U.S. patent number RE41,281 [Application Number 10/833,280] was granted by the patent office on 2010-04-27 for liquid crystal display device.
This patent grant is currently assigned to Merck Patent Gesellschaft mit beschrankter Haftung. Invention is credited to James Hanmer, Mark Verrall.
United States Patent |
RE41,281 |
Hanmer , et al. |
April 27, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Liquid crystal display device
Abstract
The invention relates to a liquid crystal display device
comprising a liquid crystal cell and at least one compensation film
or a combination of polarizer and optical compensators comprising
at least one compensation film, said compensation film comprising
at least one layer of an isotropic polymer obtainable by
polymerization of a mixture of a polymerizable mesogenic material
comprising: a) compound having one or two more polymerizable
functional group, in the presences b) an initiator, c) optionally a
non-polymerizable compound having two or more polymerizable
functional groups and d) optionally a stabilizer, characterized in
that said layer of an anisotropic polymer has a hometropic or
tilted hometropic molecular orientation. The invention also relates
to methods of manufacturing said compensation films. The invention
further relates to mixtures of chiral polymerizable mesogenic
material used for manufacturing of said compensation films.
Inventors: |
Hanmer; James (Southampton,
GB), Verrall; Mark (Taoyuan, TW) |
Assignee: |
Merck Patent Gesellschaft mit
beschrankter Haftung (Darmstadt, DE)
|
Family
ID: |
8222964 |
Appl.
No.: |
10/833,280 |
Filed: |
June 18, 1997 |
PCT
Filed: |
June 18, 1997 |
PCT No.: |
PCT/EP97/03168 |
371(c)(1),(2),(4) Date: |
December 30, 1998 |
PCT
Pub. No.: |
WO98/00475 |
PCT
Pub. Date: |
January 08, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09214495 |
Dec 30, 1998 |
06379758 |
Apr 30, 2002 |
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Foreign Application Priority Data
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Jul 1, 1996 [EP] |
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96110579 |
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Current U.S.
Class: |
428/1.1; 428/1.5;
252/299.01 |
Current CPC
Class: |
G02B
5/3016 (20130101); C09K 19/2007 (20130101); G02F
1/13363 (20130101); C09K 19/38 (20130101); C09K
19/2014 (20130101); G02F 2413/03 (20130101); C09K
2019/0448 (20130101); G02F 2413/07 (20130101); G02F
1/133638 (20210101); C09K 2323/05 (20200801); G02F
2413/15 (20130101); C09K 2323/00 (20200801) |
Current International
Class: |
C09K
19/52 (20060101); C09K 19/38 (20060101); G02F
1/133 (20060101) |
Field of
Search: |
;428/1.1,1.5
;252/299.01,299.63,299.66,299.67 ;349/117 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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42 26 994 |
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524028 |
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529813 |
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606940 |
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622789 |
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628847 |
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EP |
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643121 |
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EP |
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0699938 |
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704513 |
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Apr 1996 |
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EP |
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823442 |
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Feb 1998 |
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EP |
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860455 |
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Aug 1998 |
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EP |
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2299333 |
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Oct 1996 |
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GB |
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2306470 |
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May 1997 |
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GB |
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WO-9016005 |
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Dec 1990 |
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WO |
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WO 9509379 |
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Sep 1994 |
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WO |
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WO-9422977 |
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Oct 1994 |
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WO |
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WO-9612209 |
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Apr 1996 |
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WO |
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WO-9625470 |
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Aug 1996 |
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WO |
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WO-9744409 |
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Nov 1997 |
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WO |
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WO-9744702 |
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Nov 1997 |
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WO |
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Other References
English abstract EP 860455 cited by examiner .
English Abstract EP 823442. cited by examiner .
English Abstract WO 974409. cited by examiner.
|
Primary Examiner: Wu; Shean C
Attorney, Agent or Firm: Millen, White, Zelano, Branigan,
P.C.
Claims
What is claimed is:
1. A liquid crystal display device comprising: a liquid crystal
cell and at least one compensation film or a combination of
polarizers and optical compensators comprising at least one
compensation film, said compensation film comprising at least one
layer of an anisotropic polymer obtained by polymerization of
polymerizable mesogenic material comprising a) two or more
mesogenic compounds having at least one rod-like or board-like
mesogenic group and at least one polymerizable functional group, in
the presence of b) an initiator, c) optionally a non-mesogenic
compound having two or more polymerizable functional groups, and d)
optionally a stabilizer, wherein said layer of an anisotropic
polymer has a homeotropic or tilted homeotropic molecular
orientation, wherein said mesogenic compounds having at least one
rod-like or board-like mesogen and at least one polymerizable
functional group are compounds of formula I P--(Sp--X).sub.n--MG--R
I wherein P is a polymerizable group, Sp is a spacer group having 1
to 20 C atoms, X is a group selected from --O--, --S--, --CO--,
--COO--, --OCO--, --OCOO-- or a single bond, n is 1, MG is a group
according to formula II
--(A.sup.1--Z.sup.1).sub.m--A.sup.2--Z.sup.2--A.sup.3-- II wherein
A.sup.1, A.sup.2 and A.sup.3 are independently from each other:
1,4-phenylene or 1,4-phenylene in which one or more CH groups is
replaced by N, 1,4-cyclohexylene or 1,4-cyclohexylene in which one
or two non-adjacent CH.sub.2 groups is replaced in each case by O
or S, 1,4-cyclohexenylene, or naphthalene-2,6-diyl, wherein in each
case the group is unsubstituted, or mono- or polysubstituted with
halogen, cyano, nitro, alkyl having 1 to 7 C atoms, alkoxy having 1
to 7 C atoms, alkanoyl having 1 to 7 C atoms, alkyl having 1 to 7 C
atoms wherein one or more H atoms is replaced by F or Cl, alkoxy
having 1 to 7 C atoms wherein one or more H atoms is replaced by F
or Cl, or alkanoyl having 1 to 7 C atoms wherein one or more H
atoms is replaced by F or Cl, Z.sup.1 and Z.sup.2 are each
independently --COO--, --OCO--, --CH.sub.2CH.sub.2--,
--OCH.sub.2--, --CH.sub.2O--, .[.--CH.dbd.CH, --C.ident.C.].
.Iadd.--CH.dbd.CH--, --C.ident.C--.Iaddend., --CH.dbd.CH--COO--,
--OCO--CH.dbd.CH-- or a single bond, m is 0, 1 or 2, and R is alkyl
having up to 25 C atoms, alkyl having up to 25 C atoms which is
mono- or polysubstituted by halogen or CN, wherein, in each case,
one or more non-adjacent CH.sub.2 groups is optionally replaced, in
each case independently from one another, by --O--, --S--, --NH--,
--N(CH.sub.3)--, --CO--, --COO--, --OCO--, --OCO--O--, --S--CO--,
--CO--S-- or --C.ident.C-- in such a manner that oxygen atoms are
not linked directly to one another, or alternatively R is halogen,
cyano or has independently one of the meanings given for
P--(Sp--X).sub.n--, wherein said polymerizable mesogenic material
contains at least 75% by weight of compounds of formula I.
2. A liquid crystal display device as claimed in claim 1, wherein
said device .[.it.]. comprises a broad band reflective
polarizer.
3. A liquid crystal display device as claimed in claim 2, wherein
the phase retardation of the compensation film is opposite in sign
to the phase retardation of the broad band reflective polarizer
over the range of viewing angles from 0 .Iadd.to .Iaddend..+-.90
degrees.
4. A liquid crystal display device as claimed in claim 1, wherein
the compensation film is a composite film comprising two or more
layers of an anisotropic polymer at least one of said layers having
a homeotropic or tilted homeotropic orientation.
5. A liquid crystal display device as claimed in claim 4, wherein
at least one layer of said composite compensation film has an
optical symmetry axis with a diffusion orientation than the optical
symmetry axis of at least one other of said layers.
