CA1116773A - Surfactant-free polymer emulsion coating composition and two-stage method for preparing same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Surfactant-free emulsion coating compositions of superior film-forming properties are produced by a two-stage method comprising, in a first stage, forming a mixture of polymerizable monomers comprised of defined proportions of a carboxylic acid monomer, such as acrylic acid, and a C1-C8 alkyl acrylate or methacrylate, polymerizing said mixture, neutralizing the polymer product with a sufficient amount of an amine or base to make it water-dispersible and forming an emulsion of the polymer with water, then, in a second stage, forming a mixture of polymerizable monomers comprised of defined proportions of a C1-C8 alkyl acrylate or methacry-late and adding this monomer mixture and a polymerization catalyst to the emulsion produced in said first stage and heating the mixture thus formed to effect polymerization and produce the emulsion coating composition. The method produces an emulsion comprised of polymers of higher molecu-lar weight than producible by conventional emulsion coating forming means and without the use of a surfactant as done conventionally.

Description

2~ ~
lllG773 This invention relates to coating compositions.
More particularly, it relates to novel surfactant-free poly-mer emulsions having highly superior properties for use as film coatings for metal and glass surfaces and to a method for preparing these emulsions.
In view o~ the increasing strictness of anti-air pollution laws, the art is turning more and more from organic solvent-based coating systems to water-based systems. These water-based coatings are made by polymerization of a monomer mix which contains some carboxyl group-carrying monomer, or by polycondensation of mono-, di- or polybasic acids with polyols to form an acrylic, poly~ster or alkyd resin. These polymers are water-soluble or dispersible in the presence o~
an amlne and an organic cosolvenl;. From the applicatlon standpoint, these water-based compositions are easy to apply, similar to sol~ent based coating~3, and give uniform, water-free films of high gloss. Amino resin-type cross-linking agents, such as hexamethoxymethyl melamine, are used to achieve water-resistant films after baking.
Most amino resins react primarily with the reactive hydroxyl and amide groups of the polymers so that af~er cur-ing the films formed ~rom these water-soluble compositions contain some unreacted carboxyl groups. Also, the water-soluble acrylic polymers used in coatings are o~ relatively low average molecular weights~ i.e. from about ~,000 up to abou~ 50,000. Also, to achie~e reasonable resis~ance and hardness properties in the cured films, high levels of cross-linking agent have to be used. Still further, to achieve good water solubility (or dispersibility) significant levels ~o of amine and cosolvent have to be used in the coating compo-sitions so that the amount of amine and solvent emitted from the coatings during baking is considerable. Thus, the water-- 1 - q~s ~1~6~

soluble compositionsJ while having advantages, such as ease of application and uniformity and high gloss in the cured films, are still less flexible than desired and lack some desirable properties such as good water and detergent resis-tance.
On the other hand, the well-known emulsion-type coating compositions, in which the ~olymers are of relatively high molecular weight, do not require such large amounts of cross-linking agents as do the water-soluble polymer composi-tions and so provide cured films of high flexibility and good durability and mechanical resistance properties. However, the emulsion polymer systems present other problems, such as poor wetting of the metal substrate and tendency of the films to crater. Also, because they form a film by the coalescence of the emulslon particles they often give low gloss or a mud-caking effect. The emulsion systems also require a relatively large amount of cosolvent in order to reduce blistering. The main problem with emulsions, however, is the presence therein of surfactants which are required ~o form a stable emulsion and also to overcome the wetting and adherency problems of the emulsions. Unfortunately, the surfactants remain in the film after eross-lin~ing and adversely affect the water and corrosion resistance of the film as well as the adhesion of the coating to the metal surface.
While, therefore, both the water-soluble coating systems and the emulsion systems have certain advantages and disadvantages, it is the ob~ect of the present invention to provide a coating system having most of the advantages of both the water-soluble and the emulsion systems, but without their disadvantages.
In accordance with the invention, there is provided a unique surfactant-free emulsion coating system formed by a ne~l procedural technique and having a distinctive set of 1~7~3 advantageous properties as will be shown hereinafter.
Thus the present invention provides a t~a-stage method for prepar-ing a surfactant-free polymer emulsion product which comprises, in a first stage, (1) forming a mixture of polymerizable monomers comprising, by weight from about 3 to about 15% of a carboxylic acid or anhydride selected from the group consisting of acrylic, methacrylic and maleic acid and their anhydrides and the Cl-C8 alkyl half esters of maleic acid, from about 30 to about 97% of a Cl-C8 aIkyl acrylate or Cl-C8 alkyl methacrylate, from 0 to about 25% of a C2-C4 hydroxy alkyl ester of a cæboxylic acid or acrylamide or methacrylamide and from 0 to about 35% styrene, (2) polymerizing said mixture in the presence of a polymerization catalyst, a suitable solvent, and optional.ly a molecular weight regulator to form a polymer having an average molecu~ar weight of from about 3000 to about 50,000, t3) neutralizing the polymer with an amine or k~se to the extent required to make the poly-mer water-dispers.ible and (4) orming a dispersion of the polymer in water, and, in a second stage, (5) forming a second mixture of polymerizable mono-mers comprising, by weight, frcm about 40 to about 100~ of a Cl-C8 aLkyl acrylate or Cl-C8 alkyl methacrylate, from about 0 to about 25~ of a C2-C4 hydroxyalkyl ester of a carboxylic acid or acrylamide or methacrylamide and from akout 0 to about 35~ of styrene, (6) combining said second mQn~mer mixture and a polymerization catalyst with the dispersion produced in step ~4), the proportion of the second stage monomer m xture combined being such as to comprise frcm about 20 to about 80~ of the total weight of the first and second stage monomer mixtures, and (7) heating the mixture so formed to effect polymerization and produce the polymer emulsion product.
The preparation of the emulsion polymer of the invention is carried out in two stages~
(1) In the first stage there is produced a conventional OE boxyl group-containing polymer by a conventional solution or bulk polymerization technique. The polymer is then water~dispersed ~or solubilized) by partial or full neutralization thereof with an organic amine or base and appli-cation of high shear agitation.

