Room temperature cure antimicrobial coating that demonstrates a balance of properties includes low dissolution and good cohesion and adhesion

Room temperature cure, antimicrobial coatings that demonstrate a balance of properties including low dissolution and good cohesion and adhesion are provided. Such coatings generally exhibit a greater zone of microbial inhibition, greater cohesion and a greater degree of adhesion to target surfaces when compared to high temperature cure, antimicrobial, hydrophilic coatings.

FIELD OF THE INVENTION
 The present invention relates in general to antimicrobial coatings and,
 more particularly, to room temperature cure, antimicrobial coatings that
 demonstrate a balance of properties including low dissolution and good
 cohesion and adhesion.
 BACKGROUND OF THE INVENTION
 Antimicrobial coatings can be used in a variety of space life support and
 commercial applications where control of microbial growth is of particular
 concern.
 High temperature cure, hydrophilic (optionally antimicrobial) coatings that
 rely upon an inorganic compound, such as silica, to provide hydrophilic
 characteristics to the coating, are known.
 U.S. Pat. No. 5,562,949 to Steele et al. discloses an optionally
 antimicrobial, hydrophilic, high temperature cure coating composition that
 contains from about 10% to about 20 wt. % of an inorganic compound (e.g.,
 silica, calc ium silicate or mixtures thereof). This reference teaches
 that complete curing of the coating occurs at temperatures up to and
 including 260.degree. C.
 U.S. Pat. No. 5,305,827 to Steele et al. discloses an antimicrobial,
 hydrophilic coating that comprises an adhesive agent (e.g., potassium
 silicate); an insolubilizer (e.g., zinc oxide); an inorganic compound
 (e.g., silica, calcium silicate, and mixtures thereof); and from about 0.1
 wt. % to about 1.0 wt. % of silver oxide. The coating of U.S. Pat. No.
 '827 is cured at a temperature of 5000.degree. F. (260.degree. C.) either
 sequentially or very slowly over a period of from 1 to 6 hours (see Col.
 5, lines 62-65 of U.S. Pat. No. '827).
 U.S. Pat. No. 5,264,250 to Steele et al. discloses a method for coating
 heat transfer surfaces of a condensing heat exchanger with the
 above-referenced antimicrobial, hydrophilic coating. Again, this reference
 teaches a cure temperature of 500.degree. F. (260.degree. C.).
 As will be readily evident to those skilled in the art, such high
 temperature cure coatings are not applicable to, nor can such coatings be
 applied in close proximity to, heat sensitive materials. Further, the need
 to cure coatings at high temperatures complicates the coating process by
 increasing the processing time and the complexity of the equipment
 associated therewith.
 It is therefore an object of the present invention to provide a room
 temperature cure, antimicrobial coating.
 It is a more particular object to provide a room temperature cure,
 antimicrobial coating that demonstrates a balance of properties including
 low dissolution and good cohesion and adhesion.
 It is yet a more particular object to provide a room temperature cure,
 antimicrobial coating that demonstrates a greater zone of microbial
 inhibition, greater cohesion and a greater degree of adhesion to target
 surfaces when compared to high temperature cure, antimicrobial,
 hydrophilic coatings.
 It is a further object to provide an air handling or water processing
 system or subsystem having chronically moist or wet surfaces that have
 been coated with such a room temperature cure, antimicrobial coating.
 SUMMARY OF THE INVENTION
 The present invention therefore provides a room temperature cure,
 antimicrobial coating. The coating, in the form of a slurry, comprises:
 a. from about 1.0% to about 3.6% by weight of an antimicrobial agent;
 b. from about 22.6% to about 33.8% by weight of an adhesive agent;
 c. from about 12.8% to about 18.7% by weight of an insolubilizer for
 insolubilizing the adhesive agent; and
 d. from about 47.4% to about 60.3% by weight of water or a water-based
 solvent,
 where the sum of the components is 100% by weight, based upon the total
 weight of the slurry.
 The present invention also provides an air handling or water processing
 system or subsystem having chronically moist or wet surfaces that have
 been coated with the room temperature cure, antimicrobial coating
 described hereinabove.