6. A compensation film comprising at least one layer of an
anisotropic polymer with homeotropic or tilted homeotropic
molecular orientation, wherein said compensation film is obtained
by A) coating a mixture of a polymerizable mesogenic material
comprising a) two or more mesogenic compounds having at least one
rod-like or board-like mesogenic group and at least one
polymerizable functional group, b) an initiator, c) optionally a
non-mesogenic compound having two or more polymerizable functional
groups, and d) optionally a stabilizer on at least one substrate in
the form of a layer, B) aligning said mixture in a homeotropic or
tilted homeotropic orientation, C) polymerizing said mixture by
exposing it to heat or actinic radiation, D) optionally repeating
steps A), B) and C) at least one more time, and E) optionally
removing said at least one substrate from the polymerized material,
wherein said mesogenic compounds having at least one rod-like or
board-like mesogen and at least one polymerizable functional group
are compounds of formula I P--(Sp--X).sub.n--MG--R I wherein P is a
polymerizable group, Sp is a spacer group having 1 to 20 C atoms, X
is a group selected from --O--, --S--, --CO--, --COO--, --OCO--,
--OCOO-- or a single bond, n is 1, MG is a group according to
formula II --(A.sup.1--Z.sup.1).sub.m--A.sup.2--Z.sup.2--A.sup.3--
II wherein A.sup.1, A.sup.2 and A.sup.3 are independently from each
other: 1,4-phenylene or 1,4-phenylene in which one or more CH
groups is replaced by N, 1,4-cyclohexylene or 1,4-cyclohexylene in
which one or two non-adjacent CH.sub.2 groups is replaced in each
case by O or S, 1,4-cyclohexenylene, or naphthalene-2,6-diyl,
wherein in each case the group is unsubstituted, or mono- or
polysubstituted with halogen, cyano, nitro, alkyl having 1 to 7 C
atoms, alkoxy having 1 to 7 C atoms, alkanoyl having 1 to 7 C
atoms, alkyl having 1 to 7 C atoms wherein one or more H atoms is
replaced by F or Cl, alkoxy having 1 to 7 C atoms wherein one or
more H atoms is replaced by F or Cl, or alkanoyl having 1 to 7 C
atoms wherein one or more H atoms is replaced by F or Cl, Z.sup.1
and Z.sup.2 are each independently --COO--, --OCO--,
--CH.sub.2CH.sub.2--, --OCH.sub.2--, --CH.sub.2O--, .[.--CH.dbd.CH,
--C.ident.C.]. .Iadd.--CH.dbd.CH--, --C.ident.C--.Iaddend.,
--CH.dbd.CH--COO--, --OCO--CH.dbd.CH-- or a single bond, m is 0, 1
or 2, and R is alkyl having up to 25 C atoms, alkyl having up to 25
C atoms which is mono- or polysubstituted by halogen or CN,
wherein, in each case, one or more non-adjacent CH.sub.2 groups is
optionally replaced, in each case independently from one another,
by --O--, --S--, --NH--, --N(CH.sub.3)--, --CO--, --COO--, --OCO--,
--OCO--O--, --S--CO--, --CO--S-- or --C.ident.C-- in such a manner
that oxygen atoms are not linked directly to one another, or
alternatively R is halogen, cyano or has independently one of the
meanings given for P--(Sp--X).sub.n--, wherein said polymerizable
mesogenic material contains at least 75% by weight of compounds of
formula I.
7. A compensation film as claimed in claim 6, wherein at least one
substrate is a plastic film.
8. A compensation film as claimed in claim 6, wherein the mixture
of the polymerizable mesogenic material comprises at least one
mesogen having one polymerizable functional group and at least one
mesogen having two or more polymerizable functional groups.
9. A compensation film as claimed in claim 6, wherein the mixture
of the polymerizable mesogenic material comprises at least two
mesogens having one polymerizable functional group.
10. A composition film as claimed in claim 6, wherein the
polymerized material forms a three-dimensional network.
11. A compensation film according to claim 6, wherein the mixture
of the polymerizable mesogenic material consists essentially of:
a1) 15 to 85% by weight of at least one mesogen according to
formula I having one polymerizable functional group, a2) 10 to 85%
by weight of at least one mesogen according to formula I having two
or more polymerizable functional groups, b) 0.01 to 5% by weight of
an initiator, c) 0 to 20% by weight of a non-mesogenic compound
having two or more polymerizable functional groups, and d) 0 to
1000 ppm of a stabilizer, wherein said polymerizable mesogenic
material contains at least 75% by weight of compounds of formula
I.
12. A compensation film according to claim 6, wherein, the mixture
of the polymerizable mesogenic material essentially consists of a)
75 to 99% by weight of at least two mesogens according to formula I
having one polymerizable functional group, b) 0.01 to 5% by weight
of an initiator, c) 0 to 20% by weight of a non-mesogenic compound
having two or more polymerizable functional groups, and d) 0 to
1000 ppm of a stabilizer.
13. A mixture of a polymerizable mesogenic material comprising a)
75 to 99% by weight of two more achiral mesogenic compounds having
at least one rod-like or board-like mesogen and one polymerizable
functional group in the presence of b) 0.01 to 5% by weight of an
initiator, c) 0 to 20% by weight of a non-mesogenic compound having
two or more polymerizable functional groups, and d) 0 to 1000 ppm
of a stabilizer, wherein said two or more achiral mesogenic
compound having at least one rod-like or board-like mesogen and one
polymerizable functional group are compounds of formula I
P--(Sp--X).sub.n--MG--R I wherein P is a polymerizable group, Sp is
a spacer group having 1 to 20 C atoms, X is a group selected from
--O--, --S--, --CO--, --COO--, --OCO--, --OCOO-- or a single bond,
n is 0 or 1, MG is a group according to formula II
--(A.sup.1--Z.sup.1).sub.m--A.sup.2--Z.sup.2--A.sup.3-- II wherein
A.sup.1, A.sup.2 and A.sup.3 are independently from each other:
1,4-phenylene or 1,4-phenylene in which one or more CH groups is
replaced by N, 1,4-cyclohexylene or 1,4-cyclohexylene in which one
or two non-adjacent CH.sub.2 groups are replaced in each case by O
or S, 1,4-cyclohexenylene, or naphthalene-2,6-diyl, wherein in each
case the group is unsubstituted, or mono- or polysubstituted with
halogen, cyano, nitro, alkyl having 1 to 7 C atoms, alkoxy having 1
to 7 C atoms, alkanoyl having 1 to 7 C atoms, alkyl having 1 to 7 C
atoms wherein one or more H atoms is replaced by F or Cl, alkoxy
having 1 to 7 C atoms wherein one or more H atoms is replaced by F
or Cl, or alkanoyl having 1 to 7 C atoms wherein one or more H
atoms is replaced by F or Cl, Z.sup.1 and Z.sup.2 are each
independently --COO--, --OCO--, --CH.sub.2CH.sub.2--,
--OCH.sub.2--, --CH.sub.2O--, .[.--CH.dbd.CH, --C.ident.C.].
.Iadd.--CH.dbd.CH--, --C.ident.C--.Iaddend., --CH.dbd.CH--COO--,
--OCO--, CH.dbd.CH-- or a single bond, m is 0, 1 or 2, R is alkyl
having up to 25 C atoms, alkyl having up to 25 C atoms which is
mono- or polysubstituted by halogen or CN, wherein, in each case,
one or more non-adjacent CH.sub.2 groups is optionally replaced, in
each case independently from one another, by --O--, --S--, --NH--,
--N(CH.sub.3)--, --CO--, --COO--, --OCO--, --OCO--O--, --S--CO--,
--CO--S-- or --C.ident.C-- in such a manner that oxygen atoms are
not linked directly to one another, or alternatively R is halogen
or cyano.
14. In a method of compensating the viewing angle dependence of the
phase retardation of light transmitted by a broad band reflective
polarized by providing a compensation film to achieve said
compensating, the improvement wherein said compensation film is a
film according to claim 6.
15. A liquid crystal display device according to claim 2, wherein
the bandwidth of said broad band reflective polarizer is at least
100 nm.
16. A liquid crystal display device according to claim 2, wherein
the bandwidth of said broad band reflective polarizer is at least
150 nm.
17. A liquid crystal display device according to claim 4, wherein
at least one of said layers of anisotropic polymer has an optical
symmetry axis with a tilt angle, relative to the plane of the
layer, of less than 90 degrees but greater than 45 degrees.
