Note: Descriptions are shown in the official language in which they were submitted.
CA 02503703 2011-11-24
REDUCED VISIBILITY INSECT SCREEN
Field of the Invention
The invention relates to insect screens, such as, for example, for windows and
doors, that are less visible than conventional insect screens. A screen or
screening is a
mesh of thin linear elements that permit ventilation but excludes insect
pests. To the
ordinary. observer, the screens are less visible in the sense that the
interference to
observing a scene either on the exterior or the interior of the screen is
substantially
reduced.
Background of the Invention
Insect screens are installed on windows and doors in homes to promote
ventilation while excluding insects. Insect screens are, however, widely
regarded as
unattractive. From the inside of a window, some screens obstruct or at least
destract
from the view to the outside. From the outside, many people believe that
screens
detract from the overall appearance of a home or building. Homebuilders and
realtors
frequently remove screens from windows when selling homes because of the
improved appearance of the home from the outside. Homeowners frequently remove
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screens from windows that are not frequently opened to improve the view from
the
inside and the appearance of the window.
A wide variety of insect screen materials and geometries are available in the
prior art. Fiberglass, metallic and synthetic polymer screens are known. These
screens suffer from reduced visual appeal due to relatively low light
transmission,
high reflection, or both. Standard residential insect screens include a mesh
with
horizontal and vertical elements. The most common insect screens have about 18
elements per inch in one direction and 16 elements per inch the other
direction, often
expressed as being an 18x16 mesh. Some standard screens have an 18x14 mesh.
The
typical opening size is about 0.040 inch by 0.050 inch. Screens designed to
exclude
gnats and other very small insects usually include screen elements in a 20x20
mesh.
The most common materials for the screen elements are aluminum and vinyl-
coated
fiberglass. Stainless steel, bronze and copper are also used for insect screen
elements.
Typical element diameters for insect screens are 0.011 inch for aluminum,
bronze,
and some stainless steel offerings and 0.009 inch for galvanized steel and
stainless
steel.
Some products on the market advertise a black or charcoal colored screen
mesh that is allegedly less visible from the inside of a house. Color coating
changes
and material changes have made some incremental improvements in the visual
appeal
of screening to the average observer, but most observers continue to object to
the
darkening effect that current insect screening causes in observing scenes from
inside
and outside.
Summary of the Invention
We have found unique features for the elements used to form insect screening
that maximize transmission and minimize reflection resulting in reduced
visiblity of
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the screening and enhanced viewing through it. The awareness of the insect
screen is
substantially reduced while the ability to observe details of the viewed scene
is greatly
enhanced.
A reduced visibility insect screening is described where the transmittance of
the screening is at tleast about 0.75 and the reflectance of the screening is
about 0.04
or less.
In an alternative embodiment, an insect screening material includes screen
elements having a diameter of about 0.005 inch (0.13 mm) or less. The screen
elements have a tensile strength of at least about 5500 psi (about 40 mega
Pascals).
Again, the transmittance of the screening is at least about 0.75 and the
reflectance of
the screening is about 0.04 or less.
In another embodiment of the invention, a screening is described including
screen elements having a diameter of about 0.005 inch (about 0.1 mm) or less
and a
coating on the screen elements having a matte black finish. The transmittance
of the
screening is at least about 0.75 and the reflectance of the screening is about
0.04 or
less.
In further alternative embodiments, the transmittance of the screening is at
least about 0.80 or the reflectance of the screening is about 0.03 or less, or
0.02 or
less. The screening may have an open area of at least about 75%, or at least
about
80%. The screening may define mesh openings having a largest dimension not
greater than about 0.060 inch (about 1.5 mm).
The screen elements may have a diameter less than about 0.005 inch (about
0.1 mm), and may have a tensile strength greater than about 5500 psi (about 40
mega
Pascals). The screen elements may be made of a metal such as steel, stainless
steel,
aluminum and aluminum alloy, or a polymer such as polyethylene, polyester and
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nylon. Alternatively, the screen elements may be made of an ultra high
molecular
weight polyethylene or an amide such as polyamide, polyaramid and aramid.
In one embodiment, the screen elements include a coating, specifically a black
matte coating such as electroplated black zinc. In one embodiment the screen
elements are made of stainless steel with an electroplated black zinc coating.
Brief Description of the Drawings
The invention may be more completely understood by considering the detailed
description of various embodiments of the invention that follows in connection
with
the accompanying drawings.
Figure 1 is a fragmentary view of an insect screen in accordance with the
invention.
Figure 2 is a fragmentary view of a portion of the insect screen shown in
Figure 1.
Figure 3 is a perspective view of the insect screen shown in fragmentary view
in Figure 1.
Figure 4 is a diagram illustrating light paths in reflection from a window
unit
with a screen.
Figure 5 is an illustration of inside and outside viewing perspectives of an
insect screen on a window unit.
Figure 6 is a graph showing the reflectance for embodiments of the invention
and comparative example screen embodiments.
Figure 7 is a graph showing the transmittance for embodiments of the
invention and comparative example screen embodiments.
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Figure 8 is a graph showing the transmittance versus the reflectance for
embodiments of the invention and comparative example screens.
Figure 9 is a diagram showing specular and diffuse reflections from a matte
surface.
Figure 10 is a photograph taken through a microscope of uncoated screen
elements.
Figure 11 is a photograph taken through a microscope of stainless steel screen
elements coated with a coating of electrodeposited black zinc.
Figure 12 is a photograph taken through a microscope of stainless steel screen
elements coated with flat paint.
Figure 13 is a photograph taken through a microscope of stainless steel screen
elements coated with gloss paint.
Figure 14 is a photograph taken through a microscope of stainless steel screen
elements coated with chromium carbide through a physical vapor deposition
(PVD)
process.
