Double glazed windows containing a molecular sieve zeolite adsorbent having a preadsorbed low molecular weight polar material

An improvement in sealed insulating glass having an adsorbent disposed about all or part of the interior periphery of the glass is described. The improvement lies in employing a molecular sieve zeolite capable of adsorbing water and incapable of or having a very limited capacity for adsorbing nitrogen and oxygen as the adsorbent. This capability is obtained by using a molecular sieve zeolite whose pore size of 3 angstrom units does not adsorb oxygen and nitrogen as well as employing a molecular sieve zeolite whose effective pore diameter of about 4 angstrom units or larger permit the entry of oxygen and nitrogen but which has acquired an ability to suppress such adsorbtion by being pretreated by preadsorbing a minor amount of a low molecular weight polar material such as water vapor, ammonia, methanol etc. Preventing the adsorbtion and desorbtion of oxygen and nitrogen in a double glazed window eliminates pressure variations within the window space created by such gas movement.

BACKGROUND OF THE INVENTION 
Double glazed windows have been in use for some time as described in 
"Windows--Performance, Design and Installation" by Beckett and Godfrey, 
Van Nostrand Reinhold, New York (1974). A double glazed window consists of 
two parallel panes of glass which are spaced apart to leave an air space 
between the two panes and having the periphery of the space between the 
two panes closed by a moderately flexible sealant which extends between 
the two panes along their peripheries, holding them apart and enclosing a 
generally rectangular parallelepiped body of air between the two panes. 
Polybutene resins and polysulfide resins are commonly used as sealants in 
the construction of the double glazed windows. 
The purpose of a double glazed window is to provide thermal insulation and 
insulation against noise. At the time of their writing, Beckett and 
Godfrey noted the problem of condensation of water vapor contained in the 
air in the space between the two panes when the temperature of the air 
space drops below its dew point and noted that, "In the context of 
windows, condensation can occur both on the surface of the glass and on 
the frame facing the room and with double windows, additionally within the 
cavity between the two glazings. Whenever it occurs, the results can be 
very troublesome, impairing the view out and leading to the deterioration 
of the paint work and window frames." They note also that dehydrating 
agents and desiccants such as silica gel may be placed in the cavity to 
adsorb moisture from the entrapped air and so contribute to the 
suppression of condensation. 
Double glazed windows, commonly referred to as sealed insulating glass, 
commonly have a narrow body of solid adsorbent positioned in the space 
between the two panes and lying in close proximity to the sealing resin 
which both holds the two panes together and apart. The solid adsorbent is 
commonly held in a generally rectangular aluminum tube which is either 
perforated or not completely sealed so that the enclosed air may have 
contact with the adsorbent and this adsorbent may lie along all or part of 
the interior periphery of the sealed insulating glass. 
Passage of time and acquisition of experience has shown that condensation 
of water vapor is not the sole condensation problem attending the use of 
double glazed windows but that additionally over a period of time some 
decomposition of organic sealants occurs releasing condensible vapors such 
as hydrocarbon vapors or organic sulfide vapors which may also condense on 
the interior surface of the glass panes. It is current practice to use as 
the adsorbent to suppress condensation, a synthetic zeolite, sometimes 
referred to as a molecular sieve, or silica gel, or activated alumina, or 
a mixture of synthetic zeolite and a second adsorbent such as silica gel. 
The use of a second adsorbent to supplement large pore molecular sieve 
adsorbents was based on the observation that the rapid adsorption of water 
vapor by the molecular sieve reduces its capacity for adsorption of 
hydrocarbon vapors or organic sulfides. The molecular sieves which have 
been employed have all had pore diameters of such size that nitrogen 
molecules and oxygen molecules as well as water vapor molecules were able 
to penetrate the pores of the adsorbent. 
The use of molecular sieve zeolites of this character has given rise to a 
problem which appears not to have been recognized heretofore, but if it 
has been recognized, either it has been ignored or no solution for it has 
been proposed so far as is now known. 
The relatively recent discovery of the "energy problem" portends a great 
increase in the use of double glazed windows going far beyond current use 
in predominantly glass covered skyscrapers and extending to extensive use 
in dwelling houses and apartments. 
The seemingly certain large increase in the use of double glazed windows 
suggests that they be constructed to provide maximum efficiency and life 
and suggests that the problem which attends the use of adsorbents which 
adsorb not only water vapor but also nitrogen and oxygen can no longer be 
ignored. 
