Process for extending the shelf life of gaseous olefinic propellants in polyurethane foams

Abstract

The invention described herein generally pertains to a composition and a method for improving the shelf life of a gaseous hydrofluoroolefin propellant, the improvement comprising at least the increased aromatic polyester polyol(s) in combination with a tertiary amine catalyst comprising at least two cyclohexyl rings and an aliphatic metal salt catalyst, the amine catalyst having less than 10% nitrogen on a weight basis.

Claims

1. A two-component polyurethane foam comprising a reaction product of: an A-side diisocyanate with an HFO-1234ze propellant; and a B-side blend with an HFO-1234ze propellant; the polyurethane foam reaction product comprising: at least two aromatic polyester polyols and no more than approximately 10 wt. % aliphatic polyether polyol, and wherein the at least two aromatic polyester polyols comprise: ##STR00022## having a viscosity at 77 F. (25 C.), of between approximately 2,000-4,500 cP; and n being a value sufficient to achieve the viscosity; and ##STR00023## having a viscosity at 77 F. (25 C.) of between approximately 2,500-3,500 cP; and n being a value sufficient to achieve the viscosity; at least two catalysts comprising: at least one tertiary amine catalyst comprising at least two cyclohexyl rings; at least one aliphatic metal salt catalyst; and up to about 1.5 wt. % water.

2. The polyurethane foam of claim 1 which further comprises no more than 1 wt. % of an aliphatic polyether polyol.

3. The polyurethane foam of claim 1 comprising: essentially no added water.

4. The polyurethane foam of claim 1 in which at least one of the at least two aromatic polyester polyols comprises: at least two aromatic rings.

5. The polyurethane foam of claim 1 wherein the at least one tertiary amine catalyst comprises no more than 11 wt. % nitrogen.

6. The polyurethane foam of claim 5 wherein the at least one tertiary amine catalyst comprises no more than 10 wt. % nitrogen.

7. The polyurethane foam of claim 1 wherein the aliphatic metal salt is a metal alkanoate.

8. The polyurethane foam of claim 7 wherein the metal alkanoate is a potassium alkanoate.

9. The polyurethane foam of claim 8 wherein the potassium alkanoate is potassium octoate.

10. The polyurethane foam of claim 1 which further comprises: a halogenated plasticizer.

11. The polyurethane foam of claim 10 which further comprises: a brominated phthalate diol flame retardant.

12. The polyurethane foam of claim 11 which further comprises: at least one surfactant.

13. The polyurethane foam of claim 12 in which the A-side and B-side further comprise: an inert pressurizing gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plot of the catalytic decay ratio (CDR) as a predictive prognosticator of polyurethane foam properties over time with various tertiary amine catalysts using the HFO-1234ze propellant.

DETAILED DESCRIPTION OF THE INVENTION

(2) The best mode for carrying out the invention will now be described for the purposes of illustrating the best mode known to the applicant at the time of the filing of this patent application. The examples and figures are illustrative only and not meant to limit the invention, which is measured by the scope and spirit of the claims.

(3) Currently, the only SNAP approved acceptable replacement for HFC-134a in low pressure spray polyurethane foams is the Honeywell Solstice GBA blowing agent. This molecule presents significant technical challenges to a polyurethane foam chemist or formulator based on the inherent olefinic structure of the molecule, which was designed to break apart in the atmosphere.

(4) The most significant challenge with the molecule is formulating a product that will meet the aggressive shelf life requirements of the low pressure spray polyurethane foam industry. Currently formulated products are pressurized into cylinders under a pressure of approximately 200-250 psi. The products are exposed to a large range of temperatures based on the end use application, and are delivered without the aid of proportioning units, etc.

(5) Investigations to date prove degradation of the Solstice1234ze propellant molecule and failure of the blown foam system when Solstice 1234ze is used as a drop-in replacement for HFC-134a wherein only the propellant is substituted in the formulation.

(6) While Solstice 1234ze has desirable ODP and GWP characteristics, the propellant interacts with polyols and other additives in the B-side containers during prolonged storage (defined as greater than 3 months when using accelerated testing protocols, i.e., storage at 50 C. for 12 days) in ways which negatively impact the final characteristics of polyurethane foams in comparison to the same foams blown using conventional blowing agents such as HFC-134a. The sprayed two-component polyurethane foam fails with the olefinic propellant using standard polyurethane foam components as illustrated below.

