AQUEOUS POLYMER COMPOSITIONS CONTAINING GLYCEROL ESTERS AS PLASTICIZERS

This application is a continuation of and claims benefit of United States Patent Application No. 12/406,511 , filed March 18, 2009, the content of which is fully incorporated herein by this reference.

[0001] The present invention relates to aqueous polymer compositions containing a group of glycerol esters that have not previously been described as effective plasticizers for these types of polymer compositions in the absence of other additives. Preferred members of this group of esters exhibited unexpectedly large viscosity increases in aqueous polymer dispersions in addition to effectively reducing the glass transition temperature of the dispersed polymer.

BACKGROUND

[0002] Aqueous polymer compositions suitable for use as adhesives, sealants, waxes, polishes, coatings, including paints, overprint varnishes and inks contain as the film- forming ingredient a finely divided film- forming polymer in the form of a suspension. These compositions also typically may include one or more compounds that function as surfactants, plasticizers and coalescing agents to assist in formation of a continuous film when the dispersion is applied to a substrate.

[0003] One of the functions of a coalescing agent is to lower the minimum temperature at which the suspended polymer particles will form a continuous film on a substrate, referred to as MFFT. Coalescing agents are typically volatile, and evaporate shortly following application of the film. While plasticizers may also assist in formation of a coherent film, they are non- volatile and therefore remain in the applied film, imparting desirable properties such as softening of the polymer. Attorney Docket 8898/94304

[0004] Known plasticizers for aqueous film-forming compositions, as distinguished from coalescing agents, include the esters and ethers listed in U.S. Patent No. 5,442,001, which issued to Jones et al. on August 15, 1995. The '001 patent does not describe esters of glycerol.

[0005] PCT Application WO 2008/054277 Al describes the use of triesters of glycerol with carboxylic acids containing from 1 to 5 carbon atoms as coalescing agents for "aqueous binder compositions". The binder compositions are described as useful in waterborne paints, adhesives and sealants. As indicated on page 2 of this application, "the low plasticizing property of the present invention enables the formation of a hard film to an acceptable hardness development rate". Hence, glycerol esters are not considered to be functioning as plasticizers in the applied film.

[0006] U.S. Patent No. 3,668,158 describes aqueous polymer emulsions for use in adhering a plastic film to a non-metallic substrate. In addition to a film- forming polymer, a copolymer of a 1 -olefin and a vinyl ester of a lower carboxylic acid, the emulsions contain 1) as a coalescent, a water-soluble ester of a mono Cl to C4 alkyl ether of a C2 to C8 glycol with a C2 to C4 saturated monocarboxylic acid; and 2) a "plasticizing ester" of glycerin and a C2 -C4 saturated monocarboxylic acid. Both the coalescent and the plasticizing ester are required to achieve the desired adhesion. The '158 patent indicates that lower esters of glycerol (i.e. the triacetate) gave better performance relative to tributyrate.

[0007] The present invention is based on the discovery that for many aqueous polymer dispersions useful as coatings, adhesives, polishes and sealants and other end-use applications, both the desired film- forming properties of the dispersion and properties exhibited by the final film are improved using a specified class of glycerol esters without the alkyl ether coalescents described in the aforementioned '158 patent.

SUMMARY

[0008] Film- forming properties of aqueous polymer dispersions and the properties exhibited by films from these dispersions are improved using plasticizers that inlcude mono-, di- and triesters of glycerol. The dispersions are useful as aqueous coatings, sealants, adhesives, Attorney Docket 8898/94304

polishes, films and inks. The plasticizers of this invention can be used with any of the organic polymers conventionally used in aqueous film-forming compositions, including polyvinyl acetate, copolymers of vinyl acetate with ethylene or other olefins, acrylic polymers, acrylic/styrene copolymers, polyesters, polyurethanes, elastomeric styrene/butadiene copolymers and neoprene and are compatible with other plasticizers and coalescents.

