Coated article with low-E coating having low visible transmission

Abstract

This invention relates to a coated article including a low-emissivity (low-E) coating. In certain example embodiments, the low-E coating is provided on a substrate (e.g., glass substrate) and includes at least first and second infrared (IR) reflecting layers (e.g., silver based layers) that are spaced apart by contact layers (e.g., NiCr based layers) and a dielectric layer of or including a material such as silicon nitride. In certain example embodiments, the coated article has a low visible transmission (e.g., no greater than 60%, more preferably no greater than about 55%, and most preferably no greater than about 50%).

Claims

1. A coated article including a coating supported by a glass substrate, the coating comprising: a first dielectric layer comprising silicon nitride on the glass substrate; first and second infrared (IR) reflecting layers comprising silver on the glass substrate and located over the first dielectric layer comprising silicon nitride, the first IR reflecting layer being located closer to the glass substrate than is the second IR reflecting layer, wherein no metal oxide based layer is located between the glass substrate and the first IR reflecting layer; a first contact layer comprising Ni located over and directly contacting the first IR reflecting layer comprising silver; a second dielectric layer comprising silicon nitride located over and directly contacting the first contact layer comprising Ni; a second contact layer located over and directly contacting the second dielectric layer comprising silicon nitride; the second IR reflecting layer comprising silver located over and directly contacting the second contact layer; a third contact layer comprising Ni located over and directly contacting the second IR reflecting layer; a third dielectric layer comprising silicon nitride located over and directly contacting the third contact layer comprising Ni; a layer comprising zirconium oxide located over the third dielectric layer comprising silicon nitride; wherein each of the first and second IR reflecting layers comprising silver is at least twice as thick as the layer comprising zirconium oxide; and wherein the coated article has a visible transmission, measured monolithically, of from about 20-55%.

2. The coated article of claim 1, wherein each of the first and second IR reflecting layers comprising silver is at least three times as thick as the layer comprising zirconium oxide.

3. The coated article of claim 1, wherein the layer comprising zirconium oxide further comprises nitrogen.

4. The coated article of claim 1, wherein the second dielectric layer comprising silicon nitride is amorphous.

5. The coated article of claim 1, wherein the coating further comprises another contact layer comprising Ni located below and directly contacting the first IR reflecting layer comprising silver, and wherein the another contact layer comprising Ni is located between and directly contacting the first IR reflecting layer and the first dielectric layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross sectional view of a coated article according to an example embodiment of this invention.

(2) FIG. 2 is a cross sectional view showing the coated article of FIG. 1 provided in an IG window unit according to an example embodiment of this invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

(3) Coated articles herein may be used in applications such as IG window units, laminated window units (e.g., for use in vehicle or building applications), vehicle windows, monolithic architectural windows, residential windows, and/or any other suitable application that includes single or multiple glass substrates.

(4) In certain example embodiments of this invention, the coating includes a double-silver stack. Referring to FIG. 1 for example, in certain example embodiments of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: first 9 and second 19 infrared (IR) reflecting layers comprising or consisting essentially of silver, the first IR reflecting layer 9 being located closer to the glass substrate 1 than is the second IR reflecting layer 19; a first contact layer comprising NiCr 7 located under and directly contacting the first IR reflecting layer comprising silver 9, a second contact layer 11 located over and directly contacting the first IR reflecting layer comprising silver 9; a dielectric layer comprising silicon nitride 14 located over and directly contacting the first contact layer comprising NiCr 11; a third contact layer comprising NiCr 17 located over and directly contacting the layer comprising silicon nitride 14; the second IR reflecting layer comprising silver 19 located over and directly contacting the second contact layer comprising NiCr 17; a fourth contact layer comprising NiCr 21 located over and directly contacting the second IR reflecting layer 19, and wherein the second IR reflecting layer comprising silver 19 is at least as thick as the first IR reflecting layer comprising silver 9. In certain preferred embodiments, it has been found that surprisingly beneficial results can be achieved when the second IR reflecting layer comprising silver 19 is thicker than the first IR reflecting layer comprising silver 9, more preferably when second IR reflecting layer 19 is at least 10 angstroms () thicker (more preferably at least 20 angstroms thicker) than the first IR reflecting layer comprising silver 9. The coating includes three dielectric layers 3, 14 and 24 of or including silicon nitride, as shown in FIG. 1. Moreover, the coating includes a layer (e.g., overcoat) 27 of or including zirconium oxide and/or zirconium oxynitride. In certain example embodiments, this layer of or including zirconium oxide and/or zirconium oxynitride 27 is thinner than one or both of the IR reflecting layers 9, 19 comprising silver in the coating. In certain example embodiments of this invention, each of the IR reflecting layers comprising silver 9 and 19 is at least twice as thick, and more preferably at least three times as thick, as the layer 27 or including zirconium oxide and/or zirconium oxynitride. In certain example embodiments of this invention, the coating includes only two IR reflecting layers 9, 19 of or including silver or the like.

