Randolph B. Krafcik, The Sherwin-Williams Company, USA

Transcription

1 Minimizing Viscosity hanges when Tinting in Architectural Paints: Understanding Structure/ Property Relationships Between Latex, HASE Thickeners and Surfactants Randolph B. Krafcik, The Sherwin-Williams ompany, USA Architectural latex paints can experience large changes in viscosity when tinting with universal colorants. This can be especially true when tinting paints to darker colors that are popular in today s interior Architectural paints. These darker colors can use up to 12 ounces of colorant/ gallon, with a resultant viscosity showing as large as a 40 KU viscosity drop in some interior paints containing associative thickeners. This paper explores the root cause of viscosity change when tinting with universal colorants. The contribution of individual components in universal colorants on viscosity change will be shown. HASE thickeners with different hydrophobic groups were synthesized to determine whether the problem could be solved through HASE thickener design. New latexes were prepared incorporating hydrophobic ethoxylated monomers (used in HASE thickeners) directly into the polymer backbone. Paint testing using these Hydrophobically Modified (HM) small particle size latexes showed positive viscosity properties compared to control latexes without hydrophobic modification. 1. Introduction Associative Thickener Mechanism: Associative thickeners are used extensively by Sherwin- Williams to impart targeted rheological properties in paint. These thickeners ultimately impact what the customer feels when applying paint and what they see in the flow and leveling and spatter of the finished product. Much work has been done in the paint industry on understanding the mechanism of associative type thickeners. 1-7 Excellent review articles have been written by Glass 8 and Winnik 9 on this subject. The generally accepted mechanism for associative thickeners involves the formation of a transient network between associative thickeners and particles (latex and pigment) in the coating. The hydrophobic moieties in associative thickeners can form loops and bridges and are thought to both self-associate and adsorb onto latex and pigment surfaces. A simplified model for the association network is shown in diagram 1. The addition of universal colorants can change the final viscosity properties of paints containing associative thickeners. Surface-active components in colorants compete with associative thickeners for adsorption onto latex surfaces. Much research has been carried out to understand the interactions of surfactants, coalescent solvents and other paint components with associative thickeners omponents in universal colorants can compete for adsorption sites on particle surfaces and can hinder or enhance associations between thickener hydrophobes. When viscosity is lowered with certain colorants, components in colorants can disrupt the associative network set up by the associative thickeners and affect viscosity. A simple model to help visualize this disruption is shown in diagram 2. This paper highlights studies to understand the root cause of viscosity change when colorants are added into paint and attempts to answer 3 basic questions: 1. What is the contribution of individual components in colorants to viscosity change? 2. an issue be addressed through HASE thickener design? 3. an issue be addressed through latex modification?

2 DIAGRAM 1 ASSIATIVE THIKENER NETWRK DIAGRAM 2 DISPLAEMENT F ASSIATIVE THIKENERS BY ADDED SURFATANTS ompetition for Association Sites RSETTES* 2. Experimental Thickener and latex response to surfactants/ colorants were tested using both a simple pigmentless paint formula and a fully formulated paint system. Pigmentless Paint to Screen Associative Thickeners: Pigmentless paint was used as a screening test to determine a thickener s viscosity response in latex only, without the complications of pigments, surfactants and other components which are present in a fully formulated paint. Pigmentless paint was prepared by blending 100g of a vinyl acrylic latex (55% solids, controlled lot) with 100g of water in an 8 oz. can. A standard level of associative thickener (level dependent on the type of thickener used) was added to the pigmentless paint. With HASE type thickeners, the final ph of the pigmentless paint was adjusted to ph above 8.5 with 2-amino-2-methyl propanol. Viscosity measurements were taken TM (off-the-mill) after 10 minutes of mixing. To check the thickeners anticipated response to tinting, 2 grams of an octylphenol ethoxylated surfactant, Igepal A-630 from Rhodia, was added to the pigmentless paint. Viscosity was again measured after mixing for 5 minutes. The change in viscosity was compared before and after surfactant addition. Pigmentless Paint to Screen Latex: A screen test to determine the viscosity response of latexes was run in a pigmentless paint using a HEUR type thickener. The pigmentless paint was prepared in an 8 ounce can by diluting 75g of the test latex with 75g of water. 18.4g of Acrysol RM-825 was added separately to an 8 oz. container and diluted with 7g of Butyl arbitol and 14.6g of water. This HEUR blend was added to the pigmentless paint and mixed for 10 minutes at medium speed until uniform. Viscosity measurements were recorded. To determine anticipated response to universal colorants, 2 g of Igepal A-630 was added and viscosity recorded. olorant response in a Vinyl Acrylic (VA) Ultradeep Satin Paint: Additional testing of thickeners and latexes were done in a fully formulated prototype Interior Vinyl Acrylic Ultradeep Satin Paint. This particular formula shows a large viscosity change with addition of universal colorants. When testing HASE type thickeners in this paint, the amount of thickener is adjusted to a targeted KU viscosity range. New latexes under testing were substituted for the VA latex on a weight solids basis in the same Ultradeep Satin paint formula. Four different universal colorants: Black, Blue, N Red and Red xide were added at 12 ounces of colorants per gallon of paint. Viscosity measurements were recorded before and after adding the 4 different colorants.

