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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to composite energy control sheets and to window
units incorporating such sheets.
For at least the past several decades many people have striven to develop a
window cover or shade which would allow sunlight's visible wave lengths
(0.4-0.7 micrometer) to pass through a glazed window into a room but which
would simultaneously reduce glare and exclude sunlight's heat-generating
near infrared wave lengths (0.7-2.5 micrometers). Lion, U.S. Pat. No.
2,774,021, for example, discloses a window shade in which a transparent or
translucent self-supporting cellulosic foil is coated with a
transparent-reflective layer of metal on the side adjacent the window, a
protective layer of varnish or the like optionally being applied over the
metal layer to reduce corrosion or mechanical damage. Subsequent
refinements of Lion's window unit (i.e., windowpane plus shade) have
included inner storm windows, where the solar control sheet is sealed or
attached to the window frame to provide a dead air space between the glass
and the shade.
Antonson et al, U.S. Pat. No. 3,290,203 describes and claims a window unit
in which a transparent foil (especially a polyester foil) is provided with
a transparent-reflective metal layer on one face, the metal layer being
covered by a transparent protective layer which in turn in adhered to the
inside of a conventional windowpane. This type of window unit, which is
simple, compact and convenient, has been found more effective than the
Lion window unit in blocking the entry of solar-generated near infra-red
energy into a room. The transparent protective layer may be either a
coating or, if desired, a second polyester foil adhered in place, as is
shown in, e.g., Windorf, U.S. Pat. No. 3,775,226; in the latter case,
either of the two polyester foils may be adhered to the windowpane. The
adhesive which bonds the solar control sheet to the windowpane may be
water-soluble (cf. the aforementioned Antonson et al patent),
pressure-sensitive, pressure-sensitive but water-activatable (c.f.
Theissen, U.S. Pat. 3,681,179), or of a "cling" nature (cf. Burger, U.S.
Pat. 4,095,013).
As will be apparent from the foregoing discussion, work in the solar energy
control sheet art has been almost exclusively concerned with keeping
sunlight's heat and glare from affecting the comfort of those inside a
room, hence, energy control sheets have been most widely used in those
geographical areas where the outside temperature rarely falls below
0.degree. C. Studies have shown, however, that windows not only contribute
heavily to high air conditioning energy usage in the summer but also
contribute significantly to high heating costs in winter. The thermal
conductance (or "U" value*) of a single glazed window typically exceeds 5
kcal/.degree.C. hr. m.sup.2, whereas a well-insulated wall has a U value
less than 0.5 and a well-insulated ceiling has a U value less than 0.2.
Thus, heat can be lost through a conventionally glazed window at a rate
over an order of magnitude greater than through insulated walls or
ceilings. In cold regions, attempts to make the occupants of a room
comfortable in winter have usually involved adding external storm windows
(which is not always feasible) and drawing opaque drapes across the face
of the window, thereby blocking any view of the outside.
*The insulative (or "R" value) is the reciprocal of a "U" value; e.g., a U
value of 0.1 is equivalent to an R value of 10. In English units, U is
expressed as BTU/.degree.F. hr. ft.sup.2. In metric units, U is expressed
as kcal/.degree.C. hr. m.sup.2.
Prior to the present invention, those persons in cold countries who
occupied rooms where the windows were protected with solar control sheets
(especially where such sheets were adhered to the inner surface of a
windowpane) often felt cold in winter for at least two reasons.
Solar-originating near infra-red energy (0.7-2.5 micrometers) was
reflected back outside; additionally, heat inside the room was transferred
to the windowpane by radiation and convection and lost to the outside.
Nearly half of such loss was caused by internal infra-red energy (wave
length range of about 4-40 micrometers) radiating from the skin of room
occupants, as well as from the outside of objects in the room, to the
solar control sheet, where it was absorbed by the foil adjacent the room,
transmitted by conduction to the metalized layer, further conducted to the
windowpane and then radiated to the outside. Although there has been a
desire to maintain the visual advantages of solar energy control sheets
while improving their poor insulative properties, no means for achieving
such an objective has previously been provided. Thus, for example, it has
been suggested* that the conventional infra-red absorbing polyester foil
could be replaced with polyethylene (which is relatively transparent to
infra-red rays), but it has been found impractical to apply a metal vapor
coating to polyethylene for use in a solar energy control sheet, one or
more of such properties as handling, adhesion, reflectivity and optical
clarity being unsatisfactory.