(5) In order to increase durability, along with optics and thermal properties, and avoid significant structural changes before and after HT, coated articles according to certain example embodiments of this invention have a center dielectric layer 14 of or including silicon nitride and lower contact layers 7, 17 are based on NiCr (as opposed to ZnO). It has also been found that using metallic or substantially metallic NiCr (possibly partly nitrided) for layer(s) 7, 11, 17 and/or 21 improves chemical, mechanical and environmental durability (compared to using ZnO lower contact layers below silver and/or highly oxided NiCr upper contact layers above silver). It has also been found that sputter-depositing silicon nitride inclusive layer 14 in an amorphous state, so that it is amorphous in both as-coated and HT states, helps with overall stability of the coating. For example, 5% HCl at 65 degrees C. for one hour will remove the coating of U.S. Pat. No. 7,521,096, whereas the coating shown in FIG. 1 and the examples herein will survive this HCl test. And in high temperature and high humidity environment, there is less damage to the coating of FIG. 1 and the examples herein after ten days of exposure, than to the coating of the '096 patent after two days of exposure. And regarding high corrosive chemicals such as those used for brick wash, corrosion resistance is such that edge deletion need not be performed in certain example IG and laminated embodiments. Similarly, for mechanical abrasion tests, thermal cycling and salt fog tests, the coatings of the examples herein were found to be better than that of the '096 patent. Moreover, it has been found that making the top Ag based IR reflecting layer 19 thicker than the bottom Ag based IR reflecting layer 9 improves certain optical characteristics of the coating. The coating can be used as-coated, or heat treated, due to the relatively low E* values discussed herein. For example, when the coating 30 is located surface #2 of an IG window unit (as shown in FIG. 2), low glass side reflective E* values due to heat treatment indicate that the coated article has approximately the same transmission and color characteristics as viewed by the naked eye both before and after heat treatment (e.g., thermal tempering), and thus can be used either as-coated or as heat treated without significantly affecting optical characteristics thereof.

(6) In certain example embodiments of this invention such as FIG. 1, heat treated or non-heat-treated coated articles having multiple IR reflecting layers (e.g., two spaced apart silver based layers) are capable of realizing a sheet resistance (R.sub.s) of less than or equal to 5.0 (more preferably less than or equal to 4.0, even more preferably less than or equal to 3.0). The terms heat treatment and heat treating as used herein mean heating the article to a temperature sufficient to achieve thermal tempering, heat bending, and/or heat strengthening of the glass inclusive article. This definition includes, for example, heating a coated article in an oven or furnace at a temperature of least about 580 degrees C., more preferably at least about 600 degrees C., for a sufficient period to allow tempering, bending, and/or heat strengthening. In certain instances, the HT may be for at least about 4 or 5 minutes. The coated article may or may not be heat treated in different embodiments of this invention.

