Waterborne clay-containing emulsion paints with improved application performance

Abstract: This invention relates to a paint composition comprising a clay-containing pigment system, a latex binder, a polysaccharide thickener, and 0.005% to 2%, based upon the weight of the pigment, of a blocking agent which serves to prevent more than 20% of the polysaccharide thickener from being adsorbed onto the clay pigment surface, whereby the paint composition exhibits improved appearance and application performance.

Description: The invention relates to the use of hydroxyethylcellulose-based thickeners in hydrophilic clay-containing emulsion paints. Similar thickeners have been used in paper coating compositions (EP 0 651 093 A1 which is a prior art document under Art. 54(3,4) EPC), in coating compositions for miscellaneous substrates (US 4,298,511) as well as in waterproof roof coatings (US 4,749,731). Prior to the present invention, latex paints containing clay as a pigment extender or containing calcium carbonate with clay impurities as the pigment extender, made it difficult to work with hydroxyethylcellulose (HEC) or hydrophobically modified hydroxyethylcellulose (HMHEC) from an application point of view. These paints often showed a gel structure and drew threads when applied with a roller. In waterborne emulsion paints, cellulose derivatives like hydroxyethylcellulose (HEC), methylhydroxyethylcellulose (MHEC), methylhydroxypropylcellulose(MHPC), ethylhydroxyethylcellulose (EHEC) and carboxymethylcellulose (CMC) are used as rheology modifiers. These cellulose ethers thicken latex paints, providing the paints with stability, water retention and a pseudoplastic flow behavior. The cellulose ethers are used in an amount of 0.1% w/w up to 4.0% w/w on total paint, depending on the binder content of the paint. Hydroxyethylcellulose (HEC) and hydrophobically modified hydroxyethylcellulose (HMHEC) can be considered as the more popular types of cellulose ethers for use; clays are used as pigment extenders in emulsion paints in the United States while calcium carbonate is the most widely used type in European flat emulsion paint formulations, although in certain European areas, silicates and dolomites are used as well. In paint systems containing hydrophilic clays, strong adsorption of HEC and HMHEC onto these clays occurs. This can affect the performance of the polymers in these paints dramatically. Indistemper paints, which are often based on calcium carbonate containing clay impurities like montmorrillonite or bentonite, this results in a gelly paint structure. This gelly structure does not allow a good flow and application of the paint. For this reason, methylcellulose derivatives and carboxymethylcellulose are the preferred thickeners in these paints, since these cellulose ethers do not strongly adsorb, so do not show the undesired gelation. Modification of HEC or HMHEC is needed in order to make them suitable for use as thickeners for clay containing flat emulsion paints. The above-described performance deficiencies of HEC and HMHEC as a result of their strong adsorption onto clay are also valid for ethylhydroxyethylcellulose (EHEC) and hydrophobically modified ethylhydroxyethylcellulose (HMEHEC). It is in meeting this need that the present invention provides an advance in the state of the art of the use of HEC, HMHEC, EHEC and HMEHEC as thickeners in emulsion paints containing hydrophilic clays or calcium carbonate extenders containing clay impurities. This invention relates to a water-borne emulsion paint composition comprising a clay containing pigment system, a latex binder, a polysaccharide thickener selected from the group consisting of hydroxyethylcellulose, hydrophobically modified hydroxyethylcellulose, ethylhydroxyethylcellulose, hydrophobically modified