WO2004029695A2

WO2004029695A2 - Processe for preparing retarders

Info

Publication number: WO2004029695A2
Application number: PCT/JP2003/012324
Authority: WO
Inventors: Tadashi Ito
Original assignee: Fuji Photo Film Co., Ltd.
Priority date: 2002-09-26
Filing date: 2003-09-26
Publication date: 2004-04-08
Also published as: JP4117173B2; WO2004029695A3; KR100970355B1; TW200415373A; AU2003264944A1; JP2004151122A; KR20050073460A; CN1685252A; AU2003264944A8; CN1685252B; TWI293373B

Abstract

A novel process for preparing a rolled-up retarder comprising a transparent substrate and two or more optically-anisotropic layers respectively formed of a composition comprising a liquid-crystalline compound on or above one surface thereof. The process comprises steps for preparing plural optically anisotropic layers while keeping a long substrate unrolled and a step of rolling up the long substrate after forming all of optically-anisotropic layers thereon.

Description

DESCRIPTION

PROCESSE FOR PREPARING RETARDERS

Technical field

The present invention relates to a process for preparing a retarder having two or more optically-anisotropic layers respectively formed of a composition comprising a liquid-crystalline compound. The present invention also relates to a retarder prepared by the process , and in particular , to a retarder which can be used as a quarter wave plate in reflective-type liquid crystal display devices, writes pickups for optical disks or anti-reflective films.

Related art

Retarders, in particular quarter wave (λ/4) plates, can be used for various purposes and have already been practically used. It is described in JPA Nos. 1998-68816 and 1998-90521 (the term "JPA" as used herein means an "unexamined published Japanese patent application") that quarter wave plates having a λ/4 retardation over a wide wavelength region can be prepared by stacking two sheets of optically-anisotropic polymer films. It is also described in JPA Nos. 2000-206331, 2001-4837, 2001-21720 and 2001-91741 that quarter wave plates having a λ/4 retardation over a wide wavelength region can be prepared by laminating at least two optically-anisotropic layers respectively formed of a liquid-crystalline compound.

In the former method, it is necessary to cut the two polymer films at predetermined angles and stick the obtained chips each other in order to adjust the optical directionality (optical axis and slow axis) of the two polymer films and to obtain a required optical property. Such a process is so tangled that the quality of the productions tends to lower due to misalignment of the axes , the yield ratio tends to lower, the production cost tends to increase, and the deterioration of the productions tends to occur due to contamination. Moreover, the polymer films are intrinsically disadvantageous in precisely adjusting the retardation values required for the λ/4 plate.

On the other hand, in the latter method, which is advantageous in readily providing a wide-band λ/4 plate, it is necessary an alignment layer for preparing an optically-anisotropic layer formed of aligned liquid-crystalline molecules . The necessity for preparing the alignment layer increases production costs. It has also been known that when a quarter wave plate comprising two optically-anisotropic layers respectively formed of aligned liquid-crystalline molecules is prepared, preparing the upper optically-anisotropic layer without forming an alignment layer on the surface of the lower optically-anisotropic layer often results in degradation of accuracy and uniformity in liquid-crystal alignment and in developing alignment defects, so that it has been required to form an alignment layer every time an optically-anisotropic layer formed of aligned liquid-crystalline molecules is formed.

Summary of the present invention

One object of the present invention is to provide a process capable of solving the aforementioned problems , and more specifically, to provide a process, by which a retarder comprising two or more optically-anisotropic layers respectively formed of aligned liquid-crystalline molecules can be prepared, capable of contributing to improvements in accuracy and uniformity of the liquid crystal alignment and to lowering alignment-defects and the production cost.

In one aspect, the present invention provides a process for preparing a rolled-up retarder comprising a transparent substrate and two or more optically-anisotropic layers respectively formed of a composition comprising a liquid-crystalline compound on or above one surface thereof; comprising a step of forming an alignment layer on a surface of a long transparent substrate having a longitudinal direction under continuous feeding along the longitudinal direction, and further comprising the steps of:

(a) rubbing a surface of the alignment layer or a surface of a layer formed on or above the alignment layer;

(b) applying a composition comprising a liquid- crystalline compound to the rubbed surface;

(c) solidifying the composition applied to the rubbed surface in the step (b) , to thereby form an optically-anisotropic layer;

(d) repeating the steps (a) through (c) at least once again while keeping the substrate unrolled; and

(e) rolling up the transparent substrate having at least two optically-anisotropic layers thereon.

As embodiments of the present invention, there are provided the process wherein at least one of the steps (a) is a step of rubbing a surface of an optically-anisotropic layer comprising a modified polyvinyl alcohol having a hydrocarbon group containing 9 or less carbon atoms; the process wherein the liquid-crystalline compound used in at least one of the steps (b) is a rod-like liquid-crystalline compound having a polymerizable group; and the process wherein the liquid-crystalline compound used in at least one of the steps (b) is a discotic liquid-crystalline compound having a polymerizable group.

In another aspect, the present invention provides a retarder prepared by the above process.

In the present specification , the term of "substantially" for an angle means that the angle is in the range of an exact angle ± 5 degrees. Preferably, the difference from the exact angle is less than + 4 degrees, and more preferably less than ± 3 degrees. In the present specification , the term of "homogeneous alignment" is used for not only an exact homogenous alignment but also any alignments with a mean tilt angle in a range from 0 to 40 degrees. In the present specification , the term of "vertical alignment" is used for not only an exact vertical alignment but also any alignments with a mean tilt angle in a range from 50 to 90 degrees. In the present specification , "a slow axis" means a direction showing a maximum refractive index .

Brief description of the drawings

Fig. 1 is a schematic drawing showing a process flow of a method of fabricating a wave plate of the present invention.

Fig. 2 is a schematic drawing of an exemplary wave plate of the present invention. Fig. 3 is a schematic drawing of an exemplary circular polarizer plate using the wave plate of the present invention.

Fig. 4 is a schematic plan view showing an exemplary punching process for producing conventional polarizer plates.

Fig. 5 is a schematic plan view showing an exemplary punching process for producing 45° polarizer plates for use in the present invention.

Fig. 6 is a schematic view showing an exemplary layer constitution of the circular polarizer plate of the present invention.

Fig. 7 is a schematic view showing another exemplary layer constitution of the circular polarizer plate of the present invention.

Fig. 8 is a schematic plan cross-section drawing showing a circular polarizer plate fabricated in Example 2.

Detailed description of the invention [Process for Preparing Retarder]

An exemplary process for preparing a retarder of the present invention is shown in Fig. 1. Fig. 1 shows an exemplary process for preparing a retarder having two optically-anisotropic layers schematically.

First, a long transparent substrate, of which portion is shown in Fig.l, is continuously fed, and a coating liquid for forming an alignment layer, comprising a modified polyvinyl alcohol or the like, is applied to the surface of the transparent substrate 1, to thereby form an alignment layer 2 (a step (1) ) . Next, the surface of the alignment layer 2 is rubbed using a rubbing roll 3 or the like (a step (a) ) . A coating liquid comprising a liquid-crystalline compound is applied to the rubbed surface to form a layer 4' (a step (b) ) . The liquid-crystalline molecules in the layer 4 ' are aligned in a predetermined alignment state depending on surface properties of the alignment layer 2 and the rubbing direction. The liquid-crystalline molecules in the layer 4' are subsequently immobilized in such an alignment state by polymerization or the like under irradiation of heat and/or active radiation ray, to thereby form an optically-anisotropic layer 4 (a step (c) ) . The steps (a) through (c) are repeated to thereby form an optically-anisotropic layer 5. Thus the retarder comprising two optically-anisotropic layers can continuously be prepared. After the optically-anisotropic layer 5 was formed, the substrate having two optically-anisotropic layers thereon is rolled up, and may be stored, conveyed, and cut into various forms and subjected to target applications.