[0009] An aqueous film-forming polymer composition is provided that includes an aqueous emulsion that includes 1) an aqueous phase, 2) a suspended phase comprising particles of a film- forming organic polymer, and 3) an amount of glycerol ester effective for plasticizing said polymer. The glycerol ester is selected from the group consisting of mono-, di- and triesters of glycerol, and mixtures thereof. Glycerol esters which can be utilized have a general formula

X - CH ₂ - CH - CH ₂ - X

X wherein 0 to 2 X groups are hydroxyl and 1 to 3 X groups are O

- O - C - R ¹ wherein R ¹ is -(CH ₂ ) _n -CH ₃ , where n is 0 to 5, wherein all R ¹ groups are identical, and wherein if n is 0, then 1 to 2 X groups are hydroxyl

[0010] A method is provided for making an aqueous film-forming polymer composition. The method includes dispersing particles of film-forming organic polymer in an aqueous phase to form an aqueous dispersion of film- forming polymer. A glycerol ester of the general formula is blended with the aqueous dispersion of film-forming polymer in an amount effective for plasticizing the polymer.

DETAILED DESCRIPTION

[0011] The present plasticizers are compatible with a wide variety of film-forming polymers typically used in aqueous compositions. These polymers include but are not limited to acrylic Attorney Docket 8898/94304

polymers, acrylic/styrene copolymers, polyvinyl acetate and copolymers, including but not limited to ethylene/vinyl acetate copolymers, acrylics, polyurethanes, styrene/butadiene copolymers and neoprene.

[0012] Useful glycerol esters include mono-, di, and triesters of glycerol and carboxylic acids containing from 2 to 6 carbon atoms, including but not limited to glycerol mono- and diacetates, glycerol mono-, di- and tripropionate, glycerol mono-, di- and tributyrate, up to and including glycerol mono-, di- and trihexanoates. In an important asepect, the ester is compatible with the desired aqueous polymer dispersion. Compatibility of a given ester with the aqueous polymer dispersion can be easily determined by blending the desired amount of glycerol ester with the polymer dispersion at the desired temperature.

[0013] The present invention is based, in part, on the discovery that to maximize plasticization of the dispersed polymer particles and to reduce the polymer's glass transition temperature, the average molecular weight of the ester phase of the polymer dispersion should typically be maximized, preferably to a point just short of separation of the ester from the dispersion at the desired plasticizer concentration level. In this aspect, the average molecular weight of the ester phase of the polymer dispersion is about 239 to about 386. The present glycerol ester and blends thereof typically constitute from about 0.1 to about 50 weight percent, preferably from about 0.1 to about 20 weight percent of the aqueous film-forming polymer composition.

[0014] In another aspect, the glycerol esters include a blend of the tri-, di- and monoesters, of glycerol. In this aspect, the blend in about 15 to about 25 parts of the monoester, about 45 to about 55 parts of the diester, and about 25 to about 35 parts of the triester, In an important aspect, the blend includes about 20 parts of the monoester, about 50 parts of the diester, and about 30 parts of the triester.

[0015] The glycerol esters may be used as the only plasticizer in aqueous polymer compositions. Alternatively, these esters may be used in combination with one or more of the plasticizers conventionally used in aqueous polymer dispersions. These additional plasticizers include but are not limited to esters derived from a) the reaction of monofunctional alcohols with Attorney Docket 8898/94304

mono functional acids; b) the reaction of glycols or diols with monofunctional acids such as benzoic acid, or c) the reaction of an alkyl or aromatic dicarboxylic acid such as phthalic acid with a monofunctional or polyfunctional alcohol. Esters of benzoic acid together with mono- and diesters of the isomeric cyclohexanedicarboxylic acids, also referred to as hexahydrophthalic acids, are preferred classes of auxiliary plasticizers. Other plasticizers that can be used include but are not limited to compatible members of the following families: citrates, sulphonamides, alkyl sulfonic acid esters, adipates, saturated low molecular weight polyesters, isobutyrates and glutarates.

