Low-VOC waterborne coatings for use in industrial maintenance painting.Increasingly demanding environmental regulations for industrial maintenance coatings have put pressure on manufacturers and users of both solventborne and waterborne coating systems. The lowering of volatile organic compound volatile organic compound Environment Any toxic cabon-based (organic) substance that easily become vapors or gases–eg, solvents–paint thinners, lacquer thinner, degreasers, dry cleaning fluids (VOC (Vertical Online Community) See vertical portal. ) levels to below 100 g/L is being considered for industrial maintenance coatings in many regions of the U.S. This article discusses the development of waterborne acrylic latex latex, emulsion of a polymer (e.g., rubber) in water (see colloid). Natural latexes are produced by a number of plants, are usually white in color, and often contain, in addition to rubber, various gums, oils, and waxes. polymers for use in high performance, VOC-compliant coatings applied to steel and concrete structures. Formulation and coating properties of these polymers are described, with an emphasis on comparisons of performance to traditional, higher VOC waterborne and solventborne coatings.
Environmental regulations have put increasing pressure on all members of the coatings industry to develop and use coatings that have lower impact on our environment. Raw material suppliers are constantly working to develop new resins and additives that allow paint manufacturers to produce coatings with favorable health, safety, and environmental profiles. In addition, painting contractors and end-users such as homeowners and facility owners are constantly asking for higher performing products. Those two desires are often difficult to bring together in a new product, especially when it comes to lowering volatile organic compound (VOC) levels. Waterborne latex coatings are one technology which provides an opportunity to reduce VOC levels relative to traditional solventborne technologies. However, technical challenges still exist, considering the low-VOC targets posed by many existing and proposed regulations. In particular, properties such as hardness, dirt pickup resistance, block and print resistance, and the ability to withstand freeze-thaw cycles freeze-thaw cycle
in cryosurgery, the process of rapid freeze and slow thaw that results in cell death. Often repeated a set number of times according to the size and nature of lesion being treated. , can be difficult to achieve. Using latex polymers with lower glass transition temperatures The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state). is an obvious route to coatings that require less coalescing coalescing (kōles´ing),
n a joining or fusing of parts. solvents and have lower VOC demands, but this seemingly simple solution also leads to many of the problems already mentioned.
Industrial maintenance painting of steel and concrete structures is still done mainly with solventborne coating technologies. It is estimated that about 80% or more of the coatings used in these applications are solventborne, with epoxies This article is about the band named the Epoxies. For the adhesive, see Epoxy.
The Epoxies are an American band from Portland, Oregon formed in 2000. Heavily influenced by punk rock and New Wave the band has described themselves as robot garage rock. , polyurethanes, and alkyds making up the bulk. (1) Only about 16% by volume of industrial painting relies on waterborne acrylic latex coatings, while architectural applications today overwhelmingly utilize latex-based coatings. However, the use of waterborne coatings for industrial maintenance has grown considerably since the 1970s, when they were virtually non-existent. Waterborne acrylics now find use in a variety of light and medium duty industrial applications. Overall, the phenomenal growth of waterborne acrylic has been driven by a number of factors, including compliance with VOC regulations, ease of clean-up, less hazardous waste Hazardous waste
Any solid, liquid, or gaseous waste materials that, if improperly managed or disposed of, may pose substantial hazards to human health and the environment. Every industrial country in the world has had problems with managing hazardous wastes. disposal and its associated costs, lower risk of health hazards health hazard Occupational safety Any agent or activity posing a potential hazard to health. Cf Physical hazard. due to exposure to solvents, less concerns with flammability flam·ma·ble
Easily ignited and capable of burning rapidly; inflammable.
[From Latin flamm and the impact on insurance costs, their one-component ease of use, and, finally, their proven performance capabilities in real world settings. (2)
As with architectural coatings, industrial maintenance (IM) coatings are coming under increasingly stringent VOC regulations in many areas of the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. and around the globe. For example, in July 2006, the South Coast Air Quality Management District The South Coast Air Quality Management District (SCAQMD), formed in 1976, is the air pollution agency responsible mainly for regulating stationary sources of air pollution for most of Los Angeles, San Bernardino, Riverside County, and all of Orange county. (SCAQMD SCAQMD South Coast Air Quality Management District
SCAQMD Southern California Air Quality Management District ) in California lowered VOC levels for industrial maintenance coatings to 100 g/L. Such regulatory pressures will continue to move IM coatings towards waterborne, high-solids solventborne, and other technologies that are able to comply with these strict limits. At the same time, end-users are unwilling to sacrifice coatings performance for these often high-performance coatings.
This article describes our efforts to find a solution to the issues of decreasing VOC limits and the continued desire for higher performing IM coatings. In particular, the development of a new waterborne acrylic binder for direct-to-metal (DTM DTM
dermatophyte test medium. ) coatings will be discussed. The new binder provides both lower VOC levels (< 100 g/L) and higher performance (e.g., gloss, durability, and corrosion resistance) than currently available binders, and is based on novel technology which leads to improved pigment distribution in both the wet paint and dry film. This new approach to making latex paints involves the formation of composite particles through the controlled adsorption adsorption, adhesion of the molecules of liquids, gases, and dissolved substances to the surfaces of solids, as opposed to absorption, in which the molecules actually enter the absorbing medium (see adhesion and cohesion). of latex particles onto the pigment surface. Evidence for the formation of the latex polymer-pigment composites is presented, as well as a description of how this new method for controlling film structure affects the properties and performance of industrial maintenance coatings.