Although the process for preparing an exemplary retarder having two optically-anisotropic layers is shown schematically in Fig.l, it is also possible to repeat the steps (a) to (c) n times (where, n represents an integer of 2 or more, the same shall apply hereinafter) to thereby manufacture a retarder having n layers of the optically-anisotropic layers. By leaving the retarder unrolled, that is by not carrying out the step (e) , until all of the optically-anisotropic layers are formed the present invention makes it possible to prepare a retarder comprising plural optically-anisotropic layers respectively formed of liquid-crystalline molecules aligned with a high accuracy and uniformity and with less amount of alignment defects, even when no alignment layer is formed between the adjacent optically-anisotropic layers (between the layer 4 and layer 5 in Fig. 1) . This consequently makes it possible to omit the step of forming the alignment layer between the optically-anisotropic layers, and contributes to lowering costs of the production.

In the present invention, conditions and materials applied to the steps (a) through (c) for the first through π-th times are selectable in an independent manner. For example, directions of the rubbing carried out in the plural steps (a) , or species of the liquid-crystalline compound used in the plural step (b) may be identical or differen each other.

Next, the individual steps, and various members and materials employed in the present invention will be described in details. [Transparent Substrate]

A transparent substrate is used in the present invention. The transparent substrate herein refers to a substrate having a light transmittance of 80% or more. Wavelength dispersion of the transparent substrate is preferably small, and more specifically a ratio of Re400/Re700 of less than 1.2 is more preferable. The transparent substrate also preferably has a small optical anisotropy, and more specifically an in-plane retardation (Re) of 20 nm or less is preferable, and 10 nm or less is more preferable.

The transparent substrate is preferably composed of a polymer film. Available examples of the polymer include cellulose ester, polycarbonate, polysulfone, polyether sulfone, polyacrylate and polymethacrylate . Among these, cellulose ester is preferable, acetyl cellulose is more preferable, and triacetyl cellulosed is most preferable. In particular for the case where triacetyl cellulose is used, the compound preferably has a degree of acetylation of 60.25 to 61.50. The polymer film is preferably ' formed by the solvent cast method.

In the present invention, the substrate having a longitudinal axis is used. The substrate may be in a rolled up form. A coating liquid for forming an optically-anisotropic layer is applied to a surface of the long substrate continuously. It is preferable that the substrate is cut into pieces of a necessary size after all of the optically-anisotropic layers are formed thereon. Thickness of the transparent substrate is preferably 20 to 500 micro meters, and more preferably 40 to 200 micro meters. In order to improve adhesiveness between the transparent substrate and a layer formed thereon (adhesion layer, homogenous alignment layer, vertical alignment layer or optically-anisotropic layer), it is also allowable to subject the transparent substrate to a surface treatment (e.g., glow discharge treatment, corona discharge treatment, ultraviolet

(UV) treatment, flame treatment, saponification) , or to provide an adhesion layer (undercoat layer) on the transparent substrate. Saponification is preferable as the surface treatment .

[Alignment layer]

In the present invention, the alignment layer is formed on the substrate while continuously conveying the long substrate along the longitudinal direction. The alignment layer has a function of aligning the liquid-crystalline molecules applied to the surface in a predetermined alignment. Alignment layers prepared by rubbing a surface of layers formed of organic compounds, desirably polymers, may be employed in the present invention. Species of the polymers for composing the alignment layer are determined depending on a desired alignment (in particular, mean tilt angle) of the liquid-crystalline molecules .

In order to align liquid-crystalline molecules homogenously, it is necessary to use an alignment layer formed of a polymer not lowering a surface energy of the alignment layer. Such an alignment layer has been generally used. The examples of the polymers preferably used in such alignment layers include polyvinyl alcohol, polyimide derivatives and nylon.

For the purpose of improving adhesiveness with the liquid-crystalline compound layer to be formed thereon, the alignment layer preferably has a polymerizable group. The polymerizable group can be introduced in a form of a side chain of a repetitive unit, or in a form of a substituent for a cyclic group. It is preferable to use the alignment layer capable of forming chemical bonds with the liquid-crystalline compound at the interface, and such an alignment layer is disclosed in JPA No. 1997-152509.

Thickness of the alignment layer is preferably 0.01 to 5 micro meters, and more preferably 0.05 to 3 micro meters. [Rubbing Treatment]

In the step (a) , the alignment layer formed on the transparent substrate is rubbed. The surface of the optically-anisotropic layer formed in the steps (a) through (c) may be rubbed.

The rubbing treatment may be carried out by rubbing the surface of a layer with paper or cloth several times along a constant direction. The alignment of the liquid-crystalline molecules may be predetermined by a rubbing direction. The rubbing treatment can be carried out along a direction at a predetermined angle relative to the longitudinal direction of the long-substrate. The rubbing is preferably carried out along the parallel direction to the longitudinal direction, or along the direction at an angle within a range from -45° to +45° relative to the longitudinal direction.

While the rubbing can be carried out by a method selected from various known rubbing methods, it is preferable to use at least one rubbing roll. For example, a rubbing roll is disposed in the contact with a surface of a layer formed on or above the long-substrate, and is rotated while conveying the long-substrate along the longitudinal direction, so that the surface of the layer is rubbed along a direction predetermined by the rotating direction of the rubbing roll . An apparatus used for the rubbing is preferably equipped with a mechanism capable of freely adjusting an angle between moving directions of the rubbing roll and stage . The rubbing roll described herein refers to a roll having an appropriate rubbing cloth material on the surface .

Next, the composition comprising a liquid-crystalline compound is applied to the rubbed surface (step (b) ) , and the composition is cured to thereby form an optically-anisotropic layer (step (c) ) .

[Optically-Anisotropic Layer Comprising Liquid-Crystalline Compound]

The liquid-crystalline compound used in the step (b) is preferably a rod-like liquid-crystalline compound or a disk-like liquid-crystalline compound, and more preferably a rod-like liquid-crystalline compound having a polymerizable group or a disk-like liquid-crystalline compound having a polymerizable group .

The examples of the rod-like liquid-crystalline compounds include azo ethines, azoxys, cyanobiphenyls , cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes , cyano-substituted phenylpyrimidines , alkoxy-substituted phenylpyrimidines , phenyl dioxanes, tolans and alkenylcyclohexyl benzonitriles . Not only low-molecular-weight liquid-crystalline compounds as mentioned above but also high-molecular-weight liquid-crystalline compounds can be used. The rod-like liquid-crystalline compound denoted by the Formula (I) is desirably used.

Formula (I)

Q¹-L¹-A¹-L³-M-L⁴-A²-L²-Q²

In the Formula (I) , Q¹ and Q² respectively denote a polymerizable group; L¹, L², L³ and L⁴ respectively denote a single bond or a divalent linking group provided that at least either of L³ and L⁴ denotes -0-CO-O- ; A¹ and A² respectively denote a C2-20 spacer group; and M denotes a mesogen group.