[0016] Many of the glycerol esters suitable as plasticizers in the present aqueous polymer compositions are commercially available. Those which are not available can be prepared using known esterification reactions involving glycerol and a monocarboxylic acid containing from 2 to 6 carbon atoms. The molar ratio of acid to glycerol will be substantially equivalent to the average number of esterified hydroxyl groups per molecule desired in the final ester. In the case of the tributyl ester, this product is commercially available as either a n-butyl or iso-butyl or mixtures of esters.

[0017] In another aspect, the objectionable odor of higher glycerol esters such as the tributyrate can be masked using small quantities of fragrances including but not limited to juniper oil. Mixed esters of butyric acid are very low in odor.

[0018] Aqueous polymer dispersions containing the plasticizers of this invention can be prepared using conventional techniques for preparing these compositions. Typically the glycerol ester or a mixture of these esters is added to a stirred aqueous dispersion of the film- forming polymer(s). In addition to the dispersed polymer and water, the dispersion can contain one or more of the additional ingredients typically present in aqueous polymer dispersion, including but not limited to surfactants, coalescing agents, wetting agents, pigments and dyes.

[0019] The plasticizers of this invention can be used with any of the organic polymers conventionally used in aqueous film-forming compositions. Suitable polymers for use in the present aqueous compositions include but are not limited to polyvinyl acetate, copolymers of Attorney Docket 8898/94304

vinyl acetate with ethylene or other olefins, acrylic polymers, acrylic/styrene copolymers, polyesters, polyurethanes, elastomeric styrene/butadiene copolymers and neoprene.

[0020] The glycerol ester plasticizers of this invention are suitable alone or in combination with known plasticizers discussed hereinbefore in a wide variety of aqueous polymer emulsions for numerous end use applications. These applications include but not limited to adhesives, varnishes, paints and other types of protective and decorative coatings, caulks, sealants, polishes, inks, and protective films.

[0021] An environmentally important advantage of the present esters is that they may be prepared using glycerol and carboxylic acids obtained from naturally occurring materials in contrast to petroleum-based alcohols and acids.

[0022] Film- forming properties of aqueous polymer dispersions and the properties exhibited by films from these dispersions are improved using plasticizers that include mono-, di- and triesters of glycerol.

Effect on Viscosity

Blend of Triester with homopolymer Blend of Triester with copolymer

% Viscosity Increase % Viscosity Increase

Parts 1 hour 1 Day 3 Days Parts 1 hour 1 Day 3 Days

0 0

8 15-25 15-25 15-25 45-55 45-55 45-55

10 15-25 15-25 15-25 95-10595-10595-105

12 45-55 45-55 45-55 7 80-90 80-90 170-180 Attorney Docket 8898/94304

Blend of Mono/Di/Tri with homopolymer Blend of Mono/Di/Tri with copolymer

% Viscosity Increase % Viscosity Increase

Parts 1 hour Parts 1 hour

0 0

20-30 20-30 30-40 40-50 45-55 45-55

10 30-40 40-50 50-60 85-95 90-100 90-100

12 50-60 50-60 60-70 7 145-155 145-150 150-160

Effect on Tg

Blend of Triester with homopolymer Blend of Triester with copolymer

Parts Amount Decreased Parts Amount Decreased

10 4.5-5.5 3.5-4.5

12 9-10 10.5-11.5

Blend of Mono/Di/Tri with homopolymer Blend of Mono/Di/Tri with copolymer

Parts Amount Decreased Parts Amount Decreased

10 7.5-8.5 4.5-5.5

12 9-10 10-11 Attorney Docket 8898/94304

Effect on Open Time

Blend of Triester with homopolymer Blend of Triester with copolymer

Parts Seconds Increased Parts Seconds Increased

10-20 5-15

10 25-35 20-30

12 30-40 30-40

Blend of Mono/Di/Tri with homopolymer Blend of Mono/Di/Tri with copolymer

Parts Seconds Increased Parts Seconds Increased

10-20 2.5-7.5

10 20-30 5 5-15

12 20-30 7 5-15

[0023] The following examples describe preferred embodiments of the present plasticizers and plasticized compositions. These examples should not be interpreted as limiting the scope of the present invention as described in the accompanying claims. Unless otherwise specified all parts and percentages are by weight and reported measurements and other data were obtained under ambient conditions. Attorney Docket 8898/94304