The problem may be defined as follows. In the northern part of the 
temperate zone the temperature of the air enclosed between the two panes 
of a double glazed window may easily rise to 110.degree. F. or above on a 
warm summer day and may fall to 0.degree. F. or below on a cold winter 
night. At the lower temperatures in this range, the molecular sieve 
zeolites currently used adsorb not only water vapor but also adsorb 
substantial amounts of oxygen and nitrogen. At higher temperatures 
adsorbed oxygen and nitrogen tend to be released from the adsorbent and 
migrate back into the gas space enclosed between the two panes. The 
resultant cycles of adsorption and desorption with temperature variation, 
both day-night variation and seasonal variation, results in significant 
changes in the pressure of the air enclosed between the two panes. The 
pressure of the enclosed air may commonly vary by 6% or more merely as a 
result of adsorption or desorption of oxygen and nitrogen. This pressure 
variation is, of course, amplified by the affect of temperature. For 
example, with rising temperature, not only are nitrogen and oxygen 
desorbed from the molecular sieve zeolites now in use, but in addition the 
rise in temperature itself causes an increase in the pressure of the gas 
enclosed between the two relatively rigid panes. Conversely, with falling 
temperature, the adsorption of nitrogen and oxygen increases with a 
resultant lowering of the pressure of the gas in the space enclosed 
between the two panes and in addition, the lowering of the temperature 
itself causes a further reduction in the pressure of the enclosed gas. 
These continuing fluctuations in pressure cause some distortion of view 
through the double glazed windows and, further, these fluctuations cause a 
backward and forward movement of the panes themselves with a resultant 
tendency to weaken the seals between the two panes formed by the resins 
and ultimately to permit openings between the exterior air and the 
enclosed air through the sealing resin which permits the enclosed space to 
more or less breathe with the result that over a period of time capacity 
of the adsorbent to take up additional water vapor introduced through such 
breathing is exhausted.

BRIEF DESCRIPTION OF THE INVENTION 
Pursuant to the present invention, the adsorbent which is disposed along 
the periphery of the space enclosed by the two panes of a double glazed 
window is a mixture of two adsorbent components. One adsorbent suitable as 
a first component is a molecular sieve zeolite which strongly adsorbs 
water vapor and which is either incapable of adsorbing nitrogen and oxygen 
molecules or has been preconditioned so that its capacity to adsorb oxygen 
and nitrogen is greatly reduced. One specific adsorbent meeting these 
requirements is the 3 A molecular sieve manufactured and sold by Union 
Carbide Corporation and by W. R. Grace & Co. This material has an average 
pore diameter in the range about 3 angstrom units, strongly and readily 
adsorbs water vapor and it does not adsorb either oxygen or nitrogen. 
The chemical composition of this particular molecular sieve is indicated by 
the following formula: 
EQU K.sub.9 Na.sub.3 [(AlO.sub.2).sub.12 (SiO.sub.2).sub.12 ].XH.sub.2 O 
the water content of the composition varies with the degree of dryness or 
activation of the zeolite but in the desired activated state should not 
exceed about 1.5% of the weight of the total composition. Other adsorbents 
suitable for use as the first component and which do not adsorb nitrogen 
or oxygen because of small average pore diameter may be obtained by 
starting with a sodium zeolite having average pore diameter size about 4 
angstrom units and displacing a substantial part of the sodium with 
potassium. The resultant potassium or partly potassium sieve has a reduced 
average pore diameter which permits entry of water vapor molecules into 
the pores and excludes oxygen and nitrogen molecules from the pores. 
Still another type of adsorbent which may be used as the first component of 
the mixture is a molecular sieve zeolite which has effective pore 
diameters which permit entry of oxygen and nitrogen into the pores, e.g., 
effective pore diameters of about 4 A or larger but which has been 
pretreated by preadsorbing a minor amount of a low molecular weight polar 
material such as water vapor, ammonia, methanol, ethanol, methyl amine and 
the like. Preadsorption of such materials has been reported to suppress 
oxygen and nitrogen adsorption but the mechanism of the suppression has 
not been explained nor has use of such pretreated adsorbents in double 
glazed windows been suggested. [Breck, et al., Journal of the American 
Chemical Society, 78,5963 (1956)]. 