.~ ~

67'73 (2) In the second stage, there is ~ded to the dispersion of stage I a blend of partially water-soluble and partially water-insoluble monomers, hereinafter referred to as the stage II n~nomers, together with a free radical initiator. Upon initiation of the polymerization, the stage II monomers poly~erize in the stage I dispersion, which results in grafting and the formation of a very stable emulsion without the presence of any added surfactant. -The grafting of the stage II n~nc~ers onto the stage I
polymer increases -the overall molecular weight of the system and also produces an en~lsion of excellent mechanical stability. Because the pro-oess of the invention requires a water-solubilizing group, such as ca~-boxyl-containing monomer, only in the stage I polymer, the total content of water-solubilizing sites in the stage I and stage II monomers can be de-creased. This decrease in carboxyl groups in the total of stage I and stage II monomers permits a significant recluction in the amDunt of neutral-izing amine requir~d. On the other hand, if the stage I and stage II
nmonomers are initically combined ~in a sinyle stage polymeriza-tion process) to make a solution polymer, the resulting dispersion is either very un-stable or no dispersion is Eormed at al].. While not intencling to be limit-ed in any way by theoretical considerations, it is believed that in a normal water-borne solutïon polymer only a portion of the - 3a -r~
~..

6~7~3 carboxyl groups are on the outside of the polymer particle and only this portion of the particle is able to solubilize the particle in water. ThusJ the remainder of the carboxyl groups are buried inside the particle where they are ineffec-tive as water-solubilizing sites. On the other hand, in polymers made by the process of this invention, the stage I
monomers which contain the carboxyl groups are concentrated on the surface of the final polymer, whereas the stage II
monomers which contain no carboxyl groups and which,therefore, have no, or only an insignificant water-solubilizing e~fect, are contained in the inside of the polymer particle.
In stage I Of the process, a mixture o~ mQnomers composed of about 3-15% of at least one polymerizable carbox-ylic acid or anhydride and at le~st one other polymerizable monomer is used. Acrylic acid or anhydride and maleic acid or anhydrlde are preferred as the carboxyllc acld or anhy-dride, although other acids or anhydrides may be used, for example, a-methacrylic acid or anhydride and the Cl-Cg alkyl half esters of maleic acid, such as the 2-ethylhexyl ester.
The other polymerizable monomer may suitably be an acrylic acid ester~ such as methyl, ethyl, propyl, butyl, or 2-ethylhexyl acrylates or methacrylates~ 2-hydroxyethyl acry-late or methacrylate, 2-hydroxypropyl acrylate or methacry-late and ethylhexyl acrylate. Also, styrene, vinyl toluene or acrylamide may be used along with or instead of the acrylic esters in the monomer mixture A wide ~ariety o~ amines may be used in stage I of the process. Thus, although dimethylethanol amine is gener-ally pre~erred~ other amines such as diethanol amine, diethyl 3o ethanol am~ne~ butyl aminel 2-amino, 2-methyl-1-propanol, tris hydroxymethyl amino methane and morpholine are suitable amines.
The stage II monomer mixture contains no polymer-~.6 ~ 73 izable acid~ but is composed of monomers such as methyl~
ethyl, propyl and butyl acrylates or methacrylates, beta-- h~droxyethyl and beta-hydroxypropyl acrylate or methacrylate, acrylamide and isobutoxymethyl acrylamide. Also, acryloni-trile and styrene may be used. The preferred monomer mixture, however, is composed of 2-hydroxyethyl acrylate, butyl acry-late~ and methyl methacrylate.
Suitable monomer mixtures for use in Stage I and Stage II of the process of the invention are shown in Table 3o 11~6 ~'~73 a) h O O U~ u~lo o o o lo P~ ~ o ~ ~I
~ tOD ~ ~ O ~1 ~

a) ~ ~ ~ U~ O ~ ~ o a) ,~ o Q) ~ O
h ~ ~ ,~ ~1 ~3 X .1: 1~ 0 0 0 O O O
~_ H
a) b~ h ~d ~ O
~a h ~H U2 h O O I O O
h h O ~ '~
0 ~
h ~: O ~ h o O V cl; ~ n3 ¢ ~ :~ C) h ~S 'C ~ o~ ¢
h r-l ~ a) ~ ~, h c.) o ¢ ~:: O E3 Q~ ¢
X a) Q h ~ ~ X t~
O ~ C0 ~ ~ h O H a) O CO 0~ ~ O H (I) O
.s~ O v c.) C~ v ~ v .
v ~ V CA) V ~ ~ v v V C~ ¢ u~

