 scored a "4" on the hot-blocking resistance test, whereas Example 21 scores a "4 to 5" and Example 22 scores a "5".

Example 23

Example 23 was prepared by charging a stainless reaction vessel with 85 parts of deionized water, 2.24 parts of a polystyrene seed latex following by heating to 80°C.

Then, 0.32 part ammonium persulfate dissolved in 45 parts deionized water are added continuously to the reactor over 300 minutes. A monomer stream containing 36.4 parts of 2- ethyl hexyl acrylate, 26.0 parts methyl methacrylate, 1.43 parts methacrylic acid and 1.17 parts acrylic acid was added over 156 minutes. Then from 156 to 240 minutes a stream of 27.4 parts of methyl methacrylate, 4.7 parts of 2-ethylhexyl acrylate, 1.5 parts MPTS, 0.77 part methacrylic acid and 0.63 part acrylic acid was added to the reactor.

Example 23 was evaluated in a clear coat formulation of the following composition:

TABLE X

^aSee notes ^{a e} from Table III.

'A wax additive commercially available from Byk Chemie.

The coating was evaluated for blocking by condition 1A/1 B as described above in section C1 Example 1. The samples for evaluating water and ethanol/water resistance were prepared by applying a 150 μm wet film onto wood and drying for 2 days at room temperature. The samples were evaluated by applying to each of them a filter paper soaked in a 50/50 ethanol/water mixture. The filter paper was removed from various samples after 30 minutes, 1 hour and 5 hours. The films were then visually inspected. The sample exposed to the filter paper for 5 hours was inspected 24 hours after the filter paper was removed.

The films were tested for water-spotting resistance in the same manner, except that all films were inspected immediately after removal of the filter paper. The results of the ethanol/water spotting and water spotting tests were rated on a scale from 0 to 5, with 5 being best.

Examples 24 to 28

These latex Examples 24-28 were prepared according to the procedure given for Example 1. The composition is given in Table XI.

TABLE XI

¹ 2-hydroxyethyl acrylate;

² glycidyl methacrylate;

³ aceto acetoxy ethyl methacrylate; sulfoethyl methacrylate- sodium salt

⁵ 2-acrylamido-2-methylpropane sulfonic acid sodium salt ^β See notes 2, 3, 5 and 6 from Table I.

The resulting latexes were evaluated in essentially the same formulation as Example 23 except that only 2 parts by weight of the methylglycol:methoxybutanol mixture were used. The latexes were evaluated for blocking, water resistance and ethanol resistance using the same methods used for evaluating Example 23. The results are as reported in Table XII. TABLE XII

Claims

CLAIMS:

1. An aqueous emulsion having an aqueous phase and a dispersed polymer phase, wherein the dispersed polymer phase comprises particles of a polymer of monomer mixture including:

(a) from 5.5 to 15 percent, based on the weight of all monomers, of a mixture of ethylenically unsaturated hydrophilic monomers, wherein said hydrophilic monomer mixture includes

( 1 ) at least 0.5 percent, based on the total weight of all monomers, of at least one monomer having a carboxyl or carboxylate group and/or

( 2 ) at least 0.8 percent, based on the total weight of all monomers, of at least one monomer having a sulfonic acid, sulfonate or sulfosuccinate group;

(b) from 0.5 to 10 percent, based on the weight of all monomers, of one or more ethylenically unsaturated, addition polymerizable monomers containing a silicon atom to which is bound at least one hydrolyzable group, provided that the linkage between the silicon group and the ethylenic unsaturation is not hydrolyzable,

provided that when less than 1.5 percent by weight of monomer (b) is present, said monomer mixture further comprises at least 0.1 percent, based on the weight of all monomers, of a monomer having at least two ethylenically unsaturated, addition polymerizable groups.

2 . The aqueous emulsion of Claim 1 , wherein the monomer mixture contains component (a)(1).

3 . The aqueous emulsion of Claim 2, wherein monomer mixture component (a) includes an ethylenically unsaturated, addition polymerizable monomer having at least one carboxyl or carboxylate group, and at least one other monomer which does not contain an ionic group or a precursor of an ionic group.

