BACKGROUND

The present invention relates to water-re¬ sistant polymeric emulsions and processes for manufac¬ turing polymeric emulsions.

Oil-base products exist for rendering the surface of a substrate water-resistant. However, the long term availability of these products is doubtful because of increasing environmental restrictions on oil-based products.

SUMMARY OF THE INVENTION

The present invention provides water-based polymeric emulsions that are used to render the surface of a substrate water-resistant. The polymeric emul¬ sions contain at least about 40 percent solids and comprise a (i) a polymer, (ii) water, and (iii) a surfactant. Usually, the emulsion comprises less than about 1 weight percent surfactant based on the total monomer weight in the polymer. The polymer comprises about 25 to about 90 weight percent soft monomer, about 10 to about 75 weight percent hard monomer, about 1 to about 5 weight percent olefinic carboxylic acid mono¬ mer, and about 0.5 to about 5 weight percent cross- linking monomer. As used in the specification and claims, the term "soft monomer" means a monomer whose homopolymer has a T _q of less than about -20° C; the

term "hard monomer" means a monomer whose homopolymer has a T_ of greater than about 30° C; and the terms "weight percent hard monomer," "weight percent soft monomer," "weight percent olefinic carboxylic acid monomer," and "weight percent cross-linking monomer" each mean the total dry weight of the respective con¬ stituent ingredient employed in making the polymer divided by the total weight of the monomers employed in making the polymer, this quotient being multiplied by 100%. Generally, the emulsions have a surface tension of at least about 45 dynes/cm and the polymers have an average particle size of less than 250 nm. When the emulsion is applied to a surface and dried, it forms a water-resistant film.

The invention also encompasses a process for making the emulsion. The process comprises the steps of (a) delay adding the soft monomer, the hard monomer, the olefinic carboxylic acid, the cross-linking agent, and additional catalyst to a charged reactor to form an emulsion; and (b) proximate the end of the delay addi¬ tion step, adjusting the pH of the emulsion to sub¬ stantially neutralize all carboxylic acid groups on the polymer to stabilize the emulsion. The language "delay adding" is a term of art that means adding ingredients during at least a portion of the polymerization period.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, each polymeric emulsion comprises a (i) polymer, (ii) water, and (iii) a surfactant. Generally, the emulsion

comprises less than about 1 weight percent surfactant. As used in the specification and the claims, "weight percent surfactant" is defined as the total dry weight of the surfactant(s) employed in making the polymer divided by the total weight of the monomers employed in making the polymer, this quotient being multiplied by 100%. Preferably the emulsion comprises less than about 0.5 weight percent surfactant.

In general, when all other parameters are held constant, the lower the surfactant content of the polymer, the more insensitive the polymer is to water and the higher the surface tension of the emulsion. Typically, the emulsion has a surface tension of at least about 45 dynes/cm, and preferably about 45 to about 65 dynes/cm.

The surfactant is normally a copolymerizable surfactant, an anionic surfactant, a nonionic surfact¬ ant, or a mixture of two or more of these surfactants. Exemplary copolymerizable surfactants include, but are not limited to, sulfoethylmethacrylate, vinylsulfonate salts, sulfopropylmethacrylate, styrene sulfonate salts, 2-acrylamido-2-methylpropanesulfonic acid salts, and mixtures thereof. Anionic surfactants include, but are not limited to, alkylphenolethoxylate sulfates and sulfonates, alkylsulfates and sulfonates, and mixtures thereof. Nonionic surfactants include, but are not limited to, alkylarylpolyether alcohols, alkylphenolet- hoxylates, alkylethoxylates, ethyleneoxide/propylene oxide block copolymers, and mixtures thereof.

The polymer generally comprises about 25 to about 90 weight percent of a soft monomer, about 10 to about 75 weight percent of a hard monomer, about 1 to about 5 weight percent of an olefinic carboxylic acid, and about 0.5 to about 5 weight percent of a cross- linking agent, and typically has a T_ of about -50° to about 50° C. Preferably, the polymer comprises about 2 to about 4 weight percent olefinic carboxylic acid and about 1 to about 3 weight percent cross-linking agent.