(7) FIG. 1 is a side cross sectional view of a coated article according to an example non-limiting embodiment of this invention. The coated article includes substrate 1 (e.g., clear, green, bronze, or blue-green glass substrate from about 1.0 to 10.0 mm thick, more preferably from about 1.0 mm to 3.5 mm thick), and low-E coating (or layer system) 30 provided on the substrate 1 either directly or indirectly. The coating (or layer system) 30 includes, for example: bottom dielectric silicon nitride layer 3 which may be Si.sub.3N.sub.4, or of the Si-rich type silicon nitride for haze reduction, or of any other suitable stoichiometry silicon nitride in different embodiments of this invention, lower contact layer 7 (which contacts bottom IR reflecting layer 9), first conductive and preferably metallic or substantially metallic infrared (IR) reflecting layer 9, upper contact layer 11 (which contacts layer 9), dielectric silicon nitride based and/or inclusive layer 14, lower contact layer 17 (which contacts IR reflecting layer 19), second conductive and preferably metallic or substantially metallic IR reflecting layer 19, upper contact layer 21 (which contacts layer 19), dielectric silicon nitride layer 24 which may be Si.sub.3N.sub.4, of the Si-rich type for haze reduction, or of any other suitable stoichiometry silicon nitride in different embodiments of this invention, and overcoat layer 27 of or including a material such as zirconium oxide (e.g., ZrO.sub.2) and/or zirconium oxynitride. The contact layers 7, 11, 17 and 21 each contact an IR reflecting layer (e.g., layer based on Ag). The aforesaid layers 3-27 make up low-E (i.e., low emissivity) coating 30 that is provided on glass or plastic substrate 1. Layers 3-27 may be sputter-deposited on the substrate 1 in certain example embodiments of this invention, with each layer being sputter-deposited in vacuum using one or more targets as needed (the sputtering targets may be ceramic or metallic). Metallic or substantially metallic layers (e.g., layers 7, 9, 11, 17, 19 and 21) may be sputtered in an atmosphere containing argon gas, whereas nitrided layers (e.g., layers 3, 7, 11, 14, 17, 21 and 24) may be sputtered in an atmosphere containing a mixture of nitrogen and argon gas. The contact layers 7, 11, 17 and 21 may or may not be nitride in different example embodiments of this invention.

(8) In monolithic instances, the coated article includes only one glass substrate 1 as illustrated in FIG. 1. However, monolithic coated articles herein may be used in devices such as laminated vehicle windshields, IG window units, and the like. As for IG window units, an IG window unit may include two spaced apart glass substrates. An example IG window unit is illustrated and described, for example, in U.S. Patent Document No. 2004/0005467, the disclosure of which is hereby incorporated herein by reference. FIG. 2 shows an example IG window unit including the coated glass substrate 1 shown in FIG. 1 coupled to another glass substrate 2 via spacer(s), sealant(s) 40 or the like, with a gap 50 being defined therebetween. This gap 50 between the substrates in IG window unit embodiments may in certain instances be filled with a gas such as argon (Ar). An example IG unit may comprise a pair of spaced apart clear glass substrates each about 3-4 mm thick, one of which is coated with a coating 30 herein in certain example instances, where the gap 50 between the substrates may be from about 5 to 30 mm, more preferably from about 10 to 20 mm, and most preferably about 16 mm. In certain example instances, the low-E coating 30 may be provided on the interior surface of either substrate facing the gap (the coating is shown on the interior major surface of substrate 1 in FIG. 2 facing the gap 50, but instead could be on the interior major surface of substrate 2 facing the gap 50). Either substrate 1 or substrate 2 may be the outermost substrate of the IG window unit at the building exterior (e.g., in FIG. 2 the substrate 1 is the substrate closest to the building exterior, and the coating 30 is provided on surface #2 of the IG window unit).

(9) In certain example embodiments of this invention, one, two, three, or all four of contact layers 7, 11, 17, 21 may be of or include NiCr (any suitable ratio of Ni:Cr), and may or may not be nitrided (NiCrN.sub.x). In certain example embodiments, one, two, three or all four of these NiCr inclusive layers 7, 11, 17, 21 is substantially or entirely non-oxidized. In certain example embodiments, layers 7, 11, 17 and 21 may all be of metallic NiCr or substantially metallic NiCr (although trace amounts of other elements may be present). In certain example embodiments, one, two, three or all four of NiCr based layers 7, 11, 17, 21 may comprise from 0-10% oxygen, more preferably from 0-5% oxygen, and most preferably from 0-2% oxygen (atomic %). In certain example embodiments, one, two, three or all four of these layers 7, 11, 17, 21 may contain from 0-20% nitrogen, more preferably from 1-15% nitrogen, and most preferably from about 1-12% nitrogen (atomic %). NiCr based layers 7, 11, 17 and/or 21 may or may not be doped with other material(s) such as stainless steel, Mo, or the like. It has been found that the use of NiCr based contact layer(s) 7 and/or 17 under the silver-based IR reflecting layer(s) 9, 19 improves durability of the coated article (compared to if layers 7 and 17 were instead of ZnO).