~67t73 The proportions of the Stage I and Stage II monomer mixtures suitable for use in the process of the invention are such that either mixture can comprise from about 20 to about 80 weight percent, preferably about 50 weight percent, of the total of the two mixtures.
A more complete understanding of the invention will be had from the following examples and tests.
Example 1 Stage I
ComponentsAmount (~ms.) (1) Acrylic acid 140 (2) Butyl acrylate 820

(3) Methyl methacrylate1040

(4) n-Dodecyl mercaptan 25

(5) Dicumyl peroxlde 40

(6) Propylene glycol 90

(7) 2-ethoxy ethanol 60 The propylene glycol and 2-ethoxy ethanol (compo-nents 6 and 7) were charged to a 3 liter 4-necked ~lask 20 ` equipped with a stirrer, thermometer, gas inlet tube and reflux condenser. Air in the flask was displaced by nitro-gen and the contents heated to reflux temperature (130~ 5C.).
Components 1-5 were mixed together, and when the peroxide was completely dissolved the mixture was added at a uniform rate to the 4-necked flask over a 2 hour period during which the temperature gradually rose to 155C. After holding at this temperature for two hour6, the batch was cooled to 100C.
and 2.4~ wt. of dimethyl amino ethanol (DMAE) was stirred in to form an amine salt of the polymer~ After cooling to 80C.
3o a 500-gram portion of the reaction mixture was transferred to a steel beaker. With the aid of a high speed stirrer having a blade tip speed of approx. 800 ft./min., 600 gms.

of water at 70C. were added slowly to the mixture, thereby producing a thin milky dispersion having a pH of 7.2~ a solids content of 42%, and viscosity of 200 centipoises.
Cooling to room temperature was done in a water bath.
Stage II - A monomer mix composed of 7 gms. of 2-hydroxy ethyl acrylate, 41 gms. of but~l acrylate and 5~ gms. of methyl methacrylate was sparged with nitrogen and then slowly added to a mixture of 240 gms. of the emulsion pre-pared in Stage I and 100 gms. of de-airated water in a flask equipped with stirrer, gas inlet tube, thermometer and reflux condenser. A blanket of nitrogen was maintained over the liquld in the flask. The addition of the monomer mix made the mixture thicker than the initial Stage I emulsion. Next, 0.4 gm. o~ ammonium persulfate l~98~) was added to 12 gms. of de-airated water and this mixture was slowly stirred into the reaction mixture in the ~la~k causing some reduction in viscosity. Mild heat was applied to the flask so that the contents were raised to 65C. in about 1 hour. Thereafter, the contents were held for three additional hours at 65-70C.
and then cooled to room temperature. The monomers had poly-merized almost completely, since analysis showed only 0.2 unreacted monomer. Solids content was 44~, pH 7.1, and viscosit~ 125 centipoises. There was a negligible amount of coagulum. A 0.003" wet film drawn down on aluminum sheet metal was air-dried and also baked to a clear, hard, glossy ~ilm that wetted the metal well and was free of dimples and craters.
The pH of another portion of the copolymer emulsion was raised to about 8 by addition of a 20~ solution of di-methyl amino ethanol (DMAE). A commercial grade of hexakis-methoxymethyl melamine (HMMM) was then stirred into the emulsion in an amount such that it constituted 15~ of the total solids content thereof. Two percent of amine neu-~l~S~3 tralized p-toluene sulfonic acid, based on the HMMM~ was then added to catalyze the thermosetting. A 0.003" wet film drawn down on sheet aluminum was baked 1 min. at 500F.
to yield a clear, glossy, hard film. Pencil hardness was F
and reverse impact resistance was 40 inch pounds.
Example 2 Sta~e I - The procedure was similar to Example 1, except that the monomer mixture used was 7~ acrylic acid, 6~ ~-hydroxy ethyl acrylate, 41~ butyl acrylate and 46~
methyl methacrylate~ A dispersion in water was made just as in Example 1.
Stage II - A copolymer emulsion using the emulsion polymer of Stage I of Example 2 was prepared similarly to that of Stage II of Example 1 except that the added monomer mixture was composed of 1% ~hydroxyethyl acrylate, 4~
butyl acrylate and 5 ~ methyl methacr~late. Final solids was 44%, pH, 7.2 and viscosity, 115 centipoises. The com-patability of the stage I and stage II polymers is shown by the`fact that when a thin ~ilm of this product was air-dried and baked, a clear glossy film was formed. When compounded with HMMM, so as to contain 10~ of this amino compound on a solids basisJ and catalyzed with p-TSA (p-toluene sulfonic acid), a 0.003" wet film on aluminum baked in 10 minutes at ~OO~F~ to a clear glossy solvent-resistant coating with F
pencil hardness and greater than 60 inch pounds reverse im-pact resistance.
Example ~
Sta~e I - This was 155 gms. of the 2mulsion of Stage I, Example 2.
Sta~e II - Here, the monomer mixture (135 gms.) was composed of 7~ ~-hydroxyethyl acrylate, 46~ butyl acryl-ate and 47~ methyl methacrylate. The procedure involved stirring a solution of 2.5 gms. of DMAE in 145 gms. of _ g _ 6~