The polymerizable rod-like liquid-crystalline compound denoted by the formula (I) will be described in detail.

In the formula (I) , Q¹ and Q² respectively denote a polymerizable group. The polymerizable groups may be addition polymerizable (ring opening polymerizable) or condensation polymerizable . Preferably , Q¹ and Q² respectively denote a group capable of addition polymerization or condensation polymerization. The examples of the polymerizable groups are shown bellow.

H H H H .- H₃C_^C^.C. Et n-Pr- \

H C-

H H

H

O N

/ \ / \ H₂C-CH H₂C-CH

— SH —OH -NH,

The divalent linking group respectively denoted by L¹ , L² , L³ and L⁴ is preferably the one selected from the group consisting of -0- , -S- , -CO- , -NR² -CO-O- -0-CO-0- , -CO-NR²- , -NR²-CO- ,

-0-C0-, -O-CO-NR²-, -NR²-CO-0-, -NR²-CO-NR²- and single bond. R² represents a Cl-7 alkyl group or a hydrogen atom. At least either of L³ and L⁴ denotes -0-CO-O- (carbonate group) .

Among the groups denoted by a combination of Q¹ and L¹ or by a combination of Q² and L² , the preferable examples include CH₂=CH-CO-0-, CH₂=C(CH₃)-CO-0- and CH₂=C (Cl) -C0-0- , and more preferable example is CH₂=CH-CO-0- .

A¹ and A² respectively denote a C2-20 spacer group, and preferably C2-12 aliphatic group, and more preferably alkylene group. The spacer group is preferably a chain group, and may contain oxygen atoms or sulfur atoms not adjacent with each other. The spacer group may have a substitutive group, and may more specifically be substituted by a halogen atom (fluorine, chlorine, bromine), cyano , methyl or ethyl.

The mesogen group denoted by M may selected from any known mesogen groups . The preferable examples thereof are denoted by the formula (II) below.

Formula (II) -(-W¹-L⁵)_n-W²-

In the Formula (II) , W¹ and W² respectively denote a divalent alicyclic group, divalent aromatic group or divalent heterocyclic group. L⁵ is a single bond or a linking group. The examples of the linking group denoted by L⁵ include those shown as the specific examples denoted by L¹ to L⁴ in the above-described the formula (I), -CH₂-0- and -0-CH₂- . "n" is an integer of 1, 2 or 3.

The examples of W¹ and W² include cyclohexane-1 , 4-diyl , 1 , 4-phenylene, pyrimidine-2 , 5-diyl , pyridine-2 , 5-diyl , 1,3, 4-thiadiazole-2 , 5-diyl , 1,3, 4-oxathiadiazole-2 , 5-diyl , naphthalene-2 , 6-diyl , naphthalene-1 , 5-diyl , thiophene-2 , 5-diyl and pyridazine-3 , 6-diyl .

1 , 4-Cyclohexanediyl may exist in trans- and cis-stereoisomers , where either of them, and any mixture in an arbitrary mixing ratio can be used in the present invention. The trans form is more preferable . W¹ and W² may independently have substitutive group , and the specific examples of the substitutive group include halogen atom (fluorine, chlorine, bromine, iodine) , cyano, Cl-10 alkyl groups (e.g. , methyl, ethyl, propyl) , Cl-10 alkoxy groups (e.g., methoxy, ethoxy) , Cl-10 acyl groups (e.g., formyl, acetyl) , Cl-10 alkoxycarbonyl groups (e.g., methoxycarbonyl, ethoxycarbonyl) , Cl-10 acyloxy groups (e.g., acetyloxy, propionyloxy), nitro, trifluoromethyl , and difluoromethyl .

The preferable examples of the mesogen group denoted by the above-described the formula (II) are shown below, however, the mesogen group is not limited to these examples. The mesogen group may be substituted by any substitutive groups described in the above .

The specific examples of the compounds denoted by the Formula (I) will be shown below, where it is to be understood that the present invention is by no means limited thereto. The compounds denoted by the Formula (I) can be prepared by processes described in JPA No. 1999-513019.

1-1

Various discotic liquid-crystalline compounds may be employed in the present invention as a liquid-crystalline compound. The discotic liquid-crystalline compound is desirably aligned vertically, i.e. , with a tilt angle in a range of 50 to 90 degrees relative to the film plane. The examples of discotic liquid-crystalline compounds include benzene derivatives described in "Mol . Cryst. , vol. 71, page 111 (1981) , C. Destrade et al . " ; truxane derivatives described in "Mol. Cryst., vol. 122, page 141 (1985), C. Destrade et al . " and "Physics lett. A, vol. 78, page 82 (1990),"; cyclohexane derivatives described in "Angew. Chem. , vol. 96, page 70 (1984) , B.Kohne et al . " ; and microcycls based aza-crowns or phenyl acetylenes described in "J. Chem. Commun. , page 1794 (1985) , M. Lehn et al." and "J. Am. Chem. Soc . , vol. 116, page 2,655 (1994) , J. Zhang et al . " .

The Liquid crystalline compounds employed in preparing optically-anisotropic layers are not required to maintain liquid crystallinity after contained in the optically-anisotropic layers. For example, when a low-molecular-weight liquid crystalline compound, having a reacting group initiated by light and/or heat, is employed in preparation of an optically-anisotropic layer, polymerization or cross-linking reaction of the compound is initiated by light and/or heat, and carried out, to thereby form the layer. The polymerized or cross-linked compounds may no longer exhibit liquid crystallinity. The polymerization of discotic liquid-crystalline compounds is described in JP-A No. 1996-27284.

The discotic liquid-crystalline molecules desirably have polymerizable groups to be fixed by polymerization thereof. However, when a polymerizable group is directly bonded to the disk-shaped core, it tends to be difficult to maintain alignment during the polymerization reaction. Accordingly, the discotic liquid-crystalline compound desirably comprises a linking group between the disk-shaped core and the polymerizable group. That is, the discotic liquid-crystalline compound is desirably denoted by Formula (III) below.

Formula (III) D-(L-P)_n

In the formula, D denotes a disk-shaped core, L denotes a divalent linking group, P denotes a polymerizable group, and n denotes an integer from 4 to 12. The preferred examples of the disk-shaped core, "D", the divalent linking group, "L", and the polymerizable group, "P" are respectively identical to the examples (Dl) to (D15) , the examples (Ll) to (L25) and the examples (PI) to (P18) described in JPA No. 2001-4837.

In the optically-anisotropic layers, these liquid-crystalline molecules are aligned in a substantially uniformly manner, more desirably fixed in a substantially uniformly aligned manner, and most preferably fixed by polymerization reaction. For the case where a rod-like liquid-crystalline compound having a polymerizable group is used, it is preferable to immobilize the rod-like molecules while keeping a substantially homogenous alignment. "Substantially homogenous" described herein means that a mean tilt angle between the long axial direction of the rod-like molecule and the plane of the optically-anisotropic layer falls within a range from 0 to 40 degrees. It is also allowable that the rod-like liquid-crystalline molecules are obliquely aligned, or aligned so that the tilt angle gradually changes, i.e. hybrid aligned. The mean tilt angle still preferably falls within a range from 0 to 40 degrees even under oblique alignment or hybrid alignment.