18. A liquid crystal display device according to claim 4, wherein
at least one of said layers of anisotropic polymer has an optical
symmetry axis with a tilt angle, relative to the plane of the
layer, of less than 90 degrees but greater than 60 degrees.
19. A liquid crystal display device according to claim 4, wherein
at least one of said layers of anisotropic polymer has an optical
symmetry axis with a tilt angle, relative to the plane of the
layer, of less than 90 degrees but greater than 75 degrees.
20. A liquid crystal display device according to claim 1, wherein
said layer of anisotropic polymer has an optical symmetry axis
which is oriented perpendicular to the layer.
21. A liquid crystal display device according to claim 1, wherein
said layer of anisotropic polymer has an optical symmetry axis with
a tilt angle, relative to the plane of said layer, of less than 90
degrees but higher than 45 degrees.
22. A liquid crystal display device according to claim 15, wherein
the phase retardation of the compensation film is opposite in sign
to the phase retardation of the broad band reflective polarizer
over viewing angles, measured from the normal plane of the film, of
0 to +/-85 degrees.
23. A liquid crystal display device according to claim 1, wherein
said polymerizable mesogenic material contains up to 20% of
non-mesogenic compounds with two or more polymerizable functional
groups selected from alkyldiacrylates or alkyldimethacrylates
having alkyl groups with 1-20 C atoms.
24. A liquid crystal display device according to claim 1, wherein
said polymerizable mesogenic material exhibits a nematic or smectic
phase.
25. A compensation film according to claim 6, wherein said
polymerizable mesogenic material exhibits a nematic or smectic
phase.
26. A compensation film according to claim 6, wherein
polymerization is carried out in the smectic phase of said
polymerizable mesogenic mixture.
27. A compensation film according to claim 26, wherein
polymerization is carried out in the smectic A phase of said
polymerizable mesogenic mixture.
28. A compensation film according to claim 6, wherein said
polymerization mesogenic material contains 40-90% of at least one
mesogenic according to formula I having one polymerizable
functional group.
29. A device according to claim 1, wherein said polymerizable
mesogenic material further comprises one or more surface-active
compounds.
30. A compensation film according to claim 6, wherein said
polymerizable mixture further comprises one or more surface-active
compounds.
31. A mixture according to claim 13, wherein said polymerizable
mixture further comprises one or more surface-active compounds.
32. A mixture of a polymerizable mesogenic material comprising a)
at least two mesogenic compounds each having at least one rod-like
or board-like mesogen, wherein one of said mesogenic compounds has
one polymerizable functional group and another of said mesogenic
compounds has two or more polymerizable functional groups, b) 0.01
to 5% by weight of an initiator, c) 0 to 20% by weight of a
non-mesogenic compound having two or more polymerizable functional
groups, and d) 0 to 1000 ppm of a stabilizer, wherein said at least
two mesogenic compound are compounds of formula I
P--(Sp--X).sub.n--MG--T I wherein P is a polymerizable group, Sp is
a spacer group having 1 to 20 C atoms, X is a group selected from
--O--, --S--, --CO--, --COO--, --OCO--, --OCOO-- or a single bond,
n is 0 or 1, MG is a group according to formula II
--(A.sup.1--Z.sup.1).sub.m--A.sup.1--Z.sup.2--A.sup.3-- II wherein
A.sup.1, A.sup.2 and A.sup.3 are independently from each other:
1,4-phenylene or 1,4-phenylene in which one or more CH groups is
replaced by N, 1,4-cyclohexylene or 1,4-cyclohexylene in which one
or two non-adjacent CH.sub.2 groups is replaced in each case by O
or S, 1,4-cyclohexenylene, or naphthalene-2,6-diyl, wherein in each
case the group is unsubstituted, or mono- or polysubstituted with
halogen, cyano, nitro, alkyl having 1 to 7 C atoms, alkoxy having 1
to 7 C atoms, alkanoyl having 1 to 7 C atoms, alkyl having 1 to 7 C
atoms wherein one or more H atoms is replaced by F or Cl, alkoxy
having 1 to 7 C atoms wherein one or more H atoms is replaced by F
or Cl, or alkanoyl having 1 to 7 C atoms wherein one or more H
atoms is replaced by F or Cl, Z.sup.1 and Z.sup.2 are each
independently --COO--, --OCO--, --CH.sub.2CH.sub.2--,
--OCH.sub.2--, --CH.sub.2O--, --CH.dbd.CH, .[.--C.ident.C.].
.Iadd.--C.ident.C--.Iaddend., --CH.dbd.CH--COO--,
--OCO--CH.dbd.CH-- or a single bond, m is 0, 1 or 2, and R
is.Iadd., in this case of mesogenic compounds having one
polymerizable functional group, .Iaddend.straight chain or achiral
branched alkyl having up to 25 C atoms, wherein, in each case, one
or more non-adjacent CH.sub.2 groups is optionally replaced, in
each case independently from one another, by --O--, --S--, --NH--,
--N(CH.sub.3)--, --CO--, --COO--, --OCO--, --OCO--O--, --S--CO--,
--CO--S-- or --C.ident.C-- in such a manner that oxygen atoms are
not linked directly to one another, .Iadd.or, in the case of
mesogenic compounds having two or more polymerizable functional
group, R is independently P--(Sp--X).sub.n, .Iaddend. wherein
component a) consists essentially of a1) 15 to 85% by weight of
said mesogenic compound having one polymerizable functional group,
and a2) 10 to 85% by weight of said mesogenic compound having two
or more polymerizable functional groups, and wherein said
polymerizable mesogenic material contains at least 75% by weight of
compounds of formula I.
33. A device according to claim 1, wherein P is
CH.sub.2.dbd.CW--COO--, WCH.ident.CH--O--, ##STR00010## is H,
CH.sub.3 or Cl, k is 0 or 1, and Sp is a linear or branched
alkylene group having 1-20 C atoms in which, optionally one or more
non-adjacent CH.sub.2 groups is in each case replaced by --O--,
--S--, --NH--, --N(CH.sub.3)--, --CO--, --O--CO--, --S--CO--,
--O--COO--, --CO--S--, --CO--O--, --CH(halogen)--, --CH(CN)--,
--CH.dbd.CH-- or --C.ident.C--.
34. A compensation film according to claim 6, wherein P is
CH.sub.2.dbd.CW--COO--, ##STR00011## is H, CH.sub.3 or Cl, k is 0
or 1, and Sp is a linear or branched alkylene group having 1-20 C.
atoms in which, optionally one or more non-adjacent CH.sub.2 groups
is in each case replaced by --O--, --S--, --NH--, --N(CH.sub.3)--,
--CO--, --O--CO--, --S--CO--, --O--COO--, --CO--S--, --CO--O--,
--CH(halogen)--, --CH(CN)--, --CH.dbd.CH-- or --C.ident.C--.
35. A mixture of polymerizable material according to claim 13,
wherein P is ##STR00012## is H, CH.sub.3 or Cl, k is 0 or 1, and Sp
is a linear or branched alkylene group having 1-20 C atoms in
which, optionally one or more non-adjacent CH.sub.2 groups is in
each case replaced by --O--, --S--, --NH--, --N(CH.sub.3)--,
--CO--, --O--CO--, --S--CO--, --O--COO--, --CO--S--, --CO--O--,
--CH(halogen)--, --CH(CN)--, --CH.dbd.CH-- or --C.ident.C--.