EXAMPLES

Example 1: Preparation of Esters

[0024] The esters referred to hereinafter as glycerol tributyrate, glycerol trioctoate and glycerol triacetate were purchased from commercial sources.

[0025] The ester composition referred to as a mixture of glycerol mono- di- and tributyrates was prepared using the following procedure:

[0026] The following types and amounts of reactants were charged into a four-neck glass reaction vessel equipped with an agitator, inert gas inlet, packed distillation column and means to collect the water formed as a by-product of the esterification reaction: 259 parts of glycerin, 491 parts of butyric acid, and parts of 0.26 parts of zirconium carbonate and 0.13 stannous oxalate as the esterification catalyst. The resultant mixture was heated to a temperature of 230° C. and the by-product water collected. The course of the esterification was followed by gas chromatography and determination of acid number. Following completion of the reaction the reaction mixture was neutralized using sodium carbonate, bleached, and washed with water. The resulting mixture contained approximately 20 parts of the monoester, 50 parts of the diester and 30 parts of the triester.

Example 2: Preparation and Evaluation of Adhesives

[0027] Glycerol tributyrate, the mixture of the mono-, di- and tributyl esters and glycerol trioctoate were evaluated in two commercially available aqueous polymer dispersions. Glycerol triacetate and a commercial benzoate ester plasticizer available as Benzoflex ^® LA 705 were also evaluated for comparative purposes.

[0028] One of the dispersions was a product of Forbo identified as Pace ^® 383 contained a polyvinyl acetate homopolymer. The second dispersion, a product of Wacker Chemie identified as Airflex ^® 400, contained a vinyl acetate/ethylene copolymer. Attorney Docket 8898/94304

[0029] Plasticized polymer compositions were prepared from each of the dispersions by blending the polymer dispersions with the quantities of esters specified in the following tables to form a homogeneous dispersion. Compositions containing glycerol triacetate and the commercial benzoate ester were used as controls.

[0030] Stable dispersion containing glycerol trioctoate at concentrations of 8 percent in the copolymer emulsion and 12 percent in the homopolymer emulsion alone could not be prepared due to the incompatibility of this ester with the polymer at those concentration levels and was not evaluated further.

[0031] The polymer compositions contained the following amounts of polymer dispersion and ester:

Pace 383- 100 parts plus 8, 10 or 12 parts of the ester or blend being evaluated. Airflex 400 - 100 parts plus 3, 5 or 7 parts of the ester or ester blend being evaluated.

[0032] Samples of the two polymer dispersions without any plasticizer were also evaluated as controls.

[0033] The blends of polymer dispersion and ester were prepared using a Caframo ^® mixer operating at 500 rpm for a period of 10 minutes. Viscosities of adhesives were determined at the times indicated in the tables below.

[0034] The resultant blends were allowed to stand for 72 hours before being evaluated using the following tests:

[0035] Compatibility

Tg suppression (on an applied film)

Open time of a film applied using each of the dispersions,

Set time for a film applied using each dispersion.

The properties were measured using the following procedures: Attorney Docket 8898/94304

Compatibility Three mil-thick films (when wet) were drawn down on a clean glass plate. The plate was allowed to dry for 24 hours on a level surface. The films were then examined for signs of incompatibility as evidenced by opaqueness, exudation, and/or the presence of surface defects.

Viscosity

[0036] Measurements were made 1 , 24 and 72 hours or 1 and 5 days after blending in plasticizer using a Brookfield ( RVT) viscometer @ 25°C. The viscosity was allowed to stabilize for 30 seconds before recording reading.