3 Vinyl Acrylic (VA) Ultradeep Satin Paint Formula Material Weight (lbs.) Volume (gal.) Vinyl Acrylic Latex (55.0% solids) Defoamer Water Attapulgite lay Preservative Dispersant (50.0% solids) Surfactant Defoamer alcium arbonate Water Ethylene Glycol oalescing Solvent HEUR thickener(17.5% solids) Water Defoamer Ammonium Hydroxide(28%) PV 25.8 NVM 43.4 NVV Results and Discussion Understanding olorant drop: Universal colorants used by Sherwin-Williams are made using various raw materials to disperse different chromophoric pigments. These universal colorants must be compatible with both waterborne and solvent-borne paints. The main components in universal colorants are the chromophoric pigment, extender pigment, water, ethylene glycol, and various nonionic and anionic surfactants. Typical omponents in Universal olorants ABBREV Ave. % in olorant hromophoric Pigment 20 Extender Pigment 20 Water H2 20 Ethylene Glycol EG 20 ctyl Phenol Ethoxylate PE 10 Phosphate Ester Surfactants PES 1.2 Polycarboxylate Dispersant PD 1.2 Soya Lecithin SL 5 ther Dispersants

4 An experiment was done looking at the individual components in universal colorants and determining their effect on viscosity in a Vinyl Acrylic Ultradeep Satin paint. The experiment assumed the maximum amount of colorant, 12 ounces/ gallon, that is recommended for ultradeep and neutral base paints. The average level across 13 different colorants of each component (shown in table) was calculated and blended with water to keep the total volume/ gallon of paint at 12 ounces. The starting KU viscosity of the Vinyl Acrylic Ultradeep Satin paint was 140. Viscosity measurements were taken after adding the individual colorant components. Results are shown in Figure 1. FIGURE 1: KU drop with colorant components Universal olorant omponents KU drop in Ultradeep Latex Paint hange in KU viscosity Red x H2 EG PE PES PD SL Starting KU = 140 Red oxide, one of the worse colorants for KU response, dropped the KU viscosity in the Vinyl Acrylic Ultradeep Satin paint by 36 Krebs units. 12 oz. of water dropped the KU viscosity by 17 Krebs units. Ethylene Glycol gave a 21.9 KU drop. The octylphenol ethoxylate showed a 52 KU drop. The phosphate ester surfactant showed a 24.7 KU drop. The polycarboxylate dispersant showed a 20.3 KU drop. Soya lecithin showed a 2 KU increase. The octyl phenol ethoxylate was the biggest contributor to KU drop in colorants. KU Response of Thickeners to Different HLB surfactants: Another experiment was carried out in pigmentless paint to establish a baseline with 3 typical thickeners used in the industry: Rohm and Haas Acrysol TT-935, a HASE type thickener Acrysol ST-275, a polyurethane associative thickener and an SW prototype HASE thickener. A series of different HLB, nonionic nonyl phenol ethoxylate surfactants from Rhodia (Igepal line) were added at 2 grams in 8 oz. of pigmentless paint. A graph showing the KU response over different HLB values is shown in Figure 2. Figure 2: KU response of different HLB nonionic surfactants KU Response of Thickeners to 1% wt. Nonionic in Pig Paint KU viscosity HLB of added NPE TT-935 ST SW HASE