(10) Dielectric layers 3, 14, and 24 may be of or include silicon nitride in certain embodiments of this invention. Silicon nitride layers 3, 14 and 24 may, among other things, improve heat-treatability of the coated articles and protect the other layers during optional HT, e.g., such as thermal tempering or the like. One or more of the silicon nitride of layers 3, 14, 24 may be of the stoichiometric type (i.e., Si.sub.3N.sub.4), or alternatively of the Si-rich type of silicon nitride in different embodiments of this invention. The presence of free Si in a Si-rich silicon nitride inclusive layer 3 and/or 14 may, for example, allow certain atoms such as sodium (Na) which migrate outwardly from the glass 1 during HT to be more efficiently stopped by the Si-rich silicon nitride inclusive layer(s) before they can reach silver and damage the same. Thus, it is believed that the Si-rich Si.sub.xN.sub.y can reduce the amount of damage done to the silver layer(s) during HT in certain example embodiments of this invention thereby allowing sheet resistance (R.sub.s) to decrease or remain about the same in a satisfactory manner. Moreover, it is believed that the Si-rich Si.sub.xN.sub.y in layers 3, 14 and/or 24 can reduce the amount of damage (e.g., oxidation) done to the silver and/or NiCr during HT in certain example optional embodiments of this invention. In certain example embodiments, when Si-rich silicon nitride is used, the Si-rich silicon nitride layer (3, 14 and/or 24) as deposited may be characterized by Si.sub.xN.sub.y layer(s), where x/y may be from 0.76 to 1.5, more preferably from 0.8 to 1.4, still more preferably from 0.82 to 1.2. Any and/or all of the silicon nitride layers discussed herein may be doped with other materials such as stainless steel or aluminum in certain example embodiments of this invention. For example, any and/or all silicon nitride layers 3, 14, 24 discussed herein may optionally include from about 0-15% aluminum, more preferably from about 1 to 10% aluminum, in certain example embodiments of this invention. The silicon nitride of layers 3, 14, 24 may be deposited by sputtering a target of Si or SiAl, in an atmosphere having argon and nitrogen gas, in certain embodiments of this invention. Small amounts of oxygen may also be provided in certain instances in the silicon nitride layers.

(11) Infrared (IR) reflecting layers 9 and 19 are preferably substantially or entirely metallic and/or conductive, and may comprise or consist essentially of silver (Ag), gold, or any other suitable IR reflecting material. IR reflecting layers 9 and 19 help allow the coating to have low-E and/or good solar control characteristics.

(12) Other layer(s) below or above the illustrated coating may also be provided. Thus, while the layer system or coating is on or supported by substrate 1 (directly or indirectly), other layer(s) may be provided therebetween. Thus, for example, the coating of FIG. 1 may be considered on and supported by the substrate 1 even if other layer(s) are provided between layer 3 and substrate 1. Moreover, certain layers of the illustrated coating may be removed in certain embodiments, while others may be added between the various layers or the various layer(s) may be split with other layer(s) added between the split sections in other embodiments of this invention without departing from the overall spirit of certain embodiments of this invention.

(13) While various thicknesses and materials may be used in layers in different embodiments of this invention, example thicknesses and materials for the respective layers on the glass substrate 1 in the FIG. 1 embodiment are as follows, from the glass substrate outwardly (physical thicknesses recited):

(14) TABLE-US-00001 Example Materials/Thicknesses; FIG. 1 Embodiment Layer Preferred More Example Glass (1-10 mm thick) Range ({acute over ()}) Preferred ({acute over ()}) () Si.sub.xN.sub.y (layer 3) 100-500 250-450 320 NiCr or NiCrN (layer 7) 10-30 {acute over ()} 11-20 {acute over ()} 12 Ag (layer 9) 100-170 {acute over ()} 110-145 {acute over ()} 127 NiCr or NiCrN (layer 11) 10-30 {acute over ()} 11-20 {acute over ()} 10 Si.sub.xN.sub.y (layer 14) 300-1400 {acute over ()} 700-1100 {acute over ()} 865 NiCr or NiCrN (layer 17) 10-30 {acute over ()} 11-20 {acute over ()} 11 Ag (layer 19) 140-225 {acute over ()} 150-215 {acute over ()} 164 NiCr or NiCrN (layer 21) 8-30 {acute over ()} 10-20 {acute over ()} 10 Si.sub.3N.sub.4 (layer 24) 120-360 {acute over ()} 250-340 {acute over ()} 304 ZrO.sub.2 (layer 27) 25-80 {acute over ()} 25-50 {acute over ()} 35