For the case where a disk-like liquid-crystalline compound having a polymerizable group is used, it is preferable to immobilize the compound while keeping a substantially vertical alignment. "Substantially vertical" described herein means that a mean tilt angle between the disk surface and the plane of the optically-anisotropic layer falls within a range from 50 to 90 degrees. It is also allowable that the disk-like liquid-crystalline molecules are obliquely aligned, or aligned so that the tilt angle gradually changes, i.e. , hybrid aligned. The mean tilt angle still preferably falls within a range from 50 to 90 degrees even under oblique alignment or hybrid alignment.

In the present invention, the steps (a) through (c) are repeated n times (n is an integer of 2 or above) to thereby form n layers of optically-anisotropic layers, where it is preferable to allow each of the optically-anisotropic layers formed through the steps (a) through (c) for the first through (n-1 ) -th times to function as the alignment layer for the optically-anisotropic layer formed through the steps (a) through (c) for the n-th time. For the case where the lower optically-anisotropic layer is allowed to function as the alignment layer for the upper optically-anisotropic layer formed thereon, it is preferable to use a composition comprising a modified polyvinyl alcohol having a hydrocarbon group containing 9 or less carbon atoms in the combination with a liquid-crystalline compound in the step (b) , to thereby form the optically-anisotropic layer in the step (c) , and to rub the surface of thus-formed optically-anisotropic layer in the succeeding step (a) .

Next, the modified polyvinyl alcohol having a hydrocarbon group containing 9 or less carbon atoms which may be used in the combination with the liquid crystalline-compound will be described in details.

The modified polyvinyl alcohols denoted by Formula (PX) are preferred.

Formula (PX)

-(VAl)_x-(HyD)_y-(VAc)_z-

In the Formula (PX) , "Val" is a vinyl alcohol based repeating unit, "HyD" is a repeating unit having a hydrocarbon group of 9 or less carbon atoms and "VAc" is a vinyl acetate based repeating unit; x is 20 to 95 wt% , and desirably 25 to 95 wt% ; y is 2 to 98 wt% , and desirably 10 to 80 wt% ; and z is 0 to 30 wt%, and desirably 2 to 20 wt% . The term "hydrocarbon group" is used for any aliphatic groups, any aromatic groups and any combinations thereof. The aliphatic group may have a cyclic or straight or branched chain structure. The aliphatic group is desirably an alkyl group (including cycloalkyl group) or alkenyl group (including cycloalkenyl group) . The hydrocarbon group may have at least one substituent. The number of the carbon atoms included in the hydrocarbon group is from 1 to 9 , and desirably from 1 to 8.

The preferred "HyD", which is a repeating unit having a hydrocarbon group of 9 or less carbon atoms, is denoted by Formula (HyD-I) or (HyD-II) . (HyD-I) (HyD-H)

In the formulae, L¹ is a divalent linking group selected from the group consisting of -0- , -CO-, -S0₂-, -NH- , an alkylene group, arylene group and any combinations thereof; L² is a single bond or a divalent linking group selected from the group consisting of -0- , -CO-, -S0₂-, -NH- , an alkylene group, arylene group and any combinations thereof; and R¹ and R² respectively denote a hydrocarbon group of 9 or less carbon atoms. The specific examples of the linking groups formed of the aforementioned combinations are shown bellow.

Ll:-0-C0-

L2 :-0-C0-alkylene-0-

L3 : -O-CO-alkylene-CO-NH-

L : -0-CO-alkylene-NH-S0₂-arylene-0-

L5 : -arylene-NH-CO-

L6 : -arylene-CO-0-

L7 :-arylene-CO-NH-

L8 : -arylene-0-

L9 : -0-CO-NH-arylene-NH-CO-

The specific examples of "HyD" are shown bellow. )-l HyD-2 HyD-3 HyD-4

H H H H

-c-c- — C-C— — C-C— — C-C—

^H20 C₂H₅ ^H20 C₃H₇ ^H20 C₄H₉ ^H20 C₆H₁₃ 0 0 0 0

HyD-9 HyD- 10

The polymer employed as an additive in the present invention preferably has a polymerization degree of 200 to 5,000 (more preferably 300 to 3,000) and a molecular weight of 9,000 to 200,000 (more preferably 13,000 to 130,000) . Two or more species of the polymers can be used in combination.

The specific examples of the polymers are shown bellow, however, the polymer that can be employed in the present invention are not limited to these examples. PX-1 :- (VA1) ₂₁- (HyD-13) ₇₇- (VAc) ₂-

PX-2 : - (VA1) ₁₄- (HyD-13) ₈4- (VAc) ₂-

PX-3 : - (VA1) ₂i- (HyD-16) ₇₇- (VAc) ₂-

PX-4 :- (VA1) ₃4- (HyD-15) ₆₄- (VAc) ₂-

PX-5 : - (VA1) ₂₉- (HyD-12 ) ₆₉- (VAc) ₂-

PX-6 : - (VA1) ₄₆- (HyD-14) ₅₂- (VAc) ₂-

PX-7 :- (VA1) ₂i- (HyD-2) ₇₇- (VAc) ₂-

PX-8 : - (VA1) _I*_?- (HyD-8) ₈₅- (VAc) ₂-

PX-9 : - (VA1) ₂i- (HyD-13) ₇- (VAc) ₂-

PX-10 : - (VA1) ₄₆- (HyD-9) ₅₂- (VAc) ₂-

The amount of the modified polyvinyl alcohol in the optically-anisotropic layer is desirably in a range of 0.05 to 10 wt% , preferably 0.1 to 5 wt% , with respect to the weight of the liquid-crystalline compound.

The modified polyvinyl alcohol may be used in the combination with at least one condensation agent. The condensation agent is desirably a compound having an isocyanate or formyl at the terminal end. The specific examples of the condensation agent are shown bellow, however, the condensation agents that can be employed in the present invention are not limited to these examples.

Poly (1 , 4-butane diol), isophorone diisocyanate terminated

Poly (1 , 4-butane diol), tolylene 2 , 4-diisocyanate terminated

Poly (ethylene adipate) , tolylene 2 , 4-diisocyanate terminated

Poly (propylene glycol) tolylene 2 , 4-diisocyanate terminated 1 , 6-diisocyanate hexane

1 , 8-diisocyanateoctane

1 , 12-diisocyanatedecane isophorone isocyanate glyoxal

In the step (b) , it is preferable to apply a composition such as a coating liquid, comprising the liquid-crystalline compound, and if necessary, the aforementioned modified polyvinyl alcohol, a polymerization initiator or other additives listed below dissolved therein, to the rubbed surface. Organic solvents are preferably used for preparing the coating liquid. The examples of the organic solvents include amides (e.g., N,N-dimethylformamide) , sulfoxides (e.g., dimethylsulfoxide) , heterocyclic compounds (e.g., pyridine) , hydrocarbons (e.g., benzene, hexane), alkyl halides (e.g., chloroform, dichloromethane) , esters (e.g. , methyl acetate, butyl acetate) , ketones (e.g. , acetone, methyl ethyl ketone) , and ethers (e.g. , tetrahydrofuran, 1 , 2-dimethoxyethane) . Among these, alkyl halides and ketones are preferable. It is also allowable to mix two or more organic solvents. Coating of the coating liquid can be carried out by any publicly-known methods (e.g., extrusion coating method, direct gravure coating method, reverse gravure coating method and die coating method) . [Fixation of Alignment State of Liquid-Crystalline Molecules]