 The foregoing and other features and advantages of the present invention
 will become more apparent from the following description.
 DETAILED DESCRIPTION OF THE INVENTION
 Although the present inventive room temperature cure, antimicrobial coating
 will be described herein in reference to air handling or water processing
 systems or subsystems (e.g., air conditioner cooling coils) it is not so
 limited. This coating can be utilized on any surface where control of
 microbial growth is of particular concern. In particular, any chronically
 moist or wet substrate, the functionality of which can be disrupted by
 biogrowth, represents a potential application area for the present
 inventive coating. In addition, any chronically moist or wet system or
 subsystem that can shed microbes into an effluent air or water stream and
 potentially adversely effect occupant health represents another potential
 application area for this coating.
 The antimicrobial agent of the present invention provides biocidal
 characteristics to the coating. In order to prevent microbial
 proliferation, the antimicrobial agent is preferably a substance which
 slowly dissolves into a condensate and inhibits microbial growth. For
 example, if silver oxide is utilized as the antimicrobial agent, it slowly
 dissolves into the condensate in the form of silver ions. The silver ions
 diffuse through the cell walls of the microbe, and complex with the
 cellular DNA therein. This complex formation interrupts the normal role of
 DNA and thus prevents reproduction of the microbe. Conventional biocides
 which have an equilibrium dissolution rate similar to that of the adhesive
 agent and the insolubilizer described below can be employed. If the
 antimicrobial agent dissolves into the condensate at a faster rate than
 the adhesive agent and/or insolubilizer, the effectiveness of the
 antimicrobial agent can be reduced.
 Possible antimicrobial agents include salts such as arsenic salts, iodine
 salts, iron salts, mercury salts, silver salts, tin salts, and mixtures
 therein)f, with mercury salts and silver salts preferred. Silver salts are
 especially preferred. A silver salt which has proven particularly useful
 as an antimicrobial agent having an appropriate equilibrium dissolution
 rate is silver oxide, which can be purchased from Mallinckrodt Co., Paris,
 Ky., in a purified powder form.
 The preferred concentration of the antimicrobial agent, based upon the
 total weight of the slurry of the present invention, is from about 1.0% to
 about 3.6% by weight, with the more preferred concentration being from
 about 3.0% to about 3.6% by weight.
 It is noted herein that an absence of any detrimental effect on the
 desirable properties of the coating (e.g., adhesion, cohesion) when using
 such increased quantities of an antimicrobial agent is both unexpected and
 surprising. Prior studies have indicated that an increase in the
 concentration of silver oxide to the levels indicated above will result in
 a corresponding drop off in the adhesion and cohesion properties of the
 resulting coating.
 The antimicrobial agent preferably has an average particle size of from
 about 6 to about 14 microns, with about 8 to about 10 microns especially
 preferred. Particle sizes in this range contribute to desirable
 dissolution properties, increase the slurry life, components do not
 separate out as quickly, and the slurry is easier to mix.
 The adhesive agent and insolubilizer used in the present inventive coating
 collectively provide structural integrity to the coating by binding it
 together and by preventing flaking and cracking. The adhesive agent and
 insolubilizer also serve to effect good adherence to and uniformity of
 coverage of the coating on target surfaces.
 The increased cohesion/adhesion demonstrated by the present inventive
 coating, that is cured at room temperature, is surprising and unexpected.
 As is well known to those skilled in the art, curing is a process by which
 a network of cross-links is introduced into a material. As curing
 temperatures are increased, the expectation is that the level of
 cross-linking, not only within the material but also between the material
 and the surface it coats, will increase as well, thereby producing a
 stronger, tougher and more adherent material. As curing temperatures are
 decreased, the expectation is that the level of cross-linking will
 decrease thereby resulting in a weaker, less adherent material.
 Typically, the adhesive agent is potassium silicate, lead borosilicate
 glass frit, or mixtures thereof. One such adhesive agent is Kasils.RTM.
