Abstract... · Web viewFLEXIBLE CHROMATE-FREE AEROSPACE PRIMEr Jeannine Elliott, TDA Research, Inc....

FLEXIBLE CHROMATE-FREE AEROSPACE PRIMER

Jeannine Elliott, TDA Research, Inc.

Ronald Cook, TDA Research, Inc.

Keywords: Aerospace coating, flexible primer, chromate-free

ABSTRACT

Chromated polysulfide primers provide excellent corrosion protection for aircraft and a high degree of flexibility, which is required at seams and fasteners where there is a large amount of flexure. However, these coatings have several disadvantages. Hexavalent chromates are known carcinogens, and their use and disposal are strictly reg-ulated. Also, polysulfides are highly viscous, and the solvents used to reduce their viscosity are regulated due to their impact on air quality. An ideal flexible aircraft coating would provide elongation equal to or exceeding that of a polysulfide primer, corrosion protection without adding dichromate inhibitors, and would have a low viscosity (for spraying) without needing high levels of solvents (VOCs). New materials are required to meet these require-ments. New flexible coatings have been formulated to provide the needed balance of flexibility and chemical re-sistance in a fast drying, VOC compliant formula. An advanced non-chrome corrosion inhibitor package was also developed for this primer. The new primer system is flexible, chemically and water resistant and uses a propri -etary co-resin combined with existing commercially available epoxies and a flexible amine hardening agent. To this base formulation, is added a high-performance chromate-free corrosion inhibitor package. The flexible co-resin formulation meets the impact resistance requirements (GE reverse impact test per ASTM D2794-93) and passes the -65F mandrel bend test. The coating system has excellent resistance to hydraulic fluid. (MIL-PRF-32239A section 3.6.8, according to 4.6.16. with MIL-PRF-83282 hydraulic fluid). This primer coating is being for -mulated to meet MIL-PRF-32239A, Type 1, Class 2, Grade 1. The coating has been advanced to optimize adhe-sion, cure time and impact resistance. Results on testing to date will be presented.

INTRODUCTION

The corrosion of military equipment is a significant and ongoing problem; the annual cost to the Department of Defense in 2010 being $22.9 billion (1). For the U.S. Air Force, the annual cost of aircraft-related corrosion is esti-mated to be $5.43 billion. Metal substrates are protected from corrosive degradation by protective coatings that are designed to preserve structural integrity and provide corrosion protection in the specific environment(s) faced by each platform. Large aircraft can experience significant flexure due to wing bending, pressurization, take-offs, and landings. This means the protective coatings used near seams and fasteners need to be very flexible so that they do not crack and lose their protective function. Furthermore, these coatings must include an effective corro-sion inhibitor package to mitigate corrosion, especially as the coating ages and defects develop.

The chromated polysulfide primers (MIL-P-87112) in current use give excellent corrosion protection and provide

1

2019 Department of De-fense – Allied Nations

Technical Corrosion Con-

the high degree of coating flexibility required in areas where large flexures occur in the airframe. However, due to the high molecular weight of the resins in the commercial polysulfide coatings, they require high levels of solvents (600-700 g/L VOCs) to reduce the viscosity for spray application. The polysulfide coatings also use hexavalent chromate to protect against corrosion. Other disadvantages to the current polysulfide coatings include very slow dry times and release of high levels of VOC solvents while curing. The U.S. Air Force would also like to have a flexible coating that is even tougher and more flexible than the polysulfide coatings. The MIL-PRF-32239A Type 2, Class 2, Grade 1 specification requires that a flexible primer have high levels of elongation and corrosion protec-tion, without using either a high VOC formulation or the use of hexavalent chromates; unfortunately, there are no currently qualified non-chrome flexible primers that meet this specification. Although significant work has been carried out to develop primers with high levels of elongation and impact resistance, each has had problems meet -ing all of the MIL-PRF-32239A Type 2, Class 2, Grade 1 specifications. Some examples of the resin chemistries that have been evaluated include non-chromate modified polysulfide, polythiophenols, polythioureas, and glycidyl carbamates (2). These formulations have all fallen short in one way or another, for example by not meeting mini -mum impact resistance levels when filled, having unacceptably slow cure rates or poor weathering.