In the step (c) , the above-described coating liquid applied to the rubbed surface is solidified to form the optically-anisotropic layer. The liquid-crystalline molecules may be aligned in an alignment state predetermined by properties of the alignment layer and the rubbed direction. It is preferable to immobilize the liquid-crystalline molecules to thereby form the optically-anisotropic layer while keeping this alignment state. The immobilization is preferably embodied by polymerization reaction of a polymerizable group introduced into the liquid-crystalline compound. The polymerization reaction includes thermal polymerization using a thermal polymerization initiator so as to allow a polymerization reaction to proceed under heat exposure, and photo-polymerization using a photo-polymerization initiator so as to allow a polymerization reaction to proceed under active radiation ray, where the latter is more preferable. Examples of photo-polymerization initiator include a-carbonyl compounds (described in U.S. Patent Nos. 2367661 and 2367670) , acyloin ethers (described in U.S. Patent No. 244882), a-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Patent No. 2722512) , polynuclear quinone compounds (described in U.S. Patent Nos. 3046127 and 2951758) , combination of triarylimidazole dimer and p-aminophenylketone (described in U.S. Patent No. 3549367), acridine and phenazine compounds (described in Japanese Laid- Open Patent Publication No. 60-105667, U.S. Patent No . 4239850), and oxadiazole compounds (described in U. S . Patent No . 4212970) . The amount of the photo-polymerization initiator to be used is preferably 0.01 to 20 % by weight, more preferably 0.5 to 5 % by weight on the basis of solids in the coating solution. Irradiation for polymerizing the liquid-crystalline molecules preferably uses UV rays . The irradiation energy is preferably 20 mJ/cm² to 50 J/cm², and more preferably 100 to 800 mJ/cm². Irradiation may be performed under heating to accelerate the photo-polymerization reaction. The thickness of the optically-anisotropic layer is desirably from 0.1 to 10 micro meters and more desirably from 0.5 to 5 micro meters . [Optical Properties of Retarder]

It is preferable that the optically-anisotropic layer formed in the above-described steps ensures a phase difference of substantially p or p/2 at a specific wavelength. Phase difference of p at a specific wavelength (λ) can be obtained by adjusting a retardation value of the optically-anisotropic layer measured at the specific wavelength (λ) to λ/2, and phase difference of p/2 can be obtained by adjusting a retardation value of the optically-anisotropic layer measured at a specific wavelength (λ) to λ/4. When the retarder comprises two optically-anisotropic layers, it is preferable that one of the two layers generate a phase difference of p and the other generates a phase difference of p/2 at 550 nm, a wavelength which falls approximately in the middle of the visible light region. In an exemplary case where two optically-anisotropic layers are formed by repeating the steps (a) through (c) twice, one optically-anisotropic layer (first optically-anisotropic layer) preferably has a retardation value measured at 550 nm of 240 to 290 nm, and more preferably of 250 to 280 nm, and the other optically-anisotropic layer (second optically-anisotropic layer) preferably has a retardation value measured at 550 nm of 110 to 145 nm, and more preferably of 120 to 140 nm.

The retardation value herein means an in-plane retardation value defined for a light incident from the direction of the normal line on the optically-anisotropic layer, and is specifically given by the equation below: Retardation value (Re) = (nx - ny) x d where, nx and ny represent in-plane major indices of refraction of the optically-anisotropic layers , and d represents thickness (nm) of the optically-anisotropic layer.

The thickness of the optically-anisotropic layer can arbitrarily be determined so far as the layer can exhibit desired retardation values . In an exemplary case where the retarder comprises two optically-anisotropic layers both of which are formed of identical species of rod-like liquid-crystalline compound aligned homogenously, and one of which generates a phase difference of p and the other generates a phase difference of p/2 , the thickness of the optically-anisotropic layer generating a phase difference of p is preferably twice as thick as the thickness of the optically-anisotropic layer generating a phase difference of p/2. Although preferable ranges for the thickness of the individual optically-anisotropic layers may differ depending on species of the liquid-crystalline compounds to be used, it is generally 0.1 to 10 micro meters, preferably 0.2 to 8 micro meters, and more preferably 0.5 to 5 micro meters. [Constitution of Retarder]

Fig. 2 is a schematic drawing showing a representative constitution of the retarder of the present invention, comprising two optically-anisotropic layers formed of a composition comprising a rod-like liquid-crystalline compound. As shown in Fig. 2, a basic retarder comprises a long transparent substrate (S) , the first optically-anisotropic layer (A) , and the second optically-anisotropic layer (B) . The first optically-anisotropic layer (A) generates a phase difference of p, and the second optically-anisotropic layer (B) generates a phase difference of p/2. The longitudinal direction of the transparent substrate (S) and the slow axis (a) of the first optically-anisotropic layer (A) cross at 30°. The slow axis (b) of the second optically-anisotropic layer (B) and the slow axis (a) of the first optically-anisotropic layer (A) cross at an angle (y) of 60°. The first optically-anisotropic layer (A) and the second optically-anisotropic layer (B) shown in Fig. 1 respectively contain rod-like liquid-crystalline molecules (cl and c2) . The rod-like liquid-crystalline molecules cl and c2 are aligned homogenously. The longitudinal axes of the rod-like liquid-crystalline molecules (cl and c2) correspond to the slow axes (a and b) of the optically-anisotropic layers.

Although Fig. 2 showed, for the convenience sake, an exemplary constitution of the retarder in which the optically-anisotropic layer (A) (phase difference = p) is disposed closer to the transparent substrate (S) and the optically-anisotropic layer (B) (phase difference = p/2) is disposed on the outer side, it is also allowable to change the positions of the optically-anisotropic layers (A) and (B) . A more preferable constitution is, however, such as disposing the optically-anisotropic layer (A) (phase difference = p) closer to the transparent substrate (S) and the optically-anisotropic layer (B) (phase difference = p/2) on the outer side. [Circular Polarizer Plate]

The retarder of the present invention is advantageous when it is applied to a quarter wave plate used in reflective-type liquid-crystal display devices , write pickups for optical disks , or anti-reflective films. The quarter wave plate is generally configured as a circular polarizer plate as being combined with a linear polarizing film. Therefore the quarter wave plate configured as a circular polarizer plate as being combined with a linear polarizing film can readily be incorporated into devices such as reflective-type liquid-crystal display devices . The examples of the linear polarizing film include iodine-containing linear polarizing film, dye-containing linear polarizing film using dichroic dye, and poly-ene containing linear polarizing film. The iodine-containing linear polarizing film and dye-containing linear polarizing film are generally manufactured using poly (vinyl alcohol) -base films. [Constitution of Circular Polarizer]

Fig. 3 is a schematic drawing showing a representative constitution of the circular polarizer plate comprising the retarder shown in Fig. 2, comprising two optically-anisotropic layers formed of a composition comprising a rod-like liquid-crystalline compound, of the present invention. The circular polarizer plate shown in Fig. 3 comprises the transparent substrate (S) , the first optically-anisotropic layer (A) and the second optically-anisotropic layer (B) shown in Fig. 2, and further comprises a linear polarizing film (P) . The polarizing transparent axis (p) of the linear polarizing film (P) and the longitudinal direction (s) of the transparent substrate (S) cross at 45°, the polarizing transparent axis (p) and the slow axis (a) of the first optically-anisotropic layer (A) cross at 15°, and similar to as illustrated in Fig. 2, the slow axis (a) of the first optically-anisotropic layer (A) and the slow axis (b) of the second optically-anisotropic layer (B) cross at 60°. Also the first optically-anisotropic layer (A) and the second optically-anisotropic layer (B) shown in Fig. 3 respectively contain the rod-like liquid-crystalline molecules (cl and c2) . The rod-like liquid-crystalline molecules (cl and c2) are aligned homogenously. The longitudinal axes of the rod-like, liquid-crystalline molecules (cl and c2) correspond to the in-plane slow axes (a and b) of the optically-anisotropic layers (A and B) .