The binder based on the new technology that is the basis for this report will be designated as EXP-1. EXP-1 is a self-crosslinking acrylic copolymer copolymer: see polymer. with a minimum film formation temperature (MFFT MFFT Minimum Film Forming Temperature (polymer temperature transition testing instrumentation) ) of 14[degrees]C, weight solids of approximately 50-51%, and pH value of 8.5 to 9.0. In most instances, a comparison is made of EXP-1 to a commercially available, conventional waterborne acrylic emulsion emulsion: see colloid.
Mixture of two or more liquids in which one is dispersed in the other as microscopic or ultramicroscopic droplets (see colloid). Emulsions are stabilized by agents (emulsifiers) that (e.g. polymer (COM-1) that is widely used in industrial maintenance finishes. COM-1 has a MFFT of 30[degrees]C and weight solids of approximately 42%, and is typically formulated at VOC levels equal to or greater than 200 g/L. The term "conventional" is meant to imply a typical acrylic latex that is stabilized via carboxylic acid carboxylic acid: see carboxyl group.
Any organic compound with the general chemical formula −COOH in which a carbon (C) atom is bonded to an oxygen (O) atom by a double bond to make a carbonyl group (−C=O; see functionality. Commercially available paints (waterborne acrylic and solventborne alkyd al·kyd
A widely used durable synthetic resin derived from glycerol and phthalic anhydride. Also called alkyd resin.
[alky(l) + (aci)d.]
Noun 1. ) were also used as controls, and were obtained from their suppliers. The commercial waterborne acrylic coatings have VOC levels of approximately 200 g/L, and the alkyd is greater than 400 g/L. Acrylic polymers were formulated into gloss DTM coatings using exterior grades of titanium dioxide. All paints were prepared from dry powder Dry Powder
A slang term for cash reserves kept on hand to cover future obligations.
For example, if a venture capitalist expects bad times in the IPO markets you might hear him say something like, "we want to keep enough dry powder around to keep funding our pigments and extenders. Latex particles were coalesced co·a·lesce
intr.v. co·a·lesced, co·a·lesc·ing, co·a·lesc·es
1. To grow together; fuse.
2. To come together so as to form one whole; unite: using Texanol[R] solvent unless noted otherwise. EXP-1 was formulated at a VOC level of 100 g/L, and COM-1 at approximately 200 g/L. Unless noted, paints were applied with a drawdown Drawdown
The peak to trough decline during a specific record period of an investment or fund. It is usually quoted as the percentage between the peak to the trough.
Notes: bar to give 3 mils (75 [micro]m) dry film thickness, and were allowed to cure at 25[degrees]C and ~55% relative humidity relative humidity
The ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage. for two weeks prior to testing.
Film gloss was measured on coatings cast onto either phosphate-treated (Bonderite 1000) cold rolled steel panels (ACT Laboratories) or chromate-treated aluminum panels (Q-Panel). Film gloss was determined in accordance with ASTM ASTM
American Society for Testing and Materials D 523. The effect of weathering on film gloss was determined artificially using a QUV QUV Relative Magnetic Bearing (radiotelegraphy) accelerated weathering cabinet set for UV-A UV-A or UVA
ultraviolet radiation with a range of 320-380 nanometres exposure, and a cycle of 8 hours light followed by 4 hours condensation. Gloss retention upon exterior exposure was measured on chromate-treated aluminum panels exposed at an eastern Pennsylvania site. Dry hiding was estimated, using ASTM D 2805, by calculating the contrast ratio from Y-reflectance measurements using a 45[degrees]/0[degrees] reflectometer re·flec·tom·e·ter
An instrument for measuring the reflectance of a surface.
Noun 1. reflectometer - a meter that measures the reflectance of a surface (BYK-Gardner).
[FIGURE 1 OMITTED]
Corrosion resistance was evaluated by salt spray exposure (ASTM B117) on 4 in. by 12 in. hot rolled steel panels cleaned by abrasive blast to an SSPC-SP 5 (white metal) condition. Panels were scribed with a single vertical scribe scribe (skrīb), Jewish scholar and teacher (called in Hebrew, Soferim) of law as based upon the Old Testament and accumulated traditions. The work of the scribes laid the basis for the Oral Law, as distinct from the Written Law of the Torah. of 50 mm in length positioned in the bottom half of the panel, and were rated for blistering blis·ter·ing
See vesiculation. , rusting, and undercutting.
Dirt pickup resistance (DPU DPU Data Processing Unit
DPU DePauw University (Indiana, USA)
DPU Democratic Pacific Union (Taiwan)
DPU DePaul University
DPU Defects Per Unit
DPU Digital Processing Unit ) was measured by applying a slurry slurry,
n a thin mixture of insoluble material floating in liquid.
solids in suspension. Used as a method of feeding pigs—slurry is pumped through fixed lines and delivered to troughs by hoses equipped with gasoline pump fittings. of brown iron oxide The material used to coat the surfaces of magnetic tapes and lower-capacity disks. to the coating surface, allowing the slurry to dry for several hours, and then washing the pigment from the surface under running water and applying light pressure with a piece of clean cheesecloth cheese·cloth
A coarse, loosely woven cotton gauze, originally used for wrapping cheese.
a light, loosely woven cotton cloth
Noun 1. . The Y-reflectance was measured before application of the slurry and after cleaning, and the ratio ([Y.sub.final]/[Y.sub.initial]) was reported as the dirt pickup resistance. DPU was measured on coatings dried for one week at 25[degrees]C and ~55% relative humidity, and on coatings exposed for one week to UV-A accelerated weathering.