*See, e.g., American Institute of Physics Conference Proceedings, No. 25,
Efficient Use of Energy, Part III, p. 292, New York, NY, 1975
SUMMARY
The present invention is an improved and surprisingly effective form of
energy control sheet. When incorporated into a window unit in the outside
wall of a room, this new product not only effectively excludes externally
originating heat and glare during the summer but also substantially
reduces heat loss from internally originating radiation of infra-red
energy during the winter or, indeed, whenever the outside temperature is
lower than the inside temperature.
The invention makes it possible to modify a window unit located in the
external wall of a room, such units conventionally comprising a plurality
of transparent strata including (a) a glazing unit having an inside face
oriented toward the interior of the room and an outside face oriented
toward the exterior of the room, said glazing unit comprising at least one
rigid transparent stratum (or pane) whose inner face coincides with the
inside face of the glazing unit, and (b) a flexible, transparent energy
control stratum which is located adjacent to* said glazing unit or, in the
case of the multi-pane glazing unit, adjacent to either surface of one of
its component panes, and which is a flexible, unitary, multi-layer sheet
comprising a transparent-reflective metal layer bonded to a transparent
polymeric support layer and protectively covered by a transparent
polymeric layer. Most (if not all) of the presently commercial solar
energy control sheets utilize support layers of polyester foil (biaxially
oriented polyethylene terephthalate), which offers the combined advantages
of strength, flexibility, clarity and moderate cost. Other polymers which
can be made into functional support foils include polyvinyl fluoride,
polyvinylidene fluoride, polycarbonates, polystyrene, polymethyl
methacrylate, polyimides, polyamides, ionomers, etc., as well as esters
and mixed esters of cellulose, stabilizers against degradation caused by
ultraviolet light being included where appropriate. Unfortunately,
however, all of these polymers have low infra-red radiation transmission
properties and high infra-red radiation absorption properties.
*To avoid any misunderstanding, the phrase "adjacent to" as used herein is
intended to mean either near to or in contact with.
The improvement lies in making two changes in the energy control stratum,
viz., (1) selecting a transparent polymeric protective layer which
transmits at least about 80%* of the normal room temperature radiant
energy in the wave length of 4 to 40 micrometers and (2) locating the
energy control stratum other than adjacent the outside face of the glazing
unit and orienting it so that the protective layer does not contact any
surface of the glazing unit. As a result of this modification of otherwise
conventional energy control sheets and their use, window units of the
invention not only effectively exclude externally originating heat and
glare but also ensure the retention of most internally originating
infra-red energy and thereby significantly improve the insulative
effectiveness of the window unit in cold weather. The infra-red
transmitting polymeric protective layer should be thick enough to afford
adequate protection for the metal layer but thin enough to minimize
absorption of radiant energy; a range of 5-50 micrometers has been found
satisfactory. The protective layer is desirably a polymer of monomers
consisting essentially of lower alkylene monomers of acrylonitrile;
however, small amounts of other monomers may be copolymerized with the
alkylene or acrylonitrile monomers, and small amounts of polymers formed
from such other monomers may be blended with the polyalkylene or
polyacrylonitrile to improve handling, processing, etc.
*A corollary of the high transmittance is low absorption (corresponding
less than 20%).
One effective way to employ the energy control film of the invention is to
adhere the support foil to the inside face of a conventional glazing unit.
When infra-red rays pass from a room through the polymeric protective
layer in such an installation, about 85-95% are reflected from the
metalized layer back through the protective layer and their heating value
thus retained in the room. The polymeric support foil, which in previous
solar energy control sheets was located adjacent the room, was quite
transparent to the visible spectrum but it transmitted only about 50-60%
of the rays in the infra-red spectrum, the remainder being absorbed. Thus,
for 100 units of infra-red energy directed toward the inner face of prior
art solar control sheets, no more than about 25-30%
(0.90.times.0.55.times.0.55) was actually returned to the room.
Simple and desirable as the invention may appear in retrospect, those
working in the solar control sheet art for decades have failed to
recognize how it might be arrived at, even though suitable polymeric
materials have long been available.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing, all thicknesses are greatly exaggerated to
facilitate understanding.
FIG. 1 is a cross-sectional view of a portion of one type of window unit
incorporating the present invention; and
FIG. 2 is a cross-sectional view of a porion of another type of window unit
incorporating the invention.
FIG. 3 is a cross-sectional view of a portion of a third type of window
unit incorporating the invention.
DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
In the drawing, FIG. 1 illustrates a window unit of the type where a
composite energy control sheet of the invention is adhered to the inside
face of a glazing unit. FIG. 2 depicts a cross-sectional view of a window
unit of the type where the composite energy control sheet is located
inside the glazing unit but is spaced therefrom. Window units of the
latter type include those in which the energy control sheet is either
semi-permanently attached to the window frame or mounted on a roller so
that it can be moved up and down as necessary. Thus, window units of the
type shown in FIG. 2 can have the edges of the energy control sheet
mounted in a track at the window edges, sealed to the window frame or held
in place with flexible magnets.
FIG. 3 shows a hermetically sealed double pane glazing unit in which an
energy control film of the invention is adhered to the interior face of
one of the panes. Such a mounting procedure, which would normally be
carried out during the process of making the glazing unit, offers certain
advantages over the window units shown in FIGS. 1 and 2. For example, the
thickness of the protective layer can be held to a minimum, there being
essentially no danger of physical contact. It has also been found that the
pane adjacent the room is maintained at a somewhat higher temperature and
hence that condensation of moisture is substantially reduced.
In FIG. 1, window unit 10 comprises composite energy control sheet 20
laminated to the inner face of single-pane glazing unit 30. Energy control
sheet 20 comprises polymeric foil support layer 21, to one face of which
is bonded transparent-reflective metal layer 22, which may be a vapor
deposited layer of aluminum, silver, gold, copper, or any other excellent
reflector of radiant energy over the solar and infra-red spectrum, i.e.,
0.3-40-micrometer wave length. It has been found that this metal layer
should have a sheet resistance of less than 20 ohms/square, and preferably
less than 10 ohms/square, in order to possess both adequate transparency
to visible light rays and good reflectivity of infra-red rays.
Since a thin metallic coating is subject to corrosion, mechanical abrasion,
or both, it is necessary to protect it with a thin polymeric layer 24,
which may be applied by extruding, coating, laminating or, preferably,
adhering with an extremely thin layer of adhesive 23. Polymeric layer 24
is selected on the basis of both its ability to protect metal layer 22 and
its transparency to infra-red radiation. The thickness of layer 24 should
be at least about 5 micrometers, and preferably at least about 10
micrometers, for adequate abrasion resistance, and when the protective
layer is applied by coating from a solvent, 5-15 micrometers is a fairly
typical value. When preformed foils of the protective polymeric layer are
employed, it is likewise generally desired to employ thicknesses of at
least about 5 micrometers (preferably at least about 10 micrometers to
facilitate handling), but thicknesses as great as 25-50 micrometers can be
employed successfully. It will be appreciated that the less the thickness
of protective layer 24, the greater its infra-red transmission. Likewise,
of course, the less the thickness of adhesive layer 23, the less its
absorption of infra-red energy.
Composite energy control sheet 20 is adhered to the inside face of glazing
unit 30 by means of adhesive layer 26, which may be any of those commonly
used in the solar control industry today. For example, adhesive layer 26
may be the dried deposit of an aqueous solution of a water-soluble
adhesive which is either coated on the inside face of glazing unit 30 just
before applying energy control sheet 20 or coated on energy control sheet
20 during manufacture, dried and activated with water before application
to glazing unit 30. Similarly, adhesive layer 26 may be normally tacky and
pressure-sensitive adhesive or any of the so-called "cling" vinyl
adhesives. In order to minimize the deteriorative effect of ultra-violet
light on any of the polymer layers in energy control sheet 20, it is
highly desirable to interpose a coating 25, containing a UV absorber,
between polymer layer 21 and adhesive layer 26; alternatively, a UV
absorber may be incorporated in polymer layer 21 or adhesive layer 26.
In normal use, solar radiation is directed toward face 31 of glazing unit
30, passing through glazing unit 30, adhesive layer 26, UV-absorbing layer
25 (if present) and polymeric foil 21. A significant amount of the solar
radiation (including rays in both the visible spectrum and the near
infra-red spectrum) is then reflected from metal layer 22 back through
polymeric foil 21, UV-absorbing layer 25 (if present), adhesive layer 26
and glazing unit 30, thereby reducing the light level, heat and glare
inside the room in which window unit 10 is employed. While glare and heat
transmission into the room are greatly reduced, sufficient light is
transmitted into the room through metal layer 22, adhesive layer 23 (if
present) and protective polymeric layer 24 to permit normal activities to
be carried on in comfort. Some near infra-red solar energy is absorbed in
polymeric foil 21, where it is converted to heat and re-transmitted
outside by either conduction or radiation through glazing unit 30.