There are no special limitations on the linear polarizing film to be combined with the retarder of the present invention, where available examples include iodine-containing linear polarizing film, dye-containing linear polarizing film using dichroic dye, and poly-ene containing linear polarizing film. The iodine-containing linear polarizing film and dye-containing linear polarizing film are generally formed of poly (vinyl alcohol) -base films. The linear polarizing film is preferably stacked with the retarder of the present invention so as to align the transparent axis thereof inclined at 45° away from the longitudinal direction of the transparent substrate of the retarder. Use of the linear polarizing film having the transparent axis of polarization inclined at 45° away from the longitudinal direction thereof (simply referred to as "45° linear polarizing film", hereinafter) makes it no more necessary to adjust angles in the stacking, and facilitates fabrication of the circular polarizer plate of the present invention. Since the transparent axis of the linear polarizing film formed of the stretched film substantially coincides with the stretching direction, stretching of the film in a direction inclined at 45° away from the longitudinal direction thereof can successfully produce the 45° linear polarizing film. The 45° linear polarizing film can be prepared by stretching a film in a direction inclined at 45 degrees relative to the longitudinal direction of the film, referring to conditions, configuration of the available apparatus and so forth described in paragraphs [0009] to [0045] in JPA No. 2002-86554.

There are no special limitations on the polymer film to be stretched in the present invention, so that films comprising any appropriate thermoplastic polymer are available. Examples of the polymer include polyvinyl alcohol (PVA) , polycarbonate, cellulose acylate and polysulfone. PVA is preferably used as the polymer. While PVA is generally obtained by saponifying polyvinyl acetate, the PVA may also contain any component co-polymerizable with vinyl acetate, such as unsaturated carboxylic acid, unsaturated sulfonic acid, olefins and vinyl ethers. It is also allowable to use modified PVA containing acetoacetyl group, sulfonic acid group, carboxyl group, oxyalkylene group and the like.

While there are no special limitations on the degree of saponification of PVA, it is preferably adjusted within a range from 80 to 100 mol% in view of solubility and so forth, and more preferably from 90 to 100 mol%. While there are no special limitations also on the degree of polymerization of PVA, it is preferably adjusted within a range from 1 , 000 to 10 , 000 , and more preferably 1,500 to 5,000.

Dyeing of PVA can produce the linear polarizing film, where the dyeing process can be proceeded by adsorption from vapor phase or liquid phase. In one exemplary process for the liquid phase adsorption using iodine, the absorption is carried out by immersing a PVA film into an aqueous iodine-potassium iodide solution. Contents of iodine and potassium iodide are preferably 0.1 to 20 g/L and 1 to 100 g/L, respectively, and a weight ratio of iodine and potassium iodide preferably falls within a range from 1 to 100. Time for the dyeing is preferably 30 to 5,000 seconds, and the solution temperature is preferably within a range from 5 to 50°C. The dyeing method is not only limited to immersion, but allows arbitrary means such as coating or spraying of iodine or a dye solution. The dyeing process may precede or follow the stretching process , where the dyeing before the stretching is particularly advantageous because the film is appropriately swollen and to thereby facilitate the stretching. Besides iodine, it is also preferable to use dichroic dyes for the dyeing. Specific examples of the dichroic dyes include dye compounds such as azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes and anthraquinone dyes. Although those soluble in water are preferable, not limitative thereto. It is also preferable that these dichroic dyes have introduced therein a hydrophilic substitutive group such as sulfonic acid group, amino group and hydroxyl group. Specific examples of the dichroic dye include C.I. Direct Yellow 12, C.I. Direct Orange 39, C.I. Direct Orange 72, C.I. Direct Red 39, C.I. Direct Red 79, C.I. Direct Red 81, C.I. Direct Red 83, C.I. Direct Red 89, C.I. Direct Violet 48, C.I. Direct Blue 67, C.I. Direct Blue 90, C.I. Direct Green 59, C.I. Acid Red 37, and those described in JPA Nos. 1989-161202, 1989-172906, 1989-172907, 1989-183602, 1989-248105, 1989-265205 and 1995-261024. These dichroic molecules are used in a form of free acid, alkali metal salt, ammonium salt or salts of amines. Mixing of two or more of these dichroic molecules successfully produces polarizers having various hues. Compounds (dyes) or mixtures of various dichroic molecules designed to exhibit black color when contained in polarizer elements or polarizer plates and when the transparent axes thereof are crossed normal to with each other are preferable, since they have a high transmittance in a single-plate form and a high polarization ratio.

In the stretching of PVA for preparing the linear polarizing film, it is preferable to add an additive for crosslinking to PVA. In particular for the case where the oblique stretching process of the present invention is adopted, direction of orientation of PVA may be misaligned due to tension in the process unless the PVA film is sufficiently cured at the exit of the stretching process, so that it is preferable to allow the crosslinking agent to be contained in the PVA film by immersion or coating of a solution of such crosslinking agent before or during the stretching process. The crosslinking agents disclosed in the U.S. Reissue Patent No. 232897 are available for the present invention, where boric acids are most preferably used.

The stretching process is also desirably applicable to fabrication of so-called polyvinylene-base linear polarizing film, where polarizing function of which is ascribable to conjugated double bonds in the poly-ene structure obtained by dehydrating and dechlorinating PVA and poly (vinyl chloride) .

The 45° linear polarizing film, prepared by stretching a film in a direction inclined at 45° relative to the longitudinal direction of the film, can be configured without any modification as a polarizer plate and used as the retarder of the present invention, but it is more preferably used as the polarizer plate after being laminated a protective film on one side or both sides thereof. There are no specific limitations on the species of the protective film, and available examples thereof include cellulose esters such as cellulose acetate, cellulose acetate butylate and cellulose propionate; polycarbonate; polyolefin; polystyrene; and polyester. Retardation value of the protective film exceeding a certain value is, however, not desirable since oblique misalignment between the transparent axis and the orientation axis of the protective film results in conversion of linear polarization into circular polarization. The retardation value of the protective film is preferably small, which is typified by 10 nm or less at 632.8 nm, and more preferably 5 nm or less. Cellulose triacetate is particularly preferable as a polymer for composing the protective film having such a low level of retardation value. Polyolefins such as ZEONEX and ZEONOR (trade names, products of ZEON Corporation, JAPAN) , and ARTON (trade name, product of JSR Corporation, JAPAN) are used desirably. Other available examples thereof include non-birefringent optical resin materials described in JPA Nos. 1996-110402 and 1999-293116.

Although an adhesive possibly used between the linear polarizing film and the protective layer is not specifically limited, PVA resins (including PVAs modified with acetoacetyl group, sulfonic acid group, carboxyl group, oxyalkylene group, etc.) and aqueous boron compound solution are available, and among these , the PVA resins are preferable . Thickness of a dried layer of the adhesive preferably falls within a range from 0.01 to 10 micro meters, and more preferably 0.05 to 5 micro meters.