de-airated water into the emulsion of stage I, then stirring in the mixture of monomers. Finally, 0.4 gms. of ammonium persul~ate in 18 grams of water were added dropwise. Mild heating and stirring were then applied until the flask con-tents reached 50C. The heat was then removed ~nd the con-tents held at 50-55C. for four hours. After cooling to room temperature the viscosity was 200 centipolses, pH 7.5 and solids 44.1~. A 0.00~" wet film on sheet aluminum air dried clear and glossy. When the copolymer emulsion was blended with ~n~MM to yield 18~ o~ the latter and catalyzed with 0.55% p-TSA (based on the amino resin) a 0.003" wet film on sheet aluminum baked in 20' at 250F. to a clear, hard, glossy film having rever~e impact resistance o~ ~60 inch pounds, F pencil hardness, and resistance to 200 rubs 1~ with a methyl ethyl ketone soak~d towel.
Example 4 Stage I - The procedure here was the same as th~t ~or Stage I of Example 1, except that the monomer mixture used was 7~ acrylic acid, ~0~ st~rene, 27% methyl methacryl-ate and 36~ butyl acrylate, and the propylene glycol was replaced by ethoxy ethanol.
Sta~e II - A copolymer emulsion using the emulsion of Stage I above was prepared in a fashion similar to that of Stage II, Example 1, except that the added monomer mixture was 7.5~ ~-h~droxyethyl acrylate, 27.5% styrene, 28~ methyl methacrylate and 37% butyl acrylate, and the pH of the emul-sion was adjusted with DMAE to 8.5 at the start of the co-polymerization. The finished copolymer emulsion had a ~is-cosity o~ 140 centipoises, a pH of 7.1 and a solids content ~o o~ 43 4~. When compounded with HMMM and p-toluene sulfonic acid as in Example 3, this product yielded films on aluminum which baked in 30l at 250F. to hard, glossy, solvent-resistant coatings '773 Example 5 Stage I - The follo~ing materials were used to prepare a polymer emulsion in the same fashion as in stage I
of Example l: Acrylamide lO0 gms., acrylic acid l~0 gms., butyl acrylate 820 gms., methyl methacr~late 940 gms., di-cumyl peroxide 40 gms., n-dodecyl mercaptan 30 gms., propy-lene glycol 90 gms. and ethoxy ethanol 120 gms. Half of the ethoxy ethanol was mixed with the monomers to effect solubility of the acrylamide. The resultant polymer was partially neutralized by 2.4% DMAE and then dispersed in water to 4 ~ solids using a high speed mixer.
Stage II - To 250 gms. of the emulsion of Stage I
above and 150 gms. de-airated wa1;er there was added with good agitation 50 gms. methyl methacrylate, 49 gms. butyl acrylate, l gm. of 2-hydroxyethy:L acrylate, and l/2 gm. azo-bis isobutyronitrile. Unde~ a nitrogen blanket the above was heated with stirring to 75~C., held lO hrs. and then - cooled to room temperature. The pH was 7.4~ the viscosity 140 centipoises and the solids content 38.8~. This copoly-mer emulsion was compounded with ll~ of a polymeric partiall~
methylated melamine-formaldehyde resin (80~ concentration in water) to yield a clear baking enamel of 42~ solids. When cast as a 0,00~" thick wet film on sheet aluminum and then baked 20 mlnutes at 250F. the cured coating had good gloss, clarity, flow and color, and no crater or dimple defects, Reverse impact was 60 în. lbs , and MEK resistance was in excess of 200 rubs.
The clear baking enamels of the foregoing examples may be pigmented with titanlum dioxide to yield white high gloss enamels having utilit~ as coatings for sheet metal, coiled metalJ and fabricated metal items.