.Iadd.36. A mixture according to claim 32, wherein MG is selected
from formulae II-1 to II-16 --Phe--Z.sup.2--Phe-- II-1
--Phe--Z.sup.2--Cyc-- II-2 --PheL--Z.sup.2--Phe-- II-3
--PheL--Z.sup.2--Cyc-- II-4 --Phe--Z.sup.2--PheL-- II-5
--Phe--Z.sup.1--Phe--Phe-- II-6 --Phe--Z.sup.1--Phe--Cyc-- II-7
--Phe--Z.sup.1--Phe--Z.sup.2--Phe-- II-8
--Phe--Z.sup.1--Phe--Z.sup.2--Cyc-- II-9
--Phe--Z.sup.1--Cyc--Z.sup.2--Phe-- II-10
--Phe--Z.sup.1--Cyc--Z.sup.2--Cyc-- II-11
--Phe--Z.sup.1--PheL--Z.sup.2--Phe-- II-12
--Phe--Z.sup.1--Phe--Z.sup.2--PheL-- II-13
--PheL--Z.sup.1--Phe--Z.sup.2--PheL-- II-14
--PheL--Z.sup.1--PheL--Z.sup.2--Phe-- II-15
--PheL--Z.sup.1--PheL--Z.sup.2--PheL-- II-16 wherein Phe is
1,4-phenylene, PheL a 1,4-phenylene group which is substituted by
at least one group L, L is F, Cl, CN or an optionally fluorinated
alkyl, alkoxy or alkanoyl group having 1 to 4 C atoms, and Cyc is
1,4-cyclohexylene. .Iaddend.
.Iadd.37. A mixture according to claim 36, wherein L is F, Cl, CN,
methyl, methoxy, ethyl, ethoxy, oxamethyl, oxaethyl, or
trifluormethyl. .Iaddend.
.Iadd.38. A mixture according to claim 36, wherein L is F, Cl, CN,
NO.sub.2, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, OC.sub.2H.sub.5,
COCH.sub.3, COC.sub.2H.sub.5, CF.sub.3, OCF.sub.3, OCHF, or
OC.sub.2F.sub.5. .Iaddend.
.Iadd.39. A mixture according to claim 32, wherein MG is selected
from formulae IIa to IIn ##STR00013## wherein L is F, Cl, CN or an
optionally fluorinated alkyl, alkoxy or alkanoyl group having 1 to
4 C atoms, and r is 0, 1 or 2. .Iaddend.
.Iadd.40. A mixture according to claim 39, wherein the group
##STR00014## .Iaddend.
.Iadd.41. A mixture according to claim 32, wherein one of said at
least two polymerizable mesogenic compounds is selected from
formula Ia and the other of said at least two polymerizable
mesogenic compounds is selected from formulae Ib to Ig:
##STR00015## wherein x and y are each independently 1 to 12, A is a
1,4-phenylene or 1,4-cyclohexylene group, R.sup.1 is halogen, cyano
or an optionally halogenated alkoxy group with 1 to 12 C atoms, and
L.sup.1 and L.sup.2 are each independently H, halogen, CN, or an
alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms. .Iaddend.
Description
The invention relates to a liquid crystal display device comprising
a liquid crystal cell and at least one compensation film or a
combination of polarizers and optical compensators comprising at
least one compensation film, said compensation film comprising at
least one layer of an anisotropic polymer obtainable by
polymerization of a mixture of a polymerizable mesogenic material
comprising a) at least one mesogen having at least one
polymerizable functional group, in the presence of b) an initiator,
c) optionally a non-mesogenic compound having two or more
polymerizable functional groups and d) optionally a stabilizer,
characterized in that the layer of the anisotropic polymer has a
homeotropic or tilted homeotropic molecular orientation.
The invention also relates to methods of manufacturing said
compensation films. The invention further relates to mixtures of
polymerizable mesogenic material used for the manufacturing of said
compensation films. The invention also relates to the use of said
compensation films for compensating the viewing angle dependence of
the phase retardation of light transmitted by a broad band
reflective polarizer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a and 1b show a display device according to preferred
embodiments of the present invention.
FIG. 2 shows the spectrum of a broad waveband reflective polarizer
that can be used together with the inventive compensation films in
a special embodiment of the invention.
FIG. 3 shows the measurement setup according to example 1 of the
present invention.
FIG. 4 shows the luminance versus viewing angle for a broad
waveband reflective polarizer when used with or without a
compensation film according to the present invention.
FIG. 5 shows the color difference versus viewing angle for a broad
waveband reflective polarizer when used with or without a
compensation film according to the present invention.
EP 0 606 940 discloses a cholesteric reflective polarizer that
produces circularly polarized light or, when used together with a
quarter wave retardation film, linearly polarized light of a high
luminance over a broad range of wavelengths. However, the optical
properties of this polarizer, e.g. the luminance and the contrast
ratio, are significantly deteriorating with increasing viewing
angles.
It has therefore been desired to have available a compensation film
that, when used together with a broad waveband cholesteric
reflective polarizer like the one described above, would improve
the optical properties of the polarizer over a wide range of
viewing angles.
Compensation films have been described in prior art. Usually
uniaxially stretched films of an isotropic or LC polymer are used
for this purpose. Compensation films made of polymerized mixtures
of reactive mesogens have also been mentioned.
JP 05-142531. for example discloses a compensator that comprises a
nematic liquid crystal polymer which is aligned in the normal
direction of the film. The compensator is made by aligning a liquid
crystal that is homeotropically oriented in a glass cell. However,
the alignment of a liquid crystal as disclosed in JP 05-142531 is
often difficult to achieve and requires high temperatures.
Furthermore, the method of polymerizing in a glass cell with
subsequent removal of the glass plates as described in the JP
05-142531 is complicated and not suitable for industrial large
scale production.
Heynderickx, Broer et al. in Mol. Cryst. Liq. Cryst. 203 (1991),
113-126 describe a compensation film for STN displays made of a
polymerized mixture of an achiral mesogenic diacrylate and a chiral
dopant. The liquid crystal molecules in this film have a planar
orientation, i.e. an orientation, parallel to the film plane.
However, polymerizable liquid crystalline compositions containing
only one polymerizable compound as disclosed in this document in
general exhibit high melting points, which in turn requires high
temperatures for alignment and polymerization, which is a serious
drawback when manufacturing such films.
Furthermore the compensators described by JP 05-142531 and
Heynderickx, Broer et al. are used for compensating liquid crystal
displays, for example STN displays, but they are not designed for
the compensation of a broad waveband reflective cholesteric
polarizer in combination with a liquid crystal display.
Consequently there has been a considerable demand for a
compensation film that, when used together with a broad waveband
cholesteric reflective polarizer, enhances the optical properties
of the polarizer over a wide range of viewing angles, that is easy
to fabricate and does not have the disadvantages of the
compensation films of prior art as discussed above.
One of the aims of the present invention is to provide a
compensation film having these properties. Another aim of the
invention is to provide a liquid crystal display device comprising
such a compensation film. Other aims of the present invention are
immediately evident to the person skilled in the art from the
following detailed description.
It has been found that these aims can be achieved by providing a
compensation film with a homeotropic or tilted homeotropic
molecular orientation according to the present invention.
The object of the invention is a liquid crystal display device
comprising a liquid crystal cell and at least one compensation film
or a combination of polarizers and optical compensators comprising
at least one compensation film, said compensation film comprising
at least one layer of an anisotropic polymer obtainable by
polymerization of a mixture of a polymerizable mesogenic material
comprising a) at least one meosgen having at least one
polymerizable functional group, in the presence of b) at initiator,
c) optionally a non-mesogenic compound having two or more
polymerizable functional groups and d) optionally a stabilizer,
characterized in that said layer of an anisotropic polymer has a
homeotropic or tilted homeotropic orientation.
In a preferred embodiment of the invention the liquid crystal
display device is characterized in that it comprises a broad band
reflective polarizer. The bandwidth of the wavelength band
reflected from this broad band reflective polarizer is at least
100, preferably at least 150 nm.
In another preferred embodiment of the invention the liquid crystal
display device is characterized in that the phase retardation of
the compensation film is opposite in sign and substantially equal
in magnitude to the phase retardation of the broad band reflective
polarizer over a wide range of viewing angles.
In another preferred embodiment of the invention the liquid crystal
display device is characterized in that the compensation film is a
composite film comprising two or more layers of an anisotropic
polymer at least one of said layers having a homeotropic or tilted
homeotropic orientation.
In another preferred embodiment of the invention the liquid crystal
display device is characterized in that at least one layer of said
composite compensation film has an optical symmetry axis with a
different orientation than the optical symmetry axis of at least
one other of said layers.
In yet another preferred embodiment of the invention the liquid
crystal display device is characterized in that the compensation
film comprises at least one layer of an anisotropic polymer with an
optical symmetry axis having a tilt angle relative to the plane of
the layer being in the range from less than 90 degrees but higher
than 45, preferably higher than 60, in particular higher than 75
degrees.