ethylhydroxyethylcellulose and mixtures thereof, and 0.005% to 2%, based upon the weight of the pigment, of a blocking agent, which is selected from the group consisting of poly(ethylene oxide), poly(ethylene glycol), poly(propylene oxide), poly(propylene glycol), poly(vinyl alcohol), poly(acrylic acid), salt of poly(acrylic acid), salts of poly(methacrylic acid), acrylic acid, methacrylic acid, and non-ionic surfactants of the type alkylarylethoxylate and alkylethoxylate, and which serves to prevent more than 20% of the polysaccharide thickener from being adsorbed onto the clay pigment surface whereby the paint composition exhibits improved appearance and application performance. Paper coating compositions are excluded from the scope of the present invention. It has been discovered that the appearance and application properties of clay-containing emulsion paints, thickened with cellulose derivatives as claimed such as HEC, HMHEC, EHEC or HMEHEC, can be enormously improved by combining these cellulose derivatives with so-called pre-blocking agents. These blocking agents limit or even prevent the adsorption of the thickener onto clays and clay-containing extenders. In accordance with this invention, a cellulose derivative thickening agent for clay-containing latex paints is selected from the group consisting of one or more of the following: a. Hydroxyethylcellulose (HEC) with a molecular weight of from 200,000 to 1,500,000 and a hydroxyethyl molar substitution (HE-MS) of 1.5 to 4.0; b. Hydrophobically-modified hydroxyethylcellulose (HMHEC) with a molecular weight of from 50,000 to 1,000,000 and a HE-MS of 1.5 to 4.0 with a hydrophobic modification chain of C 4 to C 22 alkyl or C 8 to C 20 alkylaryl in an amount of 0.01 to 2.0 percent by weight based on total weight of the hydrophobically-modified hydroxyethylcellulose; c. Ethylhydroxyethylcellulose (EHEC) with a molecular weight of from 200,000 to 1,500,000 and a HE-MS of 0.5 to 3.0 and a degree of ethyl substitution of 0.3 to 1.2; and d. Hydrophobically-modified ethylhydroxyethylcellulose (HMEHEC) with a molecular weight of from 50,000 to 1,000,000 and a HE-MS of 0.5 to 3.5 and a degree of ethyoxyl substitution of 0.3 to 1.2 with a hydrophobic modification chain of C 4 to C 22 alkyl or C 8 to C 20 alkylaryl in an amount of 0.01 to 2.0 percent by weight based on total weight of the hydrophobically-modified ethylhydroxyethylcellulose. In accordance with this invention, the blocking agent is selected from the group consisting of one or more of the following: a. Poly(ethylene oxide), poly(ethylene glycol), poly(propylene oxide) and poly(propylene glycol) with a molecular weight of from 100 to 1,000,000; b. Poly(vinyl alcohol) with a molecular weight of from 1,000 to 500,000 and a degree of hydrolysis of from 40 to 90 percent; c. Salts of poly(acrylic acid) and poly(methacrylic acid) and their acid equivalents with a molecular weight of from 1,000 to 1,000,000; d. Nonionic surfactants of the type alkylarylethoxylate and alkylethoxylate with 4 to 100 oxyethylene (OE) units and a hydrophobic chain of C 8 to C 20 alkylaryl or C 4 to C 24 alkyl. The upper limit of the blocking agent in the present invention is 2.0% by weight, based on the total weight of the composition, with the preferred upper limit being 1.0% by weight. The lower limit of the blocking agent is 0.005% by weight, based on the total weight of the composition, with 0.1% by weight being the preferred lower limit. When this combination of thickener and blocking agent is used, the adsorption of the cellulose derivative onto clay or a clay-contaminated extender like Bianco Meudon Tipo A does not exceed 3 mg/g. Latex paints with the above-described thickener combinations do not have a gelly structure and can be applied to a substrate by roller without drawing