7q3 ~~~~~ Example 6 Stage I - The following materials were processed in a fashion similar to that of Example 1, Stage I: 10 gms.
methacrylic acid, 80 gms. ~-hydroxyethyl acrylate~ 525 gms.
methyl methacrylate, 550 gms. butyl acrylate, 100 gms. sty-rene, 28 gms. n-dodecyl mercaptan, 28 gms. dicumyl peroxide and 120 gms. ethoxy e~hanol. When polymerization was com-pleted, the polymer solution was cooled to 110C., partially neutralized with 2.5% DMAE and upon cooling to 80C. was dispersed in water to ~2% solids. The pH was 8.1 and the viscosity 435 centipoises, both at 25C.
Stage II - To 240 gms. of the emulsion o~ Stage I
there was added with good agitation 100 gms. of water and 100 gms. of a monomer mixture composed o~ 5~ hydroxyethyl acrylate, 40~ butyl acrylate and 55~ methyl methacrylate, by weight. Then, under a nitroæen blanket, 0.4 gms. o~ ammonium persulfate dissolved in 17 gms. of water was mixed in. Heat was applied and when the flask contents had attained 65C.
the heat w~s reduced and the b~tch held at 65C. for three hrs. A~ter cooling to room temperature, the product was a thin liquid of pH 6.6, having a viscosity of 65 centipoises, and a solids content of 4~.5~. The pH was adjusted up to 7.5 using dilute DMAE and then a film was cast on glass. After the film air-dried 30' it was clear~ hard and glossy.
Example 7 Stage I - An emulsion polymer was made as in Exam-ple 1 using maleic anhydride instead of acrylic acid. Thus, the monomer mixture had the following components: maleic anhydride, 100 gms., styrene, 140 gms., butyl acrylate, 560 3 gms., methyl methacrylate~ 600 gms., and dicumyl peroxide, 28 gms. When all the maleic had dissolved, the mixture was added~ over a 2 hr. period, to 125 parts of para-cymene at a temperature of 140-160C. and the whole held at 160C. for ~1~67~3 two hours. After cooling to 1~0C., there was added 90 gms.
ethoxy ethanol and the mixture held at 150C. for 1 hour.
After being cooled to 80C., 14 gms. of DMAE were added to a 500 gm. portion of the reaction mixture. Thereafter~ the mixture was dispersed in water at 70C. as was done in Exam-ple 1. After cooling to 25C. the pH was 7.2, the solids content 42~J and the viscosity 140 centipoises.
Stage II - To 240 gms. o~ the emulsion of Stage I
above there was added 140 gms. water and 100 gms. of a monomer mixture composed of 4 gms. 2-hydroxyethyl acrylate, 10 gms. styrene, 31 gm8. butyl acrylate and 55 gms. methyl methacrylate. When the monomer was well mixed in, 0.4 ~ms.
ammonium per sul~ate dissolved in 26 gms. o~ water (de-air-ated) was slowly stirred in and the flask contents heated to 65C., held ~here ~or ~our houra and then cooled to room temperature, The solids was 40$, the viscosity 100 centi-poises and the pH 6.8. The latter value was raised to 7.1 by addition of some dilute DMAE. A film was castJ on clear glass, and after air-drying several hours the film was smooth, hard, clear, and glossy. The ~ilm was baked 10 min-utes at 300F. J cooled to room temperature, and then immersed in water. It did not blister or turn white within a ~ day period.
Example 8 Stage I - A monomer blend consisting o~ 14 parts by weight of 2-hydroxyethyl acrylate~ 15.5 parts acrylic acid, 93.5 parts butylacrylate, 108 parts methylmethacrylate~ 3.35 parts n-dodec~l mercaptan and 4.45 parts dicumyl peroxide was ~ed over a 2 1/2 hour period into a mixture o~ 10 parts 2--ethoxyethanol and 10 parts propylene glycol in a reactor equipped with a stirrer and reflux condenser. After the mono-mer addition was complete, the temperature of the reaction mixture was 148C. and was maintained at that level for an 1~67'73 _ . .. .. .
additional hour to insure complete monomer conversion.
The batch was then cooled to 90~C. and 6 parts of dimethylaminoethanol (DMAE) added. Then, under high speed agitation, 290 parts of water were slowly added without per-mitting the batch temperature to fall below 70C. The re-sulting dispersion of the water-soluble resin was o~ fine particle siza, bluish in color and of low viscosity.
Stage II - To the dispersion of Stage I there were added 240 parts of water ~ollowed by addition of approximately 70~ of a monomer blend consisting of 2.3 parts of hydroxy-ethyl acrylate, 113 parts of butylacrylate and 117 parts of methylmethacrylate. A solution of 0.93 parts of ammonium persulfate in 30 parts of water was then added followed by addition o~ the remainlng 30~ ol~ the monomer blend. Under continuous agitation the reaction temperature was raised to 50C. The exotherm o~ the reacl;lon t~len carried the tempera-ture to 70C. where it was held for 3 hours and then reduced to room temperature. The resulting 47% solids emulsion was of extremely small particle size and had a viscosity on the Gardner-Holdt sca~e of D-F.
The total monomer blend (Stage I and Stage II mono-mers) cont&ined 3.3~ acrylic acid, 3.5% hydroxyethylacrylate, 44.6~ butylacrylate and 48.6~ methylmethacrylate. Gell phase analysis of the stage I polymer dispersion ~howed an ~cra~e molecular weight of about 10,000. The final emulsion, result-ing from about 50~ o~ the stage I monomers and 50~ of the stage II monomers, showed a different molecular weight dis-tribution. Thus, the molecular weight fraction of 1OJOOO had decreased to about 32~, while about 39~ had an average mole-cular weight of about 500,000 and about 29~ had a molecular weight greater than 2,000,000. This reduction in the 10,000 molecular weight fraction from 50~ to 32~ is a clear indication that a significant amount of grafting of the stage II monomers onto the polymers formed from the stage I monomers had taken place.
The emulsion prepared above was formulated into a water-reducible coating using hexamethoxymethyl melamine (Formulation A) or a partially methylated melamine formalde-hyde (Formulation B) as cross-linking agent. Excellent glossy films were obtained which were uniformly hard and flexible.
The pertinent data are shown in Table II. The enamel solids of 56.7~ and 59.7~ obtained with Formulations A and B~ re-spectively, is very high for a water-borne coating system.
Formulatlon B cures adequately at 250F. giving an excellent gloss of 94 (60) and 71 (20). The use of ~MM as a cross-linking agent (Formulation A) requires a higher baking tem-perature, but results in a more flexible coating.
Water immersion tests on Formulations A and B at 50C. show only a slight so~tening a~ter 24 hrs. and no loss of adhesion or blistering. After drying at room temperature~
the original hardness was restored. Salt spray test on iron phosphated CRS panel and aluminum panels showed a creepage of less than 1 mm. after 240 hours exposure. No visible loss of gloss and blistering was observed.