The technical approach discussed here is based on employing an epoxy based primer produced from several flexible co-resins such that the resulting formulation has a low glass transition temperature (Tg) and a high amount of flexibility. To further improve the performance of the resin package a toughening agent was added to aid en-ergy dissipation so that the resin system would pass the GE reverse impact test, even when the resin is filled with hard pigment particles (e.g., with TiO2, alumina, extender pigments, corrosion inhibitor packages, etc.). Commer-cially available resin materials were used to facilitate the rapid transition of the coating to military use. The formu-las were based on epoxy resins because they have robust properties, good adhesion, and favorable cure kinetics.

There are just a few mechanisms that largely determine the toughness of epoxy resins (3). Toughness is the abil -ity of a material to absorb energy and plastically deform without fracturing. One definition of material toughness is the amount of energy per unit volume that a material can absorb before rupturing. Toughness requires a balance of strength and flexibility. There are a number of ways to increase toughness in polymeric systems. Studies eval-uating the use of rubber additives have shown there is a significant effect of cross-link density of the epoxy resin on the efficacy of rubber additives to toughen epoxies (4). Although the effects are sensitive to many factors (na-ture of the polymer, the number of cross-links between polymer chains, etc.), the most important considerations are the size of the rubber (or thermoplastic) particles, the number of cross-links between the particles and the host matrix and the tensile strength of the additives (3).

The nature of the rubber additives themselves also plays an important role in increasing toughness (5). They en-hance shear localization by acting as stress concentrators, and then as bulk strain energy increases, cavitation takes over and dissipates the energy, making further shear localization possible. More recently, it has been shown that hyperbranched polymers behave in a similar manner, and as a result, are also effective toughening agents for epoxies (6). In work by Bradley et al. (4), the effectiveness of adding a toughening agent was found to be depen-dent on the temperature distance between the use temperature of the polymer and the Tg of the polymers. At use temperatures within 60°C above Tg, rubber toughening is inefficient because the material is already capable of crack-tip shear deformation, even without any added rubber. For a Tg that is 60°C to 150°C below (also possibly up to 200°C below) below the operating temperature, toughness enhancement monotonically increases in moder-ately cross-linked thermosetting materials from a 5-fold to a 13-fold increase. By contrast, toughness enhance-ment over the same temperature range in a heavily cross-linked material increases only 1-fold to 3-fold. At tem-peratures more than 200°C below Tg, rubber toughening becomes ineffective because of the lack of incipient toughness in the net resin system and the consequent inability of the resin to deform at the crack tip, even adja-

2



cent to cavitated rubber particles.

The above approaches were all considered in the design of a new flexible resin system. As part of the initial se -lection process, a quick method to estimate the Tg of potential resins/polymers were identified for selection of a flexible base resin. Schut et al. (7) described a semi-empirical approach for prediction of Tg values for polymers. The method is based on a mass-per-flexible-bond (M/f) principle, and the (M/f) versus Tg plots were highly linear. The predictive accuracy was found to range from ~+/- 4 to 6 K, depending on the polymer class, which was thought acceptable for screening purposes. This Tg based approach was used to select the base epoxy co-resins.

TEST METHODS

In the MIL-PRF-32239A Type 2, Class 2, Grade 1 specification, one of the physical property tests is a low-temper -ature mandrel bend test (~ -65F) Bare AA2024-O metal panels were prepared with a non-chrome surface treat-ment from Pantheon, primed with one of the new flexible resin formulations and top-coated with Mil-PRF-85285 coating. Panels were allowed to cure in ambient conditions for 14 days. Once cured, the panels were placed in an enclosed environmental chamber maintained at -60ºF (the lowest temperature our chamber could achieve) for 24 hours (Error: Reference source not found). Immediately upon removal from the environmental chamber, pan-els were bent around the 1” mandrel bend test apparatus (Error: Reference source not found), as outlined in ASTM D522 Method B. The mandrel bend test is a pass/fail test that requires that the coating not crack (as ob-served visually or when tested using a holiday detector).

3



Figure 1. Environmental Chamber Used in Testing.

Figure 2. Cylindrical Mandrel Test Apparatus.