5 These 3 thickeners generally showed similar tendencies over the range of different HLB nonionic surfactants. Surfactants and thickener compete in their adsorption on the disperse phases. The surfactants, at the high concentration in this experiment, disrupt the transient associative network set up by the associative thickeners. Studies Investigating hanges in the Hydrophobic Group of HASE Thickeners: Recent patent activity by thickener and additive suppliers show a high level of interest in preventing viscosity drop with colorants Sherwin-Williams has been active in evaluating many commercially available products to address the colorant viscosity drop issue (beyond the scope of this presentation). A more fundamental study was undertaken to better understand the contribution of hydrophobic monomers in HASE associative thickeners in their viscosity response with universal colorants. HASE type thickeners are hydrophobically modified alkali swellable emulsions typically made with a combination of methacrylic acid (MAA), ethyl acrylate (EA) and a hydrophobic monomer through an emulsion polymerization. Each component in the HASE thickener can affect the final thickening efficiency. 27 EMULSIN PLYMERIZATIN H3 H H3 H 2 H 2 H 2 - X H 2 (H 2 H 2 ) 25 H 3 Y 22 H 45 Z MAA EA HYDRPHBE The hydrophobic monomer greatly influences the final rheology performance of the HASE thickener. Rhodia offers a commercial line of Sipomer hydrophobic monomers and has been active in this area for a number of years. 28 These Rhodia monomers are called Sipomer SEM, Sipomer BEM, Sipomer HPM 100, 200, 300 and 400. They each offer different viscosity building properties when incorporated into HASE type thickeners. The hydrophobic monomers can be classified into 3 broad categories depending on their viscosity building tendencies: low shear building (LSB) hydrophobes, medium shear building (MSD) hydrophobes and high shear building (HSB) hydrophobes. Early studies showed that the LSB hydrophobic monomers also show the largest viscosity change with colorants. More success in minimizing viscosity change with colorants appeared likely with medium build (MSB) and high shear (HSB) hydrophobic monomers. A series of prototype HASE thickeners were prepared using the same synthetic procedure but varying the MSB and HSB monomers as shown below. Hydrophobic Monomer Studies Medium shear building (MSB) High shear building (HSB) hydrophobic monomer hydrophobic monomer Prototype 1 100% 0% Prototype 2 0% 100% Prototype 3 25% 75% Prototype 4 50% 50% The HASE prototypes 1 and 2 were run in an HLB response study in a vinyl acrylic pigmentless paint. Prototype 1 made with 100% of the MSB hydrophobe showed similar response to the commercial HASE and HEUR thickeners tested. Prototype 2 made with 100% HSB hydrophobe showed a very favorable response over the HLB range and offered promise in minimizing viscosity changes. (Figure 3)

6 Figure 3: KU response over different HLB Surfactants KU Response of Thickeners to 1% wt, Nonionic in Pig Paint KU viscosity HLB of added NPE TT-935 ST PRT 1 PRT 2 The 4 prototype HASE thickeners were tested in the standard VA Ultradeep Satin paint. The amount of each HASE prototype was adjusted in the formula to a KU viscosity between Results showing viscosity response with 4 universal colorants are shown in Figure 4. FIGURE 4: KU change with olorants in Ultradeep Satin Paint UltraDeep Satin Paint KU hange w/ olorant 30 hange in KU viscosity Red X 12 oz/gal Black 12 oz/gal Blue 12 oz/gal N Red 12 oz/gal -40 olorant ST-275 TT-935 PRTTYPE 1 PRTTYPE 2 PRTTYPE 3 PRTTYPE 4 Different viscosity responses were observed between different colorants in the ultradeep satin paint tested. Red oxide tended to show a large KU drop in this paint. The blue and N Red colorants tended to increase KU viscosity and the black colorant was mixed in its response. The prototype 3 HASE thickener, containing 75% HSB and 25% MSB hydrophobes showed the best overall performance across the 4 different universal colorants. Prototype 3 worked well in minimizing viscosity drop with universal colorants in VA latex paint systems made with larger particle size (>200nm) vinyl acrylic latex. However, this thickener did not perform as well in higher performance paints made with small particle size (<125 nm) latexes. The next study focused on modifying the latex itself to determine whether changing the hydrophobic nature of the latex could impact viscosity changes with universal colorants.