The relative barrier properties of paints to electrolyte electrolyte (ĭlĕk`trəlīt'), electrical conductor in which current is carried by ions rather than by free electrons (as in a metal). diffusion were determined by measuring the change in coating resistance (Rc) during exposure to a salt solution using electrochemical electrochemical /elec·tro·chem·i·cal/ (-kem´i-k'l) pertaining to interaction or interconversion of chemical and electrical energies.
adj. impedance spectroscopy. (3) Electrochemical impedance spectra were measured on paint films applied to cold rolled steel using an EG+G Princeton Applied Research Model 273A potentiostat/galvanostat and a Schlumberger Model SI-13260 Impedance gain-phase analyzer along with platinum electrodes Electrodes
Tiny wires in adhesive pads that are applied to the body for ECG measurement.
Mentioned in: Electrocardiography . Electrical contact Noun 1. electrical contact - contact that allows current to pass from one conductor to another
tangency, contact - (electronics) a junction where things (as two electrical conductors) touch or are in physical contact; "they forget to solder the contacts" with the paint film was maintained with a 5% aqueous aqueous /aque·ous/ (a´kwe-us)
1. watery; prepared with water.
2. see under humor.
adj. NaCl solution. Coating resistance as a function of exposure time to the NaCl solution was obtained by fitting the raw impedance data to a simple model (Randles) circuit containing a parallel resistor resistor, two-terminal electric circuit component that offers opposition to an electric current. Resistors are normally designed and operated so that, with varying levels of current, variations of their resistance values are negligible (see resistance). (Rc) and capacitor (Cc).
The amount of latex adsorbed onto pigments was estimated using a centrifugation Centrifugation
A mechanical method of separating immiscible liquids or solids from liquids by the application of centrifugal force. This force can be very great, and separations which proceed slowly by gravity can be speeded up enormously in centrifugal method. Paints were first diluted in deionized water Deionized water (DI water or de-ionized water; also spelled deionised water, see spelling differences) is water that lacks ions, such as cations from sodium, calcium, iron, copper and anions such as chloride and bromide. (1 paint/2.5 water) and centrifuged at 5000 rpm for 30 min. After centrifugation, a solids measurement of the supernatant supernatant /su·per·na·tant/ (-na´tant) the liquid lying above a layer of precipitated insoluble material.
the liquid lying above a layer of precipitated insoluble material. was performed. The percentage of latex removed from the serum phase (after centrifugation) relative to the initial starting amount of latex (before centrifugation) was calculated. This percentage was taken as the amount of latex adsorbed onto the pigment. Additionally, the amount of latex adsorbed was calculated by performing a thermal gravimetric gravimetric /grav·i·met·ric/ (grav?i-me´trik) pertaining to measurement by weight; performed by weight, as a gravimetric method of drug assay.
1. measurement on the sediment after centrifugation. Both measurements were in agreement.
Film morphologies of dried paints were determined using Field Emission Scanning Electron Microscopy electron microscopy
Technique that allows examination of samples too small to be seen with a light microscope. Electron beams have much smaller wavelengths than visible light and hence higher resolving power. (FE-SEM FE-SEM Field Emission Scanning Electron Microscope ) and atomic force microscopy (AFM (Atomic Force Microscope) A device used to image materials at the atomic level. AFMs are used to solve processing and materials problems in electronics, telecom, biology and other high-tech industries. ). For FE-SEM imaging studies, Ti[O.sub.2]/latex blends were diluted and dispersed onto silicon wafers, coated with Au/Pd (~10 nm) and imaged with a JEOL JEOL Japan Electron Optics Laboratory 6700 FE-SEM. Dry films for AFM measurements were prepared by casting paints onto Mylar to give a dry film thickness of approximately 25-50 [micro]m. AFM images were collected using a Digital Instruments Nanoscope III Scanning Probe Microscope. The films were imaged by selecting small samples roughly 1/4 in. by 1/4 in. from the Mylar sheet. These samples were adhered to the sample holder with no additional sample preparation methods. The samples were imaged under ambient conditions. Three separate sections of the cast films were imaged to insure an accurate representation of the surface. The images were collected using conventional tapping mode techniques and employed a TESP TESP The Emerald Star Post (website)
TESP The Exploding Shetland Ponies (Dutch band)
TESP Tax Exempt Savings Plan (UK)
TESP Telecommunications Enterprise Strategic Program tip. The height images demonstrate the topology of the sample surface, and surface roughness (Ra) was calculated from 20 by 20 micron images using digital software.
RESULTS AND DISCUSSION
The newly developed polymer (designated as EXP-1) was designed specifically for industrial maintenance applications. In addition to the ability to be formulated into primers, topcoats, and DTM finishes with VOC levels at or below 100 g/L, the binder EXP-1 also offers new levels of performance for waterborne acrylic coatings. The improved properties include higher gloss potential, better durability and corrosion resistance, better adhesion to metal substrates, and more efficient hiding. EXP-1 also undergoes self-crosslinking after film formation via an oxidative cure mechanism, and this leads to good solvent resistance and dirt pickup resistance, and aids with the durability. Many of the property enhancements are the result of a unique proprietary chemistry built into the polymer, which causes the latex particles to associate with pigment surfaces in the wet paint. The association leads to the adsorption of latex particles onto the surface of pigment particles and the formation of latex polymer-pigment composite particles. The nature of the composite particles, and how they affect the film formation process and the various coating properties, is discussed below.
