Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-04-15
2001-11-27
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S331400, C428S419000, C528S076000, C528S085000
Reexamination Certificate
active
06322650
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an improved sealant for insulating glass windows which has a combination of the best properties of a polyurethane and a polysulfide. It further relates to a hydroxyl terminated polysulfide from which said polyurethane is made.
The term “insulating glass window” refers to a structure comprising panes of glass, the faces of which are in spaced relationship, thereby providing a space between the panes which imparts insulating properties to the structure. In its most widely used form, 2 parallel panes are positioned in spaced relationship by metallic or organic resin spacers placed inboard around the perimeter of the panes, thereby forming a U-shaped channel in which the interior faces of the pane are the legs and a side of the spacer is the base of the channel. Typically, the spacer is a hollow form filled with a water-absorbent material, such as a molecular sieve, to keep the enclosed air space dry. The U-shaped channel around the perimeter of the window is filled with a sealant which must have a combination of properties for satisfactory use. Some of those properties are as follows.
The sealant must have very low moisture vapor transmission (MVT) rate so that moisture is prevented from entering the dry space between the panes of glass. Moisture in such space tends to reduce its insulating value and it can also condense on the interior faces of the panes, creating visibility and aesthetic problems. If the sealant does not have a satisfactory MVT rate, the longevity of the insulated unit will be severely reduced.
The sealant should have good elongation and flexibility so that it “gives” during contraction and expansion of the insulated glass structure caused by temperature changes, thus relieving glass stress.
The sealant should also form an excellent bond with glass which is not degraded over long periods of use when exposed to sunlight, moisture, and large temperature changes. Lap shear strength and tensile adhesion strength are important factors of the bond strength.
In U.S. Pat. No. 3,386,963, Santaniello discloses certain isocyanate terminated polysulfide pre-polymers that are curable with polyols to form sealants and adhesives. The pre-polymers are made from hydroxyl terminated polysulfides having the formula:
HO—R′SS(R″SS)
n
R′—OH
wherein R′ and R″ are the same bivalent alipatic radical wherein the carbon chain may be interrupted by oxygen atoms and the molecular weight is from 500 to 9000. There is no teaching, however, about the properties of polyurethanes having a polysulfide backbone when R′ is polymethylene.
SUMMARY OF THE INVENTION
It is unexpected that such polyurethanes exhibit some of the best characteristics of both polymers rather than the worst of each.
It is an object of this invention, therefore, to provide a method for sealing insulating glass windows with rugged sealants that combine the excellent liquid polysulfide attributes of low argon migration, good resistance to free radical oxidation, and good workability with the polyurethane characteristics of low MVT, low water swell, good electrical resistance, good resistance to solvents and wood preservatives, and good adhesion to organic components of insulated glass windows.
It is another object of this invention to provide a sealant whose hardness is greater than that of a polysulfide-based polyurethane sealant of the prior art having the same molecular weight and cross-link density.
It is a related object of this invention to provide an isocyanate-terminated polysulfide which may be used as an intermediate or precursor in the formation of the insulated glss sealant.
These and other objects which will become apparent from the following description of the invention are achieved by splitting the polysulfide having the general structure of Formula I, as follows:
HSCH
2
CH
2
OCH
2
OCH
2
CH
2
S[S
x
CH
2
CH
2
OCH
2
OCH
2
CH
2
S]
m
S
x
CH
2
CH
2
OCH
2
OCH
2
CH
2
SH
wherein x averages 1.25, at the S—S
x
bond by reacting it as a latex dispersion in water with a dithiodialkyleneglycol and aqueous sodium sulfite at the reflux temperature, and adding hydrogen peroxide for oxidative coupling of chains having residual sulfhydryl groups. This yields a mixture of hydroxyl terminated polysulfides having an average molecular weight about 3% of the initial value and having the general structure represented by Formula II:
RCH
2
CH
2
OCH
2
OCH
2
CH
2
S[SCH
2
CH
2
OCH
2
OCH
2
CH
2
S]
n
SCH
2
CH
2
OCH
2
OCH
2
CH
2
R
wherein R═HO(CH
2
)
y
SS, y is from 2 to 6, and (n <<<m) of Formula I and is such that the molecular weight is from about 2500 to about 4000.
The general structures represented by Formula I and Formula II may be modified by a limited degree of crosslinking introduced into the product of the first step in the preparation of the well known liquid polysulfides known by the trademark LP. Up to about 2% by weight Of a crosslinking agent such as 1,2,3-trichloro-propane may be used. The two step preparation of the liquid polysulfides is described in U.S. Pat. No. 2,789,958, which is incorporated herein by reference.
The improved sealant of this invention may then be prepared by a one-step procedure wherein the hydroxyl terminated polysulfide of Formula II is reacted with a polyisocyanate at a ratio between about 1:1 and about 1:1.2, preferably about 1:1.15 (e.g., about 1:1.08), on an equivalents basis. The final stages of the reaction may take place after the partially cured sealant is in place in the window. Alternatively, the formation of the sealant may be undertaken in a two-step procedure wherein an isocyanate-terminated polysulfide is formed first and then the stoichiometric requirement of additional hydroxy-terminated polysulfide is mixed with the precursor.
DETAILED DESCRIPTION OF THE INVENTION
The dithiodialkylene glycols, wherein the alkylene group contains from 2 to 6 carbon atoms, are prepared by the method taught in U.S. Pat. No. 2,527,378, which also is incorporated herein by reference. The simplest dithiodialkylene glycol, often simply called dithiodiglycol, is the preferred one but other examples include dithiodipropylene glycol, dithiodibutylene glycol, and dithiodihexylene glycol.
In Formula II, n=11-23 or such that the molecular weight of the hydroxyl terminated polysulfide is from about 2000 to about 4000, preferably from about 2500-3500.
A wide variety of polyisocyanates can be reacted suitably with the above-described hydroxyl terminated polysulfides to prepare the polysulfide-based polyurethanes that have found in this invention to be superior insulated glass sealants. Generally, any of the organic polyisocyanates that have been proposed previously for the preparation of polyurethane resins may be employed here. Suitable polyisocyanates are, for example, isophorone diisocyanate (abbreviated as IPDI); arylene polyisocyanates such as tolylene-, metaphenylene-, methylene-bis-(phenylene-4-) (abbreviated as MDI and sold under the trademark RUBINATE 9310), biphenylene-4,4′-; 3,3′-dimethoxybiphenylene-4,4′-; 3,3′-biphenylene-4,4′-; and methylene-(tetramethylxylene-) (abbreviated as MTMXDI); alkylene polyisocyanates such as ethylene-, ethylidene-, propylene-1,2-, butylene-1,4-; butylene-1,3-; cyclohexylene-1,4-,; methylene-bis(cyclohexyl-4,4′)-; and hexamethylene-1,6-diisocyanate (abbreviated as HDI. Commercially available isocyanate-terminated prepolymers such as the MDI prepolymer sold under the trademark RUBINATE 1790 are also suitable as curing agents in this invention.
A suitable procedure for making the insulated glass sealants of this invention comprises making a sealant base first by mixing the hydroxyl terminated polysulfide, a curing catalyst, a chain stopper, a plasticizer, fillers, dehydrating agents, and thixotropic agents. The sealant base (Part A)is sold along with the curing agent (Part B)as a two part package to be combined shortly before placement around the perimeter of the U-shaped channel of a twin-paned window. The general pro
Gilmore John R.
Hobbs Steven J.
Potts Keith B.
Falk Stephen T.
Gallagher John J.
Morton International Inc.
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