(15) The second IR reflecting layer comprising silver 19 is at least as thick as the first IR reflecting layer comprising silver 9. In certain preferred embodiments, it has been found that surprisingly beneficial results can be achieved when the second IR reflecting layer comprising silver 19 is thicker than the first IR reflecting layer comprising silver 9, more preferably when second IR reflecting layer 19 is at least 10 angstroms () thicker (more preferably at least 20 angstroms thicker) than the first IR reflecting layer comprising silver 9.

(16) In certain example embodiments, the layer of or including zirconium oxide and/or zirconium oxynitride 27 is thinner than each of the IR reflecting layers 9, 19 comprising silver in the coating 30. In certain example embodiments of this invention, each of the IR reflecting layers comprising silver 9 and 19 is at least twice as thick, and more preferably at least three times as thick, as the layer 27 or including zirconium oxide and/or zirconium oxynitride.

(17) In certain example embodiments, the center silicon nitride based layer 14 is thicker than each of the other silicon nitride based layers 3 and 24, preferably by at least 100 angstroms, more preferably by at least 300 angstroms, and most preferably by 400 angstroms. Moreover, in certain example embodiments, each of the silicon nitride based layers 3, 14 and 24 is at least two times as thick as the zirconim oxide inclusive layer 27, more preferably at least three times as thick, and most preferably at least four or five times as thick.

(18) The coating 30 offers good durability and allows for lower inside and outside reflection compared to a single-silver based low-E coating. However, delta-E* values are typically in the 4-5 range. The coating, and coated articles including the coating, may be designed to appear light blue in transmission and reflection, but may become slightly more neutral after optional HT.

(19) In certain example embodiments of this invention, coated articles herein may have the following optical and solar characteristics set forth in Table 2 when measured monolithically (before and/or after optional HT). The sheet resistances (R.sub.s) herein take into account all IR reflecting layers (e.g., silver layers 9, 19). Note that before heat treatment means as annealed, but before high temperature heat treatment such as thermal tempering as described herein.

(20) TABLE-US-00002 Optical/Solar Characteristics (Monolithic - Before Heat Treatment) Characteristic General More Preferred Most Preferred R.sub.s (ohms/sq.): <=5.0 <=4.0 <=3.0 E.sub.n: <=0.08 <=0.05 <=0.04 T.sub.vis (Ill. C 2): 30-63% 45-60% 50-59%

(21) TABLE-US-00003 Optical/Solar Characteristics (Monolithic - Post Heat Treatment) Characteristic General More Preferred Most Preferred R.sub.s (ohms/sq.): <=5.0 <=4.0 <=3.0 E.sub.n: <=0.08 <=0.05 <=0.04 T.sub.vis (Ill. C 2): 30-63% 48-61% 52-60%

(22) It can be seen from the above that the heat treatment (e.g., thermal tempering) slightly increases the visible transmission of the coated article.

(23) In certain example laminated embodiments of this invention, coated articles herein which have been optionally heat treated to an extent sufficient for tempering, and which have been coupled to another glass substrate to form an IG unit, may have the above recited Optical/Solar characteristics in a structure as shown in FIG. 2 (e.g., where the two glass sheets are each 6 mm thick of clear glass with a 16 mm gap therebetween filled with 90/10 argon/air). Such IG window units may have a visible transmission of from about 20-55% in certain example embodiments of this invention.

(24) The following examples are provided for purposes of example only, and are not intended to be limiting unless specifically claimed.

Examples 1-3

(25) The following Examples 1-3 were made via sputtering coatings on 6 mm thick clear/transparent glass substrates so as to have approximately the layer stacks set forth in FIG. 1 with the respective layer thicknesses shown in the example column in the chart above regarding layer thicknesses.

(26) Set forth below are the optical characteristics of Examples 1-3 measured for a monolithic coated article as shown in FIG. 1. All values measured in the table immediately below are pre-HT. Note that f refers to film reflection, i.e., reflection from the film side of the coated article, whereas g refers to glass side reflection.

(27) TABLE-US-00004 Monolithic (Pre-HT) Characteristic Ex. 1 Ex. 2 Ex. 3 T.sub.vis (or TY)(Ill. C 2): 52.3% 54% 54.5% a*.sub.t (Ill. C 2): 2.8 4.0 3.6 b*.sub.t (Ill. C 2): 5.2 4.6 6.1 R.sub.fY (Ill. C, 2 deg.): 10.3% 8.4% 7.1% a*.sub.f (Ill. C, 2): 10.5 5.4 5.1 b*.sub.f (Ill. C, 2): 8.5 1.8 1.9 R.sub.gY (Ill. C, 2 deg.): 9.8 8.7% 8.0% a*.sub.g (Ill. C, 2): 4.3 1.9 1.3 b*.sub.g (Ill. C, 2): 5.7 9.3 9.4

(28) It can be seen from the above the examples above that the coated articles measured monolithically had desirable low visible transmission, and had fairly desirable glass side reflective color. In particular, monolithic a*.sub.g (glass side reflective a* color) was in a desirable range of from about 1 to 5, and b*.sub.g (glass side reflective b* color) was in a desirable range of from about 5 to 10. Moreover, glass side reflection (RgY) was good in that it was below 10%, more preferably no greater than 9%. These are desirable characteristics, especially when the coated article is to be put in an IG window unit as shown in FIG. 2.

(29) Set forth below are the optical characteristics of Examples 1-3 measured for a monolithic coated article after thermal tempering.

(30) TABLE-US-00005 Monolithic (Post-HT) Characteristic Ex. 1 Ex. 2 Ex. 3 T.sub.vis (or TY)(Ill. C 2): 59.8% 55.6% 54.2% a*.sub.t (Ill. C 2): 3.9 5.3 4.8 b*.sub.t (Ill. C 2): 5.0 6.2 6.6 R.sub.fY (Ill. C, 2 deg.): 10.4% 6.1% 6.7% a*.sub.f (Ill. C, 2): 14.8 5.3 6.4 b*.sub.f (Ill. C, 2): 8.2 0.3 0.6 R.sub.gY (Ill. C, 2 deg.): 9.7 9.0% 9.1% a*.sub.g (Ill. C, 2): 9.6 0.9 0.9 b*.sub.g (Ill. C, 2): 3.9 10.9 10.2

(31) It can be seen from the above the examples above that the coated articles measured monolithically had desirable low visible transmission, and had fairly desirable glass side reflective color. In particular, monolithic a*.sub.g (glass side reflective a* color) was in a desirable range in Examples 2-3 of from about 0 to 2, and b*.sub.g (glass side reflective b* color) was in a desirable range in Examples 2-3 of from about 8 to 12. Moreover, glass side reflection (RgY) was good in that it was below 10%. These are desirable characteristics, especially when the coated article is to be put in an IG window unit as shown in FIG. 2.

(32) Set forth below are the optical characteristics of IG window units including the coated articles of Examples 1-3, namely when the coated articles are located in IG window units as shown in FIG. 2 (on surface #2 of the IG unit, so that glass side reflective values are indicative of from the outside). These values are for a non-HT coated article used in the IG unit (i.e., not thermally tempered).

(33) TABLE-US-00006 IG Unit (non-HT) Characteristic Ex. 1 Ex. 2 Ex. 3 T.sub.vis (or TY) (Ill. C 2): 47.1% 48.4% 48.4% a*.sub.t (Ill. C 2): 4.1 5.1 4.6 b*.sub.t (Ill. C 2): 4.6 4.3 5.4 R.sub.fY (Ill. C, 2 deg.): 16.3% 14.8% 13.5% a*.sub.f (Ill. C, 2): 7.2 4.1 4.3 b*.sub.f (Ill. C, 2): 4.3 0.7 1.5 R.sub.gY (Ill. C, 2 deg.): 12.0% 11.0% 10.0% a*.sub.g (Ill. C, 2): 4.4 2.7 2.4 b*.sub.g (Ill. C, 2): 6.3 9.3 9.2

(34) While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.