[FIGURE 2 OMITTED]
In order to make a stable waterborne latex paint, it is usually the desire of a formulator to keep all colloidal particles in the system--whether latex polymer or pigment--separated in the wet state. Pigments are dispersed under high shear during the milling or grinding process, and stabilized with surfactants and low molecular weight polymeric polymeric /poly·mer·ic/ (pol?i-mer´ik) exhibiting the characteristics of a polymer.
1. Having the properties of a polymer.
2. dispersants. Establishment of a repulsive re·pul·sive
1. Causing repugnance or aversion; disgusting. See Synonyms at offensive.
2. Tending to repel or drive off.
3. Physics Opposing in direction: a repulsive force. barrier between particles, either by electrostatic Stationary electrical charges in which no current flows. For example, laser printers and copier machines place a positive charge of the image on a drum, and negatively charged toner is attracted onto the drum. The toner is then transferred to positively charged paper and fused to the paper by heat. or steric steric /ste·ric/ (ster´ik) pertaining to the arrangement of atoms in space; pertaining to stereochemistry.
ster·ic or ster·i·cal
n. means, prevents the pigment particles from agglomerating again once the shear is removed. In a similar manner, latex polymers are stabilized during the synthetic process by use of surface charge and steric hindrance hin·drance
a. The act of hindering.
b. The condition of being hindered.
2. One that hinders; an impediment. See Synonyms at obstacle. , and remain as discrete colloidal particles for long periods of time. Conventional acrylic polymers typically receive their surface charge from neutralized neu·tral·ize
tr.v. neu·tral·ized, neu·tral·iz·ing, neu·tral·iz·es
1. To make neutral.
2. To counterbalance or counteract the effect of; render ineffective.
3. carboxylic acid groups in the polymer backbone, as well as from surfactant Surfactant Definition
Surfactant is a complex naturally occurring substance made of six lipids (fats) and four proteins that is produced in the lungs. It can also be manufactured synthetically. molecules adsorbed on the latex surface. The paint formulator takes the stable dispersions of pigment and latex polymer, and mixes them to produce a stable paint where all particles remain separated. The stability of the wet paint relies on the ability of those particles to resist coagulation coagulation (kōăg'ylā`shən), the collecting into a mass of minute particles of a solid dispersed throughout a liquid (a sol), usually followed by the precipitation or over long periods of time.
[FIGURE 3 OMITTED]
It is also well known that the quality of pigment dispersion in the dry film has a strong effect on the appearance and barrier properties of the coating. Gloss, distinctness of image, color, hiding, and corrosion resistance are important properties for industrial coatings that are dependent on how well the pigment particles are dispersed throughout the dry film. Poor pigment dispersion in the wet state will obviously lead to a less than ideal distribution in the dry state. Figure 1 shows the film formation process for a typical latex paint prepared from a conventionally stabilized latex polymer. The first image is the ideal state for a wet paint, where all pigment and polymer particles are well dispersed. After the paint is applied to the substrate and water begins to evaporate e·vap·o·rate
1. To convert or change into a vapor; volatilize.
2. To produce vapor.
3. To draw or pass off in the form of vapor.
4. , the particles come closer together, and some agglomeration ag·glom·er·a·tion
1. The act or process of gathering into a mass.
2. A confused or jumbled mass: of the pigment particles is likely to occur. In the final film, the pigment is rarely distributed ideally throughout the film. Pigment agglomerates have formed during the drying process, and some pigment particles will be protruding pro·trude
v. pro·trud·ed, pro·trud·ing, pro·trudes
To push or thrust outward.
To jut out; project. See Synonyms at bulge. from the paint surface. One method of maintaining good dispersion during the application and drying process would be to use higher levels of dispersants and surfactants. However, in many applications it is advantageous to keep the level of these additives as low as possible because they can negatively affect properties such as water and corrosion resistance. An alternative approach to obtaining a uniform dispersion of pigment particles in dried paint films is to form latex polymer-pigment composites by adsorbing latex polymer particles onto the pigment surfaces in the wet state.
The process of forming latex polymer-pigment composite particles and their effect on the film formation process is shown in Figure 2. The process starts as in the conventional case, where the fully dispersed polymer and pigment are initially mixed to form a paint. However, in the case of a latex which adsorbs onto pigments, such as polymer EXP-1, the formation of composite particles begins fairly rapidly. Depending on the nature of the pigment surface and the resin composition, latex particles associate with and form a layer surrounding the pigment particle. The adsorbed latex particles act to keep the pigment particles separate and prevent agglomeration in the wet state. In addition, after the film is applied and water begins to evaporate, the adsorbed binder acts as a spacer to maintain the pigment separation in the drying film. The result is a dry paint film where the pigment is more optimally dispersed.