(7) TABLE-US-00003 TABLE I (Two-component PU foam composition using HFO-1234ze propellant for HFC-134a) B-side Polyol aromatic polyester polyol having a functionality 20-25% greater than or equal to 2.2 sucrose polyether polyol based on a sucrose-glycerol 25-30% mixture with a functionality of ~4.5 having a hydroxyl number of ~360 glycerine-based oxypropylated polyether polyol having 1-5% a functionality greater than or equal to 3 brominated polyether with phthalate aromatic ring. 2-15% Flame Retardant/Plasticizer tris(2-chloropropyl) phosphate 35-45% Catalyst Polycat 5 - Tertiary amine 1-5% Potassium octoate 1-5% Surfactants Silicone surfactant 0.5-1.5% Non-silicone surfactant 0.5-1.5% Total (amounts adjusted to total 100%) .sup.100% A-side Diisocyanate .sup.100%

(8) It should be noted that the propellant amounts were adjusted in A and B sides so as to compensate for viscosity differences and produce an approximately 1:1 dispensing ratio. Additionally, in addition to propellant gas, other inert gases may be included as is standard in the industry.

(9) TABLE-US-00004 TABLE II (Typical two-component foam composition using HFO-1234ze propellant) Aged Sample Result Catalytic Decay Initial Sample Results (after Ratio (CDR) Analytical Results after accelerated aging at Aged Gel (sec)/ Results initial spraying 50 C. for 12 days) Initial Gel (sec) Gel time 0:33 2:20 140/33 = 4.24 Tack Time 1:03 18:00+

(10) Over this short time period, the NFO-1234ze blown foam degrades and shows poor surface appearance as illustrated below using accelerated aging testing. By comparison, HFC-134a blown polyurethane foam looked essentially the same after the accelerated aging test. An acceptable CDR ratio would be approximately less than 2 for a spray foam and approximately less than 2.5 for a pour-in-place foam. As evidenced above, a CDR of 4.24 is unacceptable for either application. Therefore, what is quickly seen is that a compositional change in both the polyols used to synthesize the polyurethane foam coupled with a modification to the catalyst package.

(11) Additional observations of the HFO-1234ze blown two-component blown polyurethane foam include poor cell structure, a decrease in the foam rise/height and a decrease in the closed cell content as shown below.

(12) A breakdown in physical properties such as closed cell content, leads to further failures including decreased R-value/k-factor (thermal conductivity) and a decrease in performance as an air barrier. These are key performance characteristics for many applications in the industry. The foam blown from the aged cylinders showed little to no rise after it was applied. The surface showed that the blowing agent was boiling off. The foam was very soft for hours after, and still curing internally (sticky upon cut). The foam had very poor cell structure and general appearance.

(13) Additional failures of note include an increase in density, which results in significantly decreased product yields, poor compression strength, tensile strength, etc. Another failure of note with the HFO-1234ze propellant is an incompatibility over the required shelf life with the flame retardant, tris(2-chloroisopropyl)phosphate (TCPP). TCPP is the most commonly used flame retardant and is required at loading levels of approximately 40% to meet the E84 class I requirement for SPF/building codes/etc. The systems tested using HFO-1234ze fail when levels exceed much over 20% loading when using a traditional polyether/polyester polyol blend in the B-side. This is problematic when attempting to achieve a class I rating and significantly limits the applications of the foam, unless reformulated in accord with the present invention.

(14) Current generation propellant molecules like HFC-134a do not contain a carbon-carbon double bond. The new HFO-1234ze molecule contains a double bond as it is designed for degradation to maintain low global warming potential. This design was to address issues in Montreal and Kyoto protocols. This double bond is prone to attack by many other parts of the chemistry and will also degrade in pressurized systems currently used for polyurethane foams.

(15) ##STR00003##

(16) At the present time, it appears that a high content of aromatic polyester polyol(s) aids in the shelf life of HFO-1234ze when in contact with typical B-side polyurethane foam reactants. While aliphatic polyether polyol(s) and/or aliphatic polyether polyol(s)/polyester polyol(s) blends are traditionally used in polyurethane foams blown using HFC-134a, (See Table I) formulations blown with HFO-1234ze require a counterintuitive switch to at least a majority amount of aromatic polyester polyols. An improved formulation using the blowing agent HFO-1234ze is as illustrated in Table Ill.