Another flexibility test in the MIL-PRF-32239A Type 2, Class 2, Grade 1 specification is the GE reverse impact test. The mandrel bend test is a pass/fail test that requires that the coating not crack (as observed visually or when tested using a holiday detector). In the GE reverse impact test (ASTM D2794-93), the impact head with con-vex spherical segments on the head associated with 10%, 20%, 40%, and 60% elongation is dropped onto the back of the coated substrate (reverse impact) from a selected height; this is a good measure of the ability of the coating to flex or elongate without breaking when impacted. The coated side is evaluated both visually and using a pinhole detector. Error: Reference source not found shows the results of the GE reverse impact test (ASTM D2794-93) for a commonly used flexible polysulfide primer.

Impact testing of the topcoated flexible co-resin flexible primer with was done in accordance with MIL-PRF- 32239A, Section 3.6.7.1 Class 2 requirements and tested in accordance with 4.6.15.1, ASTM D2794-93 and D6905 using the GE reverse impact test method and GE impacter (Error: Reference source not found). The test uses 20 mil AA2024 O- temper test panels

Panels for mandrel bend and impact testing were prepared on 20 mil AA2024-O section pretreated with a non-chrome surface treatment from Pantheon. The flexible primers were applied to a thickness of 2-3 mils dry film

4



Figure 3. Top-coated polysulfide PPG primer with impact imprints form 36” height drop

Figure 4. Universal Impact Tester

thickness. The primer was covered within 5 hours with a MIL-PRF-85285 topcoat applied using an HVLP spray gun to 1.5-2.5 mils dry film thickness. Test panels were cured for 14 days at room temperature prior to testing.

Another key benchmark in the MIL-PRF-32239A Type 2, Class 2, Grade 1 specification for the new flexible coat-ing is chemical resistance. Hydraulic fluid testing was conducted per MIL-PRF-32239A section 3.6.8, according to 4.6.16. with MIL-PRF-83282 hydraulic fluid (Error: Reference source not found). The MIL-PRF-32239A specifica-tion calls for no blisters, delaminations, and no more than a 2-pencil change in hardness after 7 days at 150ºF in synthetic hydraulic fluid (e.g., MIL-PRF-83282).

The sample substrates for chemical resistance testing were 32 mil AA2024-T3 panels pretreated with a non-chrome surface treatment from Pantheon. The flexible primers were applied to a thickness of 2-3 mils dry film thickness. The primer was covered with a MIL-PRF-85285 topcoat applied using an HVLP spray gun to 1.5-2.5 mils dry film thickness. The topcoat is allowed to dry overnight (~18-24hr) at ambient conditions, and then the edges of the panel are dip coated (red edge coating in Error: Reference source not found) with epoxy sealing primer. This primer seals the edges of the coupon to mitigate the edge effects of solvent intrusion through the side of the panels. The edge primer is allowed to dry overnight (~18-24hr) at ambient conditions, and then the coupon is cured at 140°F overnight (~18-24hr) to complete the curing process.

Additional physical coatings tests were also run per MIL-PRF-32239A specification or ASTM standard. Pencil Hardness was measured per ASTM D3363 method B. Tape adhesion (cross-hatch) was run per ASTM D3359 method B, (per MIL-PRF-32239A Section 3.6.6.2 & 4.6.14). MEK Double Rub was conducted per MIL-PRF-32239A per Section 3.6.14 & 4.6.21). Wet Adhesion was measured per MIL-PRF-32239A Section 3.6.6.1 & 4.6.13. For these physical property tests, the coatings were applied to AA2024-T3 panels with a non-chrome sur-face pretreatment from Henkel. The primer was applied at a 3 mil dry film weight, and a MIL-PRF-85285 topcoat was applied at a dry thickness of 1.5-2.5 mil.

RESULTS AND DISCUSSION

In this section the results for mandrel bend testing, GE reverse impact testing, and coating stability to exposure to hydraulic fluid and water. Other physical property tests are also presented.

Coating Flexibility - Mandrel Bend and GE Reverse Impact Tests

To protect the metal surface, the coating must remain attached to the metal surface and must also be free of cracks/defects that allow corrosive agents (water, salts, etc.) access to the metal surface. While thicker coatings tend to provide better passive barrier properties, the energy stored in a coating by virtue of its internal strain in -creases as the coating thickness increases and, at a particular thickness, becomes sufficient to overcome the work of adhesion at the interface so that the coating spontaneously peels off. Furthermore, the Young’s modulus

5



Figure 5. Hydraulic Fluid Testing (left to right); MIL-PRF-83282 hydraulic fluid with test parts at 150ºF, preliminary test pieces after exposure

(stiffness) of a coating increases with its thickness. This can make the coating more susceptible to brittle fracture, especially at lower temperatures. In Error: Reference source not found are the results of low-temperature (-60F) mandrel bend tests.

