CN-115867837-B - Optical stack

Abstract

An optical stack includes a reflective polarizer, an absorbing polarizer, and a half-wave retarder. A half-wave retarder is disposed between the reflective polarizer and the absorptive polarizer. For substantially normal incident light and the first polarization state, the reflective polarizer reflects at least about 60% of incident light of at least a first wavelength less than the cutoff wavelength and transmits at least about 50% of incident light of at least a second wavelength greater than the cutoff wavelength. For substantially normal incident light, the half-wave retarder has a first retardation of less than about 250 nanometers (nm) at a first wavelength and a second retardation at a second wavelength. The first delay has a smaller deviation from a first half-wave delay corresponding to the first wavelength than the second delay has from a second half-wave delay corresponding to the second wavelength.

Inventors

• Adam D. Hagg
• Pu Shanyong
• Martin E. Denkel

Assignees

• 3M创新有限公司

Dates

Publication Date

20260505

Application Date

20210729

Priority Date

20200826

Claims (10)

1. 1. An optical stack, comprising: a reflective polarizer comprising a transmission axis and a reflection axis orthogonal to each other; Absorption polarizer, and A half-wave retarder, the half-wave retarder being a non-achromatic half-wave retarder and being disposed between the reflective polarizer and the absorbing polarizer such that for substantially normal incident light: For a first polarization state, the reflective polarizer comprises a transmission band having a cut-off wavelength, wherein the reflective polarizer reflects at least 60% of incident light of at least a first wavelength less than the cut-off wavelength and transmits at least 50% of incident light of at least a second wavelength greater than the cut-off wavelength; For an orthogonal second polarization state, the reflective polarizer transmits at least 70% of incident light of each of the at least first wavelength and the at least second wavelength; The half-wave retarder having a first retardation of less than 250 nanometers (nm) at the first wavelength and a second retardation at the second wavelength, wherein the first retardation deviates from a first half-wave retardation corresponding to the first wavelength by less than the second retardation deviates from a second half-wave retardation corresponding to the second wavelength, and For the first polarization state, the absorbing polarizer has a first transmittance at the first wavelength and a second, greater transmittance at the second wavelength.
2. 2. The optical stack of claim 1, further comprising a display panel disposed under the reflective polarizer opposite the half-wave retarder, the display panel configured to emit display light comprising a blue emission spectrum having a blue full width at half maximum (FWHM) defined between a minimum wavelength and a maximum wavelength, wherein the minimum wavelength is less than the cutoff wavelength of the transmission band of the reflective polarizer.
3. 3. The optical stack of claim 2, wherein the cutoff wavelength of the transmissive band of the reflective polarizer is less than the maximum wavelength of the blue FWHM.
4. 4. The optical stack of claim 2, wherein the cutoff wavelength of the transmissive band of the reflective polarizer is greater than the maximum wavelength of the blue FWHM.
5. 5. The optical stack of claim 1, wherein the cutoff wavelength of the transmissive band of the reflective polarizer is less than 550nm and greater than 450nm.
6. 6. The optical stack of claim 1, wherein the reflective polarizer comprises a total of at least 40 of a plurality of alternating first and second polymer layers, each of the first and second polymer layers having an average thickness of less than 350 nm.
7. 7. The optical stack of claim 1, wherein the second retardation is greater than 200nm, and wherein the first transmittance of the absorbing polarizer is at least 60%.
8. 8. An optical stack, comprising: A display panel configured to emit display light including a blue emission spectrum having a blue full width at half maximum (FWHM) defined between a minimum wavelength and a maximum wavelength; a reflective polarizer configured to receive and reflect a portion of the display light from the display panel as reflected polarized light, the reflective polarizer comprising a transmission axis and a reflection axis orthogonal to each other; An absorbing polarizer; a half-wave retarder, the half-wave retarder being a non-achromatic half-wave retarder and disposed between the reflective polarizer and the absorbing polarizer such that for substantially normal incident light; For a first polarization state, the reflective polarizer comprises a transmission band having a cutoff wavelength that is greater than the minimum wavelength of the blue emission spectrum of the display panel, wherein the reflective polarizer reflects at least 60% of incident light of at least a first wavelength that is less than the cutoff wavelength and transmits at least 50% of incident light of at least a second wavelength that is greater than the cutoff wavelength; For an orthogonal second polarization state, the reflective polarizer transmits at least 70% of incident light of each of the at least first wavelength and the at least second wavelength; the half-wave retarder having a first retardation of less than 250nm at the first wavelength and a second retardation at the second wavelength, wherein the first retardation deviates less from a first half-wave retardation corresponding to the first wavelength than from a second half-wave retardation corresponding to the second wavelength, and For the first polarization state, the absorbing polarizer has a first transmittance at the first wavelength and a second, greater transmittance at the second wavelength.
9. 9. The optical stack of claim 8, wherein the minimum wavelength is greater than 430nm and the maximum wavelength is less than 480nm, and wherein the cutoff wavelength of the transmissive band of the reflective polarizer is less than the maximum wavelength of the blue FWHM.
10. 10. The optical stack of claim 8, wherein the cutoff wavelength of the transmissive band of the reflective polarizer is greater than the maximum wavelength of the blue FWHM.