(17) TABLE-US-00005 TABLE III (reformulated two-component foam composition using HFO-1234ze propellant) Chemical OH # Wt. % B-side - 75 - 90% reactants/25 -10% propellant Polyol 1.sup.st Polyol Aromatic polyester polyol, f = 2.0 240 10-30 2.sup.nd Polyol Branched, hydroxyl terminated, 350 20-50 saturated, aromatic terephthalate polyester polyol, f = 2.2 Flame Retardant/Plasticizer Tris (1-chloro-2-propyl) phosphate 0.1 20-45 Flame Retardant Tetrabromophthalate diol 218 0-10 Surfactant(s) Polyether polydimethylsiloxane copolymer 0 0.5-1.5 Non-silicone organic surfactant 36 0.5-1.5 Catalyst Potassium octoate/DEG (diethylene glycol) 271 1-5 Tertiary amine 0 1-5 Other Water .sup.0-1.5 A-side - 94% MDI/6% propellant p-MDI 100%

(18) In one aspect of the invention, two aromatic polyester polyols such PS 2352 & TB-350 are employed in the B-side formulation, i.e., Both have similar viscosities, hydroxyl numbers and acid values. The main difference between the components resides at least in part in the bonding to the benzene ring in which PS 2352 has the polymeric chain bonding through ortho positions on the ring while TB-350 has the polymeric chain bonding through the para positions on the ring.

(19) TABLE-US-00006 PS 2352 Hydroxyl Number, mg KOH/g 230-250 Water, % by wt., max. 0.15 Acid Number, mg KOH/g, max. 0.6-1.0 Viscosity at 77 F. (25 C.), cP 2,000-4,500 Equivalent Weight (average) 234 Molecular Weight (average) 468 Color, Gardner 4 Density at 77 F. (25 C.), lb/U.S. gal 9.9 Specific Gravity at 77 F. (25 C.) 1.19

(20) TABLE-US-00007 TB-350 Hydroxyl Number, mg KOH/g 335-365 Water, % by wt., max. 0.15 Acid Number, mg KOH/g, max . 0.5-2.0 Viscosity at 77 F. (25 C.), cP 2,500-3,500 Color, Gardner 4-5 Specific Gravity at 77 F. (25 C.) 1.233 Functionality 2.2

(21) While two aromatic polyester polyols appear to be the preferred combination, it is believed, without being held to any one theory of operation or mechanism of action, that only one aromatic polyester polyol is required. Preliminary experimental results have shown that using 100% of the PS 2352 polyester, as well as 100% of the TB 350, produced acceptable polyurethane foams and the cured product looked good keeping the ratio of all other components the same. It is also believed that the incorporation of small amounts, e.g., less than approximately 30% of aliphatic polyether polyols will result in acceptable polyurethane foams, more preferably less than approximately 10% of aliphatic polyether polyols, and most preferably essentially no aliphatic polyether polyols.

(22) Synthesized foams that were tested without the shielding of the benzene rings collapsed or fell apart at the end of three (3) month aging tests. Without the aromatic shielding attempts, all synthesized foams were unacceptable.

(23) Associated analytical characteristics are tabularized in Table IV. As illustrated in the Table, all synthesized foams were within the limits of the catalytic decay ratio parameters of approximately 2 for a spray foam and approximately 2.5 for a pour-in-place foam (note the range of 1.0 to 1.28 below) using the accelerated aging testing protocol previously described.

(24) TABLE-US-00008 TABLE IV Initial 3 mo. 6 mo. 9 mo. 12 mo. Gel Time 39 42 42 48 50 Tack Free Time 59 1:02 62 64 69 Gx/Gi (CDR) 1.0 1.077 1.077 1.230 1.282 A/B Ratio 1.08 1.08 1.16 1.15 1.16 Surface Good Mediocre Very Good Good Good Interface Very Good Good Good Good Good Cell Structure Very Mediocre Good Good Good Good Dimensional Pass Pass Pass Pass Pass Stability

(25) In order to determine the impact of changing from a polyether polyol to a polyester polyol system, a control experiment was performed in which the above polyester polyols of PS 2352 and TB 350 were tested in comparison to a system which used only polyether polyols typically used in the industry, namely Voranol 360 and Poly G 30-280. The experiment is summarized in Table V.