The results in Error: Reference source not found suggest that with the new flexible co-resin formulations, a thick-ness above ~5.7 mils (primer plus topcoat) results in the failure of the coating to pass a -60F mandrel bend test. For the top three entries in Error: Reference source not found as long as the coating thickness is below 5.7 mils, the mandrel bend test is passed. The addition of up to 7.5 wt% of the toughening agent did not affect the perfor-mance on the -60F mandrel bend test. This result is consistent with the Dynamic Mechanical Analysis results (discussed below) which show that the glass transition temperature (and hence the flexibility) is not affected by the addition of the toughening agent. The toughening agent toughens the coating by energy dissipation but does not act as a plasticizing agent. In Error: Reference source not found (except for samples that are too thick, and one experiment where the epoxy to curing agent ratios was chosen to be off-stoichiometric), the performance of the materials in the -60F mandrel bend test was robust. One additional observation from Error: Reference sourcenot found is that the addition of the toughening agent, while it didn’t change the mandrel bend test performance, had a significant effect on the GE reverse impact test results. Without the toughening agent, the reverse impact test gave a 40% rating whereas with the toughening agent, at either 3.5% or 7% levels a 60% rating was achieved. Error: Reference source not found shows the test results from one of the test panels after the mandrel bend and reverse impact tests.

Dynamic Mechanical Analysis (DMA)

6



Table 1. Mandrel Bend and GE Reverse Impact Test Results

Figure 6. Flexible Coating Formulation 1168-94 (5.2 mil avg thickness (primer + topcoat), no cracking)

Dynamic mechanical analysis (DMA) is an instrumental technique used to study the rheological and mechanical properties of a sample. This technique applies an oscillating force to a sample and then measures the response of the sample to that force. For a perfectly elastic sample, the response will be perfectly in phase with the applied force. For samples that are not perfectly elastic, the response will be delayed. The delay is measured and re -ferred to as the phase angle (Error: Reference source not found). By analyzing the phase angle () and the mag-nitude of the response (amplitude) over a range of temperatures, information can be determined about the sam-ple.

The property of interest in the DMA measurements is the glass transition temperature (Tg) of the resins used to formulate the flexible coatings. This is the temperature at which a material changes from a hard glassy (brittle) state to an elastomeric (flexible) state. The working hypothesis is that a lower T g (and thus a smaller distance of the Tg from the -65F mandrel bend test temperature) will result in better performance on the low-temperature mandrel bend test. There are multiple ways to determine Tg with DMA data, and each method will give a slightly different number. For formulation purposes, an exact Tg value is not required, rather what is desired is the relative DMA Tg values that could be used as a measure of the success when adjusting the coating composition(s) to have a lower Tg and more flexibility at lower temperatures. As such, using the peak of the tan versus tempera-

ture curve is a convenient and easily visualized way to rank Tg values.

7



Figure 7. Phase angle and amplitude measurement with DMA

As a baseline material, the tan versus temperature curves for the flexible polysulfide primer was obtained. The polysulfide primer has very high flexibility, and as a consequence, it can pass a -65F mandrel bend test). Several of the new flexible resin formulations were then evaluated, including some formulations that previously failed in the impact testing and low-temperature mandrel bend tests. This provides a database of Tg results that can be combined with the pass/fail results of the mechanical tests. Error: Reference source not found shows the tan curves for the commercial polysulfide primer and several of the newly developed formulations.

The working hypothesis is to formulate flexible co-resins to maximize energy dissipation and thus promote flexibil-ity and toughness. The better a coating can dissipate applied energy (e.g., from an impact tester), the more likely it is to retain its needed properties (particularly, it will remain as an unbroken continuous film) following the impact. Some of the main factors that determine the maximum energy dissipation of a polymer are its backbone chem-istry, crosslink density and glass transition temperature (Tg). Another part of the working hypothesis is that the flexible resins alone would not meet the MIL-PRF-32239A flexible primer requirements. Thus, in addition to formu-lating the flexible co-resin components of the coating, toughening agents were also added.