~6~73 Table II
Formulation A B
Pounds per 100 Gallons Titanium Dioxide 258.3 279.9 Example 8 Emulsion 140.0 151.6 Dimethyl Ethanolamlne 2.3 2.5 Polycarboxylic Acid Wetting Agent 1.7 1.9 Demineralized Water 57.7 62.5 Disperse Above and Add:
Example 8 Emulslon 513.7 511.9 51.5 __ Partially methylated Melamine-formaldehyde resin -- 88.4 p-Toluene Sulfonic Acid (40,~ in isopropanol) 1.7 --Dimethyl Ethanolamine 0.7 --2-Butoxyethanol 7.1 --Demineralized Water ~5.9 --Enamel Properties Non-Volatile, ~ by wgt. 56.7 59.7 Non-Volatile, ,~ by vol. 44.1 46.7 Viscosity, Ford 4-Cup, sec. 17.0 25.0 ComE~sition of Binder Solids Example 8 Emulsion, ,~ by wgt. 84.5 79.5 Amino ~esin 14.8 20.0 Polycarboxylic Acid Wetting Agent 0.5 0.5 Catalyst 0.2 --3 Composition of Volatiles? ~rol ~

Dimethyl Ethanolamine 1.24 1.12 2-Butoxyethanol 3.42 1.77 Water 95.34 97.11 L167~ 3 Table II (Continued) Formulation _ _ Film Properties(l) Baked 20 Minutes at 250F.
Dry Film Thickness, mils. -- 1.15 Gloss, 60 __ 94 0 Gloss, 20 __ 71.0 Hardness, Knoop, KHN2s -- 8.4 Hardness, Pencil -- F-H
Impact Resistance~
Reverse, in./lbs. -- 10.0 MEK Resistance~ Double Rubs -- 200 Baked 20 Minutes at 300F.
Dry Film Thickness, mils.1.15 1.1 Gloss, 60 92.0 92.0 Gloss, 20 69.0 65.0 Hardness, Knoop, KHN2s 3.5 }0.1 Hardness, Pencil HB-F X-2H
Impact Resistance, Reverse, in./lbs. 40.0 10.0 MEK Resistance, Double Rubs 200.0 200+

Baked 20 Minutes at 350F, Dry Film Thickness, mils.1.1 --Gloss, 60 92.0 _ Gloss, 20 ~5 o __ Hardness, Knoop, KHN25 6,5 --Hardness, Pencil F-H --Impact Resistance, Reverse, in./lbs. 20.0 __ MEK Resistance, Double Rubs 200 0 __ )Fi~ls cast on Alodine 1200S treated aluminum test panels.

~6q73 The emulsion was also formulated into a coil-coating ~ormulation. The pertinent data are shown in Table III.

7o L6~7~

~ o c~ ~ o o~o o ~ ~ o + o o o o~ o~ o~ ~ ," o o ~: ~ CU O 0~O O ~ ~ O + O
~ O O O C~J ~ ~ 0 1 0 1 0 0 1 H
rl C~l O C~ O O O ,:~ 0 ~5 0 :q O O O O t~ ~ ON E~

V
~ o V ~ L~ ~1 .

e ~, 5i a~ O l~ O O ~ h O h S~
¢ ~, V ~ 4 E~ O `--..