 #1, produced by Philadelphia Quartz Co., Philadelphia, Pa. Kasil.RTM. #1
 contains 20.8% by weight silica, 8.3% by weight potassium oxide, balance
 water (i.e., 3.92 SiO.sub.2 :K.sub.2 O molar ratio). The preferred
 concentration of adhesive agent, based upon the total weight of the
 slurry, in the present invention, is from about 22.6% to about 33.8% by
 weight and the more preferred concentration is from about 22.6% to about
 32.6% by weight.
 During preparation of the present inventive coating, the adhesive agent is
 generally in the form of a water soluble material. As a result, coating
 preparation requires conversion of the adhesive agent from a water soluble
 material to a water insoluble material with an insolubilizer which does
 not adversely effect the coating. As with the antimicrobial agent, the
 insolubilizer preferably has an average particle size of from about 6 to
 about 14 microns, with about 8 to about 10 microns especially preferred
 due to improved slurry life and simplified slurry preparation.
 Possible insolubilizers include silicofluorides (SiF.sub.6) of sodium,
 potassium, barium, manganese and mixtures thereof, and inorganic oxides
 such as zinc oxide, among others. One such inorganic oxide is Kadox.RTM.
 15, 99% pure zinc oxide, produced by New Jersey Zinc Co., Ogdensborg, N.J.
 Particularly with the silicofluoride insolubilizers, sodium hydroxide can
 be used as a colloidal dispersant. The preferred concentration of
 insolubilizer, based upon the total weight of the slurry, of the present
 invention is from about 12.8% to about 18.7% by weight and the more
 preferred concentration is from about 12.8% to about 14.8% by weight.
 Typically, during preparation of the present inventive coating, the
 antimicrobial agent is combined with the adhesive agent and insolubilizer
 in a solvent that does not adversely effect the final coating, to form a
 slurry. This solvent is typically water or a water-based solvent. The
 solvent concentration generally ranges from about 47.4% to about 60.3% by
 weight with between about 50.3% to about 60.3% by weight preferred, based
 upon the total weight of the slurry.
 In accordance with the above, the preferred room temperature cure,
 antimicrobial coating, in slurry form, of the present invention comprises:
 a. from about 1.0% to about 3.6% by weight, of an antimicrobial agent;
 b. from about 22.6% to about 33.8% by weight, preferably from about 22.6%
 to about 32.6% by weight, of an adhesive agent;
 c. from about 12.8% to about 18.7% by weight, preferably from about 12.8%
 to about 14.8% by weight, of an insolubilizer for insolubilizing the
 adhesive agent; and
 d. from about 47.4% to about 60.3% by weight, preferably from about 50.3%
 to about 60.3% by weight, of water or a water-based solvent,
 where the sum of the components is 100% by weight, based upon the total
 eight of the slurry.
 In the most preferred embodiment, the room temperature cure, antimicrobial
 coating, in slurry form, of the present invention comprises:
 a. from about 3.0% to about 3.6% by weight of an antimicrobial agent;
 b. from about 22.6% to about 32.6% by weight of an adhesive agent;
 c. from about 12.8% to about 14.8% by weight of an insolubilizer for
 insolubilizing the adhesive agent; and
 d. from about 50.3% to about 60.3% by weight of water or a water-based
 solvent,
 where the sum of the components is 100% by weight, based upon the total
 weight of the slurry.
 The room temperature cure, antimicrobial coating of the present invention
 may contain other components including stabilizers, corrosion inhibitors,
 antifungal agents, etc. provided any such component does not serve to
 adversely effect the desirable properties of the coating. For example,
 silicone stabilizers that would allow a SiO.sub.2 :K.sub.2 O molar ratio
 shift from 3.92 to 5.0 may be employed.
 In preparing the present inventive coating, the slurry components are mixed
 until essentially homogenous and then utilized before the components
 aggregate or agglomerate and settle creating component rich and component
 d,void areas in the coating. The time period during which the present
 inventive coating, in the form of a slurry, may be applied is
 approximately 30 minutes. Thereafter, reagitation would be required.
 Application of the coating, in the form of a slurry, to any surface can be
 accomplished in various manners, all of which are conventional. These
 conventional processes include dipping, spraying, and painting the
 surfaces with the slurry, flowing the slurry through any inner surfaces
 and allowing it to remain a sufficient period of time to coat the inner
 surfaces, and other common coating techniques.