The term homeotropic orientation in connection with the layers of
anisotropic polymer according to the present invention is
indicating in the foregoing and the following that the optical
symmetry axis of said layer is either oriented perpendicular to or
substantially oriented perpendicular to the layer.
In analogy to this the term tilted homeotropic orientation is
indicating that the optical symmetry axis of said layer is having a
tilt angle relative to the plane of the layer being in the range
from less than 90 degrees but higher than 45, preferably higher
than 60, in particular higher than 75 degrees. In a preferred
embodiment of the present invention said tilt angle is in the range
from 88 to 75, preferably 86 to 80 degrees.
The term viewing angle as referred to in connection with an optical
film or a combination of optical films, such as compensation or
polarizer films, according to the present invention in the
foregoing and the following is to be understood as the angle of
observation relative to the normal of the plane of the film under
which for example the contrast, the brightness and/or the color
shift of the film is characterized by an acceptable level for the
envisaged application. The term wide range of viewing angles is to
be understood as comprising viewing angles measured from the normal
of the plane of the film that are ranging ideally from 0 to .+-.90
degrees and preferably at least from 0 to .+-.85 degrees. For most
applications, a range from 0 to .+-.75 degrees is acceptable. In
specific display embodiments, angles ranging from 0 to .+-.60, or
even 0 to .+-.50 degrees are still suitable.
Another object of the invention is a compensation film comprising
at least one layer of an anisotropic polymer with homeotropic or
tilted homeotropic molecular orientation, characterized in that
said compensation film is obtainable by A) coating a mixture of a
polymerizable mesogenic material comprising a) at least one mesogen
having at least one polymerizable functional group in the presence
of b) an initiator, c) optionally a non-mesogenic compound having
two or more polymerizable functional groups, and d) optionally a
stabilizer on at least one substrate in form of a layer, B)
aligning said mixture in a homeotropic or tilted homeotropic
orientation, C) polymerizing said mixture by exposing it to heat or
actinic radiation, D) optionally repeating the steps A), B) and C)
at least one more time, and E) optionally removing one or both of
the substrates from the polymerized material,
In a preferred embodiment of the invention the compensation film is
characterized in that the mixture of the polymerizable mesogenic
material contains two or more mesogens having one polymerizable
functional group.
In another preferred embodiment of the invention the compensation
film is characterized in that the polymerized material forms a
three-dimensional network.
In another preferred embodiment of the invention the compensation
film is characterized in that the mixture of the polymerizable
mesogenic material contains at least one mesogen having one
polymerizable functional group and at least one mesogen having two
or more polymerizable functional groups.
Another object of the invention is a mixture of a polymerizable
mesogenic mixture as described above.
The terms reactive mesogen, reactive mesogenic compound, reactive
liquid crystal (compound) or reactive liquid crystalline compound
as used in the foregoing and the following comprise compounds with
a rodlike, boardlike or dislike mesogenic group. These mesogenic
compounds to not necessarily have to exhibit meseophase behavior by
themselves. In a preferred embodiment of the present invention they
show meosphase behavior in mixtures with other compounds or after
polymerization of the pure mesogenic compounds or mixtures
comprising the mesogenic compounds.
In a preferred embodiment the polymerizable mixture comprises
reactive mesogenic compounds having one polymerizable group. These
compounds are in general easier and cheaper to synthesize.
Furthermore, mixtures comprising only monoreactive compounds often
show higher stability against unintended spontaneous polymerization
than mixtures comprising direactive compounds.
In another preferred embodiment the polymerizable mixture comprises
reactive mesogenic compounds having two or more polymerizable
functional groups (multifunctional compounds). Upon polymerization
of such a mixture of three-dimensional polymer network is formed. A
compensation film made of such a network is self-supporting and
shows a high mechanical and thermal stability and a low temperature
dependence of its physical properties.
In another preferred embodiment the polymerizable mixture comprises
up to 20% of a non mesogenic compound with two or more
polymerizable functional groups to increase crosslinking of the
polymer. Typical examples for difunctional non mesogenic monomers
are alkyldiacrylates or alkyldimethacrylates with alkyl groups of 1
to 20 C atoms. Typical examples for non mesogenic monomers with
more than two polymerizable groups are
trimethylpropanetrimethacrylate or
pentaerythritoltetraacrylate.
By varying the concentration of the multifunctional mesogenic or
non mesogenic compounds the crosslink density of the polymer film
and thereby its physical and chemical properties such as the glass
transition temperature, which is also important for the temperature
dependence of the optical properties of the compensator, the
thermal and mechanical stability or the solvent resistance can be
tuned easily.
The inventive polymerizable mixture is coated onto at least one
substrate in the form of a layer, aligned and polymerized. As a
substrate for example a glass or quartz sheet as well as a plastic
film or sheet can be used. It is also possible to put a second
substrate on top of the coated mixture prior to, during and/or
after polymerization. The substrates can be removed after
polymerization or not. When using two substrates in case of curing
by actinic radiation, at least one substrate has to be transmissive
for the actinic radiation used for the polymerization.
Isotropic or birefringent substrates can be used. In case the
substrate is not removed from the polymerized film after
polymerization, preferably isotropic substrates are used.
Preferably at least one substrate is a plastic such as for example
a polyethyleneterephthalate (PET), polyvinylalcohol (PVA),
polycarbonate (PC) or triacetylcellulose (TAC), film, preferably a
PET film. As a birefringent substrate for example an uniaxially
stretched plastic film can be used.
To achieve homeotropic or tilted homeotropic,alignment the
mesogenic material is preferably coated onto substrates carrying an
alignment layer. Suitable aligning agents used on glass substrates
are for example alkyltrichlorosilane or lecithine, whereas for a
plastic substrate thin layers of lecithine, silica or high tilt
polyimide orientation films as aligning agents may be used. In a
preferred embodiment of the invention a silica coated plastic film
is used as a substrate.
Polymerization of the inventive polymerizable mesogenic mixture
takes place by exposing it to heat or to actinic radiation. Actinic
radiation means irradiation with light, X-rays, gamma rays or
irradiation with high energy particles, such as ions or electrons.
In particular preferably UV light is used. The irradiation
wavelength is preferably from 250 nm to 400 nm, especially
preferably from 340 nm to 380 nm.
As a source for actinic radiation for example a single UV lamp or a
set of UV lamps can be used. When using a high lamp power the
curing time can be reduced. The irradiance produced by the lamp
used in the invention is preferably from 0.01 to 100 mW/cm.sup.2,
especially preferably from 10 to 50 mW/cm.sup.2.
The curing time is dependent inter alia on the reactivity of the
polymerizable mesogenic material, the thickness of the coated
layer, the type of polymerization initiator and the power of the UV
lamp. For mass production short curing times are preferred.
The polymerization is carried out in the presence of an initiator
absorbing the wavelength of the actinic radiation. For example,
when polymerizing by means of UV light, a photoinitiator can be
used that decomposes under UV irradiation to produce free radicals
that start the polymerization reaction. It is also possible to use
a cationic photoinitiator, when curing reactive mesogens with for
example vinyl and epoxide reactive groups, that photocures with
cations instead of free radicals. The polymerization may also be
started by an initiator that decomposes when heated above a certain
temperature.
In addition to light- or temperature-sensitive initiators the
polymerizable mixture may also comprise one or more other suitable
components such as, for example, catalysts, stabilizers,
co-reacting monomers or surface-active compounds.
In some cases it is of advantage to apply a second substrate to aid
alignment and exclude oxygen that may inhibit the polymerization.
Alternatively the curing can be carried out under an atmosphere of
inert gas. However, curing in air is also possible using suitable
photoinitiators and high UV lamp power. When using a cationic
photoinitiator oxygen exclusion most often is not needed, but water
should be excluded. In a preferred embodiment of the invention the
polymerization of the polymerizable mesogenic material is carried
out under an atmosphere of inert gas, preferably under a nitrogen
atmosphere.