Figure 15 is a diagram of an integrating sphere spectrophotometer for
measuring the reflectance and transmittance of a screen material.
Figure 16 is a front view of a test fixture for measuring the snag resistance
of a
screen material.
Figure 17 is a side view of the test fixture of Figure 16.
Figure 18 is a graph showing the single element ultimate tensile strength for
embodiments of the invention and comparative example screen embodiments.
Figure 19 is a depiction of a snag on an unbonded insect screening.
Figure 20 is a depiction of a snag on an insect screening having a paint
coating.
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Figures 21-25 are graphs plotting pounds of force applied to a rigid element
versus inches of travel as the element moved against a screen mesh fabric for
a snag
resistance test for five different examples of the invention.
Detailed Description of the Preferred Embodiments
We have found unique features for insect screening of the invention. We have
found that by reducing the size of and selecting proper color and texture for
the
elements used in the screening, reflection and transmission are controlled
such that
the visibility of the screening is markedly reduced. The insect screening of
the
invention maintains comparable mechanical properties when compared to prior
art
insect screening, but is substantially improved in visual appearance. The
insect
screening of the invention can be used in the manufacture of original screens
and can
be used in replacement screens for windows, doors, patio doors, vehicles and
many
other structures where screening is used. The insect screening of the
invention can be
combined with metal frames, wooden frames or composite frames and can be
joined
to fenestration units with a variety of joinery techniques including
adhesives,
mechanical fasteners such as staples or tacks, splines, binding the screening
material
into recesses in the screen member frame or other common screen joining
technology.
When properly installed in conventional windows and doors, the ordinary
observer
viewing from the interior or the exterior through the insect screening of the
invention
has a substantially reduced awareness of the screening and a substantially
improved
ability to observe the scene on the other side of the screen.
We have found that combination of reduced element size in the screening and
coating on the screen elements combine to provide the improved visual
properties of
the insect screening of the invention. The selected materials disclosed for
the
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screening of the invention are not limiting. Many different materials can
satisfy the
requirements of the invention.
Screen within Frame and on Fenestration Unit
Figure 1 is a fragmentary drawing of a portion of an insect screen 10 in
accordance with the present invention. The insect screen 10 consists of a
frame 20
including a frame perimeter 40 defining a frame opening. An insect screening
30 fills
the opening defined by the frame perimeter 40. The frame 20 supports the
screening
30 on all sides of the screening 30. The frame 20 is preferably sufficiently
rigid to
support the screening tautly and to allow handling when the screen 10 is
placed in or
removed from a window or door unit.
Figure 2 is a fragmentary view of a portion of the insect screening shown in
Figure 1. The spaces between screen elements 70 define openings or holes in
the
screening 30. In a preferred embodiment, the screen elements 70 include
horizontal
elements 80 and vertical elements 90. Preferably, the horizontal and vertical
elements
80, 90 are constructed and arranged to form a mesh where a horizontal metal
element
intersects a vertical metal element perpendicularly. The intersecting
horizontal and
vertical metal elements 80, 90 may be woven together. Alternatively, the
intersecting
horizontal and vertical metal elements 80, 90 may be fused together, although
they
may or may not be woven.
Figure 3 is a perspective view of the insect screen shown in Figure 1
positioned in a fenestration unit 110. The frame 20 includes two pairs of
opposed
frame members. A first pair of opposed frame members 50 is oriented along a
horizontal frame axis. A second pair of opposed frame members 60 is oriented
along
a vertical frame axis. The four frame members 50, 60 form a square or
rectangle
shape. However, the frame may be any shape.
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Goal of Making Screen Less Visible
When light interacts with a material, many things happen that are important to
the visibility of insect screening. The visibility of screening can be
influenced by
light transmission, reflection, scattering and variable spectral response
resulting from
element dimensions, element coatings, and the dimensions of the mesh openings.
In
order to reduce the visibility of the screening, the transmittance is
maximized, the
reflectance is minimized, the remaining reflection is made as diffuse as
possible, and
any spectral reflectance is made as flat or colorless as possible. To
accomplish this, it
is beneficial to use screen elements with the smallest dimensions or diameters
while
still meeting the strength requirements. Maximizing the dimensions of the grid
openings will decrease visibility, but the dimensions of the grid openings are
also
chosen to achieve the desired insect exclusion and strength qualities.
In measuring to what degree an insect screening has achieved reduced
visibility, the inventors have found that transmittance and reflectance are
the most
important factors for visibility of a screen from the exterior of a home.
Because the
sun is a much stronger light source than interior lighting, visibility of the
screen from
the exterior of the home is more difficult to reduce than visibility from the
interior, as
discussed further herein. Also, in double hung windows, the presence of an
insect
screen on the bottom half of the window contrasts with bare sash on the top
half of the
window to make the screening stand out.
Figure 4 shows light paths for one typical viewing situation involving an
observer outside a building looking at a screen and window. Figure 4 shows a
cross
sectional view of screen 404 and glass 406 in the window. The window separates
an
exterior viewing location 410 from an interior scene 412, where the screen 404
is on
the exterior side of the glass 406. Screen units are commonly positioned on
the
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exterior of the glass, in double-hung windows, sliding windows and sliding
doors.
Screening 404 is comprised of many elements, including elements 408, 414, 416,
418,
and 420. Figure 4 generally illustrates the path of light ray 400 and light
ray 402 as
they interact with screen 404 and glass 406. Light rays 402 and 404 are from
the sun,
which typically dominates the effects of any interior lights during a sunny
day. The
paths of light ray 400 and light ray 402 depict the ways in which reflectance
and
transmission affect the visibility of a screen for an outside observer of an
exterior
screen.