The second component of the adsorbent is either silica gel or activated 
alumina having average pore diameters which permit the adsorption of 
benzene vapor. Silica gel or activated alumina is placed in the air space 
between the panes of the double glazed window for the purpose of adsorbing 
hydrocarbon and/or organic sulfide vapors which get into the space 
enclosed between the two panes as a result of slow decomposition of the 
polysulfide or polyolefin resins which are commonly used to seal the 
periphery of the double glazed window and which cause staining or 
discoloration of the interior surfaces of the panes unless they are 
promptly removed from the enclosed air space. Activated carbon will also 
function efficiently as a second adsorbent but because of its color more 
than usual care must be taken to confine it to the periphery of the 
interior space in the double glazed window. Mixtures of two or more of 
silica gel, activated alumina and activated carbon may be used as the 
second adsorbent if desired. 
DETAILED DESCRIPTION OF THE INVENTION 
Molecular sieve zeolites now generally referred to in the art as Type A 
molecular sieve zeolites are described in U.S. Pat. No. 2,882,243. Type A 
zeolites are described as truncated cube octahedrons having an internal 
central cavity or cage of 11 A.degree. diameter. The central cavities are 
entered through circular apertures of much smaller diameter, the diameter 
being determined by the specific cations contained. For instance, the Type 
4 A molecular zeolite has the formula Na.sub.12 [(AlO.sub.2).sub.12 
(SiO.sub.2).sub.12 ].XH.sub.2 O. When fully hydrated X is 27, but the 
sieve is activated to give it adsorbent capability by heating to drive the 
water of crystallization off until the water content of the total 
composition is reduced to 1.5% by weight or below. The Type 4 A sieve has 
an aperture opening about 4 A in diameter. When a substantial proportion 
of the sodium content of the 4 A sieve is replaced by potassium, the 
aperture diameter is reduced to about 3 A. For example, the Type 3 A 
molecular sieve is formed by displacing sodium from the Type 4 A sieve 
with potassium to reach the formula K.sub.9 Na.sub.3 [AlO.sub.2).sub.12 
(SiO.sub.2).sub.12 ].XH.sub.2 O. The Type 3 A molecular sieve has aperture 
openings of 3 A diameter. Other molecular sieves such as Type 5 A, Type 
10X, Type 13X, etc. have larger aperture openings. 
Directionally, the diameter of the aperture opening determines which 
molecules will be able to pass through the aperture opening into the 
central cage of the zeolite and so be adsorbed. It might be expected that 
the molecular sieve having aperture openings of 4 A would permit entry of 
molecules having a kinetic diameter less than 4 A and exclude from entry 
into the central cavity molecules having kinetic diameters greater than 4 
A. The matter of entry and exclusion, however, is not quite that simple. 
Breck and Smith writing in Scientific American, January 1959, note, "One 
might expect that molecules more than a 3.5 angstrom in diameter would be 
unable to enter the crystals (of a Type A sieve having aperture diameters 
of 3.5 angstroms) but the reality is not quite so simple. We find, for 
example, that ethane molecules with a diameter of 4 angstrom units readily 
pass through the 3.5 angstrom apertures at normal temperatures; propane 
molecules 4.9 angstrom units in diameter do not. The reason becomes clear 
enough when we recall that atoms are not rigid bodies. They more nearly 
resemble pulsating rubber balls. The pulsations of both the aperture atoms 
and the incoming molecules combine to make the effective diameter of the 
aperture considerably larger than its free diameter of 3.5 angstroms. 
Moreover, the kinetic energy of the incoming molecules helps them to 
`shoulder their way` through the opening. We have found in general that at 
ordinary temperatures molecules up to 0.5 angstroms wider than the free 
diameter of the aperture can pass through it easily. Larger molecules 
enter the crystal with greater and greater difficulty; molecules 1 
angstrom wider cannot enter at all." 
The quoted material above indicates the difficulty of defining a molecular 
sieve zeolite which will admit certain molecules and exclude others in 
terms of aperture diameter and kinetic diameter of the molecules. In order 
to know whether a molecular sieve having a given aperture diameter will 
admit or exclude molecules having a kinetic diameter greater than the 
aperture opening but not more than 1 angstrom greater, it is necessary to 
make a simple test by exposing the molecular sieve to the materials with 
which it may be hoped will be excluded and determine whether or not they 
are admitted or excluded. 