[FIGURE 4 OMITTED]
Evidence of the formation of latex polymer-pigment composite particles is given in Figure 3, which shows images taken with FE-SEM of diluted latex-pigment blends using a conventionally stabilized acrylic polymer (COM-1) and the newly developed polymer EXP-1. The samples based on EXP-1 exhibit titanium dioxide (Ti[O.sub.2]) particles covered with latex particles that have associated with the pigment surface. The conventional polymer COM-1 displays little association with the Ti[O.sub.2] surface. The amount of latex adsorbed onto the pigment surface can be quantified by a centrifugation method. When tested on a simple 18 PVC PVC: see polyvinyl chloride.
in full polyvinyl chloride
Synthetic resin, an organic polymer made by treating vinyl chloride monomers with a peroxide. DTM formulation, using Ti[O.sub.2] as the only pigment, results show that EXP-1 has approximately 40% of the latex adsorbed onto the pigment. The value can vary due to changes in formulation, such as grade of Ti[O.sub.2], coalescent co·a·lesce
intr.v. co·a·lesced, co·a·lesc·ing, co·a·lesc·es
1. To grow together; fuse.
2. To come together so as to form one whole; unite: , rheology modifier (programming) modifier - An operation that alters the state of an object. Modifiers often have names that begin with "set" and corresponding selector functions whose names begin with "get". , and other additives. Among the various factors which likely affect the amount of latex adsorbed is how well the Ti[O.sub.2] is originally dispersed during the grinding process, i.e., the average particle size Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. of Ti[O.sub.2] in a particular millbase prior to composite particle formation. Based on simple geometrical considerations, the results of the centrifugation experiments imply near saturation of the available pigment surface area with adsorbed latex. Although the FE-SEM images suggest the Ti[O.sub.2] surface in that experiment is not completely saturated, the apparent disparity may have resulted from the sample preparation, where the paints were diluted and sprayed before FE-SEM imaging to ensure individual composite particles were isolated.
Based on the mechanism in Figure 2, one of the expected benefits of the composite particles is higher initial gloss. Because each pigment particle has latex polymer adsorbed on its surface, the surface of the paint film is expected to be richer in polymer than with a non-adsorbing binder. The 20[degrees]/60[degrees] gloss of 18 PVC DTM coatings based on EXP-1 and COM-1 is seen in Table 1, showing a large benefit for EXP-1. Formulations are described in Table 2. It should also be noted that the high gloss is achieved without lowering the molecular weight of the polymer, which is a route often used to yield high initial gloss with an acrylic latex. However, lowering molecular weight has other detrimental effects, such as decreasing durability and solvent-resistance properties. Evidence for a smoother, polymer-rich surface resulting from the polymer-latex composites is found in atomic force microscopy (AFM) height images of the surfaces of dry paint films, as shown in Figure 4 for 18 PVC paints based on adsorbing and non-adsorbing polymers. The AFM height images show more surface uniformity for the paint based on the adsorbing binder, which suggests a more uniform Ti[O.sub.2] distribution. The light areas of the image correspond to high points on the film. Surface roughness values (Ra) calculated from the image data were 24 and 49 nm for the coatings based on adsorbing and non-adsorbing latex polymers, respectively. Smaller Ra values imply a smoother surface, and correspond to the higher gloss observed for EXP-1.
As noted above, the formation of polymer-pigment composites gives the paint formulator the ability to achieve high gloss with a high molecular weight polymer. The high molecular weight is also expected to have a positive impact on durability, as measured by gloss retention. Gloss retention results for 18 PVC gloss DTM formulations (Table 2) based on adsorbing polymer EXP-1 and non-adsorbing polymer COM-1 are shown in Figure 5 and Table 1. The data is for paints exposed to accelerated UV-A weathering, and shows that EXP-1 has better durability compared to a commercially successful product. Figure 6 shows similar durability data comparing EXP-1, formulated into an 18 PVC DTM coating, to some commercial waterborne acrylic and solventborne alkyd DTM coatings. Again, compared to coatings that are currently used for light and medium duty maintenance applications, EXP-1 is shown to provide excellent durability under accelerated weathering conditions. Figure 7 demonstrates that the performance in actual exterior weathering is also very good compared to commercially available coatings. The data in Figure 7 compares EXP-1 to two commercial waterborne acrylic DTM coatings after 24 months of south vertical exposure at an eastern Pennsylvania site. After two years of exposure, the paint based on EXP-1 retained approximately 95% of the initial gloss, compared to 63% and 50% for the two commercial DTM coatings, respectively.
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
The weathering data suggests that the film structure resulting from adsorbing binders such as EXP-1 is a major cause of the improved durability. Certainly, the bulk monomer monomer (mŏn`əmər): see polymer.