 For coatings on inner surfaces formed by the flow through method, the
 coating density preferably ranges from about 0.006 to 0.009 grams/square
 centimeter (g/cm.sup.2) while the coating thickness preferably ranges from
 about 25 to 102 microns.
 Once the coating has been applied it must be dried and cured. Ultimately,
 complete removal of the water or water-based solvent is desired. Various
 manners of accomplishing water or water-based solvent removal include the
 use of a vacuum and/or flowing dry air over the coating. The present
 inventive coating is then cured at room temperature at preferably 30 to
 70% humidity for from about 2 to about 4 hours.

The present invention is described in more detail with reference to the
 following Examples which are for purposes of illustration only and are not
 to be understood as indicating or implying any limitations on the broad
 invention described herein.
 WORKING EXAMPLES
 Components Used
 In the Working Examples set forth below, the following components were
 used:
 ANTIMICROBIAL AGENT: 99.0% pure powdered silver oxide (avg. particle size=3
 microns), as ailable from Mallinckrodt Co., Paris, Ky., under the product
 designation Purified Silver Oxide Powder.
 ADHESIVE AGENT: a mixture of 20.8% by weight silica, 8.3% by weight
 potassium oxide, balance water, available from Philadelphia Quartz Co.,
 Philadelphia, Pa., under the product designation Kasilt.RTM. #1 (3.92
 SiO.sub.2 :K.sub.2 O molar ratio).
 INSOLUBILIZER: 99% pure zinc oxide available from New Jersey Zinc Co.,
 Ogdensbo, N.J., under the product designation Kadoxg) 911.
 WATER: distilled water.
 SILICA: a colloidal silica product available from Nyacol Products, Inc.,
 Megunco Road, P.O. Box 349, Ashland, Mass. 01721, under the product
 designation NYACOL 2050.
 INORGANIC COMPOUND: silica flour grade A-45 amorphous, available from
 Illinois Mineral Co., Cairo, Ill., under the product designation Silica
 Amorphous Grade 1160.
 Sample Preparation
 1. Coating Preparation.
 Eight different coating formulations were prepared. In particular, the
 coating components identified above were mixed in the following
 proportions at 25.degree. C. for 30 .+-. 5 seconds in a Waring.RTM.
 commercial blender (Model No. 31BL91) that was positioned on a
 Corning.RTM. stir hot plate (Model No. PC520).

Coating Formulation
 Components
 (% by wt.) PA V1 V2 V3 V4 V5 V6 V7
 ANTI- 1.1 1.3 1.1 3.1 1.0 2.8 3.3 1.1
 MICROBlAL
 AGENT
 ADHESIVE 27.7 28.3 26.7 26.2 33.8 33.2 27.6 27.4
 AGENT
 INSOLU- 6.0 14.1 18.7 18.3 16.9 16.6 13.8 13.7
 BILIZER
 WATER 49.7 56.5 53.5 52.4 48.3 47.4 55.3 54.8
 SILICA -- -- -- -- -- -- -- 3.1
 INORGANIC 15.5 -- -- -- -- -- -- --
 COMPOUND
 Coating formulation "PA", as identified above, is the same formulation that
 is disclosed and claimed in U.S. Pat. No. 5,562,949 to Steele et al.
 Coating formulations "V1" through "V7" constitute the present inventive
 antimicrobial coating. For each formulation, the ADHESIVE AGENT was added
 to the WATER first, followed by the addition of the INSOLUBILIZER and in
 formulations "PA" and "V7", also by the INORGANIC. COMPOUND and SILICA,
 respectively. The ANTIMICROBIAL AGENT was added to the formulation after
 the addition of the INSOLUBILIZER and before mixing.