When the temperature outside window unit 10 falls significantly below the
temperature inside the room, different factors come into play. All objects
and persons inside a room may be considered to have a surface temperature
of approximately 300.degree. K. and hence to function as black body
radiators, emitting energy in the infra-red spectrum, covering a wave
length of approximately 4-40 micrometers. Because of the temperature
difference between the opposite sides of window unit 10, there is then a
normal tendency to lose heat from the room by the process of radiation.
Such infra-red energy is radiated toward the outside, being directed
toward the inner surface 27 of window unit 10, where it passes first
through polymeric protective layer 24, encounters transparent-reflective
metal layer 22, and is reflected back through polymer protective layer 24
into the room. Since the infra-red rays pass through protective layer 24
twice, the amount of radiant energy which is actually returned to the room
is effectively the square of the infra-red transmission of layer 24.
Conventional solar energy control sheets are so mounted on windows that the
polymeric support foil confronts the room; since polyester polymers, which
are commonly employed as the support foil, have an infra-red transmission
value of approximately 0.5-0.6, and since about 10% of the infra-red
radiation is absorbed by or transmitted through the metal layer, the
amount of energy which is actually returned to the room, when such
conventional solar energy control sheets are used, is only about 25.30% of
that which is directed toward the window from inside. The balance of the
energy is absorbed by the support foil, where it is converted to heat, and
transmitted by conduction successively through the metal layer, protective
coating, adhesive layer, and glass window-pane, where it is lost to the
outside. In contrast, energy control sheets of the present invention are
mounted so that protective polymeric layer 27 is adjacent the room and
support foil 21 is adjacent glazing unit 30; the protective polymer layers
of the present invention are selected to have infra-red transmission
values of at least 80%, and preferably 90% or more in the thicknesses
employed; at least taking into acount the 85-95% reflectance alluded to
above, energy control sheets of the present invention thus return about
55% (0.85.times.0.80.times.0.80) of the room-origin infra-red energy to
the room.
Attention is now directed to FIG. 2, which, as previously noted, depicts a
somewhat different type of arrangement. Window unit 40 comprises glazing
unit 30 and composite energy control sheet 50, the latter being located
inside but spaced from the inner face of glazing unit 30. Sheet 50
comprises self-supporting polymeric foil 51, over one face of which is
bonded transparent-reflective metal layer 52. Protective layer 53, which
in this instance is shown as a self-supporting pre-formed polymer foil, is
adhered over metal layer 52 by means of adhesive 54. Composite solar
control sheet 50 may, and preferably does, incorporate UV-absorbers, as
discussed in connection with energy control sheet 20.
Located between glazing unit 30 and composite energy control sheet 50 is
air space 60. Solar energy strikes face 31 of glazing unit 30, radiating
through air space 60 to composite sheet 50 in substantially the same
manner described in connection with FIG. 1. In doing so, the solar-origin
infra-red (or near infra-red) energy is absorbed in polymeric foil 51,
which is heated thereby. Foil 51 then transfers some of the absorbed heat
to the air in space 60 and some to the room by conduction through metal
layer 52, adhesive 54 and protective layer 53. If tight peripheral sealing
does not exist, additional solar energy escapes from space 60 into the
room, an effect which is undesirable in summer but very desirable in
winter.
Window unit 40 is more effective in energy conservation than window unit 10
in the winter for yet another reason. When room-origin infra-red energy is
directed toward face 55, even that energy which is converted into heat in
layer 53 is not so readily transmitted to glazing unit 30 and thence
outside; because of the added thermal resistance of air space 60. If glare
is of no consequence during winter, it is even possible to move composite
sheet 50 out of the way during sunny weather, keeping it in position only
during those times when the sun is not shining. On the other hand, a solar
energy control sheet mounted in window unit 40 has a greater tendency to
impart visual distortion and is more subject to injury than when mounted
in window unit 10. Further, as has been previously noted, window unit 40
is less efficient in summer than window unit 10 unless care is taken to
provide adequate sealing at the edges.