The Type 3 A molecular sieve admits and adsorbs water molecules and 
excludes oxygen molecules and nitrogen molecules. The minimum kinetic 
diameter of a water molecule has been reported at 2.65 A and the minimum 
kinetic diameters of oxygen and nitrogen molecules, respectively, at 3.46 
and 3.64 A. To determine whether a molecular sieve prepared by displacing 
part of the sodium from a 4 A sieve with potassium will admit or exclude 
nitrogen and oxygen requires a simple test of this sort if less than half 
of the sodium has been displaced. 
As noted above, the essential property of a molecular sieve zeolite which 
can be used to solve the problem of pressure swings in the space between 
the panes of double glazed windows is that the zeolite be capable of 
adsorbing water vapor and incapable of or having only a limited capacity 
for adsorbing oxygen and nitrogen. 3 A molecular sieve has this essential 
property because its average pore diameters are too small to permit entry 
of oxygen or nitrogen molecules into the pores. Molecular sieves such as 
Types 4 A, 5 A, 10X, 13X and the like have average pore diameters which 
permit entry of oxygen and nitrogen molecules into the pores, but if they 
are pretreated by preadsorbing a small amount of a low molecular weight 
polar material such as water vapor, ammonia, methanol, ethanol, methyl 
amine and the like, then their adsorption of oxygen and nitrogen is 
greatly reduced, i.e., to less than 20 percent of the adsorption that 
would occur absent the pretreating. For convenience, molecular sieve 
zeolite adsorbents having average pore diameters about 4 A or larger on 
which minor amounts of low molecular weight polar materials have been 
preadsorbed will be referred to hereinafter as pretreated zeolites. 
The quantity of low molecular weight polar material preadsorbed on the 
pretreated zeolites consists of minor amounts up to about 0.05 ml. per 
gram of zeolite, preferably in the range 0.0125 to 0.05 of normal density 
liquid polar material per gram of activated zeolite. Expressed in another 
way, the quantity of adsorbed polar material involves minor amounts up to 
about 4 percent of the weight of the zeolite, preferably in the range 1 to 
4 percent. 
The case of water which is a preferred polar material requires special 
comment. The zeolites freshly prepared have a high water content and in 
order to impart adsorptive activity to the zeolite, it is dehydrated at 
350.degree. C. or higher, the water content being reduced below 1.5 
percent by weight as a maximum and usually to a level about 1 percent by 
weight. The residual water content is probably not adsorbed water but 
probably water of crystallization. At all events, when water is used as 
the preadsorbed polar liquid, the preadsorption is carried to the point 
where the total water content of the zeolite is from above 1.5 to about 4 
percent by weight. It should be noted that one could reach water content 
levels in this range by controlling the activation by dehydration to leave 
about 1.5 to about 4 percent by weight of water in the zeolite. Water in 
amounts above 1.5 percent by weight has the same effect as preadsorbed 
water and for present purposes such excess water is considered 
preadsorbed. 
The desired level of preadsorbed water can be accurately fixed by heating 
the adsorbent to a temperature of 600.degree. F. and maintaining it at 
such temperature for a period of four hours. A stream of dry air is passed 
over the adsorbent during the four-hour period. At the end of the 
four-hour period the adsorbent is fully activated. The resulting fully 
activated adsorbent is cooled and then exposed to water vapor until it 
shows a weight increase of 1.5 to 4 percent. It is then ready for use in a 
double glazed window where it will adsorb water vapor from the air filling 
the space between the panes but will not adsorb oxygen or nitrogen. 
The use of water as the polar material preadsorbed presents an apparent 
difference between water and the other polar adsorbents in the sense of 
total polar material present in the adsorbent because of the fact that the 
activated zeolites have a water content as water of crystallization. In 
the case of water, the preadsorption must be carried to the point where 
the total water content of the adsorbent is generally in the range above 
1.5 up to 4 percent by weight. In the case of ammonia and the other polar 
adsorbents, preadsorption to give the adsorbent a polar material content 
in minor amounts up to about 4 percent adequately suppresses oxygen and 
nitrogen adsorption, preferably amounts in the range 0.75 to 4 percent. 
The effective quantity of preadsorbed polar material may also be expressed 
in terms of percent of capacity of the adsorbent to adsorb the polar 
material, so expressed the quantity of polar material is sufficient to 
exhaust from about 3 to 15 percent of the adsorptive capacity of the 
zeolite for the particular polar material adsorbed. 