 2. Test Sample Preparation.
 Nine (9) test items manufactured from 347 stainless steel heat exchanger
 finstock samples and measuring 5.1 cm.times.5.1 cm.times.0.08 cm and
 eighteen (18) test panels also manufactured from 347 stainless steel
 panels and measuring 5.1 cm.times.5.1 cm.times.0.16 cm were weighed and
 then each set of two (2) samples coated with different coating
 formulations. The test samples were coated by dipping the samples for 30
 .+-.5 seconds into the coating formulation and repeating the dipping
 procedure 3 times until a uniform coat resulted. The coating formulations
 were used to coat the test samples within 30 minutes of mixing. Excess
 coating was removed from each sample by dabbing the bottom of each test
 sample on a clean paper towel.
 The test samples coated with coating formulations "V1" through "V7" were
 then dried or cured at room temperature at 30 to 70% humidity for two (2)
 hours. The test samples were then re-weighed and the coating weight
 determined by subtracting the weight of the coated sample from the weight
 of the sample prior to coating.
 The test samples coated with coating formulation "PA" were packaged in a
 closed container and dried or cured at room temperature at 100% humidity
 for 16 hours. The samples were then placed in a convection oven and cured
 according to the following schedule:
 0.5 hours.+-.5 minutes at 82.+-.5.degree. C.;
 1.0 hours.+-.5 minutes at 93.+-.5.degree. C.;
 0.5 hours.+-.5 minutes at 104.+-.5.degree. C.;
 0.5 hours.+-.5 minutes at 121.+-.5.degree. C.;
 1.0 hours.+-.5 minutes at 149.+-.5.degree. C.; and then
 2.0 hours.+-.5 minutes at 260.+-.5.degree. C.
 The test samples were then allowed to cool to 25 .degree. C. and weighed.
 The coating weights of the samples coated with formulation "PA" were then
 calculated as described above.
 Two separate trials were conducted. The first trial involved test samples
 coated with coating formulations "V1" and "PA" while the second trial
 involved test samples coated with coating formulations "V2" through "V7"
 and "PA". For ease of reference, these trials are reported concurrently.
 It is further noted that additional test panels coated with formulation
 "PA" were also prepared. These coated panels were not subjected to the
 high temperature cure schedule described above. Instead, these panels were
 cured at room temperature (i.e., 25.degree. C.) for 16 hours at 30 to 70%
 humidity. A simple water soak test showed that the coating on these test
 panels exhibited a drastic dissolution rate.
 Test Methods
 ANTIMICROBIAL CHARACTER: one test sample from each set of coated finstock
 samples was packaged in a polyethylene cup and labeled as "fresh-no soak"
 while the other test samples from each set were subjected to a vigorous 3
 day submerged/agitation cycle, in deionized water by submerging the
 samples in deionized water contained in glass beakers positioned on stir
 plates. Each beaker was provided with a stir bar that was activated by the
 stir plate and that served to effect constant agitation of the water
 surrounding each test sample during this 3 day period. The test samples
 were then subjected to Zone of Inhibition testing as per the Kirby Bauer
 Standard Assessment of Antimicrobial Effectiveness, with the challenge
 microorganisms being Pseudomonas cepacia and Pseudomonas aeruginosa.
 Results are reported in millimeters (mm).
 DISSOLUTION PROPERTIES: Nine (9) sets of coated test panels were separately
 stored submerged in 140 ml. of deionized water in glass containers at room
 temperature. After designated time periods, all of the deionized water was
 removed from each container and tested for pH, conductivity and for ionic:
 silver, silicon, potassium and zinc, while each tared panel was dried with
 isopropyl alcohol and dry filtered nitrogen and then weighed for the
 purpose of determining % weight loss. Each tared panel was then placed in
 a fresh container and a new charge of 140 ml of fresh deionized water
 added thereto. Water was not agitated when the panels were submerged. The
 panels were stored submerged for additional designated time periods with
 the above-referenced procedure being repeated at the end of each period.
 Results are reported in .mu.ohms (conductivity), ppm (chemical constituent
 concentrations) and % weight loss.