The foregoing description of window unit 40 has all involved an orientation
of energy control sheet 50 such that supporting foil 51 was adjacent to
glazing unit 30. So long as energy control sheet 50 is spaced from (i.e.,
not in contact with) glazing unit 30, it is almost equally satisfactory
for protective layer 53 to be adjacent thereto. In such case, the
room-originating infra-red energy is directed toward support film 51 where
much of it is absorbed and, because of the high transmittance-low
absorption characteristics of protective layer 53, and its resultant low
emittance surface, re-radiated back to the room. (If, however, protective
layer 53 were to be in actual contact with the inside of glazing unit 30,
almost all of the absorbed infra-red energy would be conducted to glazing
unit 30 and hence lost to the outside.) If energy control sheet 50 is to
be oriented in this way, it is desirable to include in protective layer 53
a suitable stabilizer against the effects of solar-origin ultraviolet
light.
In FIG. 3, window unit 70 comprises a prefabricated multi-pane glazing unit
including glass panes 71 and 72, which are spaced from each other and
peripherally hermetically sealed to provide intervening dead air space 73.
Bonded to the inner face of pane 72 by adhesive 85 is composite energy
control sheet 80, comprising polymeric foil 81, and transparent-reflective
metal layer 82, self-supporting protective foil layer 83 being bonded
thereover by adhesive 84. Window unit 70 will normally be fabricated
during the manufacture of the multi-pane glazing unit by adhering energy
control sheet to pane 72 before final assembly.
Window unit 70 may be installed in the wall of a room with either pane 71
or pane 72 facing the room with substantially equal effectiveness in
retaining room-originating infra-red energy within the room. The reason
for this phenomenon is substantially the same as discussed above in
connection with window unit 40.
In the following examples, all parts are by weight unless otherwise noted.
EXAMPLE 1
A 25-micrometer foil of biaxially oriented polyethylene terephthalate was
vapor coated with aluminum to a sheet resistance of approximately 9
ohms/square, which resulted in a visible spectrum transmission of
approximately 0.18 at 0.55 micrometer wave length. The infra-red
reflectance of this surface was measured with a spectrophotometer and
found to be 0.85. The normal emittance, measured in accordance with ASTM
test C445-61, was found to be 0.12. (Theoretically the sum of the
reflectance and emittance values should equal 1.00. It is believed,
however, that the emittance is significantly more reliable than the
reflectance value and hence that the infra-red reflectance of the
aluminized film may be taken to be 0.88.) The aluminized surface was then
coated with a 30.5-micron layer of polyethylene having a density of 0.918
and a melt index of 3.0-3.9 g/10 min. at 190.degree. C. (commercially
available from Union Carbide under the trade designation "DFD-3300") by a
hot extrusion process, after which the reflectance and emittance
measurements were repeated and found to be, respectively, 0.74 and 0.24.
An extruded 30.5-micron foil of the same polyethylene was found to have an
infra-red transmission value of 0.89. The reflectance and emittance values
for a conventional solar control sheet of the type in which a 12-25
micrometer layer of biaxially oriented polyethylene terephthalate is
employed in the same effective position as the polyethylene in this
example, displayed infra-red reflectance and emittance values of,
respectively, 0.35 and 0.65.
EXAMPLE 2
On the metalized face of another sample of the aluminized polyester foil
employed in Example 1, there was coated a 2% methylethyl ketone solution
of 95:5 iso-octyl acrylate:acrylic acid pressure-sensitive adhesive and
the solvent evaporated to leave a thin (approximately 0.9-micrometer)
layer of adhesive weighing 1.08 g/m.sup.2. A 12.7-micrometer foil of
biaxially oriented isotactic polypropylene which had been subjected to
corona treatment was then bonded to the adhesive-coated surface using a
pair of squeeze rolls at room temperature. Prior to lamination, the
polypropylene foil had an infra-red transmission value of 0.92, and the
normal emittance of the laminate was found to be 0.25.
Using the data contained in a U.S. Government report entitled "Residential
Energy Consumption, Single Family Housing", it was assumed that a typical
home located in the area of Baltimore, Maryland, has 16.7 square meters of
windows and 3.7 square meters of glazed patio doors, all 20.4 square
meters being single glazed. A garage is assumed to be located on the west
side of the house, the exterior glass area being distributed on the
remaining three sides as follows: north facing, 7.1 m.sup.2 ; south
facing, 8.3 m.sup.2 ; east facing, 5.0 m.sup.2. Draperies are used on 70%
of the glass area and shading on 20%. A computerized study was then made
to show the energy savings resulting from adhering, to the inside of all
glass surfaces, (1) the protectively coated face of a conventional solar
energy control sheet and (2) the polyester film face of the solar energy
control sheet of this Example 2. Results are tabulated below:
TABLE I
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Energy Savings Obtainable
With Solar Energy Control Sheets
Conventional Solar Solar Energy Control
Energy Control Sheet
Sheet of Example 2
Load Equivalent Load Equivalent
Type of
Reduction,
Source Reduction,
Source
Energy Kilowatt Energy Kilowatt
Energy
Required
Hours Saved Hours Saved
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Cooling
2,344 400 kg of coal
2,344 400 kg of coal
Heating
141 19.7 liters of
2,315 326 liters of
fuel oil or fuel oil or
20.0 m.sup.3 of 330 m.sup.3 of
natural gas natural gas
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If the polypropylene face of the solar energy control sheet of Example 2 is
adhered to the inside of all glass surfaces, performance is essentially
the same as for conventional solar energy control sheets, dramatically
illustrating the significance of confronting the inside of the home with
an infra-red transmissive layer.