For example, light 402 travels toward glass 406 and reflects off element 408
in
a direction away from glass 406. Reflectance is the ratio of light that is
reflected by
an object compared to the total amount of light that is incident on the
object. Solid,
non-incandescent objects are generally viewed in reflection. (It is also
possible to
view an object in an aperture mode where it is visible due to its contrast
with a light
source from behind it. A smaller screen element size decreases the visibility
of a
screen viewed in the aperture mode.) Accordingly, objects generally appear
less
visible if they reflect lower amounts of light. A perfectly reflecting surface
would
have a quantity of 1 for reflectance, while a perfectly absorbing surface
would have a
quantity of 0 for reflectance.
Another quality that affects the visibility of screening is transmittance.
When
looking through screening, a viewer sees light emanating from or reflected
from
objects on the other side of the screening. As transmittance of the screening
decreases, the viewer sees less light from the objects on the other side of
the
screening, and the presence of the screening becomes more apparent.
Transmittance
is defined as the ratio of light transmitted through a body relative to the
total amount
of light incident on the body. A value of 0 for transmittance corresponds to
an object
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which light cannot penetrate. A value of I for transmittance corresponds to a
perfectly transparent object. In the case of a window in a home viewed through
an
exterior insect screen by an outside observer, the light seen has traveled
through the
screen twice, as shown in Figure 4. For example, the light 400 travels away
from the
viewer and through the screen 404. Next, the light is reflected off the window
406
and travels back through the screen 404 toward the outside viewer's eye.
Reducing the visibility of an exterior screen to an outside viewer is
considered
the most difficult because the intensity of sunlight is so much greater than
lights
within a building. If the visibility of an exterior screen for an exterior
viewer is
minimized, the screen will also be less visible for an inside viewer of an
exterior
screen, and for an inside and outside viewer of an interior screen. However,
another
important optical feature for invisibility of a screen to an inside viewer is
a small
element size, as will be further discussed. If the reflectance is minimized,
the
transmittance is maximized, and the screen element diameter is sufficiently
small, the
screening will be much less perceptible to inside viewers than conventional
screens.
To achieve an insect screen that has reduced visibility, it is desirable to
design
insect screens with a low reflectance and high transmittance. Material choices
and
characteristics like color and texture can reduce reflectance. For example,
dark matte
colors reflect less light than light glossy colors or shiny surfaces. Reducing
the cross-
sectional area of the material and increasing the distance between the screen
elements
can increase transmittance. However, material that is too thin may not be
strong
enough to function properly in a typical dwelling. Similarly, insects may be
able to
pass through the screen if the distance between the elements is too large.
Therefore, it
is desirable to obtain a combination of strength, optical and mechanical
characteristics
within functional limits to achieve a screen with reduced visibility.
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Inside and Outside Viewers
With reference to Figure 5, a cross-sectional view of a dwelling 500 is shown
to illustrate how inside and outside observers view screens. Dwelling 500
separates
the outside 502 from the inside 504. An inside viewer 506 is illustrated
inside 504 of
the dwelling 500 while an outside viewer 508 is illustrated outside 502.
Window 510
is located in a wall of dwelling 500 and also separates the inside 504 from
the outside
502. Screen 512 covers the window 510 on the outside 502 side of window 510.
The inside viewer 506 in Figure 5 is separated from window 510 by the width
of sink 518, which represents a typical close range interior viewing distance,
frequently about 2 feet. The closer the viewer 506 stands to the screen 512,
the more
obvious the screen 512 will appear. For example, at 12 inches, which is a
relatively
close range interior viewing distance, the normal visual resolution of the
human eye is
about 0.0035 inch (about 0.09 mm). Elements having a diameter of less than
about
0.0035 inch will likely not be perceived by a viewer of normal eyesight at a
distance
of 12 inches (30.5 cm). Therefore, the perceived visibility is affected by the
diameter
of the screen elements and the distance between the viewer 506 and the screen
512.
At about 24 inches, the normal visual acuity is about 0.007 inch. For this
reason,
elements having a diameter of about 0.007 inch will not be resolvable to a
viewer at
about 24 inches from the screening.
Inside a building or dwelling, interior lighting fixtures such as light 514
provide the primary interior light source that would reflect from the screen.
Outside
of the dwelling, the sun 516 provides a much stronger light source that will
reflect off
the screen 512. Accordingly, the reflectance of the screen will generally be
of greater
importance to the visibility of the screen to the outside viewer 508 than to
the inside
viewer 506, because much more light is incident on the screen from the
exterior 502
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than from the interior 504. However, the shape of the elements, which are
normally
round, may cause sunlight to be reflected into the interior of the building,
impacting
the visibility of the screen to an inside viewer.
The transmittance of the screen affects visibility of the screen for both the
inside viewer 506 and the outside viewer 508. The inside viewer 506 views the
exterior scene by the sunlight that is reflected off the outside objects and
then
transmitted through the screening 512. The less light transmitted through the
screening 512, the more the inside viewer's perception of the exterior view is
negatively affected by the screening. As discussed above in relation to Figure
4,
when looking through the screening, the exterior viewer sees light reflecting
from or
emanating from the objects on the interior side of the screening. As the
transmittance
of the screening decreases, the presence of the screening becomes more
apparent.
The perspective of inside and outside viewers has been discussed so far with
respect to a screen that is on the exterior side of a window. This is the
configuration
used in most double hung windows, sliding windows, and sliding doors. However,
many window units have screens on the interior side of the window, such as
casement
windows or awning windows. Where the screen is inside of the glass, the
reflectance
and transmittance of the insect screening will still impact the visibility of
the screen.