 ADHESION CHECK (% Wt. Loss): Nine (9) sets of coated test panels were
 weighed prior to coating to .+-.0.0001 g (X). One test panel from each set
 was reweighed after coating and curing (Y). The other test panels from
 each set were separately stored submerged in 140 ml. of deionized water in
 glass containers at room temperature. After 8 days, the panels were
 removed from each container, dried with isopropyl alcohol and dry filtered
 nitrogen and then reweighed (Y). A length of 0.5 inch wide tape (Scotch
 Brand Magic Tape, 3M Catalog Number 102) was then applied to the entire
 length of each test panel using normal finger pressure. The tape remained
 on each panel for 60 seconds and was then removed by pulling one end at
 approximately a 90.degree. angle to the panel. Each panel was then
 reweighed to.+-.0.0001 g (Z). The present weight loss was calculated by
 the following formula: % weight loss=((Y-Z)/(Y-X)).times.100. The
 previously submerged test panels were then returned to their separate
 containers, stored submerged for additional designated time periods with
 the above-referenced procedure being repeated at the end of each period.
 Examples 1 to 7 and C1 to C2
 In these examples, test items coated with the coating formulations
 designated below were tested for antimicrobial character in accordance
 with the above-referenced test method. The results are set forth in Table
 I hereinbelow.
 TABLE I
 SUMMARY OF EXAMPLES 1 TO 7 AND C1 TO C2
 Example 1 C1 2 3 4 5 6 7 C2
 Coating Formulation V1 PA V2 V3 V4 V5 V6 V7 PA
 Zone of Inhibition
 (mm)
 no immersion 3 3 3 4 5-8 5 5 3 3
 3-day immersion 3 3 4 4 4 3-5 4-7 3-4 3
 Examples 1 to 7 and C1 to C2 generally demonstrate that the present
 inventive room temperature cure, antimicrobial coating displays
 comparable, if not improved, antimicrobial character in both the fresh and
 artificially weathered state, when compared to prior art high temperature
 cure, antimicrobial coatings. Of particular note are Examples 3 to 6 which
 exhibit significantly improved antimicrobial character.
 Examples 8 to 29 and C3 to C9
 In these examples, the dissolution properties of test panels coated with
 the designated coating formulations were evaluated. In particular, in
 Examples 8 to 14 and C3 and C4 dissolution properties were evaluated by
 determining the conductivity of the water used to store the individual
 panels in accordance with the above-referenced test method. The results
 are set forth in Table IIA hereinbelow.
 TABLE IIA
 SUMMARY OF EXAMPLES 8 TO 14 AND C3 TO C4
 Example 8 C3 9 10 11 12 13 14
 C4
 Coating V1 PA V2 V3 V4 Y5 V6 V7
 PA
 Formulation
 Conductivity
 (.mu.ohm)
 0.3 days 141.5 99.1 213.0 199.7 273.0 221.0 176.0 146.0
 89.0
 3 days 15.5 8.5 28.0 31.4 32.5 37.4 32.0 21.4
 10.5
 4 days 4.8 3.7 9.6 15.3 9.8 17.6 15.3 5.0
 3.3
 5 days 2.9 2.6 5.4 13.7 6.1 15.7 15.2 3.2.
 2.3
 6 days 2.4 1.7 4.5 15.2 4.7 15.4 15.0 3.3
 2.6
 7 days 1.7 1.5 -- -- -- -- -- -- --
 10 days 4.0 3.2 -- -- -- -- -- -- --
 11 days 2.3 2.1 -- -- -- -- -- -- --
 12 days 2.3 2.3 -- -- -- -- -- -- --
 13 days 3.3 4.4 -- -- -- -- -- -- --
 Examples 15 to 21 and C5 to C6
 In these examples, the % weight loss (as a function of days submerged in
 140 ml. of deionized water) of the coated test panels used in the
 above-referenced conductivity testing was determined. The results are set
 forth in Table IIB hereinbelow.