Molecule of any of a class of mostly organic compounds that can react with other molecules of the same or other compounds to form very large molecules (polymers). composition of EXP-1 and COM-1 are different, and could account for some differences in durability. In particular, EXP-1 contains functionality that leads to crosslinking via an oxidative cure mechanism, which is known to contribute to improved durability. It is also likely that the excellent durability of EXP-1 is aided by the high polymer molecular weight. However, other studies have indicated that the benefit in durability is observed for an adsorbing binder versus a non-adsorbing binder even when the bulk monomer composition and molecular weight is nearly identical. (4) In addition, adsorbing polymers which do not contain the self-crosslinking functionality also demonstrate improved durability. This suggests it is not only the effect of high molecular weight and the self-crosslinking mechanism which leads to good durability for EXP-1. One suggestion as to how the presence of polymer-pigment composites during film formation could affect durability is depicted in Figure 8. The improved pigment dispersion in the dry film--in particular, better spacing of Ti[O.sub.2]--is the proposed reason for increased durability. Titanium dioxide plays two roles in the durability of a coating film when exposed to the elements. It is well known that the Ti[O.sub.2] acts as a catalyst for the photodegradation of polymer that is in contact with the pigment. In particular, in the presence of water, oxygen, and UV light, Ti[O.sub.2] catalyzes the formation of radical species, which then react with the polymer and lead to breakdown of the polymer backbone. However, Ti[O.sub.2] also protects the polymer underneath it in the film from photodegradation because it absorbs UV light and converts it to harmless energy (i.e., heat), thus preventing the UV light from interacting directly with the polymer backbone. When the Ti[O.sub.2] is better dispersed throughout the dry coating film, as depicted in Figure 8, it is more efficient at blocking the UV light from the underlying polymer, and thus leads to improved durability. (5)
Direct evidence for improved pigment (Ti[O.sub.2]) dispersion in the dry film comes from FE-SEM studies of cross-sections of cured coatings based on both adsorbing and non-adsorbing polymers. Figure 9 shows an FE-SEM image of a dried film consisting of two layers. The bottom layer is a coating based on an adsorbing latex polymer, and the top layer is a coating based on a conventional, non-adsorbing polymer. Both paint formulations are identical except for the polymer, and are 18 PVC gloss white DTM coatings containing Ti[O.sub.2] as the only pigment. The white spots are pigment particles, and black represents the binder. The Ti[O.sub.2] dispersion is clearly more uniform in the dry film of the adsorbing latex polymer, which is able to form polymer-pigment composites. The more even spacing Noun 1. even spacing - regularity of spacing
regularity - the quality of being characterized by a fixed principle or rate; "he was famous for the regularity of his habits" suggests that the scattering of light by Ti[O.sub.2] should be more efficient with adsorbing latex polymers such as EXP-1. Hiding measurements using contrast ratio agree with the better spacing shown by the FE-SEM images. Table 1 gives contrast ratios measured for gloss white DTM formulations based on EXP-1 and COM-1 at three different PVC levels. The contrast ratio for EXP-1 at the lowest PVC (13.6%) is still higher than the value for COM-1 at the highest PVC (18%). The difference in these PVC levels corresponds to approximately 60 lb of Ti[O.sub.2] per 100 gal of paint for the formulation evaluated. At the least, the results suggest that EXP-1 and other latex polymers which are able to form polymer-pigment composites offer the possibility to reduce Ti[O.sub.2] loadings while maintaining adequate hiding. This benefit could lead to raw material cost savings for the paint manufacturer.
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
The barrier properties of a paint film are also expected to rely on the quality of pigment dispersion. In particular, previous work has shown that corrosion resistance is affected by the level of pigment dispersion in the wet paint. (6) Electrochemical impedance spectroscopy (EIS (1) (Executive Information System) An information system that consolidates and summarizes ongoing transactions within the organization. It provides top management with all the information it requires at all times from internal and external sources. ) shows that better barrier properties are exhibited by paints prepared from latex polymers which adsorb adsorb /ad·sorb/ (ad-sorb´) to attract and retain other material on the surface; to conduct the process of adsorption.
To take up by adsorption. onto pigment surfaces. Figure 10 shows a plot of the calculated coating resistance (Rc) of paints based on adsorbing and non-adsorbing polymers as a function of exposure time to sodium chloride sodium chloride, NaCl, common salt. Properties
Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids. It forms small, transparent, colorless to white cubic crystals. solution. Paints were 18 PVC gloss white DTM formulations using Ti[O.sub.2] as the only pigment. The resistance (Rc) of the coating based on the non-adsorbing polymer dropped by approximately two orders of magnitude after about 20 min of exposure. On the other hand, the resistance of the coating based on the adsorbing binder remained high and unchanged. The results indicate adsorbing polymers, and the formation of polymer-pigment composites, lead to films that are more resistant to the penetration of electrolytes. The results are also consistent with the observation of improved pigment dispersion in the dry film, as this model would suggest that fewer pigment-pigment interfaces should exist, because each pigment surface is covered by adsorbed latex particles. The pigment-pigment interfaces would provide pathways through the film for water and other species (i.e., electrolytes).
The EIS data and model described above also correlates well with corrosion resistance as measured by salt fog exposure (ASTM B 117). (4) Figure 11 shows the appearance of steel panels, coated with 18 PVC DTM coatings based on either EXP-1 or COM-1, after 35 days of salt fog exposure. The coating based on EXP-1 offers significantly better corrosion protection, especially considering that the formulations contain only Ti[O.sub.2] and no inhibitive pigments. The performance of the coating based on COM-1 is not unexpected for a single coat of waterborne acrylic gloss DTM on blasted hot rolled steel. Although COM-1 is used successfully in industrial painting when applied in systems (e.g., primer/top-coat), this result shows the great potential for binders based on the newer technology.
One of the main features of the new polymer EXP-1 is its ability to generate polymer-pigment composite particles via adsorption onto pigment surfaces. Another feature built into the polymer is the ability to self-crosslink after film formation via an oxidative cure mechanism. (7) The crosslinking is also accelerated under exposure to UV light, which aids in generation of free radicals. As mentioned, it is thought that the self-crosslinking mechanism, which results in an increase in polymer molecular weight after film formation, is at least partially responsible for the excellent durability of EXP-1. Crosslinking also results in improvements for some other important properties, including dirt pickup resistance and solvent resistance. In particular, acceptable dirt pickup resistance can be difficult to achieve in low-VOC coatings, because the polymers are typically softer than their higher VOC analogs. The oxidative crosslinking allows coatings based on EXP-1 to have good dirt pickup resistance while also providing low VOC levels. Table 1 shows results of dirt pickup resistance tests comparing EXP-1 and COM-1 (which has a higher MFFT than EXP-1) in a gloss white DTM formulation. Initially, EXP-1 exhibits slightly lower dirt pickup resistance; however, upon curing the film under UV-A exposure, it shows improved performance to the point where it is now better than the harder binder COM-1.