To obtain polymer films with good alignment the polymerization has
to be carried out in the liquid crystal phase of the mixture of the
polymerizable mesogenic material in a homeotropic or tilted
homeotropic aligned state. Therefore, preferably a polymerizable
mixture having a low melting point is used, preferably a melting
point of 100.degree. C. or lower, in particular 60.degree. C. or
lower, so that curing can be carried out in the liquid crystalline
phase of the mixture at low temperatures. The polymerization
process is then made easier, which is of importance especially for
mass production. Curing temperatures below 100.degree. C. are
preferred. Especially preferred are curing temperatures below
60.degree. C.
Mixtures of polymerizable mesogenic material exhibiting nematic or
smectic phases may be used. In a preferred embodiment of the
invention the polymerization is carried out in the smectic phase,
especially preferably in the smectic A phase of the polymerizable
mesogenic mixture. In the smectic phase the alignment is less
easily disturbed prior to curing.
In a particularly preferred embodiment of the invention the
compensation film is used together with a reflective polarizer and
a quarter wave optical retarder. The compensation film may be
connected to the reflective polarizer as a separate optical
element. Preferably, the reflective polarizer and the compensation
film are integrated so that they form an individual optical
element. This can be done for example by laminating the
compensation film and the reflective polarizer together after
manufacturing the compensation film.
In another preferred embodiment the polymerizable mesogenic
material is coated and cured directly onto a reflective polarizer
which serves as a substrate, thus simplifying the production
process.
In yet another preferred embodiment the polymerizable mesogenic
material is coated and cured on a quarter wave optical retarder
which serves as a substrate.
The function of the inventive reflective polarizer is further
explained by FIG. 1a, which shows a display device according to a
preferred embodiment of the present invention as an example that
should not limit the scope of the invention. The main direction of
light following the optical path is from the left side to the right
side. The display device 10 consists of a side-lit backlight unit
11 with a lamp 12a and a combined light guide and reflector 12b, a
diffusor 13 and a polarizer combination consisting of a reflective
polarizer 14 comprising a layer of a liquid crystalline material
with a helically twisted molecular orientation, an inventive
compensation film 15, a quarter wave retardation sheet 16 and a
linear polarizer 17. The figure further depicts a liquid crystal
cell 18 and a second linear polarizer 19 behind the display
cell.
Light emitted from the backlight 11 is interacting with the
molecular helix structure of the reflective polarizer 14 with the
result that 50% of the intensity of the light incident on the
reflective polarizer is transmitted as circular polarized light
that is either right-handed or left-handed circular polarized
depending on the twist sense of the molecular helix structure of
the reflective polarizer, whereas the other 50% of the incident
light are reflected as circular polarized light of the opposite
handedness. The reflected light is depolarized by the backlight and
redirected by the reflector 12b onto the reflective polarizer 14.
In this manner, theoretically 100% of the light of a broad range of
wavelengths emitted from the backlight 11 are converted into
circularly polarized light. The main part of the transmitted
component is compensated by the compensation film 15 and converted
by the quarter wave retardation sheet 16 into linear polarized
light, which is then being transmitted by the linear polarizer 17,
whereas light which is not completely transferred into linear
polarized by the quarter wave retardation sheet 16, such as
elliptically polarized light, is not transmitted by the linear
polarizer 17. The linear polarized light then passes through the
display 18 and the second linear polarizer 19 to reach the viewer
20.
FIG. 1b depicts a display device according to another preferred
embodiment of the invention having essentially the same
construction as that shown in FIG. 1a, with the modification that
here the compensation film 15 is placed behind the quarter wave
retarder 16 when looking from the direction of incident light.
For a liquid crystal display comprising a combination with three
components, a broad band reflective polarizer 14, a quarter wave
retarder 16 and a linear polarizer 17, but without the inventive
compensation film 15, the luminance at normal incidence (viewing
angle 0.degree.) and at low values of the viewing angle is
increased compared to a conventional liquid crystal display
comprising a linear polarizer 17 as single component, i.e. without
the reflective polarizer 14 and quarter wave retarder 16.
However, as the display comprising the three components 14, 16 and
17 mentioned above is viewed under an increasing angle, the
increasing phase retardation by the reflective polarizer 14 itself
causes a notable reduction to the luminance, coinciding with the
value measured for the conventional display comprising the linear
polarizer 17 as a single component at a certain angle. This lowest
angle, at which the luminance of a display comprising the three
components reflective polarizer 14, quarter wave retarder 16 and
linear polarizer 17 ceases to excess that measured for a display
comprising 17 as single component, is referred to as the
`cross-over angle`.
When using an inventive compensation film 15 as a fourth component
in addition to the three components reflective polarizer 14,
quarter wave retarder 16 and linear polarizer 17 as mentioned above
in the liquid crystal display, the cross-over angle increases
significantly. In other words, the brightness enhancement, i.e. the
increase of luminance at low viewing angles, that was achieved by
using the reflective polarizer 14 and the quarter wave retarder 16,
is now extended also to large viewing angles.
The cross over angle of a display comprising a polarizer
combination comprising a compensation film according to the present
invention is preferably 30.degree. or larger, particularly
preferably 40.degree. or larger, very particularly preferably
50.degree. or larger.
The luminance of a display comprising a reflective broad band
polarizer, a quarter wave foil and a compensation film according to
the present invention is preferably larger than that of a display
that does not comprise the compensation film for viewing angles
from 0.degree. to 90.degree., i.e. for all possible viewing
angles.
The colour difference (.DELTA.E*.sub.uv in the CIE 1976 L*u*v*
color space) of a display comprising a reflective broad band
polarizer, a quarter wave foil and a compensation film according to
the present invention is preferably lower than that of a display
that does not comprise the compensation film for viewing angles
from 0.degree. to 90.degree., i.e. for all possible viewing
angles.
In a preferred embodiment of the invention the reactive mesogenic
compounds used in the mixture of the polymerizable mesogenic
material are compounds of formula I P--(Sp--X).sub.n--MG--R I
wherein
TABLE-US-00001 P is a polymerizable group, Sp is a spacer group
having 1 to 20 C atoms, X is a group selected from --O--, --S--,
--CO--, --COO--, --OCO--, --OCO--O-- or a single bond, n is 0 or 1,
MG is a mesogenic or mesogenity supporting group, preferably
selected according to formula II
--(A.sup.1--Z.sup.1).sub.m--A.sup.2--Z.sup.2--A.sup.3-- II
wherein
A.sup.1, A.sup.2 and A.sup.3 are independently from each other
1,4-phenylene in which, in addition, one or more CH groups may be
replaced by N, 1,4-cyclohexylene in which, in addition, one or two
non-adjacent CH.sub.2 groups may be replaced by O and/or S,
1,4-cyclohexylene or naphthalene-2,6-diyl, it being possible for
all these groups to be unsubstituted, mono- or polysubstituted with
halogen, cyano or nitro groups or alkyl, alkoxy or alkanoyl groups
having 1 to 7 atoms wherein one or more H atoms may be substituted
by F or Cl, Z.sup.1 and Z.sup.2 are each independently --COO--,
--OCO--, --CH.sub.2CH.sub.2--, --OCH.sub.2--, --CH.sub.2O--,
--CH.dbd.CH--, --C.ident.C--, --CH.dbd.CH--COO--,
--OCO--CH.dbd.CH-- or a single bond and m is 0, 1 or 2, and R is an
alkyl radical with up to 25 C atoms which may be unsubstituted,
mono- or polysubstituted by halogen or CN, it being also possible
for one or more non-adjacent CH.sub.2 groups to be replaced, in
each case independently from one another, by --O--, --S--, --NH--,
--N(CH.sub.3)--, --CO--, --COO-- --OCO--, --OCO--O--, --S--CO--,
--CO--S-- or --C.ident.C-- in such a manner that oxygen atoms are
not linked directly to one another, or alternatively R is halogen,
cyano or has independently one of the meanings given for
P--(Sp--X).sub.n--.
Particularly preferred are polymerizable mixtures comprising at
least two reactive mesogenic compounds at least one of which is a
compound of formula I.
In another preferred embodiment of the invention the reactive
mesogenic compounds are selected according to formula 1, wherein R
has one of the meanings of P--(Sp--X).sub.n-- given above.
Bicyclic and tricyclic mesogenic compounds are preferred.