Olefinic carboxylic acid monomers include both mono-olefinic carboxylic acid monomers and di- olefiniσ carboxylic acid monomers. Exemplary mono- olefinic carboxylic acids include, but are not limited to, acrylic acid and methacrylic acid. An exemplary di-olefinic carboxylic acid is itaconic acid. The preferred olefinic carboxylic acid monomer is metha¬ crylic aøid. However, mixtures of olefinic carboxylic acids can also be used.

.Typical cross-linking agents include, but are not limited to, N-methylol acrylamide, N-methylol methacrylamide, diacrylates, dimethacrylates, triallyl cyanurate, diallyl maleate, methyl acrylamidoglycolate methyl ether, olefinically unsaturated monomers having the formula I

R ₅ 0 \ ^Δ I

R ₁ ~ CH = C - R ₃ - C - CH ₂ - Z (I)

and mixtures thereof, wherein R^. ^: - ^s selected from the group consisting of hydrogen and halogen, R ₂ is select-

ed from the group consisting of hydrogen, halo, thio, and monovalent organic radicals, R ₃ is a divalent radical, and Z is selected from the group consisting of organoaσyl and cyano. Preferably, R-^ is hydrogen, R ₂ is hydrogen or an alkyl radical having up to about 10 carbon atoms, R ₃ is a cyclic or acyclic organic radical containing up to about 40 carbon atoms, and Z is an organoacyl having the formula II

O

II C - R. (ID

wherein R ₄ is selected from the group consisting of hydrogen and monovalent organic radicals. More prefer¬ ably, R ₃ is an acyclic radical containing up to about 20 atoms in length, with any and all side groups each being up to about 6 atoms in length, and R ₄ is hydrogen or an alkyl group containing up to about 7 carbon atoms. R ₃ is most preferably an alkylene group con¬ taining up to about 10 carbon atoms, and R ₄ is most preferably methyl. Due to its commercial availability, the preferred cross-linking agent of formula I is acetoacetoxyethyl methacrylate. However, the most preferred cross-linking agent is N-methylol acrylamide.

In one version of the present invention, the emulsion is employed as a water-resistant edge sealer for composite (or particle) boards or plywood. In this version, the weight ratio of the hard monomer to the soft monomer in the polymer is preferably about 1:1 to about 1.5:1, and the polymer preferably has a T_ of about 0° to about 20° C. Typically, in this embodiment

of the invention, the emulsion is applied to a sub¬ strate and dried at ambient temperature.

However, in a second embodiment of the inven¬ tion, the emulsion is applied to a substrate, e.g., ceramic or cement tiles, and dried at an elevated temperature,, e.g., above about 50° C. In this second version, the weight ratio of the hard monomer to the soft monomer in the polymer is preferably about 1.5:1 to about 3:1, and the polymer preferably has a T _g of about 30° to about 50° C.

In another version, the emulsion is employed as a water-resistant pressure sensitive adhesive (PSA) . In this latter version, the weight ratio of the hard monomer to the soft monomer in the polymer is prefera¬ bly about 1:4 to about 1:9, and the polymer preferably has a T_ of about -35° to about -50° C.

In all versions of the invention, the soft and hard monomers together typically constitute at least about 90 weight percent of the polymer, and preferably at least about 95 weight percent of the polymer.

The soft monomer is typically selected from the group consisting of non-functional acrylic mono¬ mers, ethylene, and mixtures thereof. As used in the specification nd claims, the term "non-functional monomer" means a monomer that is devoid of any group, e.g., hydroxyl, carboxyl, amide, and amine, that can undergo further reaction after polymerization of the

monomer; and the term "soft monomer" means a monomer whose homopolymer has a T _g of less than about -20° C. Non-functional acrylic monomers are the preferred soft monomers.

The non-functional acrylic monomers have the formula III

R ₅ O I- II CH ₂ = C - C - OR ₆ (HI)

wherein R ₅ is selected from the group consisting of hydrogen and methyl, and R ₆ is an alkyl group, prefera¬ bly having up to about 15 carbon atoms. As used in the specification and claims, the term "alkyl" means cyclic and acyclic saturated hydrocarbon groups that can be either branched or unbranched. Exemplary soft, non¬ functional acrylic monomers include, but are not limit¬ ed to, butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, isodecyl methacrylate, lauryl methacrylate, trideσylmethacrylate. 2-ethylhexyl acrylate is the preferred soft, non-functional monomer.