Generally, screens on the outside of the glass are the most obvious type to
the outside
viewer, so this is the harder configuration to address for outside viewing. As
discussed above, the size of the individual screen elements has an important
impact on
the visibility of a screen to an inside observer. If a screening possesses
reflectance
and transmittance qualities that are acceptable for outside viewing, and a
sufficiently
small element diameter, the screening will also be less visible to the inside
observer
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than conventional insect screens, whether the screen is on the inside or
outside of the
glass.
Specular versus Diffuse Reflectance
Figure 9 illustrates two types of reflection that occur from surfaces:
specular
reflection and diffuse reflection. In specular reflection, light has an angle
of reflection
measured from the normal to the surface that is equal to the angle of
incidence of the
beam measured from the normal, where the reflected beam is on the opposite
side of
the normal to the surface from the incident beam. In diffuse reflection, an
incident
beam of light is reflected at a range of angles that differ significantly from
the angle
of incidence of the incident parallel beam of light.
In Figure 9, light rays are shown interacting with a surface 902. Light ray
904
is incident on the surface 902 at an angle of incidence a;. A portion of the
light ray
904 is specularly reflected as light ray 906, where the angle of reflection a,
is equal to
the angle of incidence a;. However, light rays 908, 910, and 912 are examples
of
diffusely reflected light rays that are reflected at a range of different
reflection angles.
For reducing the visibility of screening, diffuse reflection is preferred over
specular reflection because diffuse reflection disperses the power of the
incident light
over multiple angles. In specular reflection, the light beam is generally
redirected to
the reflection angle while maintaining much of its power. Providing a dull or
roughened surface increases diffuse reflection from a screen mesh.
Reflectance & Transmittance Testing Procedure
Measurements for reflectance and transmittance may be made with an
integrating sphere spectrophotometer. For the purposes of the data presented
herein, a
Macbeth Color-Eye 7000 spectrophotometer manufactured by GretagMacbeth of
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Germany, was used to obtain transmittance and reflectance measurements for
wavelengths of 360 to 750 nm.
The spectrophotometer shown in Figure 15 contains an integrating sphere
1502 useful when measuring samples in reflection or transmission. Integrating
sphere
1502 contains front port 1510 and exit port 1508. The front port 1510 measures
about
25.4 mm in diameter.
A xenon flash lamp 1504 is located at the base of the integrating sphere.
Detector 1506 measures the amount of light emitted from integrating sphere
1502.
Detector 1506 contains viewing lens 1512 for viewing the light. Viewing lens
1512
contains a large area view.
For reflectance measurement, the spectrophotometer is set to a measurement
mode of: CRILL, wherein the letters correspond to the following settings for
the
machine: C - Reflection, specular included; R - Reflection; I - Included
Specular, I -
Included LIV; L - Large Lens; L - Large Aperture. When measuring reflectance,
the
sample is held flat against the front port 1510. Next, a light trap is placed
behind the
sample to prevent stray light from entering integrating sphere 1502. The light
source
1504 emits light into the integrating sphere 1502. Some of the light is
reflected off
the sample and exits the integrating sphere 1502 through the exit port 1508.
Once the
light exits the exit port 1508, it enters the detector 1506 through viewing
lens 1512.
The spectrophotometer produces a number that is a ratio indicating the light
reflected
by the sample relative to the light reflected by a perfectly reflective
surface.
For a transmittance measurement, the spectrophotometer is set to a
measurement mode of. BTIILL, wherein the letters correspond to the following
settings for the machine: B - Barium; T - Transmittance; I - Included
Specular, I -
Included LIV; L - Large Lens; L - Large Aperture. The front port 1510 of the
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spectrophotometer is blocked with an object coated with barium oxide,
identical to the
interior surface of the sphere 1502. When measuring the transmittance of a
sample, it
is necessary to hold the sample flat against the exit port 1508 of the
integrating sphere
1502. The light source 1504 emits light into the integrating sphere 1502. Some
of the
light exits the integrating sphere 1502 through exit port 1508. Once the light
that is
transmitted through the sample enters the detector 1506 through viewing lens
1512,
the spectrophotometer produces a number that is a ratio indicating the light
transmitted by the sample relative to the light transmitted where there is no
sample.
Data collected for reflectance and transmittance for a number of screen
samples will be described below with respect to Figures 6 and 7.
Data for Reflectance and Transmittance
Table 1 contains average values of test data for optical qualities of insect
screening embodiments.
Table 1. Optical Data for Examples
Sample Description Transmittance Reflectance
1 Black Zn Cr 0.828 0.006
2 Flat Paint 0.804 0.012
3 Glossy Paint 0.821 0.014
4 Black Ink 0.874 0.013
5 PVD Cr(x)C(y) 0.887 0.019
6 Stainless Steel Base 0.897 0.044
Examples of the present invention will now be described. Six different
samples were prepared and tested for optical qualities related to the present
invention.
Each of Samples 1-6 was formed by starting with a base screening of stainless
steel elements having a diameter of 0.0012 inch. The elements are made of type
304
stainless steel wire. The base screening has 50 elements per inch in both
horizontal
and vertical directions. It is a woven material and has openings with a
dimension of
0.0188 inch by 0.0188 inch. The open area of this base material is about 88%
relative
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to the area of a given screen sample, measured experimentally using a
technique that
will be described further herein. This material is commercially available from
TWP,
Inc. of Berkley, California. Sample 6 is the base screening without any
coating.
Figure 10 is a photograph of Sample 6 taken through a microscope.
To form Sample 1, the base screening was coated by electroplating it with zinc
and then a conversion coating of silver chromate was applied. The zinc reacts
with
the silver chromate to form a black film on the surface of the screen
elements.