With respect to Error: Reference source not found, it is clear from the tan versus temperature peaks that co-resins having a range of Tg’s and thus a range of flexibilities can be formulated. For several of the flexible resins

8



Figure 8. DMA results

in Error: Reference source not found GE reverse impact data are also available. For example, samples 91A, 91B, and 94A have average GE reverse impact values of 40%, 37%, and 50% respectively. Co-resin formulation 91A has a Tg of ~ 44C while 91B has a Tg of ~ 64.7C. The resin with the lower Tg has a higher impact strength resis-

tance. Co-resin formulation 94A is co-resin formula 91B with the addition of the toughening agent. The T g values are essentially the same, but the impact strength resistance increases from 37% for 91B to 50% for 94A showing the effect of the toughing agent to dissipate energy. This suggests the resin formulation and the toughening agent can be optimized separately to provide the desired coating properties.

Other Physical Property TestsChemical resistance properties are also very important for aerospace primers. Resistance to hydraulic fluid (per MIL-PRF-32239A section 3.6.8, according to 4.6.16) was identified as one of the more critical fluid exposure tests for evaluating candidate coating formulations.

Error: Reference source not found shows a photograph of one of the best performing flexible primer panels before and after the hydraulic fluid tests. None of the coatings had any blisters or underwent excessive softening. The pencil hardness of the flexible coatings, 9H, is significantly greater than that of the MIL-P-87112 polysulfide (plus topcoat) coating (2H) and initially exceeds the hardness of the topcoated MIL-PRF-23377 coating. In the tests, the MIL-P-87112 polysulfide coating experienced a drop of two units of pencil hardness (4H to 2H) whereas the primer plus topcoat only dropped from (9H to 8H) over the 7-day 150F test period. Four topcoated flexible primer coating exhibited hydraulic fluid resistance similar to the MIL-PRF-23377 coating system (1x pencil vs. 0x pencil hardness change, respectively). The resulting coatings did not have any blisters and did not undergo excessive softening (e.g., more than 2 pencil unit change in hardness).

Other physical property tests on the topcoated flexible primer system are shown in Table 2. Pencil hardness eval-uates the hardness and toughness of the top layer of the coatings system by scratching the coating with a probe

9



After 7 days 150F hydraulic fluid exposure

As made. No exposure

Figure 9. Flexible coating system (1168-33C + topcoat) before and after 7 days at 150°F in hydraulic fluid

(pencil lead) of known hardness. The hardness of the coating is assigned to the material designation at the point of coatings’ injury. Pencil hardness is not specified as a standalone test in the MIL-PRF-32239A but is used as a metric in the fluid resistance testing. It is included as an indication of the relative hardness of the coatings sys-tems in an unaltered state.

Table 2. Physical property testing of flexible primer and topcoat (MIL-PRF-85285) topcoat systems

Corrosion inhibitor Flexible Coating System:

Formula 1

Flexible Coating System;

Formula 2

Chromated Polysulfide

Pencil Hardness (ASTM 3359 method B)

8H 9H-8H <2H

Tape adhesion (cross hatch) ASTM 3359 method B, (per MIL-PRF-32239A Section 3.6.6.2 &

4.6.14)

4B 4B 4B

MEK Double Rub (MIL-PRF-32239A per Section 3.6.14 &

4.6.21)

Pass Pass Pass

Wet Adhesion (per MIL-PRF-32239A Section 3.6.6.1 & 4.6.13)

4A 5A 4A

VOC level per ASTM D6886 <200 g/L <200 g/L ~700 g/L

Adhesion of the coating system to the substrate was assessed by two methods, tape adhesion, and wet adhesion. They are similar to each other, in that both incorporate the mechanical cutting of the coating and then assessing the coating adhesion to the substrate via the removal of tape pull off. The cross-hatch tape adhesion uses a cross-hatch pattern cut into the coating system down to the substrate. The wet tape adhesion calls for an “X” shape cut to be made in the coating to the substrate. The adhesion is determined by applying tape to the coating surface, ensuring intimate contact with a known force application, and then removing the tape. The ASTM method allows for the interpretation of coating lifted (sticking to the tape) and assigns a rating to the adhesion of the coating. The MEK double rub is a measurement of the solvent resistance of the coating system. A cloth wet with MEK is rubbed across the top surface of the coating in a defined number of strokes (25 “back and forth”), and the resulting surface is reviewed for dissolution of the topcoat. If evidence of primer is detected, the system fails. The dry time is a measurement of the time needed for the primer to cure enough to support the addition of the topcoat. The MIL-PRF-32239A calls for a dry to touch (whereby the topcoat can be applied) time of 5 hours for the primer. VOC calculations were done using the “VOC calculator, via ASTM D6886”.