Description

Optical stack Technical Field The present disclosure relates generally to optical stacks, and in particular to optical stacks for backlights. Background In backlights, reflective polarizers are typically used to circulate the light and enhance the final efficiency and brightness of the display. In addition, an absorbing polarizer or the like is used in combination with the liquid crystal module to polarize light for proper adjustment by the liquid crystal module. In some manufacturing processes, a roll-form reflective polarizer may have a reflection axis (i.e., block or slow axis) in the transverse direction (i.e., the width direction of the roll). The roll-form absorbing polarizer may have an absorption axis along the length of the roll. In some cases, it may be desirable to align the reflection axis of the reflective polarizer with the absorption axis of the absorbing polarizer within the optical stack. In conventional manufacturing processes, one or both rolls of polarizer are cut and rotated, thereby increasing manufacturing time and process expense. Disclosure of Invention In a first aspect, the present disclosure provides an optical stack. The optical stack includes a reflective polarizer, an absorbing polarizer, and a half-wave retarder. The reflective polarizer includes a transmission axis and a reflection axis that are orthogonal to each other. A half-wave retarder is disposed between the reflective polarizer and the absorptive polarizer. For substantially normal incident light and a first polarization state, the reflective polarizer includes a transmission band having a cutoff wavelength. The reflective polarizer reflects at least about 60% of incident light of at least a first wavelength less than the cutoff wavelength and transmits at least about 50% of incident light of at least a second wavelength greater than the cutoff wavelength. For substantially normal incident light and an orthogonal second polarization state, the reflective polarizer transmits at least 70% of incident light of each of at least the first wavelength and at least the second wavelength. For substantially normal incident light, the half-wave retarder has a first retardation of less than about 250 nanometers (nm) at a first wavelength and a second retardation at a second wavelength. The first delay has a smaller deviation from a first half-wave delay corresponding to the first wavelength than the second delay has from a second half-wave delay corresponding to the second wavelength. For substantially normal incident light and a first polarization state, the absorbing polarizer has a first transmittance at a first wavelength and a second, greater transmittance at a second wavelength. In a second aspect, the present disclosure provides another optical stack. The optical stack includes a display panel, a reflective polarizer, an absorbing polarizer, and a half-wave retarder. The display panel is configured to emit display light including a blue emission spectrum having a blue full width at half maximum (FWHM) defined between a minimum wavelength and a maximum wavelength. The reflective polarizer is configured to receive and reflect a portion of display light from the display panel as reflected polarized light. The reflective polarizer includes a transmission axis and a reflection axis that are orthogonal to each other. A half-wave retarder is disposed between the reflective polarizer and the absorptive polarizer. For substantially normal incident light and the first polarization state, the reflective polarizer includes a transmission band having a cutoff wavelength that is greater than a minimum wavelength of the blue emission spectrum of the display panel. The reflective polarizer reflects at least about 60% of incident light of at least a first wavelength less than the cutoff wavelength and transmits at least about 50% of incident light of at least a second wavelength greater than the cutoff wavelength. For substantially normal incident light and an orthogonal second polarization state, the reflective polarizer transmits at least 70% of incident light of each of at least the first wavelength and at least the second wavelength. For substantially normal incident light, the half-wave retarder has a first retardation of less than about 250nm at a first wavelength and a second retardation at a second wavelength. The first delay has a smaller deviation from a first half-wave delay corresponding to the first wavelength than the second delay has from a second half-wave delay corresponding to the second wavelength. For substantially normal incident light and a first polarization state, the absorbing polarizer has a first transmittance at a first wavelength and a second, greater transmittance at a second wavelength. Drawings Exemplary embodiments disclosed herein may be more fully understood in view of the following detailed description taken in conjunction with the accompanying drawings. The figures are not necessarily drawn to scale. L