Adsorbents for use in double glazed windows to control condensation of 
water vapor and of hydrocarbons or organic sulfides on the interior 
surfaces of the panes may be prepared by mixing Type 3 A molecular sieve 
zeolite with either a silica gel adsorbent or an activated alumina 
adsorbent having pore diameters sufficiently large to permit the 
adsorption of benzene molecules. 
These adsorbent mixtures should contain a minimum of about 15 percent by 
weight of the Type 3 A molecular sieve zeolite or pretreated zeolite and a 
minimum of about 25 percent by weight of silica gel or activated alumina. 
Both adsorbents are in the form of small particles having a mesh size 
generally in the range 10 to 30. The mesh size of the particles is not 
critical but sizes in this range facilitate filling the perforated 
aluminum tubes which are laid along the interior periphery of the double 
glazed window. 
An alternate heretofore unrecognized solution to the problems associated 
with the adsorption and desorption of oxygen and nitrogen is one in which 
a second adsorbent component is not required. It involves the use of a 
molecular sieve with pores sufficiently large to permit the adsorption of 
benzene vapor, i.e., having effective pore diameters above 6 A, preferably 
6 A to 13 A, but which has been pretreated by preadsorbing a minor amount 
of a low molecular weight polar material such as water vapor, ammonia, 
methanol, ethanol, methyl amine and the like. When disposed along the 
periphery of the space enclosed by the two panes of a double glazed 
window, these pretreated larger pore molecular sieves are capable of 
coadsorbing hydrocarbon and organic sulfide vapors and additional water 
vapor, but pressure fluctuations due to the adsorption and desorption of 
oxygen and nitrogen would be eliminated or greatly reduced. 
The quantity of the adsorbent mixture theoretically required to control 
water vapor condensation and hydrocarbon condensation is quite small being 
somewhat less than 7 grams for a 3 foot by 5 foot double glazed window 
having a one-half inch space between the panes. Because, however, minor 
imperfections in the sealing of the two panes of double glazed windows are 
unavoidable in a fair proportion of them which permits migration of water 
vapor from the outside air into the interior space, because hydrocarbon or 
organic sulfide release is more rapid during the curing of the resin and 
prompt removal of these vapors is necessary to avoid staining of the 
interior surface, and because consumers are demanding extended warranties 
on the life of double glazed windows, the quantity of adsorbent disposed 
along the periphery of the interior space should be a quantity in the 
range about 0.01 gram to 1.0 gram of adsorbent for each cubic inch of 
space enclosed between the two panes, larger amounts may be used if 
desired but ordinarily no benefit attends the use of larger amounts. In 
the event that more than two panes of glass are used, i.e., a triple 
glazed window is produced the same adsorbent loading would be used in the 
spaced between adjacent panes. 
While it is preferred to use a mixture of particulate molecular sieve 
zeolite with particulate silica gel, activated alumina or activated 
carbon, effective suppression of condensation with simultaneous avoidance 
of pressure fluctuations due to nitrogen and oxygen adsorption and 
desorption may be achieved by filling some rectangular aluminum tubes with 
the molecular sieve zeolite and others with the second adsorbent and then 
placing zeolite filled tubes along one or more peripheral sides of the 
space enclosed between the two panes and tubes filled with the second 
adsorbent along one or more of the remaining peripheral sides. 
Additionally, the filling of the rectangular aluminum tubes may be carried 
out not only by pouring granular adsorbent into the tubes but also, if 
desired, the adsorbents may be compressed into rod-like shape sized to 
slide into the aluminum tubes. 
While the greater proportion of the double glazed windows now manufactured 
employ the combination of polyolefin or polysulfide resins and adsorbent 
filled aluminum tubes to maintain spacing between the two panes and seal 
the periphery of the space enclosed between the panes, some double glazed 
windows are manufactured using lead strips and an adhesive to close the 
space between the panes and maintain the spacing between them. In such 
windows, the second adsorbent is not required because there are no resin 
decomposition products to contend with, only a zeolite molecular sieve 
adsorbent capable of adsorbing water vapor and incapable of adsorbing 
nitrogen and oxygen need be used. In this type of double glazed window, 
from about 0.01 to 0.6 grams of adsorbent per cubic inch of enclosed space 
adequately suppress water vapor condensation.