undesired threads. Extender Pigments The types of extenders that can be used in this invention are basically two groups of products: a) clay-type extenders and b) calcium carbonate extenders contaminated with hydrophilic clay-types. a. Clay-type Extenders Examples of these clays are generally Kaolinites, chemically composed of SiO 2 (30-50 wt. %), Al 2 O 3 (30-50 wt. %), small amounts of alkalis (K 2 O, Na 2 O) and iron oxide (Fe 2 O 3 ). Other clays that may be used as extenders in this invention are calcined clays with low loss on ignition. Examples of such clays for use in the instant invention are: Clays Manufacturer SiO 2 (wt. %) A l 2 O 3 (wt. %) Loss on Ignition (wt. %) Kaolin FP75 Dorfner 48 36 12 Spesswhite ECC 47 38 13 DB Plate 1000 Euroclay - - - China Clay Grade B ECC 48 37 12.1 China Clay Grade C ECC 48 37 11.9 China Clay Grade D ECC 47.5 37 12.1 China Clay Grade E ECC 48.5 36.5 11.0 Polestar 200 ECC 54.7 41.7 - Amazon 88 CADAM 45.1 37.8 13.9 b. Contaminated Carbonates Calcium carbonates are available in relatively purified form like the Durcal-products, Omyacarb-series and Omyalite-series of OMYA. However, many producers of cheaper and less purified products also exist. These cheaper calcium carbonates can be contaminated with many types of clays. However, the contamination with very hydrophilic clays causes the problems with HEC in heavily pigmented paint systems. Examples of these clay contaminants are attapulgite clay, hectorite clay, montmorrillonites, and bentonite clay. One example of such a problem-causing calcium carbonate is the Bianco Meudon Tipo A used in the Italian paint market. Latex Types The problem of strong structure build-up in the paint is mainly known in paint systems, where poly(vinyl acetate) VeoVA co-polymer binders are used as latex. Examples of these binders which are partially stabilized with hydroxyethyl cellulose as protective colloid are: Binder Marketed By Ravemul PC2 Enichem, Italy Vinavil 03V Montedipe, Italy Uramul VV50 DSM Resins, The Netherlands Mowilith DM21 Hoechst, Germany Acrilem 30VVAC ICAP, Italy Latex paints of this invention provide excellent capacity to hide the substrate that it is to cover. The capacity to hide the substrate is controlled mainly by the pigment volume concentration (PVC) and the coating thickness. The PVC has certain limits dictated by economics and the capacity of the pigment binding vehicle. The latex paint of this invention, for example, when used in flat paints may have a PVC of from 50 to 100%. The coating thickness is determined in part by the viscosity developed in the composition. Other factors exist such as other coating properties and application characteristics, such as brush drag, flow, and leveling of the coating composition for developing the type of viscosity for a particular type of paint. The practice of the invention is further illustrated by the following examples: Adsorption experiments in the Examples were performed as follows: A 50 wt. % solids suspension of clay in water was prepared. 0.5 wt. % of thickener was added and dissolved in the pigment slurry or suspension and then stored for 24 hours at 25°C. The system was then centrifuged at 20,000 rpm for three hours. The amount of hydroxyethylcellulose or ethylhydroxyethylcellulose of the supernatant was determined via the Sealed Tube Zeisel method for measuring ethoxyl and hydroxyethyoxyl content. These pigment slurries were also made in the presence of blocking agents in order to determine the effect of the blocking agent on the adsorption of the cellulosics onto clay and carbonate extenders. Example 1 The Adsorption of HEC and HMHEC Onto a Clay-Containing Extender As a Function of Different Types of Pre-Blocking Agents Example Blocking Agent Type % w/w Adsorption onto Bianco Meudon Tipo A of HEC (mg/g) 1A None - 