Drying time as specified in MIL-PRF-32239A section 3.5.4 specifies that “Coatings system components desig-nated as primers shall be dry to topcoat within five hours.” A dry time determination was done on one of the best flexible primer formulations. Two samples were made, one unmodified and another modified with a small amount (< 1.2% of total resin, epoxy + curing agent) of a commercially available catalyst for the dry time measurements. The samples were applied to AA2024-T3 panels that had a non-chrome pretreatment product from Pantheon that was applied by brush application and cured at 75°F at 50% RH. The catalyzed sample was dry to topcoat in four hours, and even the uncatalyzed sample was dry to topcoat within five hours.

10



The best-performing coatings had excellent performance on all the screening tests. These results are encourag-ing since the coating film formation has not been fully optimized. Corrosion testing is ongoing and will be reported in a future paper. The in-house developed chromate-free corrosion system has previously demonstrated excel-lent corrosion in other MIL-SPEC coatings over AA2024 and AA7075 materials (Error: Reference source notfound).

SUMMARY

New flexible epoxy co-resin formulations that meet the impact resistance requirements (GE reverse impact test per ASTM D2795) and pass a -60 °F mandrel bend test have been developed. The new flexible primer plus top-coat system also has excellent resistance to hydraulic fluid. Furthermore, coatings pass most of the requirements in the MIL-PRF-32239A Type 2, Class 2, Grade 1 specification including dry times and low VOC levels.

AcknowledgmentsThe work by is supported by Air Force SBIR Contract # FA8650-17-C-5071 (TPOC Michael Spicer at WPAFB).

REFERENCES

1. Herzberg, Eric. (2010) Cost of Corrosion to DoD, LMI Study, Maintenance Sym. Nov 15, 2010

2. Harkal, Umesh, Muehlberg, A.J., Webster, D.C. UV curable glycidyl carbamate based resins, Prog. Org. Coat-ings 73 (1), 19, (2012)

3. Riew, C. K, and Anthony J. Kinloch. "Toughened Plastics 1: Science and Engineering." (1993).

4. Bradley, WL, et al., The synergistic effect of cross-link density and rubber additions on the fracture toughness of polymers (No. CONF-900802). ACS, Washington, DC. (1993).

5. Yee, A. F., & Pearson, R. A. Toughening mechanisms in elastomer-modified epoxies. Journal of materials sci-ence, 21(7), 2462-2474, (1986).

6. Flores, M., Fernández-Francos, X., Ferrando, F., Ramis, X., & Serra, À. Efficient impact resistance improve-ment of epoxy/anhydride thermosets by adding hyperbranched polyesters partially modified with undecenoyl chains. Polymer, 53(23), 5232-5241(2012).

7. Schut, J., Bolikal, D., Khan, I. J., Pesnell, A., Rege, A., Rojas, R. and Kohn, J. Glass transition temperature prediction of polymers through the mass-per-flexible-bond principle. Polymer, 48(20), 6115-6124, (2007).

11



12



MIL-PRF-27725 type I fuel tank coating

New Chromate-free fuel tank coating

No inhibitor coating

With Chromate Conversion Coating Pretreatment

MIL-PRF-27725 type I fuel tank coating

TDA Chromate-free fuel tank coating

No inhibitor coating

With Chrome-free Pretreatment

Figure 10. TDA Chromate-free Coating [center] compared to chro-mated MIL-PRF-2775 type I fuel tank [left] coating and blank (no in-

hibitor coating) [right] after 2000 ASTM B117 on both chromate con-version coating [Top] and chromate-free surface treatment [Bottom]

Abstract... · Web viewFLEXIBLE CHROMATE-FREE AEROSPACE PRIMEr Jeannine Elliott, TDA Research, Inc....

Documents

Transcript of Abstract... · Web viewFLEXIBLE CHROMATE-FREE AEROSPACE PRIMEr Jeannine Elliott, TDA Research, Inc....