(26) TABLE-US-00009 TABLE V (polyol study using HFO-1234ze propellant) B-side- 86% reactants/ 17% propellant Chemical Wt. % Wt. % Polyester Polyol PS 2352 15.0 TB-350 36.0 Polyether Polyol Voranol 360 36.0 Poly G 30-280 15.0 Flame Retardant/Plasticizer Tris (1-chloro-2-propyl) phosphate 36.6 41.6 Flame Retardant Tetrabromophthalate diol 5.0 Surfactant(s) Polyether polydimethylsiloxane copolymer 1.0 1.0 Non-silicone organic surfactant 1.0 1.0 Catalyst Potassium octoate/DEG (diethylene glycol) 2.0 2.0 Polycat-12 2.5 Other Water 0.9 0.9 A-side- 94% MDI/6% propellant MDI 100 100

(27) As used above, Voranol 360 is a sucrose/glycerine (30/70) rigid polyether polyol having a nominal M.W. of 610 and an average OH # of 4.5. It is a multi-functional polyether polyol with high functionality (e.g. 4.4-4.5) for dimensional stability. Poly G 30-280 is a polyether triol having a nominal M.W. of 30-280600 and an average OH # (mg KOH/g) of 274 and a maximum acid # of 0.05.

(28) The above synthesized foams were tested using the accelerated testing protocol previously identified and summarized in Table VI.

(29) TABLE-US-00010 TABLE VI Initial 3 mo. 6 mo. 9 mo. 12 mo. Polyester Polyol Results A/B 1.08 1.08 1.16 1.15 1.16 Gel Time (sec) 39 42 42 48 50 Tack Time (sec) 59 62 62 64 69 CDR 1.00 1.08 1.08 1.23 1.28 R value 5.42 4.08 5.53 5.54 5.73 % closed 96.34 44.20 82.45 94.74 80.81 cell content Polyether Polyol Results A/B 0.96 0.98 0.90 0.92 0.91 Gel Time (sec) 124 146 169 295 320 Tack Time (sec) 161 355 568 >1020 1412 CDR 1.00 1.18 1.36 2.38 2.58 R value 3.98 % closed 61.10 cell content

(30) As is easily seen, and quite counterintuitive in the industry, the polyester polyol combination was effective over the entire 12 months of accelerated aging studies, particularly as evidenced by the catalytic decay ratio, which at all times was below a threshold value of approximately less than 2 for a spray foam and approximately less than 2.5 for a pour-in-place foam using accelerated testing protocol. Further, the closed cell content and R-values were within acceptable values. This is contrasted to the polyether polyol combination, which did maintain a catalytic decay ratio of below the target values for 9 months of accelerated aging testing, but had unacceptable R-values and percentage of closed cell content. The cured foam collapse was so pronounced that samples sufficient for analysis could not be obtained.

(31) Foam Catalyst System

(32) In addition to the above sterically hindered aromatic polyester polyols, a non-conventional combination of catalysts is required. Polycat 12 (a mild amine catalyst) possesses a significant amount of steric hindrance about the central nitrogen (N) atom. That is not the case with Polycat 5 (an aggressive amine catalyst) with three tertiary amines. At least one of the keys is the requirement that one of the catalysts include Dabco K 15. A leading manufacturer of catalysts (Air Products) has characterized Polycat 12 as a pour-in-place catalyst of medium potency. It is thought that having 0.9% water in the formula initiates the blowing reaction (RNCO+H.sub.2ORNH.sub.2+CO.sub.2), which generates a lot of heat for solvation of the Dabco K-15 (potassium octoate) salt, making it active enough, early enough to provide a good synergistic total catalytic activity. It is thought that the high loading of Dabco K-15 (potassium octoate) is also important to making Polycat 12 work in an acceptable spray polyurethane foam formula. While Dabco K-15 was effective in this application, other metal salts are believed to also be effective, including but not limited to Dabco TMR 20, which is also a potassium-based catalyst.

(33) What is indicated is that the catalysts and/or co-catalysts in the formulation must have a reduced percentage of nitrogen as illustrated in Table VII below. Preferably the percentage is below 10% nitrogen on a weight basis, more preferably below 7%.

