Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
2000-06-09
2004-09-28
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyester
C428S426000, C428S430000, C428S441000, C428S480000, C428S910000, C359S359000, C359S487030, C359S494010, C359S577000, C359S580000, C359S584000, C359S586000, C359S589000, C359S601000
Reexamination Certificate
active
06797396
ABSTRACT:
TECHNICAL FIELD
This invention relates to birefringent dielectric multilayer reflecting films and laminate articles made therefrom.
BACKGROUND
A conventional automotive safety glazing is formed from a laminate made of two rigid layers, typically glass, and an anti-lacerative mechanical energy absorbing interlayer of plasticized polyvinyl butyral (PVB). The glazing is prepared by placing the PVB layer between glass sheets, eliminating air from the engaging surfaces, and then subjecting the assembly to elevated temperature and pressure in an autoclave to fusion bond the PVB and glass into an optically clear structure. The glazing may then be used in the windows, windshields or rear glass of a motor vehicle.
The laminate may also include at least one functional layer engineered to enhance the performance of the vehicle window. One important functional layer reduces entry of infrared radiation into the vehicle cabin. Infrared rejecting functional layers are typically made of metallized or dyed polymer film constructions that reflect or absorb unwanted solar radiation. When used in a windshield, the composite laminate structure should transmit at least about 70% of the light in the wavelength region sensitive to the human eye, typically from about 380 to about 700 nanometers (nm), and reject solar radiation outside the visible portion of the spectrum. When used in other glazing structures, such a side or rear windows, there are typically no limits on the level of visible transmission.
Referring to
FIG. 1A
, a pre-laminate structure
10
is shown that may be bonded to one or more glass sheets to make a vehicular safety glazing laminate. The pre-laminate
10
includes a reflective functional layer
12
that includes a polymer layer
14
and a metallized layer
16
. The functional layer
12
is bonded on at least one side to at least one layer
18
of PVB. Optionally, the functional layer
12
may be bonded to a second layer
20
of PVB. One or the other or both of the PVB layers
18
,
20
may include additional performance enhancing layers. For example, the PVB layer
20
may optionally include a shade band layer
22
.
Referring to
FIG. 1B
, the pre-laminate structure
10
may be matched with at least one, preferably two, sheets of glass
30
,
32
to form a safety glazing laminate
34
. To bond the pre-laminate
10
to the glass sheets
30
,
32
, the pre-laminate
10
and the sheets
30
,
32
are placed together. The laminate
34
is heated to cause the PVB layers
18
,
20
and the functional layer
12
to conform to the contours of the glass sheets
30
,
32
. The laminate
34
may be assembled by one of three different methods. Two of the methods use a vacuum de-airing process where a flexible band, ring or bag is placed around the edge of the laminate and connected to a vacuum system while the laminate is pre-heated to generate a temporary bonding between the glass and PVB. Another method uses a pressure roller device, referred to herein as a nip roller, which applies pressure to the laminate to de-air and to promote bonding between the layers. Compared to the vacuum de-airing processes, the nip roll process requires fewer manual process steps and allows the laminates to be assembled more quickly. For at least these reasons, the nip roll process is a preferred method for many automotive glazing manufacturers.
To enhance vehicle aerodynamics and improve outward visibility, vehicular window shapes are not planar, and increasingly include severe angles and complex curves. When the laminate
10
is placed between complex curved glass sheets and laminated with a nip roll process, or heated to bond the PVB to the glass. The functional layer
12
cannot perfectly conform to the complex curvatures, especially when the glass sheets are large. Wrinkles, folds and pleats can form in the functional layer, and, when the functional layer is metallized, cracks can form in the metallized layer
16
during nip rolling, which creates an optical defect in the safety glazing. As a result, only small size laminates with no curvature or a small one-dimensional curvature can currently be manufactured using a nip roll process.
Birefringent, non-metallic films made from alternating layers of dielectric materials, preferably polymers with differing indices of refraction, may be engineered to reflect or absorb a desired amount of light in a spectral region of interest while transmitting sufficient visible light in the visible region of the spectrum to be substantially transparent. These birefringent dielectric optical films preferably include alternating layers of a first material having a first index of refraction and a second material having a second index of refraction that is different from the first index of refraction.
The film is preferably a multilayer stack of polymer layers with a Brewster angle (the angle at which reflectance of p polarized light goes to zero) that is very large or nonexistent. The film is made into a multilayer mirror whose reflectivity for p polarized light decreases slowly with angle of incidence, is independent of angle of incidence, or increases with angle of incidence away from the normal. This multilayered film has high reflectivity (for both s and p polarized light) for any incident direction.
The reflectance characteristics of the multilayer film are determined by the in-plane indices of refraction for the layered structure. In particular, reflectivity depends upon the relationship between the indices of refraction of each material in the x, y, and z directions (n
x
, n
y
, n
z
). The film of the invention is preferably constructed using at least one uniaxially birefringent material, in which two indices (typically along the x and y axes, or n
x
and n
y
) are approximately equal, and different from the third index (typically along the z axis, or n
2
). The x and y axes are defined as the in-plane axes, in that they represent the plane of a given layer within the multilayer film, and the respective indices n
x
and n
y
are referred to as the in-plane indices.
One method of creating a uniaxially birefringent system is to biaxially orient (stretch along two axes) the multilayer polymeric film. If the adjoining layers have different stress-induced birefringence, biaxial orientation of the multilayer film results in differences between refractive indices of adjoining layers for planes parallel to both axes, resulting in the reflection of light of both planes of polarization. A uniaxially birefringent material can have either positive or negative uniaxial birefringence. Positive uniaxial birefringence occurs when the index of refraction in the z direction (n
z
) is greater than the in-plane indices (n
x
and n
y
). Negative uniaxial birefringence occurs when the index of refraction in the z direction (n
z
) is less than the in-plane indices (n
x
and n
y
).
If n
1z
, is selected to match n
2x
=n
2y
=n
2z
and the multilayer film is biaxially oriented, there is no Brewster's angle for p-polarized light and thus there is constant reflectivity for all angles of incidence. Multilayer films that are oriented in two mutually perpendicular in-plane axes are capable of reflecting an extraordinarily high percentage of incident light depending of the number of layers, f-ratio, indices of refraction, etc., and are highly efficient mirrors.
A second factor that determines the reflectance characteristics of the multilayer film is the thickness of the layers in the film stack. Adjacent pairs of layers (one having a high index of refraction, and the other a low index) preferably have a total optical thickness that is ½ of the wavelength of the light to be reflected. For a two-component system, to achieve maximum reflectivity the individual layers of a multilayer polymeric film have an optical thickness that is ¼ of the wavelength of the light to be reflected, although other ratios of the optical thicknesses within the layer pairs may be chosen for other reasons. Optical thickness is defined as the in-plane refractive index of a material multiplied b
Boettcher Jeffrey A.
Koster Brian L.
Kranz Heather K.
Liu Yaoqi J.
Mortenson David K.
3M Innovative Properties Company
Chen Vivian
Knecht III Harold C.
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