With respect to the hard monomer, hard mono¬ mers include, but are not limited to, alkylene aromatic monomers and non-functional methacrylic monomers. As used in the specification and claims, "alkenyl aromatic monomers" are defined as any organic compound contain¬ ing at least one aromatic ring and at least one ali¬ phatic-containing moiety having alkenyl unsaturation; and the term "hard monomer" means a monomer whose homopolymer has a T _q of greater than about 30° C.

Preferred alkenyl aromatic monomers are represented by the formula IV

wherein X is an aliphatic radical containing at least one alkenyl bond, Y is a substituent on the aromatic ring, and n is the number of Y substituents on the ring, n being an integer from 0 to 5. Generally, X comprises at least 2 carbon atoms, but usually no more than about 6, and preferably no more than about 3 carbon atoms. X is preferably a substituted or unsub- stituted alkenyl group. Preferred substituents on the alkenyl group are halogen radicals, e.g., chloride. However, the most preferred alkenyl group is unsubsti- tuted, i.e., a hydrocarbon, and contains only one olefinic unsaturation. Ethylene is the most preferred X. Λ ■_

Y is an organic or inorganic radical. As used throughout the specification and claims, the term "organic radical" means any group containing at least one carbon atom, and the term "inorganic radical" means any group devoid of carbon atoms. When n is 2 or more,

Y can be the same or different. If organic, Y general¬ ly contains from 1 to about 15 carbon atoms and, pref¬ erably, is an aliphatic radical. Even more preferably,

Y is a saturated aliphatic radical. If inorganic, Y is preferably a halogen. Exemplary Y substituents include halo and cyano radicals and substituted and unsubsti- tuted alkyl radicals of 1 to about 10 carbon atoms.

Preferred Y substituents are chloride and unsubstituted alkyl groups of 1 to about 6 carbon atoms. Y is more preferably a chloride radical and C to about C ₄ unsub¬ stituted alkyl radicals.

Illustrative alkenyl aromatic monomers in¬ clude styrene, p-methyl styrene, methyl styrene, o,p- dimethyl styrene, o,p-diethyl styrene, p-chlorostyrene, isopropyl styrene, t-butyl styrene, o-methyl-p-isopro- pyl styrene, o,p-dichlorostyrene, and mixture thereof. Due to its commercial availability and low cost, sty¬ rene is the preferred alkenyl aromatic monomers.

With respect to non-functional methacrylic monomers, exemplary non-functional methacrylic monomers have the formula V

CH-, 0 i - II

CH ₂ = C - C - OR ₇ (V)

wherein R ₇ is an alkyl group that preferably contains up to about 6 carbon atoms. Typical non-functional methacrylic monomers include methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, isobornyl metha¬ crylate, and mixtures thereof.

In the various embodiments of the present invention, the polymer preferably has an average parti¬ cle size (i.e., a maximum cross-sectional diameter) of less than about 250 nm. In general, for the polymer of the invention, the smaller the average particle size, the more water-resistant the polymer. Accordingly, it

is preferred that the average particle size of the polymer be- from about 85 to about 200 nm, more prefera- bly from about 90 to about 190 nm, and most preferably from about 100 to about 150 nm.

ie polymeric emulsion optionally comprises one or more other ingredients. For example, the poly¬ mer can comprise a wax. When employed, the wax is generally used in an amount sufficient to increase the water-resistance of resulting film.

In addition, the polymer optionally comprises a chain transfer agent. The chain transfer agent, when used, is typically incorporated to control the molecu¬ lar weight of the polymer, and is usually employed in a concentration of about 0.01 to about 0.5 weight percent based upon the amount of monomers used in making the polymer. The presence of chain transfer agents is particularly advantageous in PSAs where some low molec¬ ular weight polymeric components tend to be desirable.

One or more ureido-containing monomers are also optionally present in the polymer. Exemplary ureido-containing monomers include, but are not limited to, 2-ureido-ethyl acrylate, 2-ureido-methyl acrylate,

2-ureido-ethyl acrylamide, 2-ureido-ethyl methacryla- mide, and l-[2-(3-alloxy-2- hydroxypropylamino)ethyl]imidazolidin-2-one. The preferred ureido-containing monomer is

^' 1-[2-(3-alloxy-2-hydroxypropylamino)ethyl]imidazolidin >_ -2-one, commercially known as Sipomer WAM brand monomer

~ and available from Alcolac. The ureido-containing

monomers are generally used in a concentration suffi¬ cient to enhance the wet adhesion strength of the emulsion, e.g., from about 0.25 to about 1 weight per¬ cent of the polymer.