(34) TABLE-US-00011 TABLE VII Nitrogen Nitrogen Catalyst M Wt. pH (#) (%) Name Polycat 12 195.34 11.06 1 7.17 Dicyclohexylmethyl amine Polycat 8 127.23 11.77 1 11.01 Dimethylcyclohexyl amine DMDEE 244.33 9.78 2 11.47 Dimorpholinodiethyl ether NEM 115.18 1 12.16 N-Ethylmorpholine NMM 101.15 1 13.85 N-Methylmorpholine Polycat 15 189.00 11.59 3 22.23 Tetramethyldipropylene triamine Polycat 5 173.30 11.05 3 24.25 Pentamethyldiethyl triamine DMP 114.19 2 24.53 N,N-DiMethylpiperazine Dabco 33LV 112.17 10.70 2 24.97 Tetraethyl diamine Dabco T 146.23 11.05 2 19.16 N,N,N-trimethylaminoethyl ethanolamine Dabco K-15 (potassium octoate)/DEG (diethylene glycol) 0Polycat 12 (N,N-dicyclohexylmethylamine) DMDEE (2,2-dimorpholinodiethyl ether) Polycat 5 (N,N,N,N,N-pentamethyldiethylenetriamine) Polycat 8 (N,N-dimethylcyclohexylamine) N,N-dimethylhexylamine

(35) Without being bound to any one theory of operation or mechanism, it is believed that the increased presence of aromatic (e.g., benzene) rings in the polyols coupled with the increased steric hindrance attributable to the cyclohexyl rings in the amine catalysts in the B-side provides a high degree of steric hindrance to strong base/blowing agent interactions, while also serving to stabilize charge densities in polar polyurethane B-side formulas.

(36) Without the benefit of the aromatic shielding, e.g., when using Polycat-5 and Polycat-8, the foam performance degraded significantly. This was proven in the following experiment.

(37) TABLE-US-00012 TABLE VIII (catalyst study using HFO-1234ze propellant) B-side- 86% reactants/ Wt. Wt. Wt. 14% propellant Chemical % % % Polyol PS 2352 15.0 15.0 15.0 TB-350 36.9 36.9 36.9 Flame Retardant/Plasticizer Tris (1-chloro-2-propyl) phosphate 36.6 36.6 36.6 Flame Retardant Tetrabromophthalate diol 5.0 5.0 5.0 Surfactant(s) Polyether polydimethylsiloxane copolymer 1.0 1.0 1.0 Non-silicone organic surfactant 1.0 1.0 1.0 Catalyst Potassium octoate/DEG (diethylene glycol) 2.0 2.0 2.0 Polycat-8 1.63 Polycat-12 2.5 N,N-dimethylhexylamine 1.65 Other Water 0.9 0.9 0.9 A-side- 93% MDI/7% propellant MDI 100 100 100

(38) The above synthesized foams were tested using the accelerated testing protocol previously identified and summarized in Table IX.

(39) TABLE-US-00013 TABLE IX (accelerated months at 50 C.) Gx/Gi Initial 4 mo. 7 mo. 12 mo. (CDR) Polycat -12 Gel Time (sec) 32 39 45 50 1.56 Polycat -8 Gel Time (sec) 16 165 333 880 55 DMHA Gel Time (sec) 18 143 306 17 Polycat -12 Tack Time (sec) 55 59 66 96 1.74 Polycat -8 Tack Time (sec) 27 487 495 >1800 66 DMHA Tack Time (sec) 39 256 352 9.0

(40) Only the catalytic combination of a metal alkanoate with a mild tertiary amine catalyst with at least two aromatic rings in the moiety resulted in a stable system in which the catalytic decay ratio was within the satisfactory range of approximately less than 2 for a spray foam and approximately less than 2.5 for a pour-in-place foam using accelerated testing protocol as further illustrated in FIG. 1.

(41) Plasticizer

(42) While spray polyurethane foam formulations usually contain 30-40% of a plasticizer, the manufacturer, i.e., Honeywell, has shared that high levels of tris(1-chloro-2-propyl)phosphate (TCPP)+Solstice GBA is an undesirable combination for stability. However, this is not seen in the preferred combination when only aromatic polyester polyols are used.

(43) ##STR00018##
Flame Retardant (Tetrabromophthalate Diol)

(44) A conventional flame retardant is often employed in the polyurethane composition, but is optional.