7 Studies on Hydrophobically Modified (HM) Latex Structure The transient associative thickener network is also influenced by the composition of the latex used in paint Monomer composition can make the latex more hydrophobic or hydrophilic. The amount of surfactant used during the synthesis affects the final latex particle size. Smaller particle size latexes have more total surface area and can be highly influenced by addition of surface-active components into the paint system. The prototype HASE thickeners that prevented viscosity change with colorant in vinyl acrylic paints did not work as well with paints containing smaller particle size acrylic latexes (<125nm). In paints with small particle size latex, typically 25 50% less associative thickener is required to achieve a targeted viscosity (e.g. KU ). olorants and surfactants can quickly disrupt the transient associative network. Studies were undertaken to determine whether the monomer composition of the latex could be changed to minimize viscosity change with colorants. Latexes were prepared with hydrophobic monomers used in HASE type thickeners. These hydrophobic monomers create more hydrophobic sites on the HM latex for adsorption with associative thickeners. The HM latex can also self-associate with other HM latex to enhance the associative network in the paint. A simplistic model for the HM latex and the enhanced associative network is shown below: MDIFIED LATEX ENHANED ASSIATIVE NETWRK To test the HM latex concept, two hydrophobic monomers, MSB and HSB, were incorporated into a single-stage styrentated acrylic latex at 12% BTM (particle size between nm). These HM latexes were tested in pigmentless paint and compared to a control latex without the hydrophobic monomer. Results in Figure 5 show that the control latex dropped 23.3 KU s when adding Igepal A-630, while the HM modified latexes showed 8.6 KU drop with the MSB monomer and 3.8 KU drop with the HSB monomer. The hydrophobic modification also increased the overall II viscosity versus the control latex (Figure 6) in the pigmentless paint. The HM latex concept showed promise in this simple screen test. FIGURE 5: KU change HM latex in Pig Paint FIGURE 6: II change HM latex in Pig Paint KU Hydrophobically Modified Latex Pig paint 73.2 ontrol latex % MSB mod Latex before and after 2% A % HSB mod II Hydrophobically Modified Latex Pig Paint ontrol latex % MSB mod % HSB mod Latex before and after 2% -630 KU start KU with 630 II start II with 630

8 Several different types of hydrophobic monomers, were incorporated at 12% BTM into the latex synthesis and tested in an Ultradeep Satin paint. Figure 7 shows KU viscosity response in Ultradeep Sating paint (thickened with a HEUR type thickener). The control latex showed a KU drop when adding 12 oz. of the universal colorants. Minimal changes in KU viscosity were observed in the different types of hydrophobic monomers tested. The level of hydrophobic monomer incorporated into the latex also affects its viscosity performance in paint. Figure 8 shows results of varying HSB monomer in the latex from 6% to 12% modification (BTM). The minimum level of modification to prevent viscosity change with colorants in this latex was determined to be >9%. ne of the disadvantages of hydrophobically modifying the small particle size latex was an increase in final package viscosity. The solids of the final latex and the level of hydrophobe modification all play a role in the final package viscosity of the latex (beyond scope of this presentation). The results on the HM latexes were promising and show that the viscosity drop issue with universal colorants can potentially be addressed through latex modification FIGURE 7: Varying HM type in UD Satin Paint FIGURE 8: Varying HM level in UD Satin Paint 10 VARYING TYPE F HM MNMER Interior UD Satin - KU hange w/ 12oz. olorant 10 VARYING LEVEL F HSB MNMER Interior UD Satin - KU hange w/ 12oz. olorant 5 5 change in KU Red X Black Blue N Red hange in KU Red X Black Blue N Red ontrol Latex % HSB HSB/MSB BLEND % MSB % LSB % HSB2 ontrol Latex % HSB % HSB % HSB 4. onclusion Studies looking at the contributions of the individual components in universal colorants identified the largest contributor to KU drop as a nonionic surfactant present in all universal colorants. This nonionic surfactant likely interacts with the associative thickener network by disrupting the thickener adsorption onto latex and lessening the self-association between certain thickeners. Investigation of various hydrophobic monomers in HASE thickeners showed that viscosity changes with universal colorants can be minimized through proper selection of a combination of hydrophobic monomers. The optimized HASE thickener worked well in paint systems containing larger particle size (>200nm) vinyl acrylic latexes, but did not perform as well in smaller particle size (<124 nm) latexes. Smaller particle size latexes can be further modified with hydrophobic monomers to minimize their viscosity response to universal colorants. Selection of the correct combination of HASE thickener and HM latex can lead to paint systems that experience minimal viscosity change with universal colorants.

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