1~6~7~

As shown in Table III, Formulation A was modified with 10~ and 20~ of HMMM as a cross-linking agent. In a coil-coating application at the 10~ HMMM level, the excellent flexibility of T-2 bend is obtained. Even increasing the level of amino resin to 15% produces a T-3 bend. A solution polymer prepared with the same polymer composition as in Example 8 gives a flexibility of less than T 4.
Comparative Example 9 A water-soluble resin was prepared according to the procedure of stage I, Example 8, except that the monomer blend was adjusted to give the closest approximation in com-position to the total monomer blend (stage I and II monomers) of Example 8. Thus, all of the monomers were polymerlzed at once,rather than in two stages. To achieve water-solubility, the acr~lic acid content had to be raised to ~, using 45~
butylacrylate and 46~ meth~lmethacrylate as comonomers. The resulting polymer solution in 2-ethoxyethanol had a viscosity of Z-6 on the Gardner-Holdt scale and a solids content of 75%.
The average molecular weight o~ the blend was about 10,000.
A paint was formulated (Formulation C) with this - resin similar to that in Example 8 (Formulation A). The cross-linking level of the hexamethoxymethyl melamine had to be raised to 20~ to give sufficient cure and hardness to the water reducible polymer. The pertinent data with respect to this coating is given in Table IV.

3o - 20 _ TABLE IV
Formulation C - Example 9 Enamel Properties(l) Non-volatile, % by wgt. 45.0 Non-volatile, ~ by vol. 32.0 Viscosity, Ford Cup-4, sec. 69.0 Baked 20 Minutes at ~00F.
Film Thickness, mils.
Gloss, 60~ 86.0 Gloss, 20 77,0 Pencil Hardness 2B-B
Knoop Hardness 3 5 Impact Resistance, Reverse, in./lbs, 0-2 MEK Resistance, Double Rubs 200 Baked 20 Minutes at 350F.
Film Thickness, mils. 1.0 Gloss, 60 83.0 Gloss, 20 57.o Pencil Hardness F-E
Knoop Hardness 7.8 Impact Resistance, Reverse, in./lbs. 2.0 MEK Resistance~ Double Rubs 200 Solvent Composition, ~
Amine 4.1 2-Ethoxyethanol 11.9 Water 85.5 (l)Eilms cast on Alodine 1200S treated aluminum test panels.

~0 ~IL6~73 Compared to Formulation A of Example 8, the water-reducible system of Example 9 contains about 5.~ times more solvent. A formulated coating with the water-soluble resin of Example 9 has significant lower application solids than that of Example 8. To obtain a dry film thickness of 1 mil~
a wet film thickness 3.1 mil would have to be applied with the Formulation C using the resin of Example 9 compared to a wet film thickness of 2.2 for the same dry film thickness with the resin from Example 8. The likelyhood of saggingJ
tear formation in spray applying a formulation on vertical surfaces using the resin of Example 9, is therefore, signi-ficantly increased over the same formulation in Example 8.
The gloss obtained with Formulatlon C, Example 9, surprisingly is lower than that of Example 8, with the except~on of the 20 gloss at a baking temperature of 20 minutes at 300F.
The lower application solids in Example 9 (45~) compared to Formulation A of Example 8 (56.7~) also causes increased problems in flash-of~.
Applying the water-reducible system of Example 9 under coil-coating conditions on an aluminum substrate (bake 50 sec at 500F.) causes considerable blistering without flash-off. With increased flash-off time to 8 minutes, the applied film showed less than T-4 bend flexibility making it unsuitable for coil-coating.
Comparative Exa ~le_10 An emulsion polymer was prepared b~ conventional procedure, i.e. polymerizing the total monomer composition (the monomers of stage I plus the monomers of stage II) of Example 8 all at once. A sur~actant~ Aerosol A-102 (a sulfo-succinate), was used at a le~el of 2. ~ . The resulting acrylic emulsion polymer was pigmented and formulated the same as ~ormulation A~ Example 8. Because of the poor wetting char-acteristics and poor stability of the emulsiong a water-- 2~ -i7~3 soluble resin of the composition in Example 9 was used as a wetting agent for the pigment.
A film o~ the emulsion was drawn down on an alumi-num substrate. The pertinent data with respect to the film are given in Table V.
TABIE V
Formulation of Example 10 Enamel Characteristics(l) Non-volatile, ~ by wgt. 55.0 Non~volatile, ~ by vol. 43.0 Viscosity, Ford Cup-4, sec. 20~0 Baked 20 min. at 300~.
Film Thickness, mils. 1.0 Gloss, 60 65.0 Gloss, 20 35.
Knoop Hardness 4.o Pencil Hardness HB-F
Impact Resistance, reverse 40.0 MEK Resistance~ double rubs 209.0 Coil-Coating Application (50 sec. at 500F.) T-bend T-2 Pencil Hardness F-H

Solvent Composition Water 9~
Amine 1.0 Glycol Et~er 1.0 - (l)Film cast on Alodine 1200S treated aluminum tes~
panels ~0 ~L~.l6~