(45) ##STR00019##
Surfactant

(46) A conventional combination of surfactants are employed at a weight percent of about 0.5-2%. Tegostab B-8433 Polyether polydimethylsiloxane copolymer foam stabilizer Dabco LK-443 Non-silicone containing organic surfactant
Water Content

(47) Water content also appears to play a role with the presence of higher amounts of water as a blowing agent (>1.5%) negatively impacting shelf life whereas low concentrations (<1.0%) of water are acceptable. Some structural applications however, require essentially no water, as shown in Table X.

(48) TABLE-US-00014 TABLE X (water study using HFO-1234ze propellant with structural properties) B- side- 87% reac- tants/ 13% propel- Wt. Wt. Wt. Wt. Wt. Wt. lant Chemical % % % % % % Polyol PS 2352 0 20.0 20.0 20.0 20.0 20.0 20.0 TB- 350 32.5 32.5 32.5 32.5 32.5 32.5 Flame Retardant/Plasticizer Tris (1-chloro-2-propyl) phosphate 4.0.0 39.1 38.0 37.0 36.0 35.0 Flame Retardant Tetrabromophthalate diol Surfactant(s) Polyether polydimethylsiloxane copolymer 2.0 2.0 2.0 2.0 2.0 2.0 Non-silicone organic surfactant 1.0 1.0 1.0 1.0 1.0 1.0 Catalyst Potassium octoate/DEG (diethylene glycol) 2.0 2.0 2.0 2.0 2.0 2.0 Polycat-12 2.5 2.5 2.5 2.5 2.5 2.5 Other Water 0 0.9 2.0 3.0 4.0 5.0 A-side- 96.5-94.5% MDI/3.5-5.4% propellant MDI 100 100 100 100 100 100

(49) The above synthesized foams were tested using the accelerated testing protocol previously identified and summarized in Table Xl.

(50) TABLE-US-00015 TABLE XI Density Compressive Closed % H.sub.2O Gel Time (pcf) Strength (psi) R-value Cell % 0 26 3.28 48.64 5.3 78.8 0.9 33 2.34 32.35 5.1 81.9 2.0 40 1.83 22.12 5.1 76.6 3.0 48 1.57 11.64 4.3 82.5 4.0 52 1.45 9.64 4.2 81.4 5.0 56 1.27 6.42 4.0 42.4

(51) For various applications, the synthesized foam will exhibit at least the following properties illustrated in Table XII.

(52) TABLE-US-00016 TABLE XII Pour-in-place or spray foam Roof patch R-value 5-6 Compressive strength 15 psi >40 psi Closed cell content >90% >90% Gel time <30 sec. Tack-free time 30-60 sec. Dimensional stability +/5% of initial +/5% of initial E-84 rating A or B Class-II
Observations

(53) Temperature appears to be a factor with storage at reduced temperatures extending shelf life.

(54) What has been illustrated includes at least the following: high aromatic polyester polyol content, recognizing that polyether polyols possess little to no aromaticity. An SPF formula utilizing 100% aromatic polyester polyol content exhibits a shelf life of one year. The choice of flame retardant matters with flame retardants with higher aromatic content, e.g. PHT 4 diol, assisting. Those with lower aromaticity, e.g. TCPP, seem to further degrade shelf life when used in high concentrations. It is postulated (without being held to any one theory or mode of operation) that the increased presence of benzene rings in the B-side provides a high degree of steric hindrance to strong base/blowing agent interactions, while also serving to stabilize charge densities in polar polyurethane B-side formulas.

(55) Currently, the only approved acceptable replacement for HFC-134a in the low pressure spray polyurethane foam industry is the Honeywell Solstice GBA blowing agent. This molecule presents significant technical challenges to a polyurethane foam chemist or formulator based on the inherent structure of the molecule, which was designed to break apart in the atmosphere.

(56) The most significant challenge with the molecule is formulating a product that will meet the aggressive shelf life requirements of the low pressure spray polyurethane foam industry. Our products are pressurized into cylinders under a pressure of approximately 200-250 psi. The products are exposed to a large range of temperatures based on the end use application, and are delivered without the aid of proportioning units, etc.

(57) The best mode for carrying out the invention has been described for purposes of illustrating the best mode known to the applicant at the time. The examples are illustrative only and not meant to limit the invention, as measured by the scope and merit of the claims. The invention has been described with reference to preferred and alternate embodiments. Obviously, modifications and alterations will occur to others upon the reading and understanding of the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.