 TABLE IIB
 SUMMARY OF EXAMPLES 15 TO 21 AND C5 TO C6
 Example 15 C5 9 17 18 19 20 21
 C6
 Coating V1 PA V2 V3 V4 Y5 V6 V7
 PA
 Formulation
 % Weight Loss
 0.3 days 23.1 9.4 18.6 18.7 19.7 22.4 21.8 25.3
 10.0
 3 days 13.9 3.5 11.1 12.2 12.5 15.0 15.8 19.7
 3.2
 4 days 3.5 1.4 15.0 4.6 4.1 5.8 4.2 5.4
 1.6
 5 days 3.1 -- -- 3.5 5.1 4.5 4.0 3.3 0.6
 6 days 3.9 4.5 2.7 3.1 3.8 4.2 4.2 3.2
 1.8
 7 days 0.9 -- -- -- -- -- -- -- --
 10 days 1.5 1.3 -- -- -- -- -- -- --
 11 days 1.5 1.5 -- -- -- -- -- -- --
 12 days 0.2 0.l -- -- -- -- -- -- --
 Examples 22 to 28 and C7 to C8
 In these examples, the water used to submerge the test panels used in the
 above-referenced conductivity testing was tested for ionic silver. The
 results are listed in Table IIC.
 TABLE IIC
 SUMMARY OF EXAMPLES 22 TO 28 AND C7 TO C8
 Example 22 C7 23 24 25 26 27 28
 C8
 Coating V1 PA V2 V3 V4 Y5 V6 V7
 PA
 Formulation
 Silver (Ag)
 Concentration
 (ppm)
 0.3 days 3.1 0.9 5.0 6.9 4.2 4.5 5.1 4.8
 0.9
 3 days 4.5 1.5 13.2 0.1 1.6 8.4 0.6 0.7
 0.5
 4 days 3.2 1.3 9.5 1.6 1.3 1.6 0.6 1.2
 0.6
 5 days 0.9 0.3 -- -- -- -- -- -- --
 6 days 1.1 0.7 -- -- -- -- -- -- --
 7 days 0.4 0.3 -- -- -- -- -- -- --
 Examples 29 and C9
 In these examples, the water used to submerge the test panels used in the
 conductivity testing was tested for pH, ionic silicon, potassium, and
 zinc. The results are listed in Table IID.
 TABLE IID
 SUMMARY OF EXAMPLE 29 AND C9
 Example 29 C9
 Coating Formulation V1 PA
 pH
 0.3 days 9.47 9.44
 3 days 8.06 8.17
 4 days 6.81 6.95
 Silicon (S) Concentration
 (ppm)
 0.3 days 8.6 5.9
 3 days 10.3 2.3
 4 days 2.7 1.0
 Potassium (K) Concentration
 (ppm)
 0.3 days 26.0 28.0
 3 days 4.8 4.1
 4 days &lt;0.1 1.4
 Zinc (Zn) Concentration (ppm)
 0.3 days 1.0 0.3
 3 days 1.7 0.6
 4 days 0.9 0.5
 Examples 8 to 29 generally show a greater degree of initial dissolution
 when compared to Comparative Examples C3 to C9. After 3 days, Examples 8
 and C3, 15 and C5, 22 and C7 and 29 and C9 of the first trial, typically
 demonstrated a significant reduction in dissolution. After 7 days,
 comparable dissolution rates were obtained for Examples 8 and C3 and 15
 and C5.
 Examples 30 to 36 and C10 to C11
 In these examples, coated test panels were tested for adhesion properties.
 The results are set forth in Table III hereinbelow.
 TABLE III
 SUMMARY OF EXAMPLES 30 TO 36 AND C10 TO C11
 Example 30 C10 31 32 33 34 35 36
 C8
 Coating Formulation V1 PA V2 V3 V4 V5 V6 V7
 PA
 Adhesion (% Wt.
 Loss)
 pre-immersion -- -- -- -- -- 0.33 -- 1.04
 immersion
 8 days -- -- 0.49 1.17 5.17 4.88 1.28 1.34 2.74
 11 days 3.41 2.33 -- -- -- -- -- -- --
 13 days 4.36 2.54 -- -- -- -- -- -- --
 Examples 31, 32, 35 and 36 demonstrate significantly improved adhesion
 characteristics when compared to Comparative Example C11. Examples 30,33
 and 34, although showing a greater % wt. loss, are still within acceptable
 limits.
 Although the present invention has been shown and described with respect to
 detailed embodiments thereof, it will be understood by those skilled in
 the art that various changes in form and detail thereof may be made
 without departing from the spirit and scope of the claimed invention.