Sample I is shown in Figure 11. The black zinc coating bonds the horizontal
and
vertical screen elements together at their intersections. The coating
increases the
thickness of the screen element and therefore reduces the transmittance of the
resulting screening by about 0.07 compared to the uncoated screening of Sample
6.
The black finish decreases reflectance of incident light dramatically compared
to the
uncoated Sample 6.
To form Samples 2 and 3, the base screening was coated with about two to
three coats of flat black paint and glossy black paint, respectively. As the
paint was
being applied manually, the painter visually inspected the surface and
attempted to
apply a uniform coating of paint. Depending on the speed of the spray
apparatus
passing over the various portions of the surface, two or three coats were
applied to
different areas of Samples 2 and 3, based on the painter's visual
observations, to
achieve a fairly even application of paint. Photographs of Samples 2 and 3
taken
through a microscope are shown in Figures 12 and 13, respectively. The paint
coating
joins the horizontal and vertical screen elements together at their
intersections and
provides a black finish. The coating increases the thickness of the screen
element and
therefore reduces the transmittance of the resulting screening compared to the
uncoated screening of Sample 6. The black color of both Samples 2 and 3
decreases
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reflectance of incident light compared to the uncoated Sample 6, with the flat
black
paint of Sample 2 having a lower reflectance than the glossy paint.
Sample 4 was coated with black ink. The application of ink to the screening
does not significantly bond or join the horizontal and vertical screen
elements together
at their intersections. The coating of ink increases the thickness of the
screen element
a small amount and therefore reduces the transmittance of the resulting
screening
compared to the uncoated screening of Sample 6. The black finish decreases the
reflectance of incident light compared to the uncoated Sample 6.
Sample 5 was coated with chromium carbide by physical vapor deposition
(PVD). A photograph taken through a microscope of Sample 5 is shown in Figure
14.
The chromium carbide coating does not bond the horizontal and vertical screen
elements together at their intersections, but does provide a black finish. The
coating
increases the thickness of the screen element very slightly and therefore
reduces the
transmittance of the resulting screening compared to the uncoated screening of
Sample 6. The black finish decreases reflectance of incident light compared to
the
uncoated Sample 6.
Several commercially available insect screenings were tested for their optical
qualities as a basis for comparison to the samples of the invention. The
following
table contains average values of actual test data from each material.
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Table 2. Optical Data for Comparative Examples
Sample Description Transmittance Reflectance
(material, color,
manufacturer, trade
name if any)
A Al Gray, Andersen 0.658 0.025
Windows
B FG, Black, 0.576 0.029
Andersen Windows
C FG, Black, Phifer 0.625 0.025
D Al, metallic, Phifer, 0.779 0.095
Brite-KoteTM
E Al, Charcoal, 0.741 0.019
Phifer, Pet Screen
F Polyester, Black, 0.363 0.024
Phifer, Pet Screen
G FG, Gray, Phifer 0.652 0.060
Samples A, D and E are made of aluminum elements. Samples B, C, and G
are made of vinyl-coated fiberglass elements. Sample F is made of a polyester
material.
Figure 6 shows a comparison of reflectance values for both commercially
available screening Samples A-G and screenings of the present invention
Samples 1-
6. Lower values for reflectance correspond to screening that appears more
invisible
because less light is reflected in the direction of the viewer. Samples 1-4
have the
lowest values for reflectance. The least reflective commercially available
Sample E
has an average reflectance value of 0.019, which is equivalent to the average
value of
the second-most reflective Sample 5.
Figure 7 shows a comparison of transmittance values for the screen materials
set forth in the tables above. Higher values for transmittance correspond to
screens
with preferred optical qualities. Screening Samples 1-6 have higher
transmittance
values than the commercially available Samples A-G.
Figure 8 is a graph of transmittance versus reflectance for the screen
materials
set forth in the tables above. Samples 1-5 all have a transmittance of at
least about
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0.80 and a reflectance of no more than about 0.020. None of the comparative
samples
have a transmittance greater than 0.78. None of the comparative samples have
both a
transmittance of greater than 0.75 or 0.80 and a reflectance of less than
0.020, 0.025,
0.030 or 0.040, while samples 1-5 have those qualities.
Percent Open Area
The percent open area also relates to the invisibility of an insect screen.
Assuming a square mesh, the percent open area (POA) can be computed as
follows:
POA = ((W/(D+W)))2* 100
where:
D=element diameter, and W=opening width.
Many commercially available screenings have a rectangular mesh. The POA for a
rectangular mesh can be computed as follows:
POA =(I -N*D)(I -n*d)* 100
where:
N = number of elements per inch in a first direction,
D = element diameter of the elements extending in the first direction,
n = number of elements per inch in a second direction, and
d = element diameter of the elements extending in the second direction
Generally, screens appear less visible if they contain a larger percentage of
open area. For example, Sample 6 has about 88% open area, corresponding to 50
elements per inch in either direction, screen elements of woven 0.0012-inch
(0.03-
mm) type 304 stainless steel wire, and openings sized 0.0188 inch (0.5 mm) x
0.0188
inch (0.5 mm).
In contrast, standard insect screening has about 70% open area and often has
opening sizes of 0.05 inch by 0.04 inch. Standard gnat-rated insect screens
often have
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CA 02503703 2005-04-07
a percent open area of about 60% and opening sizes of about 0.037 inch by
0.037 inch
with elements of about 0.013 diameter.
Decreasing the wire diameter can increase the percent open area. It is
desirable to select a wire diameter that allows for the largest percent open
area while
maintaining suitable strength. Screening is commercially available made of
unwelded
5056 aluminum wire of 0.011-inch (0.28 mm) diameter. The term unwelded
indicates
that the horizontal and vertical elements are not bonded or welded together at
their
intersections. Importantly, type 304 stainless steel wire has almost three
times the
tensile strength of 5056 aluminum wire. Accordingly it is possible to use a
smaller
wire diameter of 0.0066 inch (0.17 mm) of type 304 stainless steel to achieve
tensile
strength similar to the 5056-aluminum screening.