4.5 1B Calgon N 0.25 3.7 1C Tamol 731 0.25 3.5 1D PEG 400 0.25 4.8 1E Tamol 963 0.25 3.8 1F Lutrol E 4000 0.25 1.9 1G Lopon 885 0.25 4.0 1H Pigment Verteiler A 0.25 0.0 1I Airvol 803 0.25 0.0 1J Sodium Dodecyl Sulfate 0.25 11.2 1K Antarox CO430 0.25 4.0 1L Antarox CO970 0.25 0.6 Example Blocking Agent Type % w/w Adsorption onto Bianco Meudon Tipo A of HMHEC (mg/g) 1M None - 6.7 1N Calgon N 0.25 9.4 1O Tamol 731 0.25 12.5 1P PEG 400 0.25 4.0 1Q Tamol 963 0.25 4.0 1R Lutrol E 4000 0.25 0.0 1S Lopon 885 0.25 4.1 1T Pigment Verteiler A 0.25 0.8 1U Airvol 803 0.25 0.0 1V Sodium Dodecyl Sulfate 0.25 11.7 1W Antarox CO430 0.25 5.8 1X Antarox CO970 0.25 2.5 The above-given examples 1A through 1X demonstrate that only specific products can be used as a blocking agent to limit the adsorption of HMHEC onto Bianco meudon Tipo A. Lutrol E 4000 (as marketed by BASF), a poly(ethylene glycol) with a molecular weight of approximately 4000, pigment Verteiler A (as marketed by BASF), an ammonium salt of poly(acrylic acid), Airvol 803 as marketed by Air Products), a poly(vinyl alcohol) (molecular weight about 10,000; 88-89% hydrolysis) and Antarox CO970 (as marketed by GAF), a nonylphenol ethoxylate (50 EO units) are able to reduce the adsorption of HMHEC onto the extender. These blocking agents are able to form hydrogen bonds with clay or the clay present as contaminant in calcium carbonate extenders. Higher molecular weight poly(ethylene glycol) (Lutrol E 4000) is more efficient than lower molecular weight material (PEG 400). Nonylphenol ethoyxylate surfactants become more efficient as a blocking agent when increasing the number of EO-units in the product (see Antarox CO970 versus Antarox CO430). The ammonium salt of poly (acrylic acid) is more efficient as a blocking agent than the sodium salt (see Pigment Verteiler A versus Lopon 885 and Tamol 963). Example 2 The differences in adsorption values are reflected in differences in paint properties of the paints based on the Bianco Meudon Tipo A and the various combinations of HMHEC and blocking agents. The following examples (2A-2T) exhibit the practice of the invention in a flat emulsion paint having a pigment volume concentration (PVC) of 94%. The paint samples were prepared under Cowles conditions with a high speed dissolver. The paint formulation is given in Table 3. Paint Formulation Containing Bianco Meudon as Pigment Extender; PVC : 94%; Solids: 58 % w/w Parts by Weight Water 287.1 Preservative CA24 1.0 Pigment Verteiler A 1.0 Calgon N 1.5 Agitan 280 1.0 Ammonia 1.0 Bianco Meudon 665.0 Texanol 2.0 Ravemul PC2 33.0 Thickener by demand Blocking Agent 3.0 Water 97.5 Total 1093.1 The paint was thickened with Natrosol Plus® grade 330 HMHEC and Natrosol® 250 MBR HEC combined with different blocking agents. The test results are shown in Table 4 and Table 5. Combination of (Natrosol® 250 MBR) HEC With Different Pre-blocking Agents in a Flat Emulsion Paint (PVC 94) Based on Ravemul PC2 With Bianco Meudon Tipo A As An Extender Example HEC (Wt. %) Blocking Agent Type SV SYV Appearance Roller Application 2A 0.36 None 109 800 -- -- 2B 0.28 Pigment Verteiler A 100 250 + + 2C 0.30 Calgon N 116 1600 -- -- 2D 0.24 Sodium Dodecyl Sulfate 101 900 -- -- 2E 0.31 Tamol 731 107 700 -- -- 2F 0.33 Antarox CO970 112 250 + + 2G 0.34 Antarox Co430 106 450 +- + 2H 0.26 Airvol 803 110 250 + + 2I 0.30 Lutrol E 4000 114 200 + + 2J 0.37 PEG 400 100 500 +- + Combination of HMHEC (Natrosol Plus® 330) With Different blocking Agents in a Flat Emulsion Paint (PVC 94) Based on Ravemul PC2 With Bianco Meudon Tipo A As An Extender Example HEC (Wt. %) Blocking Agent Type SV SYV Appearance Roller Application 2K 0.37 None 109 650 - - 2L 0.40 Pigment Verteiler A 108 200 + + 2M 0.26 Calgon N 114 1800 -- -- 2N 0.26 Sodium Dodecyl Sulfate 112 600 - - 2O 0.36 Tamol 731 