A surfactant-containing seed is another optional ingredient present in the polymer. The seed generally has an average particle size of less than about 80 nm, and preferably within the range of about 25 to about 60 nm. Exemplary seeds are comprised of alkenyl aromatic monomers, acrylate monomers, and mixtures thereof. Usually, styrene and/or butyl acry¬ late monomers are employed in manufacturing the seed.

The emulsions of the present invention are made, for example, by a delayed addition polymerization process. Typically, the delay-addition polymerization process comprises forming a monomer mixture containing about 25 to about 90 weight percent soft monomer and about 10 to about 75 weight percent hard monomer, about 1 to about 5 weight percent olefinic carboxylic acid monomer, and about 0.5 to about 5 weight percent cross- linking monomer. Water is added to a reactor and heated, generally to about 150° to about 190° F., while preferably purging the reactor with an inert gas, such as nitrogen, to remove substantially all oxygen from the reactor. A catalyst is then added to the reactor. Preferably, a locus for polymerization (e.g., a sur¬ factant and/or a surfactant-containing seed) is added to the reactor before, simultaneously with, or after the catalyst addition to form a reactor charge. After the addition of the catalyst and locus for polymeriza-

tion, the delay-addition of the monomer mixture is then commenced. The ensuing reaction forms the emulsion of the present invention. The addition of the monomer mixture typically takes up to about 3 hours. During the delay-addition of the monomer mixture, additional catalyst is typically also added to the reactor. In an alternative synthesis procedure, a portion, for example up to about 1/2 of the monomer mixture, is added to the reactor at the beginning of the reaction along with the addition of the initial catalyst and/or seed and/or surfactant.

Xn order to stabilize the emulsion, toward the end the monomer mixture addition, the pH of the emulsion is typically adjusted. Generally, the pH of the emulsion is adjusted to at least about 6, prefera¬ bly to about 6 to about 10, and most preferably to about 6 to about 8. Adjusting the pH to within these ranges substantially neutralizes all olefinic carboxyl¬ ic acid groups on the polymer.

fFsually the pH of the emulsion is adjusted from about 30 minutes before to about 30 minutes after terminating the addition of the monomer mixture. Preferably, the pH adjustment occurs within about 15 minutes after terminating the monomer mixture addition.

After finishing the monomer mixture addition, further catalyst is commonly added while maintaining the emulsion at the elevated reaction temperature to ensure that substantially all of the monomers polymer¬ ize. The same catalyst can be used whenever one is

employed. Exemplary catalysts include, but are not limited to, t-butyl hydroperoxide, sodium persulfate, hydrogen peroxide, and mixtures thereof.

The emulsion is allowed to cool to ambient or room temperature after all the monomer mixture and catalyst have been added. Usually, the pH of the cooled emulsion is adjusted, if necessary, to about 8 to about 10. Typically, a base is employed in each instance where the pH of the emulsion is adjusted. Exemplary bases are selected from the group consisting of amine-containing bases, hydroxide-containing bases, and mixtures thereof. Dimethylamine, diethylamine, aminopropanol, ammonium hydroxide, and sodium hydroxide are typical bases, with volatile bases being preferred, and ammonium hydroxide being the most preferred.

The polymerization process yields the poly¬ meric emulsion of the present invention. The solids content of the emulsion is generally at least about 40 weight percent, preferably within the range of about 45 to about 60 weight percent, and more preferably within the range of about 45 to about 55 weight percent.

In use, the emulsion is applied to at least a portion of a surface of a substrate. Upon drying, the emulsion forms a water-resistant film. Accordingly, the emulsion of the instant invention is capable of enhancing the water-resistance of a substrate (e.g., particle board and plywood) and/or maintaining the desirable characteristics of a composition when exposed to moisture (e.g., PSAs).

EXAMPLES

The following examples demonstrate the prepa¬ ration of exemplary polymeric emulsions within the scope of the present invention as well as the reduction in swelling exhibited by particle board coated with the emulsion after the emulsion-coated particle board is submerged in water. However, the invention is not limited to the examples, but is defined by the claims.