4 . The aqueous emulsion of Claim 3, wherein monomer mixture component (a) includes methacrylic acid, acrylic acid, fumaric acid, maleic acid, itaconic acid or succinic acid, and 2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate.

5 . The aqueous emulsion of Claim 2, wherein the monomer mixture further contains component (a)(2).

6 . The aqueous emulsion of Claim 5 wherein monomer mixture component (a)(2) includes a sulfonated monomer with a hydrocarbon chain of six or more carbon atoms.

7 . The aqueous emulsion of Claim 6 wherein monomer mixture component

(a)(2) further includes a sulfonated monomer without a hydrocarbon chain of six or more carbon atoms.

8 . The aqueous emulsion of Claim 5 wherein monomer mixture component (a)(2) includes a sulfonated monomer without a hydrocarbon chain of 6 or more carbon atoms.

9 . The aqueous emulsion of claim 1 wherein monomer mixture component (a)(2) is present.

10 . The aqueous emulsion of Claim 9 wherein the monomer mixture component (a)(2) includes a sulfonated monomer with a hydrocarbon chain of 6 or more carbon atoms.

11 . The aqueous emulsion of Claim 10 wherein the monomer mixture component (a)(2) further includes a sulfonated monomer without a hydrocarbon chain of 6 or more carbon atoms.

12 . The aqueous emulsion of Claim 9 wherein the monomer mixture component (a)(2) includes a sulfonated monomer without a hydrocarbon chain of 6 or more carbon atoms.

13 . The aqueous emulsion of claim 1 wherein the silicon atom is bound to 2 or 3 hydrolyzable groups.

14 . The aqueous emulsion of Claim 3 wherein the silicon atom is bound to two or three hydrolyzable groups.

15 . The aqueous emulsion of Claim 9 wherein the silicon atom is bound to 2 or 3 hydrolyzable groups.

16 . The aqueous emulsion of Claim 1 wherein component (c) of the monomer mixture is selected such that the polymer has an MFFT of less than or equal to 6┬░C.

17 . The aqueous emulsion of Claim 1 wherein component (c) of the monomer mixture is selected such that the polymer has an MFFT of more than35┬░C.

18 . The aqueous emulsion of Claim 3 wherein monomer mixture component (a)(2) is a mixture of sodium styrene sulfonate and sodium C_1(M2 alkyl allyl sulfosuccinate.

19 . The aqueous emulsion of Claim 5 wherein monomer mixture component (a)(2) is a mixture of sodium styrene sulfonate and sodium C_10.12 alkyl allyl sulfosuccinate.

20 . The aqueous emulsion of Claim 18 wherein the silicon atom is bound to 2 or 3 hydrolyzable groups.

21 . An aqueous emulsion having an aqueous phase and a dispersed polymer phase, wherein the dispersed polymer phase comprises particles of a polymer of monomer mixture including:

(a) from 3 to 15 percent, based on the weight of all monomers, of a mixture of ethylenically unsaturated functional monomers, wherein said functional monomer mixture includes:

( 1 ) at least 0.5 percent, based on the total weight of all monomers, of at least one monomer having a carboxyl or carboxylate group;

( 2 ) at least 0.8 percent, based on the total weight of all monomers, of at least one monomer having a sulfonic acid, sulfonate or sulfosuccinate group, or both (1) and (2);

(c) from 75 to 96 percent, based on the weight of all monomers, of a nonfunctionalized vinyl aromatic monomer, a nonfunctionalized ester of acrylic or methacrylic acid, or a mixture thereof,

provided that when less than 1.5 percent by weight of monomer (b) is present, said monomer mixture further comprises:

at least 0.1 percent, based on the weight of all monomers, of a monomer having at least two ethylenically unsaturated, addition polymerizable groups, wherein said monomer mixture is polymerized in two stages, in which monomers which together form a polymer having a T_gof less than 25┬░C are polymerized in a first stage and monomer which together form a polymer having a T_g of at least 60┬░C are polymerized in a second stage.

22. A coating composition comprising the aqueous emulsion of Claim 1.

23. A coating composition comprising the aqueous emulsion of Claim 21.

24. A coating composition containing the aqueous emulsion of any of Claims 1 to 21.