Tg Suppression

[0037] Adhesive films were drawn down at a 6mil thickness and allowed to dry for 48 hours under ambient conditions. The films were then cut and prepared for analysis using a TA Instruments DSC 2920. Analysis was performed between -60 ⁰ C and 105 ⁰ C employing a heating rate of 10°C/min. Reported Tg values was taken at the onset of the transition.

Set Time

[0038] A two bar method was used to measure set times. One bar is used to meter adhesive application and the other bar is used to press the two substrates together. The metering bar was a #16 Meyer rod. The substrate used was 50 Ib. uncoated unbleached Kraft, and testing was conducted at ambient. The test strips were one and one half inches wide (bottom) or one inch wide (top), and twelve inches long. The top strip was centered over the bottom strip and clamped down. About one milliliter of glue was placed at the clamp and the top substrate was laminated with minimum pressure to the bottom one. The assembly was immediately removed from the clamp and a timer started. The strips were delaminated and the time to go to 80-100% fiber tear across the width of the substrate was noted. This time is the set time.

Open Time

[0039] A three-bar (one to meter and two to laminate the substrates) method was employed. Fifty pound unbleached Kraft paper was used as the substrate and the test conditions were 23 ⁰ C and 50% R.H. A #16 Meyer rod was used to meter the adhesive. The size of the paper strips were the same as described in the procedure for determining set time. A #14 rod and a 1/4" diameter draw-down rod (press down) were assembled with rubber bands. The two pieces of paper were Attorney Docket 8898/94304

clamped as in set time and the top sheet was woven through the two bars so that the 1/4" rod was press down rod. The rods were placed at the clamp. About one milliliter of adhesive was placed at the point on the bottom substrate just below the two bars and drawn down with the #16 rod. A timer was started and the adhesive was left "open", i.e. exposed to atmospheric conditions, before the top strip was laminated to the bottom strip. The procedure was repeated, if a bond was formed, until the point was reached that the adhesive could no longer form a bond. The open time is the maximum time interval between application of the adhesive and bringing the substrates together within which a satisfactory bond can be obtained.

[0040] The results of the preceding tests are summarized in the following tables. Comparative examples are indicated by the letter C.

All parts are by weight per 100 parts of polymer dispersion.

Viscosity Response

Homopolymer with Tributyrate Copolymer with Tributyrate

Viscosity, cps After Viscosity, cps After Parts 1 Hour 1 Day 3 Days Parts 1 Hour 1 Day 3 Days 0 4050 4050 4050 0 2650 2650 2650

4900 4800 5050 3 3950 3850 3950

10 5500 5400 5750 5 5400 5200 5400

12 6000 5950 6250 7 4900 4800 7300

Homopolymer with Triacetate (C ) Copolymer with Triacetate (C )

Viscosity, cps After Viscosity, cps After Parts 1 Hour 1 Day 3 Days Parts 1 Hour 1 Day 3 Days 0 4050 4050 4050 0 2650 2650 2650

8 4900 4900 5100 3 3400 3450 3550

10 5050 5250 5450 5 4000 4000 4150

12 5400 5600 5800 7 4850 5350 5500 Attorney Docket 8898/94304

Homopolymer With Copolymer With Mono-/Di-/Tributyate Blend Mono-/Di-/Tributyrate Blend

Viscosity, cps After Viscosity, cps After Parts 1 Hour 1 Day 3 Days Parts 1 Hour 1 Day 3 Days 0 4200 4300 4200 0 2900 2950 2900

8 5150 5500 5700 3 4150 4400 4350

10 5750 6150 6500 5 5450 5650 5650

12 6500 6800 6900 7 7200 7350 7400

Homopolymer With Copolymer With

Benzoflex® LA Benzoflex®LA705 Benzoflex® LA 705

Viscosity, cps After Viscosity, cps After Parts 1 Hour 1 Day 3 Days Parts 1 Hour 1 Day 3 Days

0 4050 4050 4050 0 2650 2650 2650

8 4600 4800 5200 3 3700 3650 3800

10 5500 5450 5700 5100 4950 5050

12 5700 5600 5900 7 6700 6700 6900

[0041] The compatibility of the various individual plasticizers was examined. The only one found to be incompatible was the glycerol trioctanoate. Testing was discontinued on this plasticizer.