107 550 - -- 2P 0.27 Antarox CO970 108 150 + + 2Q 0.28 Antarox CO430 106 350 +- +- 2R 0.37 Airvol 803 109 200 + + 2S 0.35 Lutrol E 4000 114 100 + + 2T 0.36 PEG 400 100 300 +- + Example 3 Another experiment was performed to demonstrate that the effect of combining the cellulose ether with a blocking agent is also valid for EHEC and HMEHEC. EHEC was Bermocol E 351 FQ polymer and the HMEHEC was Bermocol EHM100 polymer. The influence of using a combination of HMEHEC and a blocking agent on the paint properties is shown in the flat emulsion paint (PVC94) based on Ravemul PC2 material. Examples 3A-3D illustrate these benefits (see Table 6). Combination of (HM)EHEC with Lutrol 4000 In a Flat Emulsion Paint (PVC 94) Based On Ravemul PC2 With Bianco Meudon Tipo A as an Extender Example EHEC (wt %) HME HEC (wt. %) Lutrol E 4000 (wt. %) SV (KU) SYV (g) Appearance Roller Application 3A 0.35 - - 106 700 -- -- 3B 0.31 - 0.25 109 200 + + 3C - 0.34 - 110 600 - - 3D - 0.29 0.25 111 150 + + Example 4 In paint systems with strong hydrophilic clays like Spesswhite, the amount of blocking agent needs to be increased in order to limit the adsorption of HEC, EHEC, HMHEC and HMEHEC onto these types of clay. This is illustrated by the results of adsorption experiments shown in Examples 4A and 4B (see Table 7) using Lutrol E 4000 as a blocking agent. Influence of the Addition of a Blocking Agent on the Adsorption of HEC (Natrosol 250 MBR) Onto Spesswhite, a Hydrophilic Clay ex ECC. Example Wt % Blocking Agent Adsorption of HEC Onto Spesswhite (mg/g) 4A - - 10.0 4B 0.25 Lutrol E 4000 9.8 4C 0.5 Lutrol E. 4000 3.6 4D 1.0 Lutrol E 4000 0.3 The combinations of HEC, EHEC, HMHEC or HMEHEC with blocking agents can be used in the form of a powder blend, fluidized polymer system or as a solution of subject materials.

Claims: A water-borne emulsion paint composition excluding paper coating compositions comprising a clay containing pigment system, a latex binder, a polysaccharide thickener selected from the group consisting of hydroxyethylcellulose, hydrophobically modified hydroxyethylcellulose, ethylhydroxyethylcellulose, hydrophobically modified ethylhydroxyethylcellulose and mixtures thereof, and 0.005% to 2%, based upon the weight of the pigment, of a blocking agent, which is selected from the group consisting of poly(ethylene oxide), poly(ethylene glycol), poly(propylene oxide), poly(propylene glycol), poly(vinyl alcohol), poly(acrylic acid), salt of poly(acrylic acid), salts of poly(methacrylic acid), acrylic acid, methacrylic acid, and non-ionic surfactants of the type alkylarylethoxylate and alkylethoxylate, and which serves to prevent more than 20% of the polysaccharide thickener from being adsorbed onto the clay pigment surface whereby the paint composition exhibits improved appearance and application performance. The composition of claim 1 wherein the polysaccharide thickener is hydroxyethylcellulose with a molecular weight of from 200,000 to 1,500,000. The composition of claim 2 wherein the hydroxyethylcellulose has a molar substitution of 1.5 to 4.0. The composition of claim 1 wherein the polysaccharide thickener is hydrophobically modified hydroxyethylcellulose with a molecular weight of from 50,000 to 1,000,000. The composition of claim 4 wherein the hydrophobically modified hydroxyethyl cellulose has a hydroxyethyl molar substitution of 1.5 to 4.0. The composition of claim 5 wherein the hydrophobically modified hydroxyethyl cellulose has a hydrophobic modification of C 4 to C 22 alkyl or C 8 to C 20 alkylaryl in an amount of 0.01 to 2.0% by weight based on total weight of the hydrophobically modified hydroxyethylcellulose. The composition of claim 1 wherein the polysaccharide thickener is ethylhydroxyethylcellulose with a molecular weight of from 200,000 to 1,500,000. The composition