Additional materials may be selected within the scope of the present invention
to increase the percent open area by decreasing the diameter of the screen
elements.
These materials include, but are not limited to: steel, aluminum and its
alloys, ultra
high molecular weight (UHMW) polyethylene, polyesters, modified nylons, and
aramids. It is also possible to use an array of man-made fibers for
generalized use in
the industrial arts. An example of this material is sold under the trademark
KEVLAR .
Generally, the percent open area corresponds roughly to the percentage of
transmittance through a particular screening. However, accepted techniques for
calculating percent open area like those expressed above do not account for
the
elements crossing each other in the screening, and therefore over-estimate the
percent
open area by a few percent. The amount of error inherent in these calculations
depends on the thickness of the wire.
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Strength of Screen Elements
Figure 18 illustrates the single element ultimate tensile strength for
elements
of Sample 6 and comparative Samples A, B, D, E and F. Samples 1-5 consist of
the
same material as Sample 6 but with a coating added. Therefore Samples 1-5 have
ultimate tensile strengths that are about the same as for Sample 6. The
electroplated
zinc coating applied to Sample 1 may in fact increase the ultimate tensile
strength of
those elements.
As discussed above, the diameter of the elements in Sample 6 is much smaller
than commercially available insect screen elements. Therefore, inventive
elements
must have a higher tensile strength than elements used in prior screening
materials to
achieve similar strength specifications as prior screening materials. In
Figure 18,
ultimate tensile strength is charted in Ksi or 1000 x psi. The tensile
strength for the
elements of Sample 6 is about 162 Ksi, which is over three times stronger than
Sample D, which is the strongest element in the commercially available Samples
A,
B, D, E and F. A minimum desirable tensile strength for the screen elements is
about
5500 psi or more, or about 6000 psi or more. Preferably, at least about a
tenth of
pound of force is required to cause a single screen element to break. About
0.16-
pound force is required to break a 0.0012-inch stainless steel element of
Sample 6.
Snag Resistance
Snag resistance is a measure of how a screen reacts to forces that could cause
a break, pull, or tear in the screen elements, such as clawing of the
screening by a cat.
Snag resistance is important because birds, household animals, and projectiles
come
into contact with screens.
Figures 16 and 17 show a test fixture 1700 used to measure snag resistance.
Test fixture 1700 includes a screen guide 1702 made from two 0.5 x 6-inch
pieces of
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fiberglass laminate material 1710 and 1712. The pieces 1710 and 1712 are
approximately 0.060 inches thick and arc used to guide the screen cloth 1704
during
the test by placing the screen cloth 1704 between pieces 1710 and 1712 of
screen
guide 1702. The pieces 1710 and 1712 contain an upper clearance hole to attach
the
screen guide 1702 to an instrument that measures the maximum load. Pieces 1710
and 1712 also contain a lower clearance hole to support a snagging mandrill
1706.
When preparing a sample of screening 1704 for a test, a 2-inch x 6-inch
sample strip of screen 1704 is cut out so that the warp and weft directions
lie with and
perpendicular to the test direction. The warp direction is along the length of
a woven
material while the weft direction is across the length of the woven material.
The
screen guide 1702 is hung from a load cell gooseneck and a snagging mandrill
1706 is
carefully passed through the screen 1704. The test is started and the snag
mandrill
1706 is moved through the screen 1704 at the rate of 0.5 inch/minute and
continued
until 0.5 inch is traveled. At this point, the test is terminated and the
sample is
removed. Care must be taken not to damage the sample when removing it from the
test fixture. Several measurements may be recorded, including the maximum load
obtained and the load at a specific extension divided by the extension (lb-
force/in).
Samples were also visually inspected to determine the failure mode. Three
failure modes are generally possible with insect screens. The first failure
mode is
element breakage because the joints hold and the sections of element between
the
joints break. The second failure mode is joint breakage. This occurs when the
elements hold and the joints break. The third failure mode occurs when the
elements
break and the joints slip. This third failure mode is a combination of element
breakage and joint breakage. Generally, element breakage is the preferred
failure
mode because it disturbs less surface area on the screen.
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Figure 19 illustrates a screen with unbonded elements corresponding to
Sample 6 after undergoing the snag resistance test described above. The screen
elements appear to have slid together due to the force of the snagging
mandrill 1706.
Figure 19 is generally an example of the joint breakage failure mode. As no
coating
forms a bond at the intersections of the elements in Sample 6, any joint
strength is due
to frictional forces between the elements in the weave.
Conversely, Figure 20 shows a screen with elements coated and joined at their
intersections by paint after undergoing the snag resistance test. Unlike the
unbonded
elements shown in Figure 19, the painted elements appear to have broken at
several
locations rather than merely sliding together. Figure 20 is an example of the
element
breakage and joint breakage failure mode discussed above. The failure mode
shown
in Figure 20 is preferred over the failure mode shown in Figure 19 because
less
surface area is disturbed on the screen, creating a more desirable appearance,
and a
less visible screening, after a snag.
To achieve an element breakage mode, the joint strength needs to be sufficient
to cause the elements to give way before the joints when a snagging force is
applied to
the screening. On the other hand, it may be desirable in some situations to
select
element and joint strength so that joint breakage occurs before element
breakage,
resulting in a more resilient screen. When a force is applied to this type of
screening,
the element stays intact while the bonds break or slip. The force on the
element is
then distributed to the other adjacent bonds.