Attorney Docket 8898/94304

Tg of 3 mil-Thick Film

Homopolymer w. Tributyrate Copolymer w. Tributyrate

Parts Tg Parts Tg

8 13.79 ⁰ C 3 0.71 ⁰ C

10 8.66 ⁰ C 5 -3.21 ⁰ C

12 4.01 ⁰ C 7 -10.26 ⁰ C

Triacetate [C]

Homopolymer w. Triacetate Copolymer w. Triacetate

Parts Tg Parts Tg

8 15.04 ⁰ C 3 1.76 ⁰ C

10 9.06 ⁰ C 5 -0.54 ⁰ C

12 7.27 ⁰ C 7 -6.14 ⁰ C.

Homopolymer w. Mono-, Di-, Copolymer w. Mono-, Di-,

Tributyrate Blend Tributyrate Blend

Parts Tg Parts Tg

8 8.07 ⁰ C 3 -7.7 ⁰ C

10 0.6 ⁰ C. 5 -12.8 ⁰ C.

12 -1.4 ⁰ C. 7 -18.1 ⁰ C. Attorney Docket 8898/94304

Homopolymer w. Benzoflex LA705[C] Copolymer w. Benzoflex LA705 Parts Tg Parts Tg

8 17.4 ⁰ C. 3 -3.O ⁰ C.

10 13.5 ⁰ C . 5 -6.1 ⁰ C.

12 8.6 ⁰ C. 7 -7.4 ⁰ C.

Open Time Homopolymer w. Tributyrate Copolymer w. Tributyrate

Parts Seconds Parts Seconds

0 5 0 10

8 20 3 20

10 30 5 25

12 35 7 35

Homopolymer w. Triacetate[C] Copolymer w. Triacetate

Parts Seconds Parts Seconds

0 5 0 10

8 25 3 15

10 25 5 20

12 35 7 35 Attorney Docket 8898/94304

Homopolymer w Mono-/Di-/Tri- Copolymer w Mono-/Di-/Tri-

Butyrate Blend Butyrate Blend Parts Seconds Parts Seconds

0 1 0 10

8 15 3 15

10 25 5 20

12 25 7 20

Homopolymer w. Benzoflex ® LA 705 Copolymer w. Benzoflex® LA 705 Parts Seconds Parts Seconds

1 0 10

5 3 15

10 15 5 20

12 15 7 25

Set Time (sec.) Average of 3 Measurements

Homopolymer with Tributyrate Copolymer With Tributyrate

Parts Seconds Parts Seconds

0

3

10 5

12 7 Attorney Docket 8898/94304

Homopolymer with Triacetate [C] Copolymer with Triacetate Parts Seconds Parts Seconds

0 8 0 7

8 8

10 9 5

12 9 7

Homopolymer With Mono-/Di-/Tri- Copolymer with Mono-/Di-/Tri-

Butyrate Blend Butyrate Blend

Parts Seconds Parts Seconds

0 6 0 3

8 5 3 2

10 3 5 3

12 5 7 3

Homopolymer With Copolymer With Benzoflex® LA 705 Benzoflex® LA 705 Parts Seconds Parts Seconds

10 4 5 2

12 3 7 2

[0042] The data indicates that the mono, di, tributyrate blend performs unexpectedly well versus the commercial standard control, Benzoflex LA 705. The viscosity response was very good. The glycerol tributyrate also performs in the above adhesives versus the triacetin (more efficient) and the Benzoflex LA 705.