The remarkable winter energy saving resulting from use of the present
invention is readily apparent.
EXAMPLE 3
Example 2 was repeated except that the tacky acrylate adhesive was replaced
with soluble tack-free polyester laminating adhesive made by
copolymerizing 48 moles terephthalic acid, 20 moles isophthalic acid, 32
moles sebacic acid, 40 moles neopentyl glycol and 60 moles ethylene
glycol. Bonding was accomplished by laminating between squeeze rolls
heated to approximately 75.degree. C. The normal emittance of the
resultant structure was found to be 0.25.
The solar energy control sheet of this Example 3 was further processed to
make it capable of adhering to a windowpane. First, to the exposed
polyethylene terephthalate surface there was applied a solution of a
polyester resin containing, based on solids, 7.5 parts benzophenone UV
absorber, and the solvent evaporated to leave about 5.4 grams of solids
per square meter; the soluble polyester was made by polymerizing 46 moles
terephthalic acid, 42 moles isophthalic acid, 12 moles sebacic-azelaic
acid, 60 moles ethylene glycol and 40 moles neopentyl glycol. Next a
solution of a 95:5 iso-octyl acrylate:acrylamide copolymer was applied and
the solvent evaporated to leave a layer of normally tacky and
pressure-sensitive adhesive weighing 2.7 g/m.sup.2. An aqueous solution of
methyl cellulose was applied over the pressure-sensitive adhesive and the
water evaporated to render the surface tack-free but water-activatable for
application to a windowpane. When analyzed in accordance with the
previously discussed computerized study, the performance of this solar
energy control sheet was shown to be similar to that of Example 2.
EXAMPLE 4
Example 3 was repeated, substituting for the polypropylene a
16.5-micrometer foil of polyacrylonitrile having an infra-red transmission
value of 0.88. The normal emittance of the resultant laminate was 0.30.
Energy-saving performance was calculated to be slightly below that of the
films of Examples 2 and 3.
To demonstrate the effect of the insulative, or "R", value of solar energy
control sheets which include both a transparent-reflective metal layer and
a protective polymer layer of varying transparency to infra-red rays,
attention is directed to the following table, which incorporates
calculated values:
TABLE II
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Insulative Effect of Infra-Red Transmission
Properties of Protective Polymer Foils
Resistance R, .degree.C. hr m.sup.2 /-
to radiation
kcal com-
transfer, or
pared to best
"R" value, prior art
Infra-red transmission
.degree.C. hr
solar energy
of room-confronting face
m.sup.2 /kcal
control sheet
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0 .uparw. 0.225
0.10 .uparw. 0.228
0.20 .uparw. 0.232
0.30 .uparw. 0.246
0.40 .uparw. 0.261
0.50 (prior art commercial
0.295
products)
0.60 0.332
0.70 0.406
0.80 (present invention)
0.533 0.201
0.85 .dwnarw. 0.636 0.304
0.90 .dwnarw. 0.828 0.496
0.95 .dwnarw. 1.189 0.857
1.00 .dwnarw. 2.255 1.923
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It will be apparent that any of the conventional modifications of energy
control sheets may also be incorporated in sheets of the present
invention. For example, visible light transmission can be enhanced by
applying a quarter wave length coating of high refractive index material
to either or both sides of the metalized layer. Colored layers may be
incorporated to achieve specific desired visual effects, etc. Although the
abrasion resistance of the exposed polyalkylene metal-protecting layer
exceeds that of the exposed polyester foil in prior art constructions,
various coatings can be applied to the room-confronting face to further
enhance abrasion resistance and facilitate cleaning. Such layers must,
however, be either extremely thin, formed of a substance which is
inherently highly transparent to infra-red radiation or both.
* * * * *
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