Figures 21-25 illustrate the screen snag resistance of Samples 1-3 and 5-6 in
terms of pounds of force versus displacement of the snag mandrill 1706.
Samples 5
and 6, shown on Figures 21 and 22, respectively, show a relatively smooth
curve
compared to Samples 1-3, shown on Figures 23-25, respectively. A smooth curve
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CA 02503703 2005-04-07
indicates that the joints between elements are very weak or not bonded. Sample
4
would likely have results similar to Sample 6 in Figure 22, as the ink coating
does not
form significant bonds. The joints on Samples 1-3 are much stronger than the
joints
on Samples 5 and 6. Accordingly, the graph lines on Figures 23-25 for Samples
1-3
have several jagged edges. Each sharp drop in the graph corresponds to an
element
break or a bond break. Sample 2 was able to withstand the largest amount of
force of
all the samples before an element or bond break.
Size and Spacing of Exemplary Screen Elements
In Figure 2, a width or diameter W of the screen elements 70 is illustrated.
The width W may be less than about 0.007 inch or 0.0035 inch to fall beneath
the
visual acuity of a normal viewer at either 24 inches or 12 inches,
respectively. The
smaller the screen element that meets strength requirements, the less visible
will be
the insect screening. In another embodiment, W is about 0.001 inch (about
0.025
mm) to about 0.0015 inch (about 0.04 mm), or about 0.0012 inch. Stainless
steel
wire, for example, can be provided in this size range and be sufficiently
strong for use
in insect screening. Each screen element 70 has a length to span the distance
between
opposed frame members 50, 60 (Figure 1).
The plurality of screen elements 70 includes a plurality of horizontal screen
elements 80 and a plurality of vertical screen elements 90. The horizontal
screen
elements 80 are spaced apart from each other a distance Dv and the vertical
screen
elements 90 are spaced apart from each other a distance DH. The spacing
depends on
the types of insects the user wishes to exclude. Opening sizes are chosen to
exclude
the types of insects that the screening is designed to keep out. Preferably,
the largest
values for DH and Dv are selected that still exclude the targeted insects, so
that
transmittance is maximized and reflection is minimized.
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A screen mesh that excludes most insects is typically constructed with a Dv
and DH of about 0.040 inch (about 1 mm) or 0.050 inch (about 1.3 mm). For a
screen
mesh for excluding smaller insects, like gnats or no-see-Ums, a smaller mesh
opening
is necessary, such as a square opening with a DH and Dv of about 0.037 or 0.04
inch
(about 1 mm).
In embodiments of the present invention, DH and Dv may be less than about
0.060 inch (about 1.5 mm), less than about 0.050 inch (about 1.25 mm), less
than
about 0.040 inch (about 1.0 mm), or less than about 0.030 inch (about 0.75
mm). Dv
and DH may be equal to form a square opening, or they may differ so that the
mesh
opening is rectangular. For example, Dv may be about 0.050 inch (about 1.25
mm)
while DH is about 0.040 inch (about 1 mm). All other permutations of the above
mentioned dimensions for DH and Dv are also contemplated. Typically, the
vertical
and horizontal screen elements are positioned to be perpendicular to each
other and
aligned with the respective frame members.
Table 3 below lists experimentally measured screen element dimensions for
Samples 1-3 and 6. The percent black area is the percentage of the screening
that is
occupied by the screen elements. The percent open area and the black area add
to 100
for a specific screening.
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Table 3. Dimension Data for Examples
1 2 3 4 5 6
Screen Experimentally Percent Avg. Avg. Avg. Avg.
Sample Measured Open Element Element Coating Coating
Percent Black Area Diameter Diameter Thickness Thickness
Area (mm)+/- (mils) +/- (mm) +/- (mils) +/-
0.002 0.08 0.001 0.1
1 Black 17.0% 83% 0.039 1.5 0.004 0.15
Zn
2 Flat 19.6% 80.4% 0.045 1.8 0.007 0.15
Paint
3 Glossy 18.4% 81.6% 0.042 1.7 0.0006 0.24
Paint
6 14.1% 85.9% 0.033 1.3 - -
Stainless
Steel
Base
The experimental measurements of Samples 1-3 and 6 in Table 3 were
measured by backlighting a sample of each screening and taking a digital
photograph.
The percent of black area on the photo image was then measured using image
analysis
software. Knowing the number of elements that were present in each image and
the
dimensions of the sample, the average coated element thickness was calculated.
For
each of Samples 1-6, the underlying uncoated element has a diameter of 0.0012
inch,
so this amount was subtracted from the coated element diameter of column 4 to
arrive
at the average coating thickness of columns 5 and 6.
The PVD CrC coating of Sample 5 and the ink coating of Sample 4 are too
thin to be reliably measured by this experimental technique. Based on the
deposition
technique, the coating of Sample 5 is estimated to be about 0.02 mils (0.5
m).
Because this coating and the ink coating are extremely thin, the percent black
area for
Samples 4 and 5 are roughly equivalent to the uncoated Sample 6.
The plurality of horizontal and vertical screen elements 80, 90 can be
constructed and arranged to form a mesh where a horizontal screen element
intersects
a vertical screen element perpendicularly. The intersecting horizontal and
vertical
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screen elements 80, 90 may be woven together. Optionally, the intersecting
horizontal and vertical screen elements 80, 90 are bonded together at their
intersections, as described in more detail below with respect to coating
alternatives.
Materials for the Screen Mesh
In order to provide a material for the screening 30 that will withstand the
handling that is associated with screen use, several factors are important,
such as the
screen element diameter and the ultimate tensile strength of the material. In
addition,
other factors are considered in selecting a material, such as the coefficient
of thermal
expansion, the brittleness, and the plasticity of a material. The coefficient
of thermal
expansion is significant because expansion or contraction of the screen
elements due
to temperature changes may alter the normal alignment of the horizontal and
vertical
screen elements, thereby leading to visible distortion of the screening.
