Optical: systems and elements – Polarization without modulation – By relatively adjustable superimposed or in series polarizers
Reexamination Certificate
2000-07-10
2001-10-23
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Polarization without modulation
By relatively adjustable superimposed or in series polarizers
C359S490020, C359S506000
Reexamination Certificate
active
06307676
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multilayer optical device which includes a dichroic polarizer and a multilayer optical film. More particularly, the invention relates to an optical polarizer having a dichroic polarizer and a multilayer optical film with copolyester optical layers.
BACKGROUND OF THE INVENTION
Optical polarizing film is widely used for glare reduction and for increasing optical contrast in such products as sunglasses and Liquid Crystal Displays (LCD). One of the most commonly used types of polarizers for these applications is a dichroic polarizer which absorbs light of one polarization and transmits light of the other polarization. One type of dichroic polarizer is made by incorporating a dye into a polymer matrix which is stretched in at least one direction. Dichroic polarizers may also be made by uniaxially stretching a polymer matrix and staining the matrix with a dichroic dye. Alternatively, a polymer matrix may be stained with an oriented dichroic dye. Dichroic dyes include anthraquinone and azo dyes, as well as iodine. Many commercial dichroic polarizers use polyvinyl alcohol as the polymer matrix for the dye.
Another type of polarizer is a reflective polarizer which reflects light of one polarization and transmits light of another orthogonal polarization. One type of reflective polarizer is made by forming a stack of alternating sets of polymer layers, one of the sets being birefringent to form reflective interfaces in the stack. Typically, the indices of refraction of the layers in the two sets are approximately equal in one direction so that light polarized in a plane parallel to that direction is transmitted. The indices of refraction are typically different in a second, orthogonal direction so that light polarized in a plane parallel to the orthogonal direction is reflected.
One measure of performance for polarizers is the extinction ratio. The extinction ratio is the ratio of a) light transmitted by the polarizer in a preferentially transmitted polarization state to b) light transmitted in an orthogonal polarization state. These two orthogonal states are often related to the two linear polarizations of light. However, other types of orthogonal states, such as, left and right-handed circular polarizations or two orthogonal elliptical polarizations may also be used. The extinction ratios of dichroic polarizers vary over a wide range depending on their specific construction and target application. For example, dichroic polarizers may have extinction ratios between 5:1 and 3000:1. Dichroic polarizers used in display systems typically have extinction ratios which are preferably greater than 100:1 and even more preferably greater than 500:1.
Dichroic polarizers typically absorb light in the non-transmission polarization. However, dichroic polarizers also absorb some of the light having the high transmission polarization. The amount of this absorption depends on the details of the construction of the polarizer and the designed extinction ratio. For high performance display polarizers, such as those used in LCDs, this absorption loss is typically between about 5 and 15%. The reflectivity of these polarizers for light having the absorption (i.e., low transmission) polarization tends to be small. Even with surface reflections included, this reflectivity is typically less than 10% and usually less than 5%.
Reflective polarizers typically reflect light having one polarization and transmit light having an orthogonal polarization. Reflective polarizers often have incomplete reflectivity of the high extinction polarization over a wavelength region of interest. Typically, the reflectivity is greater than 50% and is often greater than 90% or 95%. A reflective polarizer will also typically have some absorption of light having the high transmission polarization. Typically, this absorption is less than about 5 to 15%.
The above two types of polarizers may be combined to make a single optical polarizer, thereby incorporating the useful characteristics of both types of polarizers. These polarizers may be formed and, optionally, oriented together. Unfortunately, the polyvinyl alcohol film used in many dichroic polarizers tends to crack under the processing conditions necessary to prepare some reflective polarizers, including, for example, those which use polyethylene naphthalate (PEN) or coPEN optical layers. These reflective polarizers may be formed by stretching a polymeric film at processing temperatures, such as 135 to 180° C., and a stretch ratio of between 2:1 and 10:1.
Dichroic polarizers may also be used with other optical devices, such as other types of reflective polarizers and mirrors. The combination of a dichroic polarizer with an IR mirror may be useful for reducing glare. The formation of the dichroic polarizer in combination with the mirror retains the processing difficulties mentioned above, especially when the mirror is made using oriented polyester layers. Thus, there is a need for improved reflective polarizers and other optical devices which can be simultaneously oriented with dichroic polarizers without cracking the dichroic polarizer film.
SUMMARY OF THE INVENTION
Accordingly, the present invention relates to optical devices which include a dichroic polarizer and multilayer polymer films formed using copolyester materials. One embodiment is an optical device having a dichroic polarizer and a multilayer optical film positioned in the same optical path as the dichroic polarizer. The multilayer optical film includes a plurality of first optical layers and a plurality of second optical layers. The first optical layer are made using a first copolyester. The first copolyester has carboxylate subunits and glycol subunits, in which 70 to 100 mol % of the carboxylate subunits are first carboxylate subunits, 0 to 30 mol % of the carboxylate subunits are first comonomer carboxylate subunits, 70 to 100 mol % of the glycol subunits are first glycol subunits, 0 to 30 mol % of the glycol subunits are first comonomer glycol subunits, and at least 0.5 mol % of the combined carboxylate and glycol subunits of the first copolyester are first comonomer carboxylate subunits, first comonomer glycol subunits, or a combination thereof. The second optical layers are made of a second polymer.
Another embodiment is an optical device having a dichroic polarizer and a reflective polarizer positioned in the same optical path as the dichroic polarizer. The reflective polarizer includes a plurality of first optical layers and a plurality of second optical layers. The first optical layer are made using a first copolyester which is birefringent and semicrystalline. The first copolyester has carboxylate subunits and glycol subunits, in which 70 to 100 mol % of the carboxylate subunits are first carboxylate subunits, 0 to 30 mol % of the carboxylate subunits are first comonomer carboxylate subunits, 70 to 100 mol % of the glycol subunits are first glycol subunits, 0 to 30 mol % of the glycol subunits are first comonomer glycol subunits, and at least 0.5 mol % of the combined carboxylate and glycol subunits of the first copolyester are first comonomer carboxylate subunits, first comonomer glycol subunits, or a combination thereof. The second optical layers are made of a second polymer which has an in-plane birefringence of about 0.04 or less, at 632.8 nm, after the reflective polarizer has been formed.
A further embodiment is a method of making an optical polarizer. The method includes forming a reflective polarizer. The reflective polarizer has a plurality of first optical layers and a plurality of second optical layers. The first optical layer are made using a first copolyester which is birefringent and semicrystalline. The first copolyester has carboxylate subunits and glycol subunits, in which 70 to 100 mol % of the carboxylate subunits are first carboxylate subunits, 0 to 30 mol % of the carboxyl ate subunits are first comonomer carboxylate subunits, 70 to 100 mol % of the glycol subunits are first glycol subunits, 0 to 30 mol % of the glycol subunits are f
Hebrink Timothy J.
Kausch William L.
Merrill William W.
Williams Brian H.
3M Innovative Properties Company
Burtis John A.
Schuberg Darren
LandOfFree
Optical device with a dichroic polarizer and a multilayer... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical device with a dichroic polarizer and a multilayer..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical device with a dichroic polarizer and a multilayer... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2590476