[FIGURE 10 OMITTED]
[FIGURE 11 OMITTED]
Crosslinking is also expected to yield good solvent resistance properties. Table 1 shows that EXP-1 provides better solvent resistance than COM-1 after air-drying for one week, as measured by MEK Noun 1. MEK - a terrorist organization formed in the 1960s by children of Iranian merchants; sought to counter the Shah of Iran's pro-western policies of modernization and opposition to communism; following a philosophy that mixes Marxism and Islam it now attacks the double rubs required to break through the film to the substrate. In addition, on exposure to UV light, EXP-1 shows a significant increase in MEK double rubs while COM-1 remains at the same level. When drying under normal ambient conditions, the full benefits of crosslinking can usually be expected within a two to four week time period. Accelerating the oxidative cure with metal driers is also possible. Table 3 shows results of MEK double rub tests for 18 PVC DTM formulations based on EXP-1, either with or without a metal drier package. The metal drier package consisted of both cobalt and calcium driers (at approximately 0.075% active metal on polymer solids) and linoleic acid linoleic acid /lin·o·le·ic ac·id/ (lin?o-le´ik) a polyunsaturated fatty acid, occurring as a major constituent of many vegetable oils; it is used in the biosynthesis of prostaglandins and cell membranes. (at 2% on polymer solids). Without the drier package, solvent resistance builds steadily over a four week drying time to give greater than 300 double rubs for a 3 mil paint film. However, with the metal drier package, a considerable boost in performance is observed, with greater than 500 double rubs achieved in only two weeks. The use of metal driers is expected to be particularly useful in interior painting applications, where the accelerating effect of UV light will not aid crosslinking. Table 3 shows that EXP-1 (with or without driers) also provides excellent solvent resistance after short exposures to UV light in both accelerated weathering and exterior exposure.
In this article, we have described the development of a new waterborne acrylic latex polymer (EXP-1) designed for both low-VOC and high performing industrial maintenance coatings. The improved performance of EXP-1 relative to currently available binders and commercial coatings is based on the use of a novel technology which enhances the pigment distribution in both the wet paint and dry film. The formation of latex polymer-pigment composite particles in the wet state leads to better pigment dispersion in the dry film, and results in significantly improved gloss, durability, hiding, and corrosion resistance. In addition, self-crosslinking via an oxidative cure mechanism leads to improvements in dirt pickup and solvent resistance, and also contributes towards the excellent durability. Direct evidence for the formation of polymer-pigment composites and improved pigment dispersion in the dry film comes from centrifugation and microscopy (FE-SEM, AFM) techniques, and correlates with the observed properties. The technology exploited in this work represents a new method for controlling the wet paint and dry film structure of waterborne acrylic latex coatings, and the demonstrated benefits suggest potentially broad utility and value in both industrial and architectural coating applications.
The authors would like to express their appreciation to Dr. John Reffner, Dr. Robert Antrim, Mr. Pete Eastman, and Mr. George Charles Sir George Frederick Lawrence Charles (June 7 1916–June 26 2004) was a Saint Lucian politician.
After his education at Saint Mary's College, Charles went to Aruba.
There he worked for an oil company for a year and became involved in trade-union activities. of the Rohm and Haas Rohm and Haas Company (NYSE: ROH), a Philadelphia, Pennsylvania based company, manufactures miscellaneous materials. A Fortune 500 Company, Rohm and Haas employs more than 17,000 people in 27 countries. The annual sales revenue of Rohm and Haas stands at about USD 8.2 billion. Central Analytical Service group for the microscopy images and thermal gravimetric analysis gravimetric analysis
The determination of the quantities of the constituents of a compound. work; and to Ms. Judy Lamon, Ms. Janet McKenna, Mr. Scott Vandrey, and Ms. Anne Bacho for their preparation of the polymers and coatings, and for performing applications testing.
(1) "U.S Paint & Coatings Market Analysis (2000-2005)," National Paint and Coatings Association, Washington, D.C., October 2001.
(2) For example, see: (a) Flynn, R.W. and Watson, D.M., "Waterborne Acrylics," in Generic Coating Types: An Introduction to Industrial Maintenance Coating Materials coating material,
n a biologically acceptable, usually porous nonmetal applied over the surface of a metallic implant with the expectation that tissue ingrowth will occur in the pores. Often a carbon polymer or ceramic substance. , Ch. 5, Smith, L.M. (Ed.), Technology Publishing Co., Pittsburgh, PA, 1996. (b) Procopio, L.J., "Waterborne Acrylic Latex Coatings for Corrosion Protection," in Waterborne Coatings Technology, Ch. 6, Pruskowski, S.J. (Ed.), Federation of Societies for Coatings Technology, Blue Bell, PA, 2004. (c) Clement, K.A., "Development of a Waterborne Paint Specification: Louisiana's Experience," J. Protect. Coat. Lin., p. 50 (January, 1989). (d) Medford, W., "Testing Low VOC Coatings in Aggressive Environments: North Carolina's Experience," J. Protect. Coat. Lin., p. 23, (May, 1995). (e) Procopio, L.J., "Protection of an Historic Lighthouse with Waterborne Acrylic Coatings: A 20-year Case Study of the Hunting Island Lighthouse," J. Protect. Coat. Lin., p. 4 (September, 2004).