of claim 7 wherein the ethylhydroxyethyl-cellulose has a hydroxyethyl molar substitution of 0.5 to 3.0. The composition of claim 8 wherein the ethylhydroxyethyl cellulose has a degree of ethyl substitution of 0.3 to 1.2. The composition of claim 1 wherein the polysaccharide thickener is hydrophobically modified ethylhydroxyethylcellulose with a molecular weight of from 50,000 to 1,000,000. The composition of claim 10 wherein the hydrophobically-modified ethylhydroxyethylcellulose has a hydroxyethyl molar substitution of 0.5 to 3.5. The composition of claim 11 wherein the hydrophobically-modified ethylhydroxyethylcellulose has a degree of ethyoxyl substitution of 0.3 to 1.2. The composition of claim 12 wherein the hydrophobically-modified ethylhydroxyethylcellulose has a hydrophobic modification of C 4 to C 22 alkyl or C 8 to C 20 alkylaryl in an amount of 0.01 to 2.0% by weight based on total weight of the hydrophobically-modified ethylhydroxyethylcellulose. The composition of claim 1 wherein the blocking agent is selected from the group consisting of poly(ethylene oxide), poly(ethylene glycol), poly(propylene oxide), and poly(propylene glycol), whereby the blocking agent has a molecular weight of from 100 to 1,000,000. The composition of claim 1 wherein the blocking agent is poly(vinyl alcohol) with a molecular weight of from 1,000 to 500,000. The composition of claim 15 wherein the poly(vinyl alcohol) has a degree of hydrolysis of from 40 to 90 percent. The composition of claim 1 wherein the blocking agent is selected from the group consisting of salts of poly(acrylic acid), salts of poly (methacrylic acid), acrylic acid, and methacrylic acid. The composition of claim 17 wherein the salts have a molecular weight of from 1,000 to 1,000,000. The composition of claim 1 wherein the nonionic surfactants have 4 to 100 oxyethylene units and a hydrophobic chain of C 8 to C 20 alkylaryl or C 4 to C 20 alkyl. The composition of claim 1 wherein the clay containing pigment system comprises extender pigments selected from the group consisting of clay-types and calcium carbonate-types contaminated with hydrophilic clay types. The composition of claim 20 wherein the clay type extenders are kaolinites or calcined clays with loss ignition. The composition of claim 20 wherein the contaminated calcium carbonate type extenders are selected from the group consisting of attapulgite clay, hectorite clay, montmorrillonites, and bentonite clay. The composition of claim 22 wherein the contaminated calcium carbonate type extenders are Bianco Meudon Tipo A extender. The composition of claim 1 wherein the paint composition has a pigment volume concentration of from 50 to 100. Use of a clay containing pigment system, a latex binder, a polysaccharide thickener selected from the group consisting of hydroxyethylcellulose, hydrophobically modified hydroxyethylcellulose, ethylhydroxyethylcellulose, hydrophobically modified ethylhydroxyethylcellulose and mixtures thereof, and 0.005% to 2%, based upon the weight of the pigment, of a blocking agent, which is selected from the group consisting of poly(ethylene oxide), poly(ethylene glycol), poly(propylene oxide), poly(propylene glycol), poly(vinyl alcohol), poly(acrylic acid), salt of poly(acrylic acid), salts of poly(methacrylic acid), acrylic acid, methacrylic acid, and non-ionic surfactants of the type alkylarylethoxylate and alkylethoxylate, and which serves to prevent more than 20 % of the polysaccharide thickener from being adsorbed onto the clay pigment surface, in the manufacture of a water-borne emulsion paint composition, excluding paper coating compositions.

Inventors: KROON GIJSBERT, KROON, GIJSBERT
Applicants: AQUALON CO, AQUALON COMPANY
Application year: 1995
Main classification: C09D5
IPC codes: C09D201, C09D7, C09D5, C09D101