EXAMPLES 1-3

.Preparation of Polymeric Emulsions

Monomer mixtures having the compositions set forth in the following Table I were prepared:

a. ST deβøtes styrene. b. 2EHA denotes 2-ethylhexyl acrylate. c. MAA denotes methacrylic acid. d. IBMA denotes isobornyl methacrylate. e. AAEM denotes acetoacetoxyethyl methacrylate.

In each of Examples 1-3, water (about 550 g)

was added to a reactor and heated while purging the reactor with nitrogen. When the water reached a tem¬ perature of either about 180° F (Examples 1-2) or about 160° F (Example 3), the ingredients listed in Table II, infra, were individually added to the reactor.

Example 1 2 3

f. 50S denotes a 30 weight percent total solids emul¬ sion containing a styrene seed having an average parti¬ cle size of about 50 nm. g. 3OS denotes a 30 weight percent total solids emul¬ sion containing a styrene seed having an average parti¬ cle size of about 30 nm.

Next, the monomer mixture shown in the above Table I and a catalyst solution comprising about 0.9 g sodium persulfate and about 27 g water were separately, but simultaneously, added to the contents of the reac¬ tor over a period of about 3 hours while maintaining the temperature within the reactor either at about 185° F (Examples 1-2) or at about 165° F (Example 3).

In Examples 1-2, at the end of the 3 hour period and after the emulsion in the reactor cooled to about room temperature, the pH of the emulsion was

raised to about 8.5 using a solution of about 10% ammonium hydroxide. In Example 3, immediately after finishing the addition of the catalyst solution and the mon mer mixture, a; solution containing about 5 ml ammonium hydroxide and about 20 ml water was added to the emulsion. After the emulsion cooled to room tem¬ perature, the 10% ammonium hydroxide solution was added in a sufficient amount to raise the pH of the emulsion to about 8.5. The total solid content of the emulsions and the average particle size of the polymers (measured with a Nonsizer N4 brand particle sizer available from Coulter Electronics) are given in Table III, infra.

a monomer mixture and a cross-linking solu¬ tion were prepared. The monomer mixture comprised about 1470.g styrene, about 1470 g 2-ethylhexyl acry¬ late, and about 90 g methacrylic acid. The cross- linking solution contained about 250 g water and about 125 g N-methylol acrylamide.

Next, water (about 2500 g) was added to a

reactor and heated while purging the reactor with nitrogen. When the water reached a temperature of about 160° F, about 4.5 g sodium persulfate and about 90 g of a 30 weight percent total solids emulsion containing a styrene seed having an average particle size of about 30 nm were individually added to the reactor.

The monomer mixture and a catalyst solution comprising about 4.5 g sodium persulfate and about 135 g water were then separately added to the contents of the reactor over a period of about 3 hours while main¬ taining the temperature within the reactor at about 165° F. Immediately after finishing the addition of the catalyst solution and the monomer mixture, a solu¬ tion containing about 50 ml ammonium hydroxide and about 100 ml water was added to the emulsion. The temperature of the emulsion was afterwards raised to about 175° F and maintained at that temperature for about 1.5 hours while adding additional catalyst solu¬ tion to reduce the concentration of any unreacted monomers. The emulsion was then allowed to cool to room temperature.

After the emulsion cooled to room tempera¬ ture, the 10% ammonium hydroxide solution was added in a sufficient amount to raise the pH of the emulsion to about 8.6. The total solid content of the emulsion was about 47.2 weight percent and the average particle size of the polymer was about 123 nm.

EXAMPLES 5-15

Water-Swelling Test

One end of particle board strips was com¬ pletely coated with an emulsion of Examples 1-4. After drying the coated strip at about 180° F for about one hour or at room temperature for about a week, the thickness of the coated end of each strip was first measured and then immersed in water for a period of about 16 hcfurs. The thickness of the coated, immersed end was measured, and the percent increase in thickness (percent swelling) was calculated. The same procedure was followed with a control, i.e., an uncoated particle board strip. The results are set forth in Table IV, infra.

TABLE IV

Particle Board Coated

The data provided in Table IV indicate that particle boards, when coated with emulsions within the scope of the present invention, exhibit a significant reduction in swelling when exposed to water.

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, the emulsion can include one or more ingredients that enhance other film and/or emul¬ sion properties. Therefore, the spirit and scope of the appended claims should not necessarily be limited to the description of the preferred embodiments con¬ tained herein.