Compared to Formulation A of Example 8~ this con-ventional emulsion gives poor gloss. Wetting of the substrate is also bad and the applied film has a tendency to pinhole and crater.
As shown in Table VI, the ~llm of the Formulation A, Example 8~ emulsion ~no surfactant) is also clearly super-ior in water resistance to the film of Example 10 containing a conventional sur~actant and is also superior to the surfac-tant-free polymer of Example 9 which contains higher levels of cross-linkm g agent.
Table VI
Water Imm_rsion (24 hrs. at 50C.) _ Pencil HardnessExample 8 (A)Example 9 Example 10 Initial F-H F-H H-2H
After Immersion HB-F B-HB 5B-4B~
~loss o~ adhesion The addition o~ the surfactant used in Example 10 to the emulsion Formulation A of Example 8 produces similar softening and adhesion problems on water immersion to those shown for Example 10.
Draw down of the formulation of Example 10 on steel causes yellow staining and flash rusting whereas the systems of Examples 8 and 9 show no such effect.
It will be appreciated from the foregoing that the emulsions of the present inventionJwhich contain no added surfactant, exhibit superior ~ilm-forming prope.rties to polymer emulsions produced by conventional emulsion polymeri-zation procedures using a regular surfactant. Thus, pig-mentation of the emulsions is very easy since direct addition of the pigment can be used and the pigment ground in the emulsion.
The emulsions show very good wetting o~ poorly cleaned metal surfaces with no creeping or pinholing occur-ring in the applied ~ilm. Also, the films made with the emulsions of the invention are of high gloss and give no mud-cracking.
Finally, the films provided b~ the emulsions exhi-bit excellent moisture resistance showing onl~ a very small loss of hardness and no loss of adhesion in the water immer-sion test.

3o

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A two-stage method for preparing a surfactant-free polymer emulsion product which comprises, in a first stage, (1) forming a mixture of polymerizable monomers comprising, by weight from about 3 to about 15%
of a carboxylic acid or anhydride selected from the group consisting of acrylic, methacrylic and maleic acid and their anhydrides and the C1-C8 alkyl half esters of maleic acid, from about 30 to about 97% of a C1-C8 alkyl acrylate or C1-C8 alkyl methacrylate, from 0 to about 25% of a C2-C4 hydroxy alkyl ester of a of carboxylic acid or acrylamide or methacrylamide and from 0 to about 35% styrene, (2) polymerizing said mixture in the pre-sence of a polymerization catalyst, a suitable solvent, and optionally a molecular weight regulator to form a polymer having an average molecular weight of from about 3000 to about 50,000, (3) neutralizing the polymer with an amine or base to the extent required to make the polymer water-dispersible and (4) forming a dispersion of the polymer in water, and, in a second stage, (5) forming a second mixture of polymerizable monomers comprising, by weight, from about 40 to about 100% of a C1-C8 alkyl acry-late or C1-C8 alkyl methacrylate, from about 0 to about 25% of a C2-C4 hydroxyalkyl ester of a carboxylic acid or acrylamide or methacrylamide and from about 0 to about 35% of styrene, (6) combining said second monomer mixture and a polymerization catalyst with the dispersion produced in step (4), the proportion of the second stage monomer mixture combined being such as to comprise from about 20 to about 80% of the total weight of the first and second stage monomer mixtures, and (7) heating the mixture so formed to effect polymerization and produce the polymer emulsion product.

2. The method of claim 1 wherein the mixture of polymerizable mono-mers in said first stage comprises from about 5 - 10% acrylic acid, about 5 - 15% of 2-hydroxyethyl acrylate and about 35 - 50% butyl acrylate and about 25 - 55% methyl methacrylate and wherein the mixture of polymerizable mono-mers in said second stage comprises about 1-10% of 2-hydroxy-ethyl acrylate, about 35-50% butyl acrylate and about 25-55%
methylmethacrylate.
3. The method of Claim 1 wherein the mixture of polymerizable monomers in said first stage comprises about 5-10% acrylic acid, about 35-50% butyl acrylate, about 25-55%
methylmethacrylate and about 10-30% styrene and wherein the mixture of polymerizable monomers in said second stage com-prises about 5-10% of 2-hydroxyethyl acrylate, about 35-50%
butyl acrylate and about 25-55% methyl acrylate.
4. The method of Claim 3 wherein the mixture of polymerizable monomers in said second stage also contains 10-30% styrene.
5. The method of Claim 1 wherein the mixture of polymerizable monomers in said first stage comprises about 5-10% acrylic acid, about 35-50% butyl acrylate, about 25-55%
methylmethacrylate and about 5-15% acrylamide and wherein the mixture of polymerizable monomers in said second stage com-prises about 5-10% 2-hydroxyethyl acrylate, about 35-50%
butyl acrylate and about 25-35% methyl acrylate 6. A polymer emulsion made by the process of
1. Claim 1.
   7. A polymer emulsion made by the process of
2. Claim 2.
   8. A polymer emulsion made by the process of
3. Claim 3.
   9. A polymer emulsion made by the process of
4. Claim 4.
   10. A polymer emulsion made by the process of
5. Claim 5.