Halogen is preferably F or Cl.
Of the compounds of formula I especially preferred are those in
which R is F, Cl, cyano, alkyl or alkoxy or has the meaning given
for P--(Sp--X).sub.n--, and MG is of formula II wherein Z.sup.1 and
Z.sup.2 are --COO--, --OCO--, --CH.sub.2--CH.sub.2--,
--CH.dbd.CH--COO--, --OCO--CH.dbd.CH-- or a single bond.
A smaller group of preferred mesogenic groups of formula II is
listed below. For reasons of simplicity, Phe in these groups is
1,4-phenylene, Phe L is a 1,4-phenylene group which is substituted
by at least one group L, with L being F, Cl, CN or an optionally
fluorinated alkyl, alkoxy or alkanoyl group with 1 to 4 C atoms,
and Cyc is 1,4-cyclohexylene. --Phe--Z.sup.2--Phe-- II-1
--Phe--Z.sup.2--Cyc-- II-2 --PheL--Z.sup.2--Phe-- II-3
--PheL--Z.sup.2--Cyc-- II-4 --Phe--Z.sup.2--PheL-- II-5
--Phe--Z.sup.1--Phe--Phe-- II-6 --Phe--Z.sup.1--Phe--Cyc-- II-7
--Phe--Z.sup.1--Phe--Z.sup.2--Phe-- II-8
--Phe--Z.sup.1--Phe--Z.sup.2--Cyc-- II-9
--Phe--Z.sup.1--Cyc--Z.sup.2--Phe-- II-10
--Phe--Z.sup.1--Cyc--Z.sup.2--Cyc-- II-11
--Phe--Z.sup.1--PheL--Z.sup.2--Phe-- II-12
--Phe--Z.sup.1--Phe--Z.sup.2--PheL-- II-13
--PheL--Z.sup.1--Phe--Z.sup.2--PheL-- II-14
--PheL--Z.sup.1--PheL--Z.sup.2--Phe-- II-15
--PheL--Z.sup.1--PheL--Z.sup.2--PheL-- II-16
In these preferred groups Z.sub.1 and Z.sup.2 have the meaning
given in formula I described above. Preferably Z.sub.1 and Z.sup.2
are --COO--, --OCO--, --CH.sub.2CH.sub.2-- or CH.dbd.CH--COO--. L
is preferably F, Cl, CN or methyl, methoxy, ethyl, ethoxy,
oxamethyl, oxaethyl or trifluormethyl. L is preferably F, Cl, CN,
NO.sub.2, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, OC.sub.2H.sub.5,
COCH.sub.3, COC.sub.2H.sub.5, CF.sub.3, OCF.sub.3, OCHF.sub.2,
OC.sub.2F.sub.5, in particular F, Cl, CN, CH.sub.3, C.sub.2H.sub.5,
OCH.sub.3, COCH.sub.3 and OCF.sub.3, most preferably F, CH.sub.3,
OCH.sub.3 and COCH.sub.3.
Particularly preferred are compounds wherein MG is selected from
the following formulae ##STR00001## wherein L has the meaning given
above and r is 0, 1 or 2.
The group ##STR00002## in this preferred formulae is very
preferably denoting ##STR00003## furthermore ##STR00004## with L
having each independently one of the meanings given above.
R in these preferred compounds is particularly preferably CN, F,
Cl, OCF.sub.3 or an alkyl or alkoxy group with 1 to 12 C atoms or
has one of the meanings given for P--(Sp).sub.n--.
If R is an alkyl or alkoxy radical, i.e. where the terminal
CH.sub.2 group is replaced by --O--, this may be straight-chain or
branched. It is preferably straight-chain, has 2, 3, 4, 5, 6, 7 or
8 carbon atoms and accordingly is preferably ethyl, propyl, butyl,
pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy,
hexoxy, heptoxy, or octoxy, furthermore methyl, nonyl, decyl,
undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy,
nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy, for
example.
Oxaalkyl, i.e. where one CH.sub.2 group is replaced by --O--, is
preferably straight-chain 2-oxapropyl (=methoxymethyl),
2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3-, or
4-oxapentyl, 2-, 3-, 4-, or 5-oxahexyl, 2-, 3-, 4-, 5-, or
6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-,
7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, for
example.
In addition, mesogenic compounds of the formula I containing an
achiral branched group R may occasionally be of importance as
comonomers, for example, as they reduce the tendency towards
crystallization. Branched groups of this type generally do not
contain more than one chain branch. Preferred achiral branched
groups are isopropyl, isobutyl (=methylpropyl), isopentyl
(=3-methylbutyl), isopropoxy, 2-methylpropoxy and
3-methylbutoxy.
P is preferably selected form CH.sub.2.dbd.CW--COO--,
WCH.dbd.CH--O--, ##STR00005## with W being H, CH.sub.3 or Cl and k
being 0 or 1,
P is particularly preferably a vinyl group, an acrylate group, a
methacrylate group, a propenyl ether group or an epoxy group, very
particularly preferably an acrylate group.
As for the spacer group Sp all groups can be used that are known
for this purpose to the skilled in the art. The spacer group Sp is
preferably linked to the polymerizable group P by an ester or ether
group or a single bond. The spacer group Sp is preferably a linear
or branched alkylene group having 1 to 20 C atoms, in particular 1
to 12 C atoms, in which, in addition, one or more non-adjacent
CH.sub.2 groups may be replaced by --O--, --S--, --NH--,
--N(CH.sub.3)--, --CO--, --O--CO--, --S--CO--, --O--COO--,
--CO--S--, --CO--O--, --CH(halogen)--, --CH(CN)--, --CH.dbd.CH-- or
--C.ident.C--.
Typical spacer groups are for example --(CH.sub.2).sub.o--,
--(CH.sub.2CH.sub.2O), --CH.sub.2CH.sub.2--,
--CH.sub.2CH.sub.2--S--CH.sub.2CH.sub.2-- or
--CH.sub.2CH.sub.2--NH--CH.sub.2CH.sub.2--, with o being an integer
from 2 to 12 and r being an integer from 1 to 3.
Preferred spacer groups are ethylene, propylene, butylene,
pentylene, hexylene, heptylene, ocytlene, nonylene, decylene,
undecylene, dodecylene, octadecylene, ethyleneoxyethylene,
methyleneoxybutylene, ethylenethioethylene,
ethylene-N-methyl-iminoethylene and 1-methylalkylene, for
example.
In the event that R or Q.sup.2 is a group of formula P--Sp--X-- or
P--Sp-- respectively, the spacer groups on each side of the
mesogenic core may be identical or different.
In particular preferred are compounds of formula I wherein n is
1.
In another preferred embodiment, the inventive compensator is
obtained by copolymerizing mixtures comprising compounds of formula
I wherein n is 0 and compounds of formula I wherein n is 1.
Typical examples representing polymerizable mesogenic compounds of
the formula I can be found in WO 93/22397; EP 0,261,712; DE
195,04,224; DE 4,408,171 or DE 4,405,316. The compounds disclosed
in these documents, however are to be regarded merely as examples
that should not limit the scope of this invention.
Furthermore, typical examples representing polymerizable mesogenic
compounds are shown in the following list of compounds, which is,
however, to be understood only as illustrative without limiting the
scope of the present invention: ##STR00006##
In these compounds x and y are each independently 1 to 12, A is a
1,4-phenylene or 1,4-cyclohexylene group, R.sup.1 is halogen, cyano
or an additionally halogenated alkyl or alkoxy group with 1 to 12 C
atoms and L.sup.1 and L.sup.2 are each independently H, Halogen,
CN, or an alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms.
The reactive mesogenic compounds disclosed in the foregoing and the
following can be prepared by methods which are known per se and
which are described in the documents cited above and, for example,
in standard works of organic chemistry such as, for example,
Houben-Weyl, Methoden er organischen Chemie, Thieme-Verlag,
Stuttgart.