(3) (a) Loveday, D., Peterson, P., and Rodgers, B., "Evaluation of Organic Coatings with Electrochemical Impedance Spectroscopy--Part 1: Fundamentals of Electrochemical Impedance Spectroscopy," JCT JCT Junction
JCT Jerusalem College of Technology
JCT Joint Contracts Tribunal (UK build contracts governing body)
JCT Journal of Coatings Technology
JCT John Christner Trucking
JCT Journal of Curriculum Theorizing COATINGSTECH, 1, No. 8, p. 46 (2004). (b) Loveday, D., Peterson, P., and Rodgers, B., "Evaluation of Organic Coatings with Electrochemical Impedance Spectroscopy--Part 2: Application of EIS to Coatings," JCT COATINGSTECH, 1, No. 10, p. 88 (2004). (c) Loveday, D., Peterson, P., and Rodgers, B., "Evaluation of Organic Coatings with Electrochemical Impedance Spectroscopy--Part 3: Protocols for Testing Coatings with EIS," JCT COATINGSTECH, 2, No. 12, p. 22 (2005).
(4) Rosano, W.R., Bleuzen, M.N., Garzon, A., Gebhard, M.S., Larson, G.L., and Procopio, L.J., "Improved Performance of Waterborne Coatings through Polymer-Pigment Composite Particle Formation," Proc. of the 28th FATIPEC Congress, 2006.
(5) Braun, Juergen H., "Titanium Dioxide--A Review," J. COAT. TECHNOL., 69, No. 868, p. 59 (1997), and references therein.
(6) Hegedus, C.R. and Kamel, I.L., "Polymer-Filler Interaction Effects on Coating Properties," J. COAT. TECHNOL., 65, No. 822, p. 37 (1993).
(7) (a) Richey, B. and Wood, T., "Use of Ambient Temperature Outside temperature at any given altitude, preferably expressed in degrees centigrade. Crosslinking to Improve the Performance of Architectural Latexes and Enamels," JOCCA--Surf. Coat. Int., Vol. 77, No. 1, p. 26 (1994). (b) Speece, D., Monaghan, G., and Richey, B., "Acrylic Ambient Temperature Crosslinking Technology in VOC Compliant Gloss Paints," Proc. of the 2004 International Coatings Expo, Chicago, IL, October 2004.
by Leo Leo, in astronomy
Leo [Lat.,=the lion], northern constellation lying S of Ursa Major and on the ecliptic (apparent path of the sun through the heavens) between Cancer and Virgo; it is one of the constellations of the zodiac. J. Procopio, Gary R. Larson, and William J. Rosano
Rohm and Haas Company*
Presented at the Federation of Societies for Coatings Technology's 2006 FutureCoat! Conference, November 1-3, 2006, in New Orleans New Orleans (ôr`lēənz –lənz, ôrlēnz`), city (2006 pop. 187,525), coextensive with Orleans parish, SE La., between the Mississippi River and Lake Pontchartrain, 107 mi (172 km) by water from the river mouth; founded , LA.
*Spring House Technical Center, 727 Norristown Rd., Spring House, PA 19477.
Table 1 -- Comparison of Polymers EXP-1 and COM-1 in an 18 PVC Gloss White DTM Formulation Paint based on: EXP-1 COM-1 Gloss (20[degrees]/60[degrees]) Initial 64/82 14/54 After 528 hr UV-A exposure 55/83 5/34 % Gloss Retention (20[degrees]/60[degrees]) After 528 hr UV-A exposure 86%/101% 36%/63% Hiding--Contrast Ratio 18.0 PVC 0.988 0.977 15.8 PVC 0.986 0.974 13.6 PVC 0.982 0.969 Dirt pickup resistance ([Y.sub.final]/[Y.sub.initial]) 1 week dry 0.89 0.91 1 week UV-A exposure 0.99 0.92 MEK double rubs 1 week air dry 96 25 1 week UV-A exposure >500 25 Hardness Konig pendulum (sec) 11.2 16.8 Pencil 2B 4B Table 2 -- Gloss White DTM Formulations Based on Polymers EXP-1 and COM-1 Paint Based On: EXP-1 COM-1 Material Lb Gal Lb Gal Grind Water 55.00 6.59 55.00 6.59 Tamol 2001 8.75 0.99 8.75 0.99 Surfynol CT-111 2.00 0.25 2.00 0.25 Tego Foamex 8050 0.25 0.03 0.25 0.03 Ammonia (28%) 2.00 0.27 2.00 0.27 Ti-Pure R-706 210.00 6.29 210.00 6.29 Grind Sub-total 278.00 14.41 278.00 14.41 Let Down Polymer 517.00 59.72 618.00 72.19 Water 130.00 15.57 14.00 1.68 Ammonia (15%) 2.00 0.25 7.00 0.89 Tego Foamex 1488 1.00 0.12 1.00 0.12 Add grind from above Texanol 20.60 2.60 51.30 6.47 Dowanol DPM 14.00 1.76 14.00 1.76 Sodium Nitrite (15%) 9.00 0.99 9.00 0.99 Water 35.00 4.19 9.50 1.14 Acrysol RM-8W 3.00 0.35 3.00 0.35 Totals 1009.60 99.97 1004.80 100.00 PVC: 18 18 Volume Solids: 36.2% 35.8% Weight Solids 47.5% 47.2% VOC (g/L): 100 180 Table 3 -- Solvent Resistance (MEK Double Rubs) of DTM Coatings Based on Polymer EXP-1, Either With or Without Metal Drier Package Without Metal With Metal Drier Package Drier Package MEK double rubs Air dry 1 week 96 184 2 weeks 148 >500 3 weeks 222 >500 4 weeks 339 >500 UV-A exposure (after 1 week air dry) 24 hr >500 >500 Outdoor exposure (after 1 week air dry) 1 week >500 >500