While thickness of the film before stretching is not specifically limited, it is preferably 1 micro meters to 1 mm from the viewpoints of stability in holding of the film and uniformity in the stretching, where the thickness is more preferably 20 to 200 micro meters.

An exemplary conventional punching pattern of the polarizer plates, and an exemplary inventive punching pattern of the polarizer plates are shown in Figs. 4 and 5, respectively. The conventional polarizing plates have, as shown in Fig. 4, an absorption axis 71, that is the stretching axis, in agreement with the longitudinal direction 72. On the other hand, the polarizer plates of the present invention have, as shown in Fig. 5, an absorption axis 81 of polarization, that is the stretching axis, inclined at 45° away from the longitudinal direction 82, where this angle of inclination is in agreement with an angle between the absorption axis of the polarizer plate, subjected to bonding with a liquid crystal cell of an LCD, and the longitudinal or transverse direction of the liquid crystal cell per se, and this makes it no more necessary to obliquely punch out the film in the punching process. This is also advantageous in that, as is obvious from Fig. 5, the polarizer plates can be produced by slitting along the longitudinal direction, rather than by punching, because the cutting line for producing the polarizer plates of the present invention straightly extends along the longitudinal direction, and this ensures excellence in the productivity.

The polarizer plate used in the present invention preferably has a high transmittance and a high degree of polarization in view of raising contrast of the liquid crystal display device. The transmittance is preferably 30% or more at 550 nm, and more preferably 40% or more. The degree of polarization is preferably 95.0% or more at 550 nm, more preferably 99% or more , and still more preferably 99.9% or more .

The linear polarizing film generally has protective films on both surfaces thereof . In the present invention , the retarder of the present invention can be functioned as the protective film on one side of the linear polarizing film. For the case where the circular polarizer plate is prepared using the 45° linear polarizing film, right-and left-handed circular polarizer plates can readily be prepared in a selective manner by changing the way of stacking. [Configuration of Circular Polarizer Plate]

Fig. 6 shows a schematic diagram of one embodiment of the circular polarizer plate of the present invention.

The circular polarizer plate shown in Fig. 6 is configured so as to stack a 45° linear polarizing film P and a protective film G on the retarder of the present invention. The retarder comprises an optically-anisotropic layers A and B (shown as a single layer in the drawing) , and a transparent substrate S. The retarder is stacked with the 45° linear polarizing film P so as that the surface of the transparent substrate S, opposite surface to that having the optically-anisotropic layers A and B formed thereon, is disposed in the contact with the surface of the 45° linear polarizing film P. In this configuration, the retarder also functions as a protective film for the 45° linear polarizing film P. Fig. 6 also shows interrelations among the longitudinal direction s of the transparent substrate S, the slow axes a, b of the optically-anisotropic layers A, B, and the transparent axis p of the 45° linear polarizing film P. In incorporation of the circular polarizer plate shown in Fig. 6 into display devices, the protective film P side is directed to the display surface side (an arrow in the drawing indicates the direction of viewing) . Circular polarization obtained by the configuration shown in Fig. 6 is a right-handed polarized light. Light comes from the direction indicated by the arrow in Fig. 6 sequentially passes through the linear polarizing film P and optically-anisotropic layers A, B, and goes out as a right-handed polarized light.

Another exemplary configuration of the circular polarizer plate of the present invention is shown in Fig. 7. The circular polarizer plate shown in Fig. 7 has a configuration in which positions of the protective film G and retarder previously shown in Fig. 6 were exchanged, where protective film G, 45° linear polarizing film P, transparent substrate S and optically-anisotropic layers A, B are stacked upwardly in this order. Thus-configured circular polarizer plate can yield a left-handed polarized light.

As is obvious from the above, a right-handed polarized light and left-handed polarized light can selectively be obtained only by changing the top and bottom of the stacking when the protective film G and the retarder are bonded to the 45° linear polarizing film P.

For the case where the protective film is used besides the transparent substrate, the protective film is preferably composed of a cellulose ester film having a high optical isotropy, where triacetyl cellulose film is particularly preferable.

Wide-range λ/4 obtainable by using the retarder and polarizer plate of the present invention specifically means that all values of retardation value/wavelength measured at 450 nm, 550 nm and 650 nm fall within a range from 0.2 to 0.3. The value of retardation value/wavelength is preferably within a range from 0.21 to 0.29, more preferably 0.22 to 0.28, still more preferably 0.23 to 0.27, and most preferably from 0.24 to 0.26.

Examples

The following paragraphs will further detail the present invention referring to specific examples. Any materials, reagents, ratio of use and operations may properly be modified without departing form the spirit of the present invention. It is therefore understood that the scope of the present invention is by no means limited by the Examples below. [Example 1]

An optically-isotropic triacetyl cellulose film of 80 micro meters thick, 680 mm wide and 500 m long, having an acetylation degree of 60.9+0.2% and a retardation value of 6.0 nm, was used as the transparent substrate. Both surfaces of the transparent substrate were saponified, and on one surface thereof, a coating solution "A", of which pH was adjusted to 4 to 5 with NH₄OH, for preparing an alignment layer, was continuously applied and dried to form a layer of 1 micro meters thick. The layer was further subjected to continuous rubbing treatment at an angle of 30° relative to the longitudinal direction of the transparent substrate. Thus, an alignment layer was prepared.

Composition of Coating Solution "A"

Modified poly (vinyl alcohol) shown below: 4 wt%

Water 72.6 wt%

Methanol 23.3 wt%

Glutaraldehyde 0.2 wt%

A coating solution prepared based on the composition below was continuously applied to a surface of the alignment layer using a bar coater, dried, heated (matured for alignment) , and irradiated with UV radiation, to thereby form an optically-anisotropic layer (A) of 2.1 micro meters thick. The optically-anisotropic layer (A) was found to have the slow axis in the direction inclined at 30° relative to the longitudinal direction of the transparent substrate, and a retardation value at 550 nm (Re550) of 259 nm.

Composition of Coating Solution for Optically-Anisotropic Layer (A)

Rod-like liquid-crystalline compound 38.1 wt%

(Exemplary Compound 1-2)

Sensitizer (A) shown below: 0.38 wt%

Photo-polymerization initiator (B) shown below: 1.14 wt%

Exemplary compound in this specification (PX-9) 0.19 wt% Glutaraldehyde 0.04 wt%

Methyl ethyl ketone 60.1 wt%

Thus-obtained optically-anisotropic layer (A) was then subjected to continuous rubbing in a direction inclined at -60° relative to the slow axis thereof and at -30° relative to the longitudinal direction, while keeping the film unrolled after preparing the optically-anisotropic layer (A) .

A coating solution prepared based on the composition below was continuously applied to the rubbed surface of the optically-anisotropic layer (A) using a bar coater, while keeping the film unrolled after the rubbing, dried, heated (matured for alignment) , and irradiated with UV radiation, to thereby form the optically-anisotropic layer (B) of 1.0 micro meters thick. The retarder (λ/4 plate) was thus prepared. An average retardation value at 550 nm (Re550) was found to be 136 nm. Angles between the longitudinal direction of the transparent substrate and the slow axis of the optically-anisotropic layer (B) were shown in Table 1.

Composition of Coating Solution for Optically-Anisotropic Layer (B)

Rod-like liquid-crystalline compound 38.4 wt%

(Exemplary Compound 1-2)

Sensitizer (A) shown above 0.38 wt%

Photo-polymerization initiator (B) shown above 1.15 wt% Alignment adjusting agent (C) shown bellow 0.06 wt%

Methyl ethyl ketone 60.0wt%

[Comparative Example 1]

In the process of Example 1, each substrate was once rolled up after the optically-anisotropic layer (A) was formed thereon, and was allowed to stand in the rolled status under an atmosphere conditioned at 25°C, 60%RH (relative humidity) for a time listed in Table 1. Thereafter the surface of the optically-anisotropic layer (A) was subjected to the rubbing similarly to as in Example 1; the optically-anisotropic layer (B) was then formed by coating, to thereby form each of the retarders which correspond to Comparative Examples 1 to 3. Angles between the longitudinal direction of the transparent substrate and the slow axis of the optically-anisotropic layer (B) of the individual samples were shown in Table 1.

Table 1

From the results shown in the Table 1, it is found that the sample allowed to stand in an unrolled status after the optically-anisotropic layer (A) showed a smaller variation in the in-plane angle between the longitudinal direction of the transparent substrate and the slow axis of the optically-anisotropic layer (B) , which indicates that the liquid-crystalline compound is uniformly aligned while keeping an ideal value. This proves the effects of the present inventio .

For the case where, after the optically-anisotropic layer (A) was formed, the aforementioned coating liquid "A" for forming alignment layer was applied to a surface of the layer (A) so as to form a layer having a thickness of 1 micro meters. After that, the optically-anisotropic layer (B) was formed by applying the aforementioned coating solution for the layer (B) to a rubbed surface of the alignment layer similarly to as described in Comparative Examples 1 to 3. No variations, such as those shown in Table 1 , were observed in the in-plane angle between the longitudinal direction of the transparent substrate and the slow axis of the optically-anisotropic layer (B) , which gave same results with that for Example 1. This apparently indicates that the angular variations after storage in the rolled status shown in Table 1 are ascribable to that the alignment layer was not formed on the optically-anisotropic layer (A) , and that the present invention is effective for the case where the alignment layer is not formed between the two optically-anisotropic layers . [Example 2]

A PVA film was dipped in an aqueous solution containing 2.0 g/L of iodine and 4.0 g/L of potassium iodide at 25°C for 240 seconds, then dipped in a 10 g/L aqueous boric acid solution at 25°C for 60 seconds, introduced into the tenter stretcher configured as shown in Fig. 2 of JPA No . 2002-86554 and stretched by 5.3 times. The tenter was then bent from the stretching direction as shown in Fig. 2 of JPA No. 2002-86554, kept at a constant width thereafter, the film was dried under shrinkage in an 80°C atmosphere, and then released from the tenter. Moisture contents of the PVA film before the stretching and after the drying were found to be 31% and 1.5%, respectively.

Difference in the travel speed of the left and right tenter clips was found to be less than 0.05%, and an angle between the center line of the film to be introduced and the center line of the film to be sent to the next process was 46°. Both of | L1-L2 | and W were found to be 0.7 m, and in a relation of | L1-L2 | = W. The substantial stretching direction Ax-Cx at the exit of the tenter was found to incline at 45° away from the center line 22 of the film to be sent to the next process. No wrinkle or deformation of the film was observed at the exit of the tenter.

The film was further bonded with a saponified cellulose triacetate film (FUJITACK, product of Fuji Photo Film Co. , Ltd. , retardation value = 3.0 nm) using a 3% aqueous PVA (PVA-117H, product of Kuraray Co. , Ltd.) solution as an adhesive, dried at 80°C, to thereby obtain a polarizer plate having an effective width of 650 mm.

The obtained polarizer plate was found to have an absorption axis inclined at 45° away from the longitudinal direction thereof. Transmittance at 550 nm and degree of polarization of the obtained polarizer plate were found to be 43.7% and 99.97%, respectively. Cutting of the film in a size of 310x233 mm, as shown in Fig. 5, was successful in obtaining polarizer plates having the absorption axis inclined at 45° with an area efficiency of 91.5%.

Next, as shown in Fig. 8, another circular polarizer plate 92 was prepared by laminating the retarder 96 prepared in the Example 1 on one surface of the iodine-containing linear polarizing film 91 prepared in the above, and by laminating on the opposite surface a saponified antidazzle antireflective film 97. Still other polarizer plates 93 to 95 were similarly prepared except that the retarders prepared in the Comparative Examples 1 to 3 were respectively used in place of the retarder 96. In all fabrication processes of these circular polarizer plates, the linear polarizing film and the retarder were laminated each other so as to confirm the individual longitudinal directions .

Each of thus-obtained circular polarizer plates 92 to 95 was irradiated with light (450 nm, 550 nm and 650 nm) from the saponified antidazzle antireflective film 97 side, and phase difference (retardation value: Re) of the transmitted light was measured at arbitrary 20 points which fall within an area of 650 mm wide and 1,000 mm long, and the ranges of variation were expressed by the maximum values and minimum values . Results were shown in Table 2.

Table 2

As shown in Table 2, the process of the present invention is successful in preparing circular polarizer plates having only a less amount of in-plane Re variation.

[Example 3: Fabrication of Reflective-Type, Liquid-Crystalline Display Device]

A polarizer plate and a retarder were removed from a commercial reflective-type, liquid-crystalline display device

("Color Zaurus MI-310", product of SHARP Corporation, Japan) , and the circular polarizer plate 92 prepared in the Example 2 was attached instead.

Visual evaluation of thus-obtained, reflective-type, liquid-crystalline display device revealed that neutral gray was displayed in any modes of white display, black display and half tone display, without developing color.

Next, contrast ratio based on reflective luminance was measured using a viewing angle measuring instrument

(EZcontrastlδOD, product of Eldim SA, France). The contrast ratios measured on the front face side was found to be 10, which were practical enough.

Industrial availability

The present invention can contribute to lowering the production costs for preparing retarders comprising two or more optically-anisotropic layers, which are respectively formed of aligned liquid-crystalline molecules without developing a lot of alignment defects.

Claims

1. A process for preparing a rolled-up retarder comprising a transparent substrate and two or more optically-anisotropic layers respectively formed of a composition comprising a liquid-crystalline compound on or above one surface thereof; comprising a step of forming an alignment layer on a surface of a transparent substrate having a longitudinal direction under continuous feeding along the longitudinal direction, and further comprising the steps of:

2. The process of claim 1, wherein at least one of the steps (a) is a step of rubbing a surface of an optically-anisotropic layer comprising a modified polyvinyl alcohol having a hydrocarbon group containing 9 or less carbon atoms .

3. The process of claim 2, wherein the modified polyvinyl alcohols is denoted by Formula (PX) :

- (VA1) _x- (HyD)_y- (VAc) ₂- where "Val" is a vinyl alcohol based repeating unit, "HyD" is a repeating unit having a hydrocarbon group of 9 or less carbon atoms and "VAc" is a vinyl acetate based repeating unit; x is 20 to 95 wt%,; y is 2 to 98 wt% , and z is 0 to 30 wt% .

4 The process of any one of claims 1 to 3 , wherein the liquid-crystalline compound used in at least one of the steps (b) is a rod-like liquid-crystalline compound having a polymerizable group.

5. The process of any one of claims 1 to 3 , wherein the liquid-crystalline compound used in at least one of the steps (b) is a discotic liquid-crystalline compound having a polymerizable group.

6. A retarder prepared by a process as set forth in any one of claims 1 to 5.