In a preferred embodiment of the present invention, the
compensation film is obtainable from a mixture of a polymerizable
mesogenic material comprising the following components a1) 10 to
99% by weight of at least one mesogen according to formula I and II
having one polymerizable functional group, a2) 0 to 90% by weight
of at least one mesogen according to formula I and II having two or
more polymerizable functional groups, b) 0.01 to 5% by weight of an
initiator, c) 0 to 20% by weight of a non-mesogenic compound having
two or more polymerizable functional groups, and d) 0 to 1000 ppm
of a stabilizer.
In a particularly preferred embodiment of the invention the mixture
of the polymerizable mesogenic material comprises 15 to 99%
preferably 40 to 99%, most preferably 75 to 99% by weight of at
least two different mesogens of component a1) and further comprises
components b) and optionally components a2), c) and d) as described
above.
The mixture according to this particularly preferred embodiment
preferably comprises two or three different mesogens according to
formula I and II having one polymerizable functional group.
Most preferably the mixture according to this particularly
preferred embodiment comprises four or more, in particular four to
eight, very particularly four to six different mesogens according
to formula I and II having one polymerizable functional group.
The ratio of each of the mesogens according to formula I and II
having one polymerizable functional group in the mixture according
to this particularly preferred embodiment is preferably 5 to 90, in
particular 10 to 80, very preferably 15 to 65% by weight of the
total mixture.
In the mixture according to the particularly preferred embodiment
described above, preferably each of the different mesogens
according to formula I and II is different in at least one of the
groups P, Sp, X, A.sup.1, A.sup.2, A.sup.3, Z.sup.1, Z.sup.2 and R
from each other of the mesogens.
The mixture according to this particularly preferred embodiment
especially preferably contains less than 10% by weight, very
especially preferably none of the compounds of component a2).
In another particularly preferred embodiment of the present
invention, the mixture of the polymerizable mesogenic material
comprises a1) 15 to 85% by weight of at least one mesogen according
to formula I and II having one polymerizable functional group, a2)
10 to 80% by weight of at least one mesogen according to formula I
and II having two or more polymerizable functional groups, and
further comprises components b) and optionally components c) and d)
as described above.
The polymerizable compounds of formula I in the mixtures according
to the preferred embodiments described above preferably contain a
mesogenic group selected of the preferred formulae II-1 to II-16.
Particularly preferably the polymerizable compounds in these
preferred mixtures are selected of the exemplary formula Ia to Ig
given above.
The mixtures of a polymerizable mesogenic material as described
above are another object of the present invention.
Without further elaboration one skilled in the art can, using the
preceding description, utilize the present invention to its fullest
extent. The following examples are, therefore, to be construed as
merely illustrative and not limitative of the remainder of the
disclosure in any way whatsoever.
In the foregoing and in the following examples, unless otherwise
indicated, all temperatures are set forth uncorrected in degrees
Celsius and all parts and percentages are by weight. The following
abbreviations are used to illustrate the liquid crystalline phase
behaviour of the compounds: K=crystalline; N=nematic; S=smectic;
Ch=cholesteric; I=isotropic. The numbers between these symbols
indicate the phase transition temperatures in degree Celsius.
EXAMPLE 1A
The following mixture was formulated
TABLE-US-00002 compound (1) 24.5% compound (2) 24.5% compound (3)
24.5% compound (4) 24.5% Irgacure 651 2.0%
Irgacure is a commercially available photoinitiator (Ciba Geigy
AG). The preparation of compound (1) is described in DE 195,04,224.
The compounds (2) to (4) can be prepared analogously.
##STR00007##
The mixture exhibits the mesophase behaviour S.sub.A 76 Ch 121
I.
To prepare a compensation film, the mixture was dissolved in
cyclopentanone and filtered through a 0.2 micron PTFE filter. A
sample was coated onto glass by means of a wire wound coating bar
(nominally 12 microns coating) and the solvent was allowed to
evaporate at 50.degree. C. under a nitrogen atmosphere. The mixture
was then cured under a nitrogen atmosphere by exposure to UV light
with an irradiance of 70 mW/cm.sup.2 for 5 minutes to give an
anisotropic polymer film with a thickness of 3 microns.
The polymer film was optically clear and showed homeotropic
orientation of the mesogenic groups with no birefringence when
viewed at normal incidence and increasing birefringence with
increasing viewing angle under a polarising optical microscope.
The glass plate with the homeotropic film was attached to a sheet
of a broad waveband cholesteric film by means of an adhesive
layer.
The broad waveband reflective polarizer film consisted of a
polymerized mixture of reactive cholesteric mesogenic compounds.
This polarizer exhibited multiple pitch lengths of the cholesteric
helix and had a broad reflection band as shown in FIG. 2 with a
bandwidth of about 260 nm.
The adhesive layer was prepared by curing a coated mixture of
hexanediol diacrylate with 1% Irgacure 651 under UV light with an
irradiance of 70 mW/cm.sup.2 for 3 minutes and had a thickness of
20 microns.
EXAMPLE 1B
In the measurements described below the luminance of light from a
commercial LCD backlight 50 passing through an embodiment as
depicted in FIG. 3 with the reflective polarizer 51 and the
inventive homeotropic compensation film 52 of 1A, a quarter wave
foil (QWF) 53 and a linear polarizer 54 (polarization axis at
45.degree. to the fast axis of the QWF) was measured using a
Minolta CS--100 colour camera 55 at a range of viewing angles
(-60.degree. to +60.degree.). The measurement results are shown in
FIG. 4.
First the results for an uncompensated polarizer combination
consisting of the reflective polarizer 51, QWF 53 and linear
polarizer 54 (curve 4b), but not containing the inventive
compensation film 52, were compared to the same experiment using
the linear polarizer 54 alone (curve 4a).
From curve 4b it can be seen that a brightness enhancement, i.e. an
increase of the luminance, of approximately 44% was measured at
normal incidence (viewing angle=0.degree.) compared to 4a. However,
as the viewing angle increased the increasing phase retardation by
the reflective polarizer itself caused a notable reduction to the
measured luminance, coinciding with the value measured for the
linear polarizer at a cross-over angle of 36.degree..
Then the results were compared to a compensated polarizer
combination consisting of the reflective polarizer 51, the
inventive homeotropic compensation film 52, the QWF 53 and,the
linear polarizer 54 (4c). The crossover angle increased from
approximately 36.degree. without the compensation film to
approximately 47.degree. with the compensation film. When comparing
the curves 4b (uncompensated) and 4c (compensated) it can also be
seen that the brightness was significantly enhanced for all viewing
angles when using the homeotropic compensation film.
FIG. 5 shows the colour difference (.DELTA.E*.sub.uv in the CIE
1976 L*u*v colour space) for the compensated (5b) and
non-compensated (5a) samples. The compensation foil causes a lower
colour difference with increasing angle, as depicted by curve 5b,
compared to the sample without compensation film (curve 5a). For
example at a viewing angle of 40.degree. the colour difference of
the sample with the compensation film is approximatley half of that
of the sample without the compensation film.
EXAMPLE 2
The following mixture was formulated
TABLE-US-00003 compound (5) 69% compound (6) 19% Irgacure 651
12%
The directive compound (5) can be prepared in an analogy to the
synthesis of the compounds described in WO 93/22397. The compound
(6) can be prepared in analogy to compounds (1) to (4).
##STR00008##
The mixture has the mesophase behaviour S.sub.A 76 N 1171.
A 20% solution of the mixture in cyclopentanone was coated onto a
silica coated PET substrate and the solvent was allowed to
evaporate. The mixture was cured by exposure to UV light at
60.degree. C. to give a homeotropically aligned film. When using
this film as a compensator in an embodiment as described in Example
1B, a crossover angle of 60.degree. was observed.
EXAMPLE 3
The following mixture was formulated
TABLE-US-00004 compound (5) 40% compound (7) 10% compound (8) 46%
Irgacure 907 4%
Irgacure is a commercially available photoinitiator (Ciba Geigy
AG). The compounds (7) and (8) can be prepared in analogy to
compounds (1) to (4). ##STR00009##
A polymer film with a homeotropic orientation that can be used as a
compensator described in the foregoing and the following was
prepared by coating, aligning and curing the above mixture as
described in example 1A.
The preceding examples can be repeated with similar success by
substituting the generically or specifcially described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
From the foregoing description, one skilled in the art can easily
ascertain the essential characteristics of this invention, and
without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *