Sealant system for an insulating glass unit

An insulating glass unit is provided having a first glass sheet spaced from a second glass sheet by a spacer frame. The spacer frame, preferably a flexible spacer frame, has a first side and a second side, with the first side located adjacent an inner-surface of the first glass sheet and the second side located adjacent the inner-surface of the second glass sheet. A sealant system, e.g. a three component sealant system, is provided adjacent each side of the spacer frame, e.g. by forming or flowing the sealant system on the outer surface of the spacer frame, to hold the glass sheets to the spacer frame. The sealant system includes a first structural sealant, such as a thermosetting material, spaced from a second structural sealant, such as another or the same thermosetting material. A moisture barrier material, preferably a thermoplastic material such as PIB, is located between the first and second structural sealant materials.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates generally to an insulating glass unit and, in
 particular, to a moisture impervious sealant system for an insulating
 glass unit and a method of making same.
 2. Description of the Currently Available Technology
 It is well recognized that insulating glass (IG) units reduce the heat
 transfer between the outside and inside of a building or other structure.
 Examples of IG units are disclosed in U.S. Pat. Nos. 4,193,236; 4,464,874;
 5,088,258; and 5,106,663 and European reference EP 65510, the teachings of
 which are herein incorporated by reference. A sealant system or edge seal
 structure of the prior art is shown in FIG. 1. The IG unit 10 of FIG. 1
 includes two spaced apart glass sheets 12 and 13 adhesively bonded to a
 rigid spacer frame 14 by a sealant system 15 to provide a chamber 16
 between the two glass sheets 12 and 13. The chamber 16 can be filled with
 a selected atmosphere, such as argon or krypton gas, to enhance the
 performance characteristics of the IG unit 10. The sealant system 15
 bonding the glass sheets 12 and 13 to the spacer frame 14 are expected to
 provide structural strength to maintain the unity of the IG unit 10 and
 prevent gas leaking out of the chamber 16 or the atmosphere from outside
 the IG unit 10 from moving into the chamber 16. The sealant system 15
 includes a layer 17 of moisture resistant sealant at the upper section of
 the spacer 14 to prevent the ingress and egress of gas into and out of the
 chamber 16 and a layer 18 of a structural type sealant, such as silicone
 to secure the sheets to the spacer. A moisture resistant sealant usually
 used in the art is polyisobutylene (PIB).
 In addition to adhering the two glass sheets 12 and 13 to the spacer frame
 14 and forming a moisture impervious barrier, the sealant system 15 should
 accommodate the natural tendency for the edges of the glass sheets 12 and
 13 to rotate or flex due to changes in atmospheric pressure in the chamber
 16 as a result of temperature, wind load and altitude changes, such as
 when an IG unit is manufactured at one altitude and installed at a
 different altitude. The spacer and selected sealant system should maintain
 the structural integrity of the IG unit as well as the sealing properties
 of the edge seal structure even during such changes.
 As will be appreciated, box spacer frames 14, such as shown in FIG. 1, are
 not well suited for allowing such flexibility. For example and with
 reference to FIG. 2, as the distance between the sheets 12 and 13
 increases because of pressure differences inside and outside of the
 chamber 16, the sealant system 15, in particular the layer 17 of the
 moisture resistant sealant, stretches and thins under stress, which
 decreases its ability to prevent atmospheric air from moving into and/or
 gas escape from the chamber 16. With rigid, box spacer frames, the
 structural sealant system 15 tends to become over stressed with time and
 fails prematurely. Additionally, the rigid spacer frame itself may become
 over-stressed and may collapse or deform or the glass sheets may become
 over-stressed at the edges and crack. Further, if the chamber between the
 glass sheets is filled with gas such as argon, krypton or other such
 insulating gas, the deformation of the sealants 17 and 18 and/or spacer
 frame 14 often results in accelerated loss of those gases from the chamber
 into the surrounding atmosphere.
 An alternative to the prior art arrangement shown in FIG. 1 is to use a
 more flexible spacer frame, e.g. of the type disclosed in U.S. Pat. Nos.
 5,655,282; 5,675,944; 5,177,916; 5,255,481; 5,351,451; 5,501,013; and
 5,761,946, the teachings of which are herein incorporated by reference.
 While such flexible spacer frames help alleviate some of the problems
 encountered with rigid spacer frames, the use of flexible spacer frames in
 and of themselves may not completely eliminate the edge breakage and vapor
 and/or gas transmission problems associated with known edge seal and/or IG
 unit construction.
 Therefore, it would be advantageous to provide an IG unit having a sealant
 system which reduces or eliminates the problems associated with known
 spacer frame and adhesive construction and a method of fabricating such an
 IG unit.
 SUMMARY OF THE INVENTION
 An insulating glass unit is provided having a first glass sheet spaced from
 a second glass sheet by a spacer frame. The spacer frame, preferably a
 flexible spacer frame, has a first side and a second side, with the first
 side located adjacent an inner-surface of the first glass sheet and the
 second side located adjacent the inner-surface of the second glass sheet.
 A sealant system incorporating features of the invention is provided on
 each side of the spacer frame to hold the glass sheets to the spacer
 frame. The sealant system includes a first structural sealant, preferably
 a thermosetting material, spaced from a second structural sealant, such as
 another or the same thermosetting material. A moisture barrier or moisture
 impervious material, preferably a thermoplastic material such as PIB, is
 located between the first and second structural sealant materials.
 A method is also provided for making and using the sealant system of the
 invention for an insulating glass unit. A spacer frame is provided between
 a pair of glass sheets to provide a chamber therebetween. The spacer frame
 is preferably a flexible spacer frame fabricated by bending or forming a
 spacer stock. The spacer frame has a base and two spaced apart legs joined
 to the base to provide a substantially U-shape. The sealant system is
 applied to the spacer frame, e.g. beads of sealant material are provided
 onto the outer surfaces of the spacer frame, e.g. onto the outer surfaces
 of the legs and optionally onto the outer surface of the base. The sealant
 system includes a bead of low moisture vapor transmission or moisture
 barrier material, e.g., a thermoplastic material such as polyisobutylene
 or hot melt butyl, located between two beads of structural sealant, e.g.,
 a thermoset material such as a silicone containing adhesive. The glass
 sheets are secured to the spacer frame by the sealant system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 For purposes of the description hereinafter, spatial or directional terms
 such as "inner", "outer", "left", "right", "back" shall relate to the
 invention as it is shown in the drawing figures. However, it is to be
 understood that the invention may assume various alternative orientations
 and step sequences without departing from the inventive concepts disclosed
 herein. Accordingly, such terms are not to be considered as limiting.
 A portion of an IG unit 11 having a sealant system 23 incorporating
 features of the invention is shown in FIGS. 3 and 4. The IG unit 11 has a
 first glass sheet 19 with an inner surface 21 and an outer surface 25. The
 first glass sheet 19 is spaced from a second glass sheet 20 having an
 inner surface 22 and an outer surface 24. The distance between the two
 glass sheets 19 and 20 is maintained by an edge assembly 26 having a
 spacer frame 28 which is adhesively bonded to the two glass sheets 19 and
 20 by the sealant system 23. Although not limiting to the invention, the
 two glass sheets 19 and 20 may be spaced about a half an inch, more
 preferably about 0.47 inch (about 1.20 cm) apart to form a chamber 30 or
 "dead space" between the two glass sheets 19 and 20. The chamber 30 can be
 filled with an insulating gas such as argon or krypton. A desiccant
 material 32 may be adhesively bonded to one of the inner surfaces of the
 spacer frame 28 in any convenient manner. E.g. as shown in FIG. 3 to inner
 surface 41 of the base 40 of the spacer frame 28.
 The two glass sheets 19 and 20 may be clear glass, e.g., clear float glass,
 or one or both of the glass sheets 19 and 20 could be colored glass. A
 functional coating 34, such as a solar control or low emissivity coating,
 may be applied in any conventional manner, such as MSVD, CVD, pyrolysis,
 sol-gel, etc., to a surface, e.g., an inner surface, of at least one of
 the glass sheets 19 or 20.
 The spacer frame 28 itself may be a conventional rigid or box-type spacer
 frame as is known in the art, e.g. as shown in FIG. 1. However, it is
 preferred that the spacer frame 28 be a flexible-type spacer frame which
 may be formed from a piece of metal, such as 201 or 304 stainless steel,
 or tin plated steel and bent and shaped into a substantially U-shaped,
 continuous spacer frame as described hereinbelow. The spacer frame 28 is
 adhesively bonded around the perimeter or edges of the spaced glass sheets
 19 and 20 by the sealant system 23.
 The spacer frame 28 shown in FIGS. 3 and 4 may be formed in conventional
 manner from a piece of metal, e.g. steel, having a thickness of about
 0.010 inch (0.025 cm). The spacer frame 28 includes a base 40 having an
 inner surface 41, an outer surface 43 and a width of about 0.25-0.875 in
 (0.64 cm to 2.22 cm). The spacer frame 28 has opposed first and second
 sides defined by a pair of opposed legs 42 and 44, respectively, which
 extend from the base 40. Each leg 42,44 has a length of about 0.300 inch
 (0.76 cm) with a stiffening element 46 having a length of about 0.05 to
 0.08 inch (0.13 to 0.02 cm) formed on the outer end of each leg 42,44.
 Each stiffening element 46 has a longitudinal axis which extends
 transverse, e.g. substantially perpendicularly, to the longitudinal axis L
 of its associated leg 42,44. The spacer 28 is configured such that each
 leg 42,44 is substantially flexible to provide for movement of the glass
 sheets 19 and 20 due to pressure or atmospheric changes as shown in FIG. 4
 and discussed further hereinbelow. Preferably, each leg 42,44 is
 sufficiently flexible to be deflectable by at least about 0.5-1.0 degree
 from the neutral position shown in FIG. 3 in which each plane having one
 of the legs 42,44 is substantially perpendicular to a plane having the
 base 40. Each leg 42,44 includes an inner surface 48 facing the interior
 of the IG unit 11 and an outer surface 50 facing the inner surface 21 or
 22 of the adjacent glass sheet 19 or 20. Although it is preferred that the
 spacer frame 28 be metal, the invention is not limited to metal spacer
 frames. The spacer frame 28 could be made of a polymeric material, e.g.,
 halogenated polymeric material such as polyvinylidene chloride or fluoride
 or polyvinyl chloride or polytrichlorofluoro ethylene. The spacer frame 28
 should be "structurally sound", meaning that the spacer frame 28 maintains
 the glass sheets 19 and 20 in spaced relationship while permitting local
 flexure of the glass sheets 19 and 20 due to changes in barometric
 pressure, temperature and wind load.
 The sealant system 23 of the invention formed between the outer surface of
 the spacer frame 28, e.g. the outer surface 50 of a spacer leg 42,44 and
 the inner surface 21 or 22 of its associated glass sheet 14 or 20, will
 now be described. The sealant system 23 is preferably a "triple seal"
 system utilizing three separate or distinct sealant regions utilizing both
 structural sealants and a moisture barrier sealant, such as a moisture
 resistant or low moisture vapor transmission rate (MVTR) sealant. As used
 herein, the terms moisture barrier, moisture resistant or low MVTR sealant
 refer to sealants which are impervious or substantially impervious to
 moisture or moisture vapor. Specifically, the sealant system 23 includes a
 first structural sealant material 56 located near the outer end of each
 leg 42,44 and a second structural sealant material 58 spaced from the
 first structural sealant material 56 and located near the base 40. The
 structural sealant materials 56 and 58 are both preferably thermosetting
 materials, i.e. materials capable of becoming permanently rigid when
 heated or cured, and preferably have a tensile strength of about 200-300
 psi at 200 percent elongation in accordance with ASTM D412. The structural
 sealant materials 56,58 are both preferably one part, hot-applied,
 chemically curing, silicone modified, polyurethane insulating glass
 sealant. An example of an acceptable sealant is PRC 590 sealant
 commercially available from PPG Industries, Inc. of Pittsburgh, Pa. A low
 MVTR sealant material 60 is positioned between the two structural sealant
 materials 56 and 58. The low MVTR sealant 60 preferably has a moisture
 vapor transmission rate of less than about 0.20 grams per square meter per
 day as measured on a 0.060 inch film and a gas permeance of less than
 about 1-3 cubic centimeters per 100 square inches per day, as measured on
 a 0.040 inch film as defined by ASTM D1434. Examples of an acceptable low
 MVTR sealant 60 include polyisobutylene (PIB) or hot melt butyl.
 In the preferred embodiment of the invention shown in FIG. 3, the first
 structural sealant material 56 has a thickness (t) of about 0.015 to 0.025
 inch (0.038-0.064 cm) and a length (x) of about 0.125 inch (0.318 cm). The
 low MVTR sealant 60 has a thickness (t) of about 0.015 to 0.025 inch
 (0.038-0.064 cm) and a length (y) of about 0.125 inch (0.0318 cm). The
 second structural sealant 58 has a length (z) of about 0.090 inch (0.23
 cm) and, as shown in FIG. 3, preferably extends across the width of the
 spacer 28, e.g., extending across the perimeter groove formed by the outer
 surface 43 of the base 40 and the marginal edges of the glass sheets 19
 and 20. This combination of sealants 56, 58 and 60 along with the
 flexibility of the spacer legs 42 and 44 provides enhanced structural
 capacity as well as low moisture and gas permeation properties to the IG
 unit 11.
 As shown in FIG. 4, when stress is applied to the IG unit 11 causing
 rotation or movement of the glass sheet 19, the structural sealants 56 and
 58 ensure that the spacer leg 44 flexes or moves with the glass sheet 19
 to help relieve the stress. For example, computer generated finite element
 analysis was conducted to compare the performance of a rigid, box-type
 spacer sealed to opposed glass sheets by a dual sealant structure (shown
 in FIGS. 1 and 2) with the performance of a flexible spacer sealed to
 opposed glass sheets by the triple sealant structure (shown in FIGS. 3 and
 4). The largest amount of stress, i.e., stretching or pulling force per
 unit area of the sealant, was found at the inner edge of the edge seal
 where the peeling force is the greatest. At a glass deflection which
 yielded a stress of about 500 psi in the dual sealant system, the triple
 sealant system with the flexible spacer had a stress of only about 150
 psi. This lower stress helps prevent premature failure of the sealant
 system 23 of the invention. Further, the dual sealant system is calculated
 to have a moisture vapor transmission of about 0.074.times.10.sup.-5
 gm-in/hr-sq.ft.-inch of mercury (Hg) while the triple sealant system of
 the invention with a flexible spacer was calculated to have a moisture
 vapor transmission of about 0.0012.times.10.sup.-5 gm-in/hr-sq.ft.-inch of
 Hg, a reduction by a factor of about sixty four. Since the MVTR sealant 60
 is dammed between the two structural sealants 56 and 58, there is little
 or no stretching of the MVTR sealant 60 as was common in the prior art.
 A method of fabricating an IG unit 11 incorporating a sealant system 23 in
 accordance with the invention will now be described. As will be
 appreciated, the IG unit 11 and spacer frame 28 may be fabricated in any
 convenient manner, for example as taught in U.S. Pat. No. 5,655,282 but as
 modified as discussed hereinbelow to include the sealant system 23 of the
 invention. For example, a substrate, such as a metal sheet of 201 or 304
 stainless steel having a thickness of about 0.010 inch and a length and
 width sufficient for producing a spacer frame of desired dimensions, may
 be formed by conventional rolling, bending or shaping techniques, for
 example as described in U.S. Pat. No. 5,655,282 . Although the sealant
 materials 56,58 and 60 may be positioned on the substrate before shaping,
 it is preferred that the sealant materials 56,58 and 60 be applied after
 the spacer frame 28 is shaped. The sealant materials 56,58 and 60 may be
 applied in any order. The second structural sealant material 58 may be
 applied with multiple nozzles, e.g., one nozzle applying the second
 structural sealant material 58 to the side of the spacer 28, i.e., on the
 outside of the leg 42 or 44, and another nozzle applying additional second
 sealant material 58 across or on the outer surface 43 of the base 40. The
 IG unit 11 is assembled by positioning and adhering the glass sheets 19
 and 20 to the spacer frame 28 by the sealant system 23 in any convenient
 manner. An insulating gas, such as argon or krypton, may be introduced
 into the chamber 30 in any convenient manner. Together, the structural
 sealant material beads act to attach the glass sheets 19,20 to the spacer
 frame 28. In the practice of the invention, a low moisture permeation and
 low gas permeation, low modulus, non-structural sealant, such as PIB or
 hot melt butyl, is contained and constrained in the space between the two
 structural sealant beads. Because of the strength and structural nature of
 the structural sealant beads, the non-structural low MVTR material does
 not deform to any great extent during loading and therefore maintains its
 original low moisture and low gas permeation properties.
 It will be readily appreciated by those skilled in the art that
 modifications may be made to the invention without departing from the
 concepts disclosed in the foregoing description. For example, although the
 exemplary embodiment described above utilized two glass sheets attached to
 the spacer, the invention is not limited to IG units having only two glass
 sheets but may be practiced to make IG units have two or more glass
 sheets, as are known in the art. Further, in the preferred embodiment of
 the invention, the sealant system was used with a spacer frame having a
 generally U-shaped cross-section; the invention, however, may be used with
 a spacer having any type of cross-section, e.g. of the type shown in FIG.
 1. Still further, the invention was discussed by providing a portion of
 the sealant system in a channel formed by the outer surface of the base of
 the spacer frame and inner marginal edge portion of the sheets extending
 beyond the outer surface of the base. The invention may be practiced by
 not providing for any sealant in the channel or in the alternative
 aligning the peripheral edge of each sheet with the outer surface of the
 base or in another alternative by the outer surface of the base extending
 beyond the peripheral edges of the sheets. Still further, the layers of
 the sealant system may be applied or flowed onto the outer surface of the
 spacer frame in any convenient manner, e.g. one layer, two layers or three
 layers flowed onto the spacer frame. Accordingly, the particular
 embodiments described in detail herein are illustrative only and are not
 limiting to the scope of the invention, which is to be given the full
 breadth of the appended claims and any and all equivalents thereof.