In one embodiment, materials from the categories of glass fibers, metals or
polymers meet the requirements for screen element strength at the desired
diameters,
such as steel, stainless steel, aluminum, aluminum alloy, polyethylene, ultra
high
molecular weight polyethylene, polyester, modified nylon, polyamide,
polyaramid,
and aramid. One material that is particularly suited for the screen elements
is
stainless steel. The high tensile strength of about 162 Ksi and low
coefficient of
thermal expansion of about 11x10-GK-I for stainless steel are desirable.
Coating or Finish Alternatives
The surface 100 of the screen elements 70 is a dark, non-reflective, and
preferably dull or matte finish. A dark non-reflective, dull or matte finish
is defined
herein to mean a finish that absorbs a sufficient amount of light such that
the screen
mesh 30 appears less obtrusive than a screen mesh 30 without such finish. The
dark
non-reflective or matte finish may be any color that absorbs a substantial
amount of
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light, such as, for example, a black color. The dark non-reflective or matte
finish can
be applied to the screen element surface 100 by any means available such as,
for
example, physical vapor deposition, electroplating, anodizing, liquid coating,
ion
deposition, plasma deposition, vapor deposition, and the like. Liquid coating
may be,
for example, paint, ink, and the like.
For example, a PVD chromium carbide coating or black zinc coating may be
applied to the screen elements in one embodiment. The black zinc coating is
preferred to the CrC coating because it is rougher, more matte, and less
shiny.
Alternatively, glossy or flat black paint or black ink may be applied to the
screen
elements. The flat paint coating is preferred to the glossy paint coating
because it is
less reflective. Other carbides can also be used to provide a dark finish,
such as
titanium aluminum carbide or cobalt carbide.
The use of a coating on the screen elements may provide the additional
advantage of forming a bond at the intersections of the screen elements. A
coating of
paint provides some degree of adhesion of the elements at the intersections.
Some
coatings such as black zinc create bonds at the intersections of the elements.
The
coating thickness and overall element diameter for Samples 1-3 and 5-6 are
listed in
Table 3 above.
The improved screening materials of the invention typically comprise a mesh
of elements in a screening material. The elements comprise long fibers having
a thin
coating disposed uniformly around the fiber. The coating comprises the layer
that is
about 0.10 to 0.30 mils (about 0.004 to 0.007 mm), preferably about 0.15 mils
(about
0.004 mm). Virtually any material can be used in the coating of the invention
that is
stable to the influence of outdoor light, weather and the mechanical shocks
obtained
through coating manufacture, screen manufacture, window or door assembly,
storage,
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distribution and installation. Such coatings typically have preferred
formation
technologies. The coatings of this invention, however, can be made using
aqueous or
solvent based electroplating, chemical vapor deposition techniques and the
application
of aqueous or solvent based coating compositions having the right proportions
of
materials that form the thin durable coatings of the invention. Both organic
and
inorganic coatings can be used. Examples of organic coatings include finely
divided
carbon, pigmented polymeric materials derived from aqueous or solvent based
paints
or coating compositions, chemical vapor deposited organic coatings and similar
materials. Inorganic coating compositions can include metallic coatings
comprising
metals such as aluminum, vanadium, chromium, manganese, iron, nickel, copper,
zinc, silver, tin, antimony, titanium, platinum, gold, lead and others. Such
metallic
coatings can be two or more layers covering the element and can include metal
oxide
materials, metal carbide materials, metal sulfide materials and other similar
metal
compounds that can form stable, hard coating layers.
Chemical vapor deposition techniques occur by placing the screening or
element substrate in an evacuated chamber or at atmosphere and exposing the
substrate to a source of chemical vapor that is typically generated by heating
an
organic or inorganic substance causing a substantial quantity of chemical
vapor to fill
the treatment chamber. Since the element or screening provides a low energy
location
for the chemical vapor, the chemical vapor tends to coat any uncoated surface
due to
the interaction between the element and the coating material formed within the
chamber.
In electroplating techniques, the element or screening is typically placed in
an
aqueous or solvent based plating bath along with an anode structure and a
current is
placed through the bath so that the screen acts as the cathode. Typically,
coating
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materials are reduced at the cathode and that electrochemical reduction
reaction
causes the formation of coatings on the substrate material.
Applications for the Insect Screen
The screening 30 can be used with or without a frame 20 in certain
applications, such as in a screen porch or pool enclosure. The insect screen
10 can be
used in conjunction with a fenestration unit 110, such as a window or door.
The
insect screen 10 may be used in any arrangement of components constructed and
arranged to interact with an opening in a surface such as, for example, a
building wall,
roof, or a vehicle wall such as a recreational vehicle wall, and the like. The
surface
may be an interior or exterior surface. The fenestration unit 110 may be a
window
(i.e. an opening in a wall or building for admission of light and air that may
be closed
by casements or sashes containing transparent, translucent or opaque material
and
may be capable of being opened or closed), such as, for example, a picture
window, a
bay window, a double- hung window, a skylight, casement window, awning window,
gliding window and the like. The fenestration unit 110 may be a doorway or
door
(i.e. a swinging or sliding barrier by which an entry may be closed and
opened), such
as, for example, an entry door, a patio door, a French door, a side door, a
back door, a
storm door, a garage door, a sliding door, and the like.
The above specification, examples, and data provide a complete description of
the manufacture and use of the composition of the invention. Since many
embodiments of the invention can be made without departing from the spirit and
scope of the